Peavey Triumph 60 on Bench

[fdesalvo]

What a week with this amp. After going across multiple hurdles to get it where it sits now, I'm dealing with a final bit of background hum that's resolved by pulling V4. The noise was twice as bad and partly resolved by refreshing the heater's filter supply and bridge, but here we are. The preamp board is 100% within spec. Any ideas out there? Already swapped tubes. I'm diving into the potentiometer/relay board now. The final frontier, perhaps. TIA, all and hope you're having a happy new year.

[xtian]

Whoa, I'm lost on this one. The Peavey T60 is a guitar. And what are "heater filters" ?

[fdesalvo]

Whoa, I'm lost on this one. The Peavey T60 is a guitar. And what are "heater filters" ?

My bad - fingers faster than my brain. Peavey Triumph 60 and the heater supply's filter caps. lol

[TomCarlos]

And here is a link to the schematic.

Triumph 60 / 120

[fdesalvo]

Thanks, Tom. I neglected to mention all preamp voltages look good. Noise not changed by pots, jacks (fx/input), channel, etc. pulling v3 cuts noise by 50%, but pulling v4 silences.

[TomCarlos]

You swapped tubes, but did you replace them? What are the chances that V3 and/or V4 are bad. Did you put these in tube sockets 1 and 2? It's always good to have a couple extra 12ax7's on hand.

UPDATE: V4 is a 12AT7. Do you have another similar tube to try there?

[g1]

How about with all tubes in, but empty cord plugged into FX return ?

[fdesalvo]

I stock new tubes. Used new complete set and no change. Also tried the fx loop to no avail. That 12at7 is running at 420+ Volts. Yikes.

[glebert]

I had a Triumph 60 with basically the same problem, but it would seem to sometimes be worse than others. I never did fix it, moved it on to someone else to try. I remember it was weird that sometimes when I would probe some V4 pins with a DMM the noise would get better, and probing others it would get worse. I thought about trying to use a gimmick capacitor to achieve a similar effect, but never got around to it.

[TomCarlos]

So, you checked physical connections around V4? Half of it feeds the reverb? On the other side, maybe the plate resistor is noisy? Did you check the cathode cap? Just thinking of the first things to look at.

[fdesalvo]

Ya, Tom. Also thinking C9, 22, 24, 30, 32, & 59 may be worth looking at. Trouble it’s this amp’s design is you can’t probe these parts while it’s assembled and operating. Frustrating, but will be satisfying to.tackle. Ty

[Enzo]

Not sure what you mean on several things.

FX loop. Checked jacks. OK, but bad jacks there rarely cause hum. But I didn't see your response to g1 suggestion to insert into FX return. Does a shorted plug into the FX return kill the hum?

By the way, is it 60Hz or 120Hz hum. Make sure, no "sounds like".

Values of parts won't generally make hum. OH yes, if a 1000uf cap is acting like a 1uf cap, sure. But a 20uf cap measuring 15 probably will not. Leakage or ESR more likely

I am not sure how interstage coupling caps would make hum.


Is the shield board in place? I think this is the models with the shield? Yes/no? There was a piece of pc board about maybe 5 inches square. Solid copper on one side. It had a couple screw posts on the board under it. and it screwed to it. If it is gone, there still should be a couple posts with screw holes. It was put right in the chassis corner right over the input jacks and early stage circuits.

Some interior shots of Triumph at Word Press; See the shield plate in the lower left corner?

https://ampstack.files.wordpress.com...mph-60-002.jpg

Pulling V4 kills anything from the entire preamp. The shorting plug in the FX return will tell us if the hum is from before the FX loop or after. You mentioned changing pots and jacks, but I don't see reports on their function. So do ANY of the controls affect the hum in ANY manner? DO they control amount or tone of the hum? Does channel selection change any aspect?


V3 seemed to help when pulled. It appears V3 is only used in the clean channel (and reverb), so again we wonder if hum problem is also in gain channels.

[fdesalvo]

Enzo,

Hey there. Blurb follow:

-Noise not shaped by the pots and the shield is in place.
—Noise is a sharp 120hz. When I compare it to my sig gen
- I didn’t see G1’s response prior, so I’ll check the shorted jack into the FX return test in the morning.
-I figured leaking dc could inject noise into the next stage.
-noise present on all channels

Ty sir

[Enzo]

Darn, I was hoping to score quick points with the shield. Oh well, back to isolating the problem.

120Hz means it is power supply ripple related. That doesn't mean it has to be bad filter caps though. A ground issue often is the cause.

Look at the input jacks, note the jacks ground to the chassis, but the other stuff all rounds to the preamp ground. That is the upside down Xmas tree symbol. Note the jack chassis connection and preamp ground are joined right there.

Now look further over, all the grounds are in the Xmas tree in a circle symbol ground - the power supply ground. Where do they all meet? Look right side center at Preamp Out jack. Note it ground to both chassis and power supply ground.

And also look left of PI tube V5, see the resistor to nowhere? 47 ohm R85. It connects the preamp and power suply grounds. Note if you measure it, it will read close to zero, not 47 ohms. That is because both ends of it are to "grounds" that are linked together through teh chassis.

If any of these ground systems gets separated, hum can result. If you measure and DO find 47 ohms, that means a break in the ground system ...somewhere.

[Enzo]

Oh, and you are facing only THREE grounds. Some of their amps have as many as SIX. Count your blessings.