Please help with my first build 5F1 with no sound

[icy_wind500]

Well well....it's a 5K OT? but I think it should read higher than that, get on to the supplier show them what you've found and get a refund or a replacement.

By the way.... would the OT take out any other parts along with it since its not working?

[loudthud]

ok I think we found the problem....
[ATTACH=CONFIG]18907[/ATTACH]

Its only 1.2V across the primary....

It looks kike the meter is set to DC volts. That won't work if you are trying to measure AC volts.

[Steve Conner]

Yeah, he's looking at the power tube idle current times the DCR of the primary. Ought to be a bit more than 1.2V I should think.

Not a complete diagnosis though: we don't know whether the OT primary is shorted, or the power tube is failing to pass current. What voltage were you getting across the power tube cathode resistor?

[tubeswell]

Yeah, he's looking at the power tube idle current times the DCR of the primary. Ought to be a bit more than 1.2V I should think.

Not a complete diagnosis though: we don't know whether the OT primary is shorted, or the power tube is failing to pass current. What voltage were you getting across the power tube cathode resistor?

He was getting about 7 Volts (across 470R) with a B+ around 360 IRRC

[tubeswell]

B+ will be over 400V...this'll be interesting

If the HT winding is 655 end to end, it'll be 327.5-0-327.5 taking into account the centre tap, which will deliver about 360 B+ with a 5Y3GT in this amp.

[telenut62]

All good in theory Tubeswell, but his AC supply is prob closer to 250V....as mine is, and that throws the B+ out quite a bit. As he's using a NOS 6V6 prob best to keep it close to the 350V. Come to think of it, would a bad 6V6 be a poss cause of his probs. I don't know if he's swapped the tubes?

[telenut62]

Ah yes it's set on the V- setting, missed that last night...was passed my bedtime...oh dear!

[loudthud]

The main problem with the amp seems to revolve around the low screen voltage. That lowers the voltage to the preamp. I had a tube once that had a broken connection to the plate internally. It drew lots of screen current, there was still good plate voltage at the socket, but no plate current and low cathode current. No plate current, no sound from the OT. Is there a DC voltage drop across the OT that would indicate plate current is flowing?

Just thinking out loud. My .022

[tubeswell]

He said the meter was on the AC setting (over on the telecaster forum) FWIW

[tubeswell]

If he's getting 327-0-327 on the secondary with the wall voltage that he's got, that will nevertheless amount to about 360VDC B+ with a 5Y3GT for this amp. (But if he's got a sovtek/russian 5Y3, it'll be higher)

[Bruce / Mission Amps]

Yes, but unless there is something bad with the power tube, miswired socket or a wrong measurement... It seems unlikely that the 10K screen node resistor would be seeing what amounts to a 17ma - 18ma current flow.
The single preamp in a 5F1 tube doesn't draw more then about 2ma-3ma and the screen of a 6V6 in these amps is similarly low at idle.
And 15ma of current through the 470 cathode biasing resistor does imply to me that the screen is drawing most of the current due to a defect in the power tube or the OT.
Let's see what he says the DC resistance of the OT primary is vs the voltage drop across it's resistance to see if there is any plate current.... hmm?

[Steve Conner]

I agree, I'd be checking all the wiring associated with the 6V6 plate circuit. Are you getting voltage at the plate pin on the 6V6 socket? If so, did you connect the wire to the right pin?

Failing that, try another 6V6 tube before condemning the OT.

[tubeswell]

He says he got 2VAC on the primary (with 5VAC applied to the secondary) here:

My boothill 5F1 Arrived ! - Page 5 - Telecaster Guitar Forum

[loudthud]

It looks like the OT is bad, probably an open primary. Finally a clear pic of the meter face. I'd feel better if the OP did a simple ohm check to confirm.