peavey century 200 bass series

[blaise]

i just purchased it, and with everything i buy, i gotta tear it apart
so much to my surprise i check output x-isters, and see 7915. i know from experience these are voltage regulators. that to me, doesn't make sense.
i could see, two of the four being a 78/7915. split power supply, then the other two, being some sort of audio amps but all four are 7915. is it possible that someone with limited knowledge just stuffed these in it, to make sound.
could anyone verify part# with their amp. it also has a bad resistor on the preamp stage that actually looks to have been cut in half, not burnt but
broken, shattered. cant read color bands. don't yet have a schematic for it.
i thought it would be easy to come by. but i now remember i've always had a hard time finding peavey schems.
well the amp works ok, but gets noisy fast
around half volume on post gain. all else working good , great distortion.
some quick tracing suggests bad resistor is feedback gain from collector to base on a 953a. i can't, find any specs on this part either. any body help I really want to bring this thing back to life. it looks like brand new, now it has to sound that way to.

[Enzo]

Are there other numbers on those "7915s?" Does the amp serial number start with "9A...?"

I suspect those are 1979 date codes on the parts. Check them with your meter diode test. DO you get reasonable junction drops? Are there numbers like 430 and 431 on some of thiem?

Does the preamp - the front panel - have op amps, or is it all transistors. If op amps, there will indeed be +/-15v, but if transistor, there will only be a single ended 24v.
What power amp board is in it - look on the foil side? Is there a small interstage transformer right on the board? What output transistors does it use?

COntact PV parts for the schematics. Their site is down today, and that includes my dealer site, so I cannot download it for you. I don't know why you would have trouble getting PV schematics, they will send you anything they have for the asking. No company in the industry is more customer friendly than PV. Perhaps if you only look online. They are not posted often because you can always get them from the factory.

953? The SPS953 can also be an MPS8097, 2N6520, 2N6539, MPSA18. Just about any little NPN signal transistor of sufficient voltage rating will work just fine. Watch the lead pinout. It was originally 2N3391A but those are obsolete.

[blaise]

does start with 9a

other # on outputs 62792. i think these are correct, i compared them to a
260 series. pa. same #s. pre stage is all x-sistor. single p-supply. i should have caught that right off, since the power transformer is not ct. duh
power board # hdp-u-874. does have coupling transformer.
and in peavey's defense, yes i have only scoured the net for schematics.
about 15 years ago i contacted them for one and they wouldn't oblige, because
i wasn't authorized repairer. have not tried since. but i will, as soon they get their site up. thanks for the cross reference. and i'll keep progress posted.
oh yeah, junction drops ok, but seams to be leaking a tad bit on one of them.
i think i'll replace the four of them anyway.

[Gtr_tech]

The "7915" is the date code for the output device. The actual part # (house numbered for Peawee) should be something like "SJ6357".

[blaise]

ok, i now have a schematic, thanks to another member.
gets weird now, pre amp board is,
century
hdp-u
3/6/73
schem. shows input signal thru 22k resistor. splits to two caps, one .05uF to
input of Q1, 935a, the other a 180pF to ground.
my board has a zener diode (? value) to input of Q1. and a 100ohm res. to gnd. a few other areas on schem shows caps where i have resistors.
rest of schem all looks right. power board is all correct.
is the schem. not for bass series.

[Enzo]

Gtr, those SJ numbers were Moto transistors, but PV also used some RCA types, and the 62792 is one of them.

I posted the PV semiconductor cross ref chart on www.ampix.org in the Enzo gallery. If you don't already have it, it comes in real handy servicing PV stuff.

Is this zener diode in the place where the .05 cap should be? Are you sure it is not a small glass capacitor? PV uses them a lot. Are you sure those "resistors" where caps ought to be are not more glass caps? Or actualy ceramic caps? They tend to be a light green body color in contrast to the resistor color. And that 100 ohm to ground, is it where that 180pf ought to be? Plug something into input jack #1 so those 22ks are no longer grounded, then measure the resistance of that "100 ohm resistor" and see if it is not really that. You can read the color code stripes as if it were a resistor, except it is in pfs instead of ohms

[blaise]

time to back to school

ok, turns out the lime green thingy's, are caps, as well as the zener glass diode, nope thats a cap too. never seen that before. well now I'm getting somewhere.
I'm on to the powerboard. power supply checks out good.
75V mild ripple. (acceptable).
first voltage divider after filtered dc. is a series of 1kohm 5w.to 15 ohm 1/4 w, to 1kohm 5w, to 15 ohm 1/4 w. to gnd.
in place of both 1k, my board has 700 ohm 5w.
is this an attempt to drive outputs harder. or is this common
for factory to adjust as needed, for biasing purposes.
also found, at collector of Q2, a 3.3k resistor, where it calls for a 1.5k.
when i say Q2 I mean, 2nd one, on signal side. the 430c.
anyway Im reading 38V, from there to gnd. specs call for 32V.
wondering if this is within tolerance ?
its been almost 10 yrs since i've done anything like this. i can't even remember how to calculate gain. worse yet i can't find my calculator,
which has all my little reminder equations in it.
fortunately i still remember ohms and watts laws.
any more help would be greatly appreciated.
p.s. cross ref. chart, most helpful. even though nobody in my town has any of the parts. not even a tip 29c. pathetic town.

[Enzo]

What exactly are we fixing now? I thought we had a noisy preamp stage. Is that not what we are about?

You mentioned leaky output xstrs. If you measured them while in circuit, I don't doubt they show leaky since the circuit only has about 20 ohms between base and emitter. if they work, they are likely fine.

You got noise, so isolate the problem, Does the master volume affect the noise? If so, the preamp is nopisy, and if not, the power amp is noisy. In the PA, most likely is a noisy 953/430.

TIP29C or use TIP31C, 2SC3298, or any general purpose NPN TO220 of 110v and a couple amp rating. And the 953 can be any small NPN signal type. I'd use a 40v or more part, but it should never see more than the base voltage of the 430.

[Gtr_tech]

Gtr, those SJ numbers were Moto transistors, but PV also used some RCA types, and the 62792 is one of them.

I posted the PV semiconductor cross ref chart on www.ampix.org in the Enzo gallery. If you don't already have it, it comes in real handy servicing PV stuff.

Oh yea....had the PV cross doc for a while. Its essential for decoding thier house numbering system.

I was thinking the amp was newer than it is....thus my thinking that it had the motorola devices in it.

[Enzo]

Nah, this sucