Just when you thought it was safe to go back to the Noobie section

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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. 

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 

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  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

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Fear not it's been inspected and deemed good to go

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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

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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

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So maybe time to get a schematic and looking over it for places to take voltage readings

 

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 

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Wow looks nice

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I wonder what that light bulb is supposed to do

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[J M Fahey]

Love it.

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A few notes here 

Looks like the "line frequency" is easy enough it's just some transformer secondaries I presume routed through a potentiometer 

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 

I was wondering what the weird red diodes were but they look like insulated jumpers 

The schematic looks simple enough maybe I can handle this 

Something I am intrigued by is the concept of "open capacitor" 
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 

Also I kind of wondering what's in that metal box section that looks like a doghouse in tube amps 

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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

[g1]

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?

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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

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So either fortunately or unfortunately I don't seem to see a problem with the beginning stages of the power supply

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(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

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So the search continues 

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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 

I know that's not always possible but that's the case for me 

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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

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Kinda early in the game but I'm wondering now if we aren't dealing yet again with a dirty switch somewhere 

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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 
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 

I think this unit has a ground problem seems like there is about 8v AC on the chassis.

 

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So I was looking this over at work getting in a pickle wondering what the heck

The schematic shows two V1 tubes 

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 

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

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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

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Some results

The last resistors I couldn't find but the others seem to check out

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Then checking V1 in B mode I possibly found the first anomaly

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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 

[Kaz Kylheku]

Sounds like the light bulb is part of a 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.