Amp project - 5w single ended EL84 circuit not working - volume loss?

[jdel77]

Hi all,

Recently I picked up this amp project for cheap - it's a 5w single ended amp made by Alien. Uses an EL84.
The issue is that the amp passes signal, however it is extremely quiet.
I've measured pins on the 12AX7's and all seems right there in terms of connectivity and voltage to the plates, however I'm suss on the EL84.
Which pins should be connected to high voltage usually in an amp like this?

The EL84 tube socket was loose and moving - the pins were solidly grounded, but the ceramic/plastic base was loose. I've replaced the socket with a new one, and reflowed all solder joints on the back of the pcb, but still the same issue - very quiet, whisper loud signal.

All pots work and affect the signal (volume, gain, treble and bass).
I have also measured all resistors and none seem to be measuring as open - all measure on my multimeter, or their values exceed the 2Meg that my multimeter can read to.
I have also measure high voltage coming in from the power transformer - 120v on each of the diode arrays on the left side of the PCB in the image below

What is volume loss usually a symptom of?

I guess the next step is to look at the capacitors.
It looks to be a solidly made amp, and the previous owner said it was working fine, then one day it stopped.

Many thanks for any help.
Jesse.

[xtian]

Google EL84 pinout.

Try a different power tube yet?

[jdel77]

Google EL84 pinout.

Try a different power tube yet?

Hi, yep I've tried different EL84's. Same deal. Looks like they have one anode connected, Pin 7, and that's getting high voltage.
I'll measure the voltages again tonight.

[Synchu]

There's a single anode in EL84 and it should be getting the high voltage.
https://www.jj-electronic.com/images/st ... f/el84.pdf

I will kindly suggest, reading your post, to go through:
http://www.valvewizard.co.uk/ (see the articles at the left)
and this:
http://www.aikenamps.com/index.php/white-papers

in their entirety, prior to messing with high voltage DC.

Apologies in advance, if I misinterpreted it, however, debugging a tube amp without knowing how to find where the high voltage goes on a standard pentode sounds very dangerous to me.

Niki

[jdel77]

There's a single anode in EL84 and it should be getting the high voltage.
https://www.jj-electronic.com/images/st ... f/el84.pdf

I will kindly suggest, reading your post, to go through:
http://www.valvewizard.co.uk/ (see the articles at the left)
and this:
http://www.aikenamps.com/index.php/white-papers

in their entirety, prior to messing with high voltage DC.

Apologies in advance, if I misinterpreted it, however, debugging a tube amp without knowing how to find where the high voltage goes on a standard pentode sounds very dangerous to me.

Niki

No harm in asking I know there's one anode in an el84, however, didn't know if other pins should be be getting voltage as well. I appreciate the post.

[pompeiisneaks]

Do you have a slightly bigger picture? The one linked is pretty small, hard for me to see. Do you have a schematic? If not, it might be worth your while to research it.

Do you have an oscilloscope or DMM?

If you have a scope, then input a signal and see if you see each stage amplifying it well, and if so, find where it drops.

If you don't have a scope but do have a DMM, then put it on AC volts and put in a sine signal at say 500mV and check at each stage of the signal path to see where it's being amplified, and where it's lost etc.

Often low output can be difficult to find, it can be bad solder joints, it can be something sending too much to earth, it can be a PI with poor reference to earth, (Since this is SE that's ruled out) etc.

~Phil

[Stevem]

If you have a ohm meter check pin 3 of the EL84 for us, does it go right to ground and you read a short, or do you read a resistance above 150 ohm?