I texted my friend with the junk store and told him I was ready to do some more shopping. As in deep dive flashlight 🔦 in hand. 110f be damned. xP
He said he is still shut down by the fire chief and as much as I love him I am disappointed that he hasn't really gotten rid of anything :grr
Anyhow I remembered I actually do have something that needs work only I wasn't too interested in working on it then it dawned on me that the Big Boys here work on lots of stuff that they don't want to but took the electronic Hippocratic oath xP and well it's time for me to not judge equipment just get on with it.
So I present to you the RCA WA-44C Audio Generator
IMG_20260729_191928593 (1).jpg
Fear not it's been inspected and deemed good to go
IMG_20260729_191901307 (1).jpg
I'm leery of this because I'm pretty sure it has tubes (high voltage) inside
So first order of the day check out on DBT
IMG_20260729_192422126_HDR.jpg
Seems to be ok that bulb is not near as bright as it looks
Next I started twiddling and checking for output which I could not get any.
However the line frequency seems operational
IMG_20260729_193837190 (1).jpg
So maybe time to get a schematic and looking over it for places to take voltage readings
xP
I'll admit one problem I have is trouble determining if something actually is not working so perhaps I should attach some scope probes to the variable frequency output :grr
Wow looks nice
IMG_20260729_201219582_HDR.jpg
I wonder what that light bulb is supposed to do
IMG_20260729_201320264.jpg
IMG_20260729_201808009_HDR.jpg
:grr
Love it. <3)
A few notes here :loco
Looks like the "line frequency" is easy enough it's just some transformer secondaries I presume routed through a potentiometer xP
As far as the rest of the unit it's SOP that nothing will be touched/desoldered/damaged/mutilated/removed without overwhelming evidence 🧾 of guilt.
All components will be presumed innocent :grr
I was wondering what the weird red diodes were but they look like insulated jumpers :tu:
The schematic looks simple enough maybe I can handle this :lmao:
Something I am intrigued by is the concept of "open capacitor" xP
When I first read about this i thought well of course every capacitor is "open" as in it will not pass DC unless it leaks
But now I think what they mean is there are faulty capacitors which will not pass signal/waveforms/AC etc
So now I may try seeing if some of these capacitors will pass signal in circuit which may be a primrose path kinda like testing resistors in circuit :grr
Also I kind of wondering what's in that metal box section that looks like a doghouse in tube amps xP
Well I actually have a plan
Upon perusal of the schematic I have learned that there is a 6X4 full wave rectifier tube that uses 6.3V heater
So that's what I'm gonna take some measurements on
You are correct about an 'open' cap. It won't allow signal through when used as a coupling cap, and it won't do any filtering when used as a filter cap; it just acts like nothing is there and will not hold any charge.
The metal doghouse is where they keep filter caps in the Fender classic tube amps, but is also sometimes used for shielding. In this case I would guess there is a big tuning capacitor in there that is being shielded.
Can you post schematic?
Yes sir thanks
Too funny I'm sitting here in my bronco sweating buckets at my daughter's graduation can't leave because the parking lot is full of cars in line going nowhere
Edit
https://radiomanual.info/schemi/ACC_instrument/RCA_WA-44C_audio_generator_user_1966.pdf
Still trying to download just the two pages of the schematic
So either fortunately or unfortunately I don't seem to see a problem with the beginning stages of the power supply
IMG_20260731_190546743 (1).jpg
(It was impossible to get at pin 7 of the 6x4 tube so I measured at the junction if the trace from it going to (what I presume) was L1
Then I measured both sides of R19
IMG_20260731_191550489 (1).jpg
So the search continues xP
Also as a NOOB I'm getting to where if I cant clip a lead on to whatever I'm measuring I just don't trust it :grr
I know that's not always possible but that's the case for me :'(
One last set of measurements after a busy day
Probing V2 a 6AQ5 tube
Results seem (to me) to be in somewhat agreement with the schematic
IMG_20260731_223525940 (1).jpg
Kinda early in the game but I'm wondering now if we aren't dealing yet again with a dirty switch somewhere :grr
This has been a pretty interesting project so far.
I was wondering about that light bulb 💡 and no I don't understand it but it has to do with gain and feedback and regeneration and possibly a guy named Larned Ames Meacham and HP 201s
Apparently it acts as a temperature dependent resistor xP
I actually wondered if it was used to set bias or something like maybe the manual would instruct the user to turn a potentiometer until the bulb lit or went out
I checked it it has IIRC about 428 ohms at room temp
So the manual says it's a bridged T circuit so I'm headed off down a rabbit 🐰 hole maybe I need to build one of these circuits out of solid state components and get familiar with its principles of operation xP
I think this unit has a ground problem seems like there is about 8v AC on the chassis.
:grr
So I was looking this over at work getting in a pickle wondering what the heck
The schematic shows two V1 tubes :grr
And I could only find one
Well I may look and sound like an idiot but let there be no doubt ....I am an idiot :dbtu:
Just to help possibly the Pros try to get an insight into the disturbing mind of the noob
I finally figured out that yes there is in fact only ONE V1 the schematic is indicating two different configurations
IMG_20260801_213939773 (1) (1).jpg
So now that I (think) I am past that I think I'm gonna find every resistor going to ground on the schematic and and test resistance
Some results
The last resistors I couldn't find but the others seem to check out
IMG_20260801_230042896 (1).jpg
Then checking V1 in B mode I possibly found the first anomaly
IMG_20260801_230049499 (1).jpg
So it's cool that I may have found something but would it cause it to have no output idk gonna have to check into this
Meanwhile need to probe the other tube xP
Sounds like the light bulb is part of a Wien bridge oscillator (https://en.wikipedia.org/wiki/Wien_bridge_oscillator) type circuit. The bulb acts as a positive-temperature-coefficient thermistor which helps the circuit have high gain on power-up to help start the oscillation, but then to limit the gain.
