K5JXH. , (boat anchor #2)  (see the Heathkit catalog 1969 for this SB401)
Topic, SB401 Transmitter.
A Minor Refurbish ,repair and full tuneup (now done)                                                  
This is my Journal , a serial process, that some might find useful getting any old rig to work.  See my first  mod. is here ,  the second is  mod. here

Finding good Boat Anchors is not easy, I don't expect it to work , just  not be a wreck , full of rust and impossible to repair, and is an exercise is pure faith buying one,  best is to look at it, in person at a ham fest, lids off. (Just like buying 50 year old car, same deal)
Be advised, there are parts here that can not be bought, or takes a year to find.  (that plastic dial is one, and RL1 bad is worse (hopeless comes to mind)   (the old dials, usually have 2 to 10 hub cracks but I cured mine)
In most cases buying 2 RIGS, to make one good one, is a best practice. This is called cannibalizing. (hint: make sure, 1 has a good dial, one has good  LMO and last one has  good relay set)
If you are missing crystals, be ready to do a long hard search and begging online in ham forums,  this worked for me.  (one can have them custom cut,  for $50 to $75 and one can make adaptors to fit other form factor crystals matching your Freq.! )
There is an official,  Service Bulletin "the SB is here" , see this PDF document with a drawing at the end.
Wow , seems I got a good  rig, but is missing  3 crystals needed to complete all alignments steps,  (got them in the mail today,  CW/tune, LSB and 28.5 band)
Relays (can be a horror):
I had to re-bend relay  RL1, (the offical component I.D) contacts to make mine work, tedious work, but I've had practice before.
As with my SB200, checked and made sure all those case grounds are good,  many tubes have grounds parts, connected  to there own socket bases. Check all this carefully, before turning on power.
The power cord needs to be replaced with a real one, with 3 wires,  or it can be a man killer,  there are internal 700volt and 250v  supplies, and if that old nasty wiring insulation is bad, (vinyl wire does that)  then the case floats to 700vdc and boom dead, ham, (silent key).
This is what must be done, see the power socket I installed.  (or have and use a real ham SHACK ground bus installed and use that huge ground  stud on the back of your rig connected to the Main SHACK ground that is tied to the AC power service entrance ground stake.)
See my photo here.
Do not run this rig with out a perfect ground !
This is not a safe 12v solid state rig here, this rig has man killer voltages inside.  Nor is this RIG with double insulated plastic cases, see, it's all aluminum.
Work only with a clear head and not tired.
Do not monkey here, if not ready to be safe.  Do not touch the hot tubes, they will burn like fire at 200C (or 428

First, I cleaned the whole rig and , corrected some minor damage, and the dead tuning knob, an easy pure mechanical fix.
The knob fails, because folks oiled the pinch roller saft (don't). (or forget to RTM and calibrated it) (RTM = read the free manual)
The Calibration is in/out and up and down, if not indexed correctly, it can not ever work right.   (I now have  spare dial, and very rare)
Make sure the LMO shift is centered
in the hole (shaft and slot seen) , that is, take off the huge knob and look, if not centered, that needs correcting first ,the green panel is not wrong, but the plastic dial plate seen at SB401 can be off or the LMO was not installed straight.
The knobs are all USA imperial inch  Allen wrench set  screws. Some are slotted screws.
Next make sure the LMO turns 5 full turns, not the stopper coupling is oil stuck, (petrified old oil) clean that next.
That metal pinch roller can last forever, it's just a pair brass spring washers, (oil-less, grease-less) there are no rubber tires etc, here.. (the plastic dial can crack , and most are)
 That  pinch roller engages the dial inner steel ring knife edge, and must INDEX correctly. (both up/down and in/out)
There are endless posts on line, on belts (o-rings) and rubber tires to fix this  LMO reduction drive, device (the pinch roller) not one is truthful. (zero!)
There are no rubbers here, tires, belts or the like kind. (these posts think the subject is the  LOAD  knob lever, shaft mode,  that heath uses 100 pound test, fishing line there when new, that frankly is sold in all Walmart fishing departments.
Some hams do buy $25 o-rings the LOAD (50ohm) pulley drive, that fits there tightly, that sell for 25cents at usaorings.com.
Oddly, the manual shows how to  install  the fishing line. (if broken or missing, it's just a spring loaded line)
See my PDF on  topic ,   TUNE Knob Fixes and calibration and my EPOXY cure for those cracks.(the plastic is very brittle and most examples are all cracked)

The LMO has this funny brass staging coupling, and loves to stick (50year old oil does that, always) and must be cleaned first, then unstuck and then I use gun oil on it. (use the best oil you can find that does not migrate, like top brand gun oils)

See my  Full manual, with annotations.

Based on Capacitor date codes and tubes, it's a 1968 transmitter 
(I phosphate'd (acid) the transformer cap and painted  it ) Zero rust there now.   (I used painters tape to protect this acid from hitting any thing else, and tilted chassis so and drips laned on my work banch) The acid is sold as brick cleaner, at Home Depot.
A New but wrong panel meter,  old one was crushed.,now works like new.
I'm very lucky to find a clean , example.
 Note the "COMPACTRON" tubes in  this rig, that has 3 tubes inside one envelope. (cute they are, in fact are Integrated, Hollow state Circuits,  IHSC?)
My Freq. dial now works just like it did, new day one . Smooth and perfect.
My outer case is near emaculate after Ajax'ing it, It was not easy finding one like that..., nor with clean bright white front panel, silk screened, markings..
I want to test it on 40 meters live, just for fun. (for  a backup TX)

 The meter is off the RX version of SB line (SB301) so has S -Units, but is better than nothing.  The number 10 is 1000 volts D.C.   (normal is 8 for 800vdc.)

Missing the LSB and tune crystal  (cured) as are all 3 bottom crystals present, LSB/USB/CW-tune

I think the 2 wire line cord is both silly and for sure unsafe,  now CURED ! You do want a  modern 3 wire cable and jack.
See how to test this rig, safely:
Same cable used on desktop PC  (PSU)  or Tekronix scopes.  (this makes the cord free of cost, as everyone has them laying about.)  I stole my connector off a dead, PSU, (Decktop PSU) that I keep in the attic for spare parts,  see more details of this below.

CARBON DATING:  (My guess is 1968)
 Facts, my oldest tube is 1965 and newest is 1974 the LMO tube is 67-22 marked, 22 workweek (June 1st) of 1967, my guess is this is original tube and makes this a 1968 Transmitter.
The 2 main PA final tubes are  late 1967 made. I think too, they are original. The USB crystal is marked 1967.
I could not decode the Mallory cap,  1-77-84-02 nor the Syncro caps (2 big black 450v) 18016733 date codes.  (lost in the sands of time... that) 
Back in 1968 they used numbers like  735 for year 1967 and work week, 35, or used Julian dates, or anti-Julian (backwards) I worked in a factory (just back from Viet Nam) and saw all these, funny codes then.
I then worked for Phillips semi , that had a 10 month calendar. (yah) If Julian dates  used, work week 1 can be July 1st.  (what a company uses, is their business and their reasons)
Some factory's used the new year as July 1st (like  car companies do) so a date, 71 might mean  1967 work week 1 (July),  or 711, with shift 1 (day shift) on the end.
My RCA tubes all are encrypted, dates ,company code is  274 (EIA) and  date code "AU" = 1965. My rig has a mix of JAN ,RCA,GE and Mullard tubes (JAN = joint army navy parts , aka...war surplus).
There is no error finding a new 67 radio with 65' year new tubes, totally normal.  (Heck  I have them NOS , still like new, 50 years old)
The SB401 has a newer LMO called 110-40 which is one 401 upgrade.

Other issues: (problems)
The mike jack is bad, pins rusty, so found a perfect DIN jack (and matching DIN plug (3pins) that fits perfect in the 5/8"(19mm) hole. Dentron 651-0300 (mouser) I'll use same pin numbers and added ground to #3. (Fits , works and looks good)
I wanted to fit a modern 8 pin ICOM jack there but could not figure out a way to do that. (I still may)
There is a new MIKE XLR connectors series, called mini, with a 0.44" panel size (ours  is 5/8" or .625"  but the new series is very expensive, Near $30 for a set of 1 plug and 1 receptacle.(Rock Star Prices?)  Thus I chose, Denton.

POWER: (as in A.C power)  Correcting a blunder...
I found a safer power cable , a modern power connector .  (as seen on all Desktop PC's or in all Tektronix scopes and gear.
This has snap in type jack,  and I Dremel'd my chassis out to fit it, using aluminum cutting bits . (accurate scribe lines laid down first)
It just does fit.
It must be installed as low as possible to clear the transformer base. (  a filtered AC jack is 10x better, but I could not fit one here)
That new green wire goes to the factory ground stud. That orange wire measures 287vdc on my rig. (don't touch it)
Now the case (chassis) will not float at 800vdc and kill the owner.  The voltage inside here are lethal,  that means, "NO SECOND chances !"

This metal chassis radio, would be totally illegal to sell new in the USA or EU, lacking the 3rd green wire, "UL" will ban it. (fail it and reject it)

This is proof that 1966 was the Halcyon days, of innocent and brave men, that floated 800v or more chassis, with wild hopes of surviving. (no 3 wire jacks in homes then)
The 2 line caps need to be removed and 2 modern UL caps inserted. 25cents each.
The C1 and C2 caps far right need to be replaced with CLASS X1/Y2 rated UL safety cap.'s,  so of they can not short out,  sitting on the line power 24/7 .   The correct caps are sold at  Mouser, at 26 cents, I see scalpers on fleabay asking , 40x more $ !
Cap. maker  Vishay #
The 2 new electrolytics C77a/b seen here, have 10x better ESR, from 5 ohms to 0.5ohms or less. (I trying go get less hum in the modulation)

You can see I am a Nichicon FAN big time.

HV Safety:
All voltage readings on my page were taken with hands in pockets, power off, chicken sticked first, connect up meter/scope, turned on, see readings hands clear of rig, power off, repeat. (military rules, and very very safe)
Let me elaborate that.
  1. Turn the Power switch off marked "FUNCTION", do not unplug the AC lines (ham radio, exicter, linear amp, PA) so that the AC line ground  stays inplace (see comment below) and active. As seen above.
  2. Wait 5minutes, see the HV needle , on the panel dial meter (set to HV) go to 0 volts? yes wait...,
  3. Chicken stick the Orange wire above  see my SB200 page on chicken stick use and creation?. and all diodes seen above, in a row, above that silver alum. huge capacitor above, just land the stick on all diodes. Is a safe way to do this.
  4. Do not chicken stick  on the the transformer black wires, those are A.C hot now.  Keep in mind left hand in pocket , right hand (if right handed) on the insulated chicken stick handle, and it's ground is connected to the  above aluminum chassis or the large ground stud on the rear.
  5. Set all dials to the correct setting now, that is needed for your next test, or test point diagnosis.
  6. Now connect your meters or scopes for a test.
  7. Now stand back, be wearing rubber sole shoes, never leather, and turn on the RIG under Test (RUG) with only 1 hand, other in pocket, and turn the power knob to STBY, wait for warmup and turn this knob to the mode you need to do the test you are doing.
  8. Repeat above, for each, meter/scope probe change, and live.
If your SHACK has a HAM bench ground buss, use that connected to the above, chassis ground lug (wing nut) and then edit line 1 above, to remove AC power line.   (the fact is the chassis needs to be keeped at real ground at all times)
Never power up this chassis with out a real ground.

Big Electrolytic CAPS:   (I ESR meter tested them first)  "Electrolytic, Capacitors"  (ESR means Electric Serial Resistance)  I have a meter that shows ESR, Farads , and leakage.
The books by Heathkit are good, but they all fail to show component I.D's fully in the parts list. and skip Capacitor voltages and diode specs, PIV and current forward max.  (the internet searches finds truth here, or very tedious schematic reads, and discovery)
Here is a list for large electrolytic cap.'s. (my C81 cap was missing and is now installed and working.)

C81,  100uf, 350v. the p/n is #25-57 
C403 and 404 are 20uf at 160vdc #25-16
C77a/b is 40 /100uf a twin cap in a large can at 350vdc   #25-59 
C78/79 are 125uf at 450vdc  #25-34
I find them at mouser, and will be tiny sized for same spec.  (I only replace failed  cap.s  for too high ESR) The caps are very crude in tolerance,  +80 -20% uF, is common back then (not so called "computer grade" at +-20% or better and are over-kill here)
Some builders even gut  the large cap above and put in new modern caps, That today are tiny, inside the old can. (It's not hard to do, but is tedious)

Tests:   (Warning most of the below we expose ourselves to lethal voltages , do not do that until you learn how to do that safely, ask an  ELMER)  What does Lethal mean?, it means NO SECOND chances! Read that 1 more time...
If this scares, you, stop, and buy a solid state rig, please, do not be macho here, the voltages are letal.
All grounds good. (first)
Resistors, all check out. ok.
Relays, are ok, I had to correct some bent contacts  on RL1, due to someone,  playing there.. not skilled.. Both Relay coils ok.
I powered up my rig ,safely  (rig means gear, means radio, transmitter, exciter, transceiver, as the case my be...) I'll call this exciter my TX.
I power it up and on for the first time now:
All tubes glow,  if not, fix that  next, a new tube, cures 99% of those, the 1% were wired wrong. (the kit in Heathkit)
Many  tubes here have one filament pin grounded to the tube socket shell, if this is rusty, or loose the filaments will  dead on that tube. V10/11 do exactly this.
Regulator (cold cathode class):
I check all DC power supply  , for proper readings and a surprise to me, my OA2 regulates at 150vdc  , in both TX and standby,  It's a good tube at 150v.(if you see 250v + here, the OA2 is DEAD) This is the only regulated supply in the whole rig.
The OA2 tube is the valve(tube) a cold cathode tube, that ionizes a gas, inside, that today would be a  Zener diode for SS gear ,  make sure it works in standby and transmit !,  holding 150vdc regulation on that power feed 150v.
IT'S NOT A ZENER, using this name is talking to the millions of solid state folks that never seen or heard of  gas tube.(most) But if you look there is Rs (Rseries) resistor that works just like a ZENER regulator, both are crude voltage regulators.
 If the series resistor is good , then the tube is bad, if it don't regulate. (assumes high side of resistor is at spec. voltage ,sure)  (side topic) Did you know the the Mighty NE-2 can be used as a regulator and uses NEON gas?
Do not break the glass case and lick or  touch these parts inside, some contain radionuclides.
Don't panic if 250v reads 287v, like mine, that is because the 250v is mostly not regulated in the classic sense (SS) (it's load Dependant ) How ever it is tuned by the engineer, in some cases with a shunt resistor to attain 10% regulation.  (SS = Sold State gear)
All supplies check for excess 60hz (or 120hz) noise  ripple,  due mostly to bad filter caps on the offending supply. (I use a scope , 10:1 probe on AC coupling to measure ripple and SEE IT)
Got GAS?: (look for it , or use your Hickok tester to find it?)

