Sound City - Concord - Tube Amp - No Signal - Please HELP

[CoopDaKill]

Hi guys,
I found a Sound City - Concord, Tube Amp. Made by Dallas Arbiter in U.K. dual EL34's It has NO Sound. Not passing signal. Just a faint hum. I'm using a 4x12 cab hooked to EXT. Speaker jack. I'm pretty sure the output tranny is OK, because I can hear noise, while taking voltage readings with my meter. I've checked the tubes. All good on my Eico 667. Checked and cleaned pots too.

There is a .01 disc cap loose, (see pic 1) can't find where it goes. ??? One lead is hooked to the ground switch. This thing is a pain because the controls are on a seperate front panel, from the amp chassis. Check out the ugly slider pots. She's ugly, but I've got to bring her to life.... I've posted pics and schematics. Thanks.

Schematic notes: The first pdf has all Sound City schematics. The Concord is on page 4.

[soundguruman]

If the cap is broken off, that's probably why.

[Jazz P Bass]

"There is a .01 disc cap loose, (see pic 1) can't find where it goes. ??? One lead is hooked to the ground switch."
Is that not the 'death cap'?
Do you have a signal generator?
If so, trace out where the signal fails.
Reduce the problem.
Is the signal reaching the EL34 grids?

[CoopDaKill]

"There is a .01 disc cap loose, (see pic 1) can't find where it goes. ??? One lead is hooked to the ground switch."
Is that not the 'death cap'?
Do you have a signal generator?
If so, trace out where the signal fails.
Reduce the problem.
Is the signal reaching the EL34 grids?

EL34's voltage redings:
pin 4 = +468 vdc
pin 5 = -40 vdc

Speaking of the "Deathcap", Should I connect the loose end to chassis ground? After all, the other end is connected to the ground switch. I've included some more pics of the loose .01 cap, and the ground switch. Sorry, I don't have a signal tracer. Thanks for all your help..........

Please bare with me, I'm still learning.

[olddawg]

EL34's voltage redings:
pin 4 = +468 vdc
pin 5 = -40 vdc

Speaking of the "Deathcap", Should I connect the loose end to chassis ground? After all, the other end is connected to the ground switch. I've included some more pics of the loose .01 cap, and the ground switch. Sorry, I don't have a signal tracer. Thanks for all your help..........

Please bare with me, I'm still learning.

Has someone retrofitted a 3 wire power cord on it? If so they may have just floated the death cap so it would be there if someone wanted it to be "original". I can't see a ground reverse switch causing a problem. If your filaments are lighting up on all tubes and you have B+ there is something else wrong. You will have to troubleshoot the signal path. If you do not have experience I would recommend taking it to a decent shop. You could hurt yourself.

[CoopDaKill]

No 3-prong cord installed. There's not many people in my area that does repair work. That's why I started trying to fix things myself. And, it's much more gratifying. I'm not a total green-horn, just not at your guy's level. And yes, I know about the lethal voltages, even when powered off. Learned that one the hard way. Made me a discharge probe after that one.... LOL... I just got an O-scope, but no probe for it yet. I'll get a probe ASAP. Any other ideas on the Concord problem? Thanks

[Jazz P Bass]

[QUOTE=CoopDaKill;286992]EL34's voltage redings:
pin 4 = +468 vdc
pin 5 = -40 vdcQUOTE]
O/K. Those are the 'static' voltages.
The amp is sitting there waiting for a signal.
Hook up something, anything, to the input jack (CD player, MP3 player, a guitar)
Now with a signal coming through the amp, monitor the grid pin of any of the two EL34 tubes.
Use a volt meter & set it to read Volts AC.
If the grid is not getting a signal then you work your way back.
If it is, let us know the amplitude of it with the amp maxed.

[g1]

Your pictures show a second cap connected to the ground switch, what is it's value and what does it connect to? The schematic shows the ground switch cap to be .05, not .01.

[olddawg]

[QUOTE=Jazz P Bass;287004]

EL34's voltage redings:
pin 4 = +468 vdc
pin 5 = -40 vdcQUOTE]
O/K. Those are the 'static' voltages.
The amp is sitting there waiting for a signal.
Hook up something, anything, to the input jack (CD player, MP3 player, a guitar)
Now with a signal coming through the amp, monitor the grid pin of any of the two EL34 tubes.
Use a volt meter & set it to read Volts AC.
If the grid is not getting a signal then you work your way back.
If it is, let us know the amplitude of it with the amp maxed.

Make sure the amp always has a load.

[CoopDaKill]

: g-one, that cap is a .047. So, that's the ground switch cap.

: Jazz P Bass, Thank You for helping me understand this a little better. I'll test those grids tomorrow, and let you know the results.

[CoopDaKill]

[QUOTE=Jazz P Bass;287004]

EL34's voltage redings:
pin 4 = +468 vdc
pin 5 = -40 vdcQUOTE]
O/K. Those are the 'static' voltages.
The amp is sitting there waiting for a signal.
Hook up something, anything, to the input jack (CD player, MP3 player, a guitar)
Now with a signal coming through the amp, monitor the grid pin of any of the two EL34 tubes.
Use a volt meter & set it to read Volts AC.
If the grid is not getting a signal then you work your way back.
If it is, let us know the amplitude of it with the amp maxed.

Hooked an Ipod to the input, with amp maxed, the output tube grids measure 1.9 VAC. So, I guess this means the input signal is NOT reaching the output tubes? Correct?

I dug out an oscilloscope from the basement, no BNC probe, of course. Ordering that ASAP. The scope is a Good Will (brand) model GOS-3310. Nothing to brag about, but I think it will work?
Thank You ALL, for your help.

[Gtr_tech]

Should work fine.

[CoopDaKill]

OK, Finally got my O-scope probe. Also using a signal generator app on an Ipod for signal input. I've probe around the circuit, but everything looks the same on my O-scope? What am I doing wrong? Thanks.

[Jazz P Bass]

You have previosly measured 1.9Vac on the output tube grids.
That is clearly not going to drive the tubes very hard.
Find where it's dropping out.
Start at the input jack.
Work your way down towards the output tubes.
Look at each I every grid.
Something must show up as abnormal.