ECC83 issue, high voltage output

[hozone]

Hello,

I'm building a guitar amplifier out of a ECC83 and a EL95 from an old radio.
Reference preamplifier schematic is the Fender Champ 5F1 (find attached), except I'm using 2k2 instead of 1k5, and I've added the tone control (Fender Brownface like).

I've built it on breadboard... all ok
Done soldering on protoboard... all ok
Review soldering and final step... fail :(

To check the failure I start testing with a 0.1V sine @ 500Hz.

The failure: I measure 120V peak to peak on output from stage 2 of the ECC83, after the decoupling cap. On breadboard I've something like 9V if i remember well.

I've found an odd thing happening (at least odd to me, that I'm not a tube expert).
I've disconnected second stage from first stage.
If I enter the test signal in stage 1 control grid, I get 4.7V output after decoupling cap on plate almost. That is ok.
If I enter the test signal in stage 2 control grid, I get 2.3V output after decoupling cap on plate almost. That is ok.
BUT, if I connect stage 1 output to stage 2 input, the output of stage 2 is not 120V almost.
What's going on here?

Later today I'll test again the tube on a breadboard, hoping to don't have damaged it during tests.
I'm testing without the power EL95 connected. I hope I've not damaged it when 120V entered it's grid on the first ignition.

Am I missing something?
Thanks!

[sluckey]

If I enter the test signal in stage 1 control grid, I get 4.7V output after decoupling cap on plate almost. That is ok.
If I enter the test signal in stage 2 control grid, I get 2.3V output after decoupling cap on plate almost. That is ok.
BUT, if I connect stage 1 output to stage 2 input, the output of stage 2 is not 120V almost.
What's going on here?

The gain of stage 1 is 47 and the gain of stage 2 is 23. When connected together (cascaded) the gain is 47 x 23 = 1081. So, if you put .1V into the first jack you should get 108.1v out of the second stage. I don't see a problem.

[hozone]

  If only I've used brain! Thanks!

So, now I've a couple of other questions.

1)
Why on my breadboard I've a 9V almost output? Something wrong there? Or my tone control is lowering the signal by 4.3V = 4.7V-0.4V, given the output of 9V/23gain_of_second_stage = ~0.4V.

2)
Isn't 120V too much for the grid control?
I mean, let's take the Champ as example. 6V6GT grid control voltage by datasheet -12.5V with 250 on plate. That is 10 times more almost than my 120V.

I'm sure I'm missing something here, my experience on tube is so little.

[shooter]

A TS (tone stack) will eat signal
the volume pot will limit the amount of signal that makes it to the grid to something reasonable (typically I like to have between 1 and 4 VAC available for the "next stage")

[sluckey]

Adding a tone control puts an additional load on the signal so it will be lower amplitude. Ever notice how distorted a champ sounds when the volume is at max? That's because the 6V6 is being way overdriven. That distorted sound is what a lot of people like about the champ. Use the volume control to lower the amplitude of the signal if you don't want to overdrive the 6V6.

[PRR]

{snip}... I'm sure I'm missing something here.....

You have showed us how Fender built it. You have not shown how YOU built it. You have one stage, you have another stage, you have a tone network.... You could have anything from 0.9V to 109V, depending how you connect these pieces.

We don't have a chalk-board here, but drawings are very useful. Pencil and cellphone?

[hozone]

Hi all,
find the issue, on my board I've a short between stage 1 output and stage 2 input.
Now it all works.
I've to lower a little the bass response, but it sounds pretty good right now.

Find attached the schematic.