Here are my actual RIPPLE readings. (all with the SCOPE)
+ 250vdc C77a (diamond key marked),  (4v-pp ) ripple  .  (both those c77caps read 1ohm ESR) So I call this Normal. This is 2% ripple at 60Hz,. 16ms period. Is a halfwave rectifier here.
-68v bias is .C403, has 400mv ripple peak.  RX or TX. GOOD. (1/2wave rectifier and a 16ms period)

Be sure to use this method of safety before the next step.
The C78,  750vdc cap ,using my 2kv scope probe shows, no  ripple at  all, I see no A/C ripple, only 50mv RF hash noise.(tiny)  Normal.

No Hollow-state volt meters, here. (VTVM):
I will tune up the TX using a scope, and not some 50 year old VTVM relic,  that is very hard to find, nor desire to own and overhaul next... (any modern 10meg. ohm input "Z"  DMM or better works too)
I will post photos of my readings, for page 96 up, in the manual below, as I make progress.  (96 up is , not owning a SB301, no Heath radios owned ! )

The knob marked tune, will not work due to the missing, factory tune /cw crystal Y10.  In fact LSB is TUNE/CW crystals are missing, corrected this fast I did.
Most of the tuning will be into a dummy load, or with V9 removed as the manual instructs.
The book shows using s VTVM (for get this relic, use a modern DMM with same spec.'s as most do now, or a scope that works 10x better) Do not go out  and buy a Hollow state, volt meter....
In modern times, things are better, we have meters that have 10meg. ohm impedances or better. ( more the rule today, try a Modern Fluke meter? or like kind?)
Most modern meters use a high "Z"OP-AMP buffer on the inputs (or FET front ends)  Z is the symbol for Impedance.

The tuning book for the SB401 uses a RF detector probe, that turns RF to DC, this is a crude device, and will work ok on a good radio, but will not show you, the signal, that can be, dead, weak or distorted or glitchy., for those issues, a scope, is mandatory, IMO.

There is no cheaper way back in 1966, with no real DMM's then , you can use a modern DMM and any , RF probe, as seen in the ARRL big book (how to make the probe or buy one.) 
Back then we had like Simpson 260/270s that had horrible ohms per volt loading spec,  and is useless here.  (it has zero electronics inside the meter, just resistors)
There are some tests that must be done with low loading capacitances probes or a scopes with a 10:1 low cap, probe. 
I have 2 Tek scopes (100mhz) one digital one analog both SS solid state.(both were $50 used, and restored by me, yes, boat anchor  scopes from 1980 are superb instruments. (the Tek 3420 DSO is just that, chock full of TTL logic)  (I learned on a Tek545)
I'm sure the best old scope is a TEK 465, (or near)  best bang for the buck , old iron.  If flush with cash, a DSO , wins !
I also have a new Owon Digital scope,(DSO) 100mhz. All three have scope probes, running near 10pf loading. (10pf, or pico farads) (10:1)  10 puff, 10 micky-mikes, 10mmf, 10uuf, etc. Pico is 10 to the minus 9th power. (in science it's 10E-9 Farads)
I don't need the RF detector probe , as stated, but  I have one , a real commercial one (mil surplus)and one home made. (I use it to demod, any modulation in the RF , if need be...)
At this point , all tubes glow, and all HV are all good. (HV = high voltages)  I define HV as any potentially harmful or fatal voltages,  100v is very painful, 1000v is death. Count on it.
The chapter in the book, seen here, starts on page 96 and ends on 100,  and is titled, Alignment, not unlike a Receiver "IF" alignment, but the transmitter needs no signal generator due to the LMO, does all that.
I am using standalone, calibration , in pure Exciter mode, and is called  unlocked mode. (here)

Only in my manual "STEP 6", did my 10:1 probe shows a very tiny loading effects (a tek probe 10pf) so used the grid current meter per the manual to eek out a tiny more peak. (My manual now has added Step numbers in blue, so I can talk about them...)
Using a modern receiver, lets me calibrate the LMO, using my dead accurate ICOM 7200. {or the like kind} (the book shows, using old long gone, relic, crystal calibrator's or good old WWV)
The tests have you peak out coils/caps,  and also null out the SSB carriers,  there is nothing at all wrong about looking at the actual RF directly with a scope, (so long as the probe does not change the tune of the circuit under test)
The book steps have one missing statement, the SB401 has many crystals missing , day 1,  so only do the steps for crystals installed. (skip the others,) everywhere it says "repeat" add, "if you have the crystal, repeat on next band, if not skip to the next band with a crystal installed"
The final pages, page 99 is "Neutralizing" the amp,  we don't have a 28.5 crystal, , now on order, from K8GNZ.(thanks !)
Last is the section named Final bias, this we do , using a real dummy load.  requires no external (hollow state meters or scopes, same with the last LMO steps and ALC , all using the built in panel meter. (I run a CANTENNA, it is the best there is, real watts per buck !)
But first, does the TX key up.? 
The SSB PTT is located on the mic jack, in my case it's new this jack and the yellow wire is the keyup line, you ground it to key up. (using anyway you want to do that, even with NO MIC  owned, we just use a jumper clip)
The manual has you key the Morse key, labeled "KEY" in the back that is a relic, 1/4" Telephone jack. (just like telephone switch board operators fiddled back in the olden days) The end is called tip, and the ground back side is called RING. 