The results for V3 are in
IMG_20260802_033534934 (1).jpg
IMG_20260802_033529794 (1).jpg
One thing I'm noticing is all my DC measurements take a while I have to sit there until they go from mV to a stable reading
Also I need to learn how to zoom in part of a schematic and make an image out of it :grr
V3B should not have any significant DC at the grid. Where is it coming from? :)
See this is where working on tubes is educational
Because I need to know what/where the grid is
I think it's the skeeter eater sticking out in the middle :loco :lmao:
Ok yeah duh :grr you're right that should be connected to C8
:tu:
I just learned that being lazy and not printing out a schematic will bite you in the ......just like a skeeter eater
ZAP :lmao: :grr
IMG_20260802_113724715 (1).jpg
IMG_20260802_113737188 (1).jpg
I don't think I'm out of the woods yet I'm gonna have to look at these some more because at least to me they don't really match up :grr
Ok wow been getting some good practice on locating the pins on tubes so maybe don't take any measurements yet too seriously :grr
IMG_20260803_012002222_HDR (1).jpg
IMG_20260803_012011860_HDR (1).jpg
Yes I did mark the #1 pins with a red sharpie xP
Anyhow my apologies :'(
But now I'm kinda making my way around the board and getting some consistent measurements
That being said...here's the latest
IMG_20260803_014310486 (2) (1).jpg
IMG_20260803_014247028 (1) (1).jpg
Time for me to make sense of some of this xP
When you say the 2 pages don't line up, I guess you mean at the switches? Yes, that is odd.
Your voltages at V3A are the only ones that seem way off. Why is that plate voltage so low? It seems a very odd circuit that is sourcing the plate voltage from the cathode of V1B, so you will need to check voltage at cathode of V1B, and on each side of R15.
Your pdf viewer is not showing you the full page, that's why they don't quite line up.
The full page images in post #17 are just slightly cropped on width, so you are missing a few bits.
Yes sir thanks I did possibly figure out there is an R22 not fully shown among others.
Also one major setback was encountering this image
IMG_20260803_152541909.jpg
I thought V3A meant the switch was on sin wave and V3B meant the switch was on square wave :grr
So seeing them connected while one was on A and the other was on B almost put me in Gary Coleman (RIP) mode xP
Anyhow thanks for your help I'm gonna keep digging
Btw a couple times I hooked up a scope to where they have pics of signal and never got anything :grr
One thing (of many) I still need to do is hook up a load to the outputs and see if it works
But the manual says in the beginning just hook up probes to configure signal so idk
xP
Well some good news finally I was gonna start checking every single ground again but started messing with it finally connecting the probes to the back instead of the heavily southeast Texas humidity oxidized front jacks.
IMG_20260803_193716798_HDR (1).jpg
One thing (duh) is my dumb A finally figured maybe put the attenuator on x10 when looking for something
That said it is EXTREMELY GLITCHY and that is on the square wave mode
My little scope doesn't do square waves too good :grr
IMG_20260803_193721599.jpg
Despite quite a bit of twiddling
Ok nm as I type I switched to sin wave and couldn't get one but kinda groped the knob a bit and bingo
IMG_20260803_194512312 (1).jpg
But now my meter is only showing about 3.6V AC
Oh well
Ok yeah and turning the big frequency wheel makes everything go nuts too
But managed this :tu:
IMG_20260803_194908234 (1).jpg
Ok yeah the big wheel doesn't even like being slightly touched
So that's cool at least there's hope
Thanks again :dbtu:
I can kinda keep up with this but it gets complicated
It's amazing how people came up with this stuff
IMG_20260803_210945213 (1).jpg
:tu:
When you have multiple tube sections in one tube package they will draw them in an incomplete circle like that, and call out the sections as A,B, sometimes even C for a triple section package. The 6U8 has a triode and pentode in each, and you have 2 of them in the unit (V1 and V3), so a total of 4 sections in those 6U8's.
It sounds like the pots may need cleaning, and maybe the tuning cap (for freq. wheel). Some of the tuning caps with metal vanes should only be blown out with air.
The scope looks like it's not triggering right, so you will have to play with that, and with the time-base knob to stretch out the waveform more.
Yes sir thanks I think what I want to do is build a simple transistor version nothing fancy
The first ones I found all used an op-amp and no disrespect but I wanted to break it down to components
I could use this as a guideline and have to guess the values of resistors and capacitors but that could be fun
IMG_20260803_233515614 (1).jpg
And not worry about being electrocuted like with these tube boat anchors ⚓
So just when you were hoping this thread would sink down like lead it's being bumped one more time xP
I put the front panel screws back in to never be removed again :tu:
In the meantime I decided to leave it on for a while and exercise all the knobs and controls and see if it would decide to work through the front terminals
I managed to get a facsimile of a square wave
IMG_20260804_135950993.jpg
IMG_20260804_140028159.jpg
And then lost it then could never get it (or anything) back again :grr
So yeah this thing needs a lot of work but im moving on for now xP
Thanks to everyone here you rock :dbtu:
(https://www.ssguitar.com/index.php?action=dlattach;attach=14877;preview)
Nice old school PCB designed using Bishop Graphics black tape and pre shaped sticky pads.
Very popular in 70s 80s I used it a lot before buying a computer to run Autotrax and Tango PCB
(https://i.ebayimg.com/00/s/MTYwMFgxMzE4/z/uIoAAOSwXQRe46A5/$_57.JPG?set_id=8800005007)
(https://i0.wp.com/eetimes.com/wp-content/uploads/dashton-0001-06.jpg)
It sure brings memories.
Always a pleasure to hear from you my friend :dbtu: