Supro 1624t combo build

[Ampzone]

Just finished a second supro 1624t kit, having some issues. Using this basic layout http://www.sluckeyamps.com/supro/supro.pdf but made a couple changes. kept the 7w 250ohm 25uf 25v arrangement like the original and left off the tremolo section entirely.

I raised the stock 1.5k on v1 35uf cap to 8.2k to make v1 pin 1 come up around 200v v1 like the schematic. v1 Pin 6 is about 110v.

I used a 10w Valco clone power Classic tone 40-18062 and matching classic tone 40-18063 10 watt output. JJ 5y3- EH6973 power tubes.

Right now the voltages all look really spot on to the original but when the vol 2 pot or tone control is turned on a bad distortion buzzing shrill honking sounds takes place. Squawking sound when you hit the standby switch to cut power. When Volume 2 is Left off the sound is fine and controls work on Vol 1 pot and tone pot.
But separate issue for some reason the amp seems not near as loud as I would expect with a single C12r 25w 8ohm Jenson 12".

Any ideas on the noise possibility and how to beef or mod this thing up for a little more output?

[xtian]

I recently built a Supro from sluckey's schematic+layout. Went very well, sounds excellent.

Notice that the two input channels are nearly identical. If one works and one doesn't, it's a wiring error, component failure, or tube failure.

[Ampzone]

Cool

Yeah, Ive measured each component no suspects yet but it gotten worse just buzz hum on any setting. Removing v1 and v2 the buzzing loud hum sound goes away. With all tubes in the multi meter probe when it touches any part the buzz stops unless you measure the 6973 plate then it goes worse noise and pulsing. like a really bad grounding issue but I cannot locate it.

[xtian]

Yeah, sounds like you've got a bad solder joint or something. Don't just measure components, measure continuity between connections.

[Ampzone]

Yeah, sounds like you've got a bad solder joint or something. Don't just measure components, measure continuity between connections.

I bet your right. Im re-floating all the solder joints then checking continuity again.

[Ampzone]

Yeah, sounds like you've got a bad solder joint or something. Don't just measure components, measure continuity between connections.

I checked up and down no luck until I swapped the OT leads on the output, pin 9 plates, then all the noise quit. Maybe polarity and not a loose joint

[g1]

So it's working correct now?
Was one of the changes to the circuit adding an NFB loop?
I was thinking about OT phasing when I read your post but didn't mention it because there was no NFB in the schematic.

[Ampzone]

So it's working correct now?
Was one of the changes to the circuit adding an NFB loop?
I was thinking about OT phasing when I read your post but didn't mention it because there was no NFB in the schematic.

Its working now. But to verify it was a phase issue I put it back like it was, no noise, very confusing. The only changes I made to circuit posted earlier was replacing a 8.2k from stock 1.5k to the 35uf cap on V1 to bring up the voltage to around 200v pin1 V1. And raising that 35uf cap to a 50uf. The tremolo circuit is left out and I went with the original 250ohm 7w 25uf instead of a 470ohm.

Assuming the issue is gone what mods could be done to add a little extra kick to this circuit?

[Ampzone]

I put the amp in its cabinet and then the noise buzzing came back- lots of distortion on the notes plus ringing. But It only happens on channel 1 if the volume and tone are turned up. channel two works fine if ch 1 volume and tone are off. the Noise stops if you put anything metal on the chassis or give it a little thump.

So far I think we can rule out the tubes, the phasing possibility. Something seems loose but where?

[g1]

I think you may have an oscillation problem.
Touching, thumping, etc. are just altering the feedback loop enough to stop it.
The oscillation is being heard as distortion.

[Ampzone]

I think you may have an oscillation problem.
Touching, thumping, etc. are just altering the feedback loop enough to stop it.
The oscillation is being heard as distortion.

Sounds likely, I just cannot find any part that is bad or any DC where it should not be. Any ideas?

[xtian]

Any ideas?

If you post some photos, that might give us some ideas...

[Ampzone]

I think you may have an oscillation problem.
Touching, thumping, etc. are just altering the feedback loop enough to stop it.
The oscillation is being heard as distortion.

Maybe a loop. would a dying OT or output tube be a possibility? Just putting the DMM + probe on DC and touching V1 35uf polarized cap either side, makes a really high pitched howl. All the voltages look spot on, I replaced the polarized caps, continuity looks goods, grounds ok.

Where would you be looking first? in a process of elimination.

[g1]

It could even be a lead dress issue. Like xtian said, some pictures of the wiring might give somebody an idea.