5f6a turnup troubles

[booginator]

I've got a 5f6a scratch build with scavenged parts leaving me puzzled. Injecting an audio signal from a portable player at the treble pot wiper I have minimal audio. My only significant dc voltage deviation is on my B+3 that runs through the 4.7k dropping resistor at ~ 430. At a bias voltage of -48 I'm drawing less than 6ma of cathode current. I should also note that this unit being a salvage project, I'm using and 18.2H choke (stock is 5H) from a jr-20 tone cabinet and a PT from a Wurlitzer 4100. I'm stumped. Thanks for any help. I figured that I'd have to either call in some adult supervision on this amp or use it for target practice.

[booginator]

I forgot to note that I get more volume running my signal through the input jacks. I think most if not all of my volume is generated from the preamp. Also tried rolling power/preamp tubes.

[1ampman]

You need to find an amp tech with test gear. The signal will have to be traced thru every tube to see where the problem is ..Did the amp ever work correctly?? Is there a schematic for it?? This is not a beginner project... sorry

[mac dillard]

what is the voltage at pin 4 of the power tubes and how are you measuring the cathode current.

[Enzo]

Your portable player puts out a volt or so of signal. The signal levels in a tube amp are way larger than that, so it is expected your output would be low when injecting that signal in the middle of the amp.

[booginator]

Thanks for the input people. The signal I inserted into the treble wiper came from the headphone jack of a ghetto blaster. I used this technique when the power amp worked and the volume was loud enough to shake dental work loose. My pin 4 output tube voltage is 466vdc. Leo's original layout calls for 432vdc, but most all of my voltage are reading ~10 north of spec. I attributed this difference to lower mains voltage commonly generated 60 years ago. Curiously my cathode bias voltage on the first preamp tube are a bit low at +1.6 vs the specified 2.5. I think this might be due to functional differences between current production and US made 12ax7's. When I sub GE 12ax7 into position 1 the cathode voltage bumps up to ~2.2vdc. I tried plugging a guitar into the amp this morning and my volume/tone roughly compare with a Fender Champ driven hard.

[g1]

So it was working fine before? And you used the same spot to inject the same signal level before?
The power tube cathode current seems a bit suspect, any chance you lost a ground there? Does voltage at both power tube pin 8's read 0V ?
Head or combo? Anything funny about speaker jack(s) ?

[mac dillard]

Are you reading the -48 bias voltage from the tube pin? If not check what voltage you have at the tube. At 6ma. cathode current your power tubes are not performing.

[booginator]

Thanks will check, tomorrow. Wife will divorce me if I don't leave it alone for a day. Will report outcome.