Help with first build. 5F1 Champ

[astark117]

Hi, I've been working on this amp for a week now, and I'm not getting any sound out of it. I have triple checked my connections and gone over all the voltages several times. Right now the pilot light comes on, the tubes all glow, and I get the following readings:

From left to right:

22uF Filter Cap: 322V
10uF Filter Cap: 280V
10uF Filter Cap: 235V
.022uF Cap 1: 139V
.022uF Cap 2: 147V
6v6 pin 8, 25uF Cap: 16.61V
between 1.5k and 22k resistor: 1.37V
12ax7 pin 3, 25uF Cap: 1.29V

Please let me know if you have any ideas why this would happen. Thanks in advance.

[loudthud]

When you say 25uF cap, is this the one connected to pin 8 of the 6V6? It would seem from your voltages that very little current is flowing in the 6V6. Check the connections to the output transformer and measure all the voltages at the 6V6 tube socket.

[astark117]

I'm sorry, I should have specified. The 25uF capacitor I listed above is connected to the 12ax7, pin 3. Pin 8 of the 6v6 reads 16.61V.

[Bruce / Mission Amps]

I see you do have a voltage drop across both 100K plate load resistors of the 12AX7, which means that both triodes are biased on.
And, the power tube is drawing idle current... so it is probably on too.
Sounds like an audio path error and it could be as simple as having one, or both of your input jacks wired wrong.
Or possibly, the speaker jack's "hot" lead is grounded... etc etc etc
Why don't you shoot a quick photo of the eyelet board and the tube connections... these are pretty simple amps and for it not to work... means a simple error too.

[nickb]

Plug into jack 1 and turn the volume up. Touch your meter probe on grid one of the 6V6. Hear anything? If no, you've narrowed the problem to the 6v6 output section.
If yes, repeat with the 12ax7 grid connected to the volume control. If you hear something then the problem is on the input 12ax7 section, if not then it's this section.
When I'm checking my wiring I find it helps to do it with someone else.

[astark117]

Thanks, I'll try and get a pic up as soon as possible, it might be a few days though. In the meantime I'll go over my input and output jack wiring, and check the audio path for shorts.

[astark117]

So I went over my input and output jack wiring and discovered that I accidentally wired all the jacks backwards. I fixed the problem and plugged it in. Now it makes this loud screaming noise, kind of like a whistling kettle. Any ideas why this may be happening?

[Chuck H]

Reverse the OT leads. If the problem stops, your done. If the problem gets worse, we're still looking.

[astark117]

Which leads were you referring to? the B+ and plate leads or the common and 8ohm leads?

[Chuck H]

Either. Whichever is easier. Actually, you can probably test if this could help by disconnecting the feedback circuit. just lift either end of the 22k resistor that's between the output jack and the last preamp cathode. If this stops the screaming, reconnect the resistor and swap either the primary or secondary OT leads.

[astark117]

Thanks, the output transformer leads were the issue. Now it plays great, except that when I get to around 11 on the volume knob it makes a popping/hissing sound. Is this a common thing? or is there an issue with the circuitry?

[Chuck H]

when I get to around 11 on the volume knob it makes a popping/hissing sound. Is this a common thing? or is there an issue with the circuitry?

Both. I've known a few "Champs" that did this. Is it a hiss that comes on as volume is increased and then a pop sound as the sound shuts off? This would be a parasitic oscillation. Probably due to lead dress, grounding or both.

[astark117]

It is, I'm going to go through the chassis and try to isolate the AC wires as much as possible. Thanks for all of your guys' help! It would have been impossible to finish without your input.

[pharmdawg]

Reverse the OT leads. If the problem stops, your done. If the problem gets worse, we're still looking.

I just finished my 5f1 and right off the bat i get the high pitched squeal ..I emailed the guy at Mojotone about the OT leeds and he told me the manifacture often changes the leeds around and that its really a try and see what happens... So im gonna try reversing the leeds ...i havent tested anything yet and im a little concerned that the 6v6 tube turned blue on me....

[astark117]

Thats what I did and it worked perfectly after that. Its also normal for the tubes to glow a bluish violet color.