I'm testing my PPT  line, on the mike jack. (yellow wire), this must work by energizing 2 relays, or all  alignment steps will  be impossible.  So this is NEXT.
The books says relays should key up, no this is wrong, it MUST key up. (if not , jump to repair mode, and do expect that after 50years, parked in an attic )
RL1 actually sends power to RL2 coil, so RL1 must key first. (humans see them both close at the same time, but in truth, there is a 10mS+ delay both to fully energize) (you can even measure this delay using a scope)
These 2 relay forms what we call TX/RX relay switching. In this case it's complex due to the usage of say an external, SB301 receiver, forming a transceiver in total.
This exciter uses RL1 to change tube bias, and is extremely important that it does this job correctly.

Here are my results.   (Can we key up, and if not?, why not)
Lets say RL1 is dead, (RL2 will be too, it's a slave of RL1)
As you can see v12b TUBE must work or you can not TX.
See cathode, R135 is self bias, keeping tube off,  unkeyed, and that the relay has 37v across it keyed.  Note the very dangerous 250v power there. (don't touch it)
TUBE means, Vacuum tubes, Fleming valves, or Hollow state electronics.
I have no plans to use a VOX ever , so will not need V12a working. (I really hate VOX, but at that era it's like omg, its like a "Ma Bell" speaker phone, oooh ahhhh..)
The PTT line yellow wire grounds the top of R137 above (68 ohms), this in turn puts pin 6 at near ground and ends Grid BIAS, I see 1v at pin 6 PTT active, and the tube switches on, that is correct, V12b is  used as a switch here. All readings in SSB mode.
Grounding pin6 kills the natural grid self bias and the tube slams to ON.
I Check that too, with the mode dialed to "TUNE", to see relays close, and I grounded my mike yellow wire, to be sure all relays work.   Mine do.  (PTT ., KEY and TUNE actions all close RL1/2)
The KEY jack is at  rear grounded, keys the relays in CW mode.
You can see D105 is the audio detector that sends a positive voltage to pin 7 and turns on the V12b.... I don't need VOX ever.

In the same topic (RL1):

The below drawing shows the 1974,  ECO ,engineering change order, (or Service Bulletin) to ground pin 7, this prevents gassy PA tubes from causing the relay to SELF energize , un-keyed. (a little horror that.)  (gas plasma sending huge currents to the screen grid, faults)
IMO, in my opinion, this is a mandatory ECO !

Sadly my pin 7 contact blade was bent, so had to fix this first, just to get the ECO upgrade to work..correctly. No new relays sold , so.... fiddle what you have.  If the coils is open, cry.... (a river)
The critical pins , are for bias only,  that will cause the tubes to be in the wrong mode, if this fails.
(I burnished my silver contacts, with just printer paper strips, then checked the for continuity (DMM/ohms) and the adjusted them if bent, some were bent.
Pin 8 has 250vdc at all time,and pin 4 keyed.  (mine is 287v so don't touch it)
By critical ,I mean just getting the SB401 to work as a stand alone , transmitter.   IF using a connected SB301 (or 303, etc) almost all pins are critical here.
Re bend any bent contacts. (can take hours of fussing here) Tell me, don't you just love open frame relays, (not)
Do not fear, black silver oxide , please, on contacts.
Power cord UNPLUGGED ! during all RELAY work above. for longer than 5 full minutes and HV dialed up,  meter showing  0v.
The contacts are silver, and we clean them with strips of paper only, never with files or sandpaper of any like kind, I slide the strips past them active state (closed by hand) maybe 3 times and say to self , that is clean. Tread lightly here, you can't buy the relays now.
The contacts are not solid silver so try to keep the plated silver, intact. ( I guess the word buff them, or dust them off is a better word?)
Do not use MOM'S silver dip, as that is acid (the MSDS don't lie) and will destroy the steel used in the relay, keep acids out of all electronics. (a rule for life)
One can buy new closed frame relays and a socket and redesign all these connections. Many have done this. Using relays from TE.COM (old PotterBrumfield)
One can use 2 , 4pole relays side by side, forming  8 poles and only 6 uses, and make this work. The HW101s are like that, coils in series...

As we do the factory book alignment we check the LMO carefully first.  (For me this is the Key STONE part)

First things First, all things above done, next is , LMO , if the LMO is dead or FUNKY, it needs to be cleaned and serviced, The grease inside, can be cleaned and serviced so it has  good ground  inside again on moving parts.
The first tests will be testing the LMO for dead spots as I tune it min to max., if found glitchy , it needs to be cleaned and lubed inside, if it acts oddly at any time.(or its own tube is gassy),  (now is the time to discover these issues and correct it...)
Live testing means V9 installed. (most of the steps are with V9 out)
We check the LMO with V9 removed (dang  my V9 tube shell is missing, and cost me $9 go get one. (tall shells are rare,today)
Now is my tuneup job, per the manual... and using a scope.
I am revising the schematic, daily for the usage of my scope, see the blue STARS  (red stars are the factory test points)
The first test point called HET OSC.  (and actual banana jack) only works with the RF detector probe, on a scope this point is near RF ground, So I moved my scope probe to the other side of that 100k resistor R27 top. and bingo, solid 40v(p-p) signal there.
Peaking the levels here is super easy and can see noise , distortions, or clipping, that no RF probe +VTVM (DMM) can see, or find. A scope is always the best tool to use, here.
All the other test points in the manual all work with the scope. Some you peak, others you null. (I have one book revision for for STEP1, HET OSC, R27 ,  connection)
The book fails to tell you in each alignment step what signals, you are measuring, it just blindly , tells you step by step. (but is covered at the end of book the whole theory of op.s and is quite good)
Keep in you mind as go what is going on, so if things are wrong, you know what might cause problems, (mixers dead, oscillators dead)

