Egnator rebel 30 no sound

[nosaj]

I've got an Egnator Rebel 30 with no sound.
Input sound through EFX return good power amp action so that half is ok.
Input signal Pin2 V1 preamp Signal passed all the way to Poweramp though low volume. Input signal at R8 signal passes to Pweramp low volume.
So one issue is the input jack somehow. Cleaned it no effect.
So I move on the the low voltage aspect.
Pin 1 V1 only getting about 7 volts not nearly enough for amplification So I check the B4+ voltage at R55 because I have not pulled the pcb out yet. C43 side getting a 137 vDC other side of resistor getting roughly 7vDc. The resistor in question is orange black brown indicating a 300ohm resistor.

So something is hinky an will require pulling the pcb for sure.

Pulling board next.
nosaj

[Chuck H]

I'd start by checking C3 and C34 to see if they're shorted. If they're not I would pull the preamp tubes one at a time testing each time to see if it might be a bad tube. Though I've never actually witnessed a 12ax7 failing like that. In either case I would expect a greater loss of voltage for B4+ if R55 is actually only 300 ohms. Kooky.

EDIT: It actually seems impossible that R55 could be 300 ohms. If that were the case with 130V across it would be dissipating over 50 watts!?!

[nosaj]

The brown and black markings are pretty sure thats what they are. The orange (maybe discolored?) But Egantor doesn't list values so I'm kinda at a loss of what it should be.

I'll have to pull the board for c3 and c4, so I'll check the tubes first, though they somewhat work when injecting V1 pin2.
nosaj

[Jon Snell]

The brown and black markings are pretty sure thats what they are. The orange (maybe discolored?) But Egantor doesn't list values so I'm kinda at a loss of what it should be.

I'll have to pull the board for c3 and c4, so I'll check the tubes first, though they somewhat work when injecting V1 pin2.
nosaj

Have a look at the Rebel 20 there are values on that and they are very similar.
It's only an amplifier, not complicated. Check the anodes for a ball park voltage and the cathodes of the triodes for a couple of volts ish. The cathodes will tell you if the valves are working.

[Chuck H]

Unfortunately the 20 has one fewer preamp tubes than the 30. So the HV rail is branced a little differently and it's not likely the values would be the same even for relative circuit position.

[g1]

The resistor in question is orange black brown indicating a 300ohm resistor.

What does it measure? Something closer to 3K ?

[Chuck H]

The brown and black markings are pretty sure thats what they are. The orange (maybe discolored?) But Egantor doesn't list values so I'm kinda at a loss of what it should be.

I'll have to pull the board for c3 and c4, so I'll check the tubes first, though they somewhat work when injecting V1 pin2.
nosaj

You can check for shorts in C3 and C34 by checking resistance to ground at R1 and R2. Unless you can tell which end is which for those resistors circuits you'll need to test at both ends. Neither should read short. I would expect tens of K ohms. Can't say without values indicated though.

[Chuck H]

What does it measure? Something closer to 3K ?

I thought that too. Thinking a red stripe could turn brown overheated. Even then it would be passing about 5W. The rating for those resistors in the Rebel 20 is 1W. I think it would blow open at that point but maybe not.

[g1]

I thought that too. Thinking a red stripe could turn brown overheated. Even then it would be passing about 5W.

Good point. How about this: 300 ohm colour code is 10K colour code backwards.

[Chuck H]

Good point. How about this: 300 ohm colour code is 10K colour code backwards.

Thank you! I didn't want to suggest it because I thought it sounded goofy. Everyone knows the first band for the numerator is at one end of the resistor and the tolerance code band is at the other, right? So if the color code started nearer the middle, the last band was closer to an end and there were no tolerance code band it would be easy to read it wrong. That seems like a long shot but I'm going to go look at some Rebel boards and see what the resistors look like.

EDIT: All the Rebel 30 resistors seem to be two bands, a numerator and a tolerance band just like normal. What's weird is that the value is different from amp to amp. Though it's hard to see I found R55 in three different amps. The numerator does look to be brown in two of them. What I see is y-bk-br (400), gy-bk-br (800) and y-p-r (4.7k)

Since 400 and 800 are no values I've ever seen in an amp I'm thinking there's something odd going on with the codes for these resistors. In the Rebel 20 the value for the most equivalent part of the circuit is 4.7k and that's without an extra 12ax7 to supply. As you can see below the 4.7k value for R55 was found in one Rebel 30 board I imaged. Could be the intended value for that resistor is 4.7k regardless of the strange markings?

[g1]

Could be the intended value for that resistor is 4.7k regardless of the strange markings?

I'd guess that it's not the markings but heat effect on the colours. Probably that one is running hotter than others around it?

[nosaj]

Ok pulled the board and the resistor. It measures 4.7k. If i have 135 going in , you need at least a 100v making it to the plate correct?
Could the resistor be breaking down with voltage? If i put in a 100v on a jig what should I expect to see on the other side of a 4.7k resistor(not as familar with Ohm as I should be but if you give me the formula I'll work it out.
Here are pics.
nosaj

[g1]

Put the resistor back in and remove C34. What happens to the voltage? If it's still low, remove V4 and recheck.

[Chuck H]

Put the resistor back in and remove C34. What happens to the voltage? If it's still low, remove V4 and recheck.

This^^^^^^^^^^^^^^^^^^^^^^^^^^

[nosaj]

199 vDC.. also noticed bottom of cap looked kinda funny. When I fired up amp to test voltage looked like I had a small fire embering at c34 opposite of the funny looking lead on the cap.
I'll throughly scrape the carbon away and seal it. I'm really disappointed in my atlas cap meter. Guess I should be using like a heathkit or something that tests at full voltage.

nosaj
Will follow up when done thanks guys.
nosaj