Questions on the Peavey VT Series 240T Tube Amp

[Enzo]

Yep, and the selector switch shorts across one or the other to darken it.

I case it helps, when reading the schematic, you see FS2 and FS3 atop the two LEDs, but that control signal is also present on the control pin of each TL604 at the end pf each channel circuit. In fact that is where the current for the LEDs comes from, The 25v rail through a resistor to pin 2 of the IC.

[TomCarlos]

Thanks Gents....

Confirmed that the LEDs come on when the plug is inserted into the Automix input. I am tracing the circuit as Enzo mentioned.

Tomorrow, I will turn my attention to the noisy output - lots of hiss. When I put the amp in Standby and run the signal from the Pre Amp Out to another amp, it is quiet. So I am guessing there is either noise on the HV line or maybe the tubes? I tried to run a line to the Pre Amp In but it is still noisy. I currently have old tubes and will get a new set. I did notice one of the sockets appears to be a tad loose - and replacing the tube sockets on this amp is a bit more tricky than others. I guess you need to drill out the rivets on all tubes to get the board out. So let's hope that can be avoided !!

[glebert]

You could pull two of the tubes at a time (moving them around so you still have a push-pull pair) and see if the hiss gets better when a particular tube is pulled or if a particular socket is empty.

[TomCarlos]

Thanks Glebert....

I found a set of new 6L6 tubes and tried what you suggested. First, sockets 1 and 3. I then moved the tubes to sockets 2 and 4. No difference, still have that hiss (or should I call it excessive "white" noise).

Will continue to investigate...

[Enzo]

I don't generally expect hiss from the power tubes. I assume you meant power amp in jack. I think it more likely you have a noisy transistor in the phase inverter. Just my opinion.

[TomCarlos]

Enzo - I did some net searching on "Mace Deuce Hiss" and found a 2011 post on the Peavey Forum page where you hinted at the Tube Driver 65837's being a potential problem. I found a similar post on the EL34World site.

I'll look through my stash of parts to see if I have a pair of 2N3439 or MJE3439 transistors. But I will also do some scoping around the P.I. circuit and looking at the Grids on V1 amd V3.

As always, thank you.

[Enzo]

Or even MJE15034 in a nice TO220. Just make sure you get the legs right, they may be different order from original part.

[TomCarlos]

Team....

Just a quick check in on this thread.

I saw that Antiques Electronic Supply sells the Peavey SDS 7204, Peavey's reference part for the 65837 MJE3439. I also found some National Semiconductor MJE3439s on the net. So when the two orders arrive, I will check the pinout on each and pick a pair to install.

I did notice excessive noise on the collector of each transistor before pulling them.

Before replacing the Tube Drivers transistors, I did some checking around IQ1 and IQ2 - See post #21 for the image. I believe their is an error on the schematic. IR21 is clearly shown as 1.0M. And in fact, that is what I see on the board. IR16 sorta looks like a 10 M on the schematic. But in fact a 1.0M is installed. The other discrepancy is with IR13. The schematic sorta looks like a 47K. But I see a 4.7K installed (and that resistor and the solder joints look original).

[Enzo]

IR16 may LOOK like 10 meg, but really. Clearly from th circuit it NEEDS to be 1 meg. But look at it, the space between the 1 and 0 is for the decimal point. The schematic is a copy, so for whatever reason the decimal point didn't make it. Lots of times little hunks of image are lost in copies. Look at IR17, it says 10k, not 1 0k. The drawing does not put spaces within multidigit numbers.

Same deal with IR13, see the space between 4 and 7? A dot went there. It was either lost in the copy degradation or simply didn't make it on the drawing.

[TomCarlos]

Ok... repair done on the Phase Inverter circuit. White noise hardly audible.

Using the Peavey SDS 7204 from Antiques Electronic Supply, I was able to drop them right into pc board without bending leads. The pins are E B C, just like the original RCA transistors. The SDS 7204 is a TO-226 package. I hope it does not overheat (comparing to the transistor that was there previously, looking like it was a TO-202 with part of the metal tab cut off). And for good measure, I also replaced IR15, IR16, IR17, IR18, IR19, IR20, IR21, and IR22, as some of those resistors had faded from spec.

While I put this amp through a week of testing, I will also look for an original Peavey 4 button footswitch. It would be a "nice to have item" for this amp. I'm always puzzled as to how the footswitches get separated from the amp.