The V9 pin 2  is the sum and difference of HET OSC and the LMO frequencies and the 1000hz modulated CW carrier , The LMO does 5 to 5.5mhz, range.  (a 500khz range only, or a tad less, depends on last calibration steps, this.)
The CW and Tune crystal is missing in mine, so there is no CW/TUNE carrier, making this step in the V9(pin2) alignment impossible. (now cured)
The book assumes you have, the  SB-301 Receiver, to connect up, hardly easy to do or find one. (I'm using my  ICOM 7200 )  I have  R71 too.
CW mode:
This is explained on page 130 in the manual, and about how R16 effects on CW carrier. (R16 unbalances the ring bridge  allowing the raw carrier to pass this point , unlike in SSB modes)
My SB401 has the revision the puts the r16, CW controls behind the SSB" Level" pot, on the same pot.  The books showed a PCB pot. that is not there.
Next V4  adds (summation) carrier and  LMO oscillator, then v5 mixer, subtracts (difference mode) the former mix from Heterodyne Osc. and on 40meter will be 4mhz, (LMO set to say, 5 mhz)
If you remember electronics school , 2 signals impressed upon  a non linear device, creates the sum and the differences, of the original 2 signals, this is what we call a MIXER, (RF usage of the word) The ARRL hand book goes into this in depth!
That pin 2 has a trap for the summation frequencies and passes only  say  3.5mhz  tuned up.
On mine the heterodyne oscillator V8A was dead, so found the coils set WAY wrong, and did full steps, in the manual, flipping the band switch,  between bands and being sure the oscillator fires off each time. Bam good.
I got all my crystals today, and now the whole rig came ALIVE !
Lots of fun seeing such and old rig RUN .

Scope photos below:
This section covers all steps in the book Alignment (calibration):  The Linear master Oscillator. (it is claimed to be stable after 10 min. warm up)
Scope view 1:  LMO out.   (this step is not in the book, this step, is to make sure the 50 year old LMO is ok, and no dead spots)
The LMO is 5 turns end to end, the pinch roller is 4:1 so 4 times 5 is 20 turns max.
Keep in mind the RIG dial shaft have stops, so the LMO will never reach full 5 turns and ends.  (close but not full, it has excess range on purpose)
 If the top tuning slide rule (old school word) goes min to max, all is ok, if not  it's mechanically messed up (just dried oil here). (see my LMO fix pdf ,here)
The SIGNAL is a clean Sine wave, hand scanned from end to end, no drop outs, (watch for that! as you turn the dial).
This LMO SIG, is very stable, you set the Freq, and it don't drift. That is why Heath bought them from TRW.  (performance and is key to using , and hearing clear SSB audio)
This is what the LMO looks like in the real analog world, seen by a modern scope DSO.
This vertical scale is volts. 1v/division. and 50nS (50e-9) per division.  It will not stay at same voltage, as you tune, and it can drop volts a bit, but never ever drop out ! (If you see it  drop out, it must be dismantled and cleaned,  3 hours labor +)
The output varies from 200nS  , 190nS period.  Voltage is very steady,  and signal is clean.
It goes with out saying, if the power supply ripple , is out of spec, don't expect success at any point. For you old folks, RIPPLE is not a "Cheap Wine DRINK". The wave is as clean as the DC power allows it to be.
This is MY test,  it's not in the book, but should be, if this is dead, ALL ELSE in unlocked mode will be dead.

End LMO, next is direct from the book, alignment, 

It goes with out  saying that using a steel "Allen" wrench does not work at all. No metal wrench tweaker, and do use these.

Scope photo 2:  (HETrodyne Oscillator. test point "HET" is a banana jack )  This Test point, is on the other end of the 100k resistor R27, V8A output.  
The Banana is DC voltage only, the other side of R27 is the raw RF side as seen below,  I'm not using my RF-Detector at all.
The book is scary in that it warns of HET OSC. not starting up when changing bands and detuning the coil to cure that.... (I guess this Culpitts Oscillator is fussy?)  The words tune to the the slower peak, wow.
Just in case I have  new, V8 tube, if this signal ever dies or gets weak, cost me $2  (20cents in 1968 cash, such a deal)!

Next on page 98 is Carrier null ,  USB mode. (fiddling both the null pot and null air cap) when done, you get only noise here  USB mode.  No carrier is best for SSB, and this MAKES IT SO.
This is  a very tiny signal below and as such, lots of noise, S/N ratio poor,  and does not progress further down stream.  I turn the pot next, and I get NOTHING here, just very little noise.( about10mV)

Then ALC set, using front panel meter, no scope needed here. (page 98) STEP 4 in my revised manual. No comments here,  its very simple step.

This is test point, "E" again with the correct crystals, and peaking out transformer CAN, "T1"  we peak this using the T1 can core slug with proper plastic tweaker. CW mode. This is STEP 2 pg 98

This peaking out of Grid and plate inductors as a pair, is done on all installed bands.  (top side crystals)
Step 5 is input to V9 , tube pin 2, grid, this tube is  not present now.  The first steps on DRIVER.

The page 98 section "DRIVER" still STEP 6 , this is PA DRIVE,   V10  pin 5 , grid, V9 now plugged in.  (dummy load for sure connected !!!) This is the first time full power hits the antenna jack, on the rear.

This level will cause excess grid drive, and I turned the level knob down fast, as the books shows to do , but I wanted to see just know how much V9 can hump out, (drive) (curiosity kills the cat?)
This is what the 6CL6 can do, in a live circuit.    The tube has 7.5watt max plate dissipation, plenty to drive the PA.  (I tired 2 tubes and both did this)
In fact the level knob, allows me to over drive the PA beyond  1mA spec. the V10 pairs grid , I did this for just 1 second, captured on Kodak moment, err,CCD flash memory... This is my bench mark for V9 out into V10. STEP 6.

Step 7 , in my guide is 8.6mhz, trap set.
Pin 5 V10 again. in CW mode.  Same as above but now setting the TRAP.
Remove crystal, 15.895 Y7 and null the signal with variable cap that is a hard to reach, see the book

Next is Step 8 carrier null,  in LSB/USB,  using the null pot and cap. named the same. this is just fine tuning this null we are already very close before.
Step 9 is Neutralizing. (need  the crystal I don't have, but is on order)
Step 10: Final Bias.
Step 11: is tuning accuracy, using an external accurate modern receiver., (this gets the rig dials to work right and be accurate)A 10minute warm up is required.
Step 12: Frequency shift adjustment. For natural sounding voice on SSB.
Step 13, is last. Final Transmitter adjustments. Ultra fine tuning the HET OSC, coils. (eeking out that last watt hidden, to the antenna)

The power amp PA out looks like the below. into the dummy.
CW out.  spec. is 100w avg, that works out  to 100v peak, doing the math.
After Doing STEP13, I got more watts.
The photos below is older, after tuning in to my "Cantenna" with 1:1 VSVR very near, all coils tuned, and the front knobs,   (do not touch this connector when transmitting or get painful RF burns)
I have only 60v-peak until the new V11 and now is 100v-p

That is the most accurate way to measure watts DIY methods, is with huge (won't overheat) dummy load 50 ohms  and a calibrated scope.
I back off the level control so grid is not over max. current.
The equations are simple:
Where P = Power, and R is the dummy load at 50 ohms.
First peak power math.  Revised for my new V11...

P = E  divided by R,    with new good tubes it's, P=  100  50  or  200watts peak. (100 squared  then divided by 50 , is peak power)
Now we do Average power, using RMS volts.
The RMS constant is just the square root of 2, so punch in 2, then the key, x    and get 1.414, 
RMS is Peak  divided by 1.414 (or V(rsm) = Vpeak / 1.414)
The recipical works too. .707 x peak = RMS.
P(avg) or  Power average. (like that external meter shows, on the tuner) is  
First the equation is:
  Pavg = (Vrms)2 R   (R= 50)  for   100v-p  x .707  is,  in English, 70.7 Vrms squared  then divided by 50 ohm is 99.97 watts. (I'm NOW GOOD)
 (my  MFJ tuner power meter shows with  new tubes it's  100watts)
end math.

Tthe crude panel meter  inside the SB401, is relative, relative to where YOU set the Pot. R36),. the AT tuners, meter is crude too, but not so bad here, but can be calibrated too, if you want.)

STEP 13,  is the final calibration, but I watch it as I do the steps,  Just be sure , no illegal oscillations occur or noise of any kinds. 
(I have a SDR rig that lets me see any  IMD problems here , 
This photo is ANTENNA OUT. (center coax pin, into huge dummy load)  the below old photo is too low at 65v, but now is  100v-peak with a new V11 Installed (8032 set)

I was Not happy with the above power output (cured now).
I took my own advice (SB200 page) and did the 1 final tube at a time test,  one plate cap off , then reversed them, on V10, V11. (for good reasons)  My HOME GROWN tube tester, for free.
I did this test watching that grid drive is kept to spec. mA.
The results are that one tube is near flat dead V11 (near DOA) one puts out 50v, other only 20v, the power meter shows (antenna tuner) shows  30wattsV10 and 3 watts V11 (so is v11 failing) Got the New tubes in the mail, and my 12v filament mod. Too !  Magic below.
The RCA data sheet shows expect  on average 47watts out of each tube. (the plate voltage and screen and grid fixed bias, sets what you get, at max RF using the RF CW level pot.)
The Heath spec. is 100w so,  mine (rear tube) is weak.  I next installed  12vac heater type , 8032 tubes.. That works just like ours, does, once the heater is fully hot.  Our tubes run in AB1 linear mode -50v grid1.
Revised power readings with fresh PA tubes,  BINGO, new 8032 fired up and I get 100v peak (200vp-p) out. to the dummy load, a true 100 watts average, in CW mode.

Had Lots of fun using the SB401 as its own tube tester, above.
The rig has a DC bias pot (R39)  for the finals, so to run just 1 tube , as a test, use 1/2 the bias per the manual, and turn the level control down and keep grid currents and plate currents at 1/2 spec.  (you are in control here and is super easy test for the finals)
What better GM transconductance test set up can we imagine?, the REAL RIG, is what matters, test the TUBES gain, using the actual radio into a dummy load, 50 ohms 100w min.

This Exciter boat anchor now lives !
I revised the manual , with major step numbers for all setups to calibration (alignments). See files below cover all that, and my custom schematic.
Conclusions, you can tune up the SB401 using a scope easy, I'd say10mhz bandwidth or more is needed,   (assumes 5-30 mhz can be seen at all on some old 1950 scope, I'd bet not)
I also see using a scope as a transmitter monitor , (like above photo) on this old rig, as that  makes it easier to tune it up, as the controls are very peaky.  
This bad fluorescent bulb works in a strong RF field.  Now you know why the Faraday shield is there. The scope is 50v/div. 200v p-p out, Mister Tesla would be proud.

Here are the the 6146/8032 load lines.

Missing parts, 
I got all my missing crystals now  except the  freq. 37.395mhz for the 28.5  band  needed  ,  so I can do the step 9 in the calibration."NEUTRALIZING"  (soon)
Most the crystals were missing, (Heath sold it that way), for sure CW/TUNE and LSB crystals were missing , and all but the lower 3 bands missing.
Wow , got my crystals from a nice HAM.  cool...  and in a flash my exciter wakes up and WORKS !

Magic tricks !, hate the high cost of 6146/A FINAL's  and finding real NOS tubes, not fake ones, more weak than yours,  well,
the famous  Glen E. Zook, K9STH has the answer: it's 12vac !, thanks Glen! 
Tired of the China scalpers (monopoly it is) selling them for $120 a pair? (and advancing fast... )
This 12v tube is same  tube spec, but 12v filaments.  Our transformer is 12vrms, so rewire the tube sockets to 12volts and now have easy to find tubes. (it's only 1 cut and 1 jump on mine, so I did !)
Buy the 8032 tubes for near 1/3 the price.  Even $3 each or less,  Used in many Police MOTRAC HHT now useless radios. I see 4 for $13 ,  on Fleabay (oops, mine now)
To do this sans switch, you must cut those pin 2 grounds and then jumper pin 2 to 2. , then wire pin v10-pin 2 to yell-grn at transformer,  this is the super easy way. The below is using the switch way. (sexy)
  • To do this mod  just cut both pins #2 ground jumps, seen on sockets,  then jump pin 2 to 2 with ,      (  Teflon wire, here, 18ga)
  • Add the switch if you want and add yel-green wire, same gage, and to pin 2 as seen below. (the red wire is unchanged and its factory jumper)
  • This works, I just got 100v peak (200v p-p) {scope} and 100 on the tuner meter, out into my huge dummy load.  Cheers !   (not only  that, but the 8032 has "dark filaments", they run cooler and last longer)

The 8032 are found all over due to near useless, Police FM radio's no longer wanted or used. A glut of tubes exists.  Three cheers to K9STH Glen.!
  I have a life time supply of finals now, super.  (and a full 100watts out)

One other mod.#3 ? that would be great, is installing a RL1 relay socket (modern) and a matching new modern relay. (needs to be a 6 POLE Double throw or the more common 4pole , times 2 side by side and coil in series like the HW100) << finding room is not easy
 Or Just 3 poles, if using as a standalone exicter, unlocked., using only pin groups, 4, 9 and 11 sets only.(bias) but Receiver Mute, needs to work to. (to protect my external SDR or FET front end Receiver )
 RL1 coil is 10k ohms and has 65v keyed,  my guess is 50v relay? (no data sheet exists on old P&B relays)

All FILES and documents, related to the above .

This is my updated  schematic as a learn more about the transmitter.
This schematic shows my phantom mic,  bias supply added. (and new ICOM jack)
The stock SB401, has a powerful, high gain mic preamp V1a, that is for very low level signals, of the low Z mic's of that era. ( 1968 or so)
Care must be taken not to overdrive the tube V1a.  (this is done by raising the value of resistor R1, seen in the top right corner of the above schematic above V1a.  I am using a stock modern ICOM mike (electrlet condensor mic)

My main tuner dial repair guide PDF.

My revised full manual.( I added, scope calibration steps)

SEE MY PAGE ON OLD SCOPES: (and my recommedations on what to buy 1985 and newer)

See my Tube GAS page

version 6,  8-20-2016    , any questions or need help, contact me on my EHAM.com , page, under my K5JXH,  name, there. I will respond.  (50+ years as an electronics tech.)
revised 12-17-2017 (I got phantom power working for my ICOM MIC's  and my custom home made Electret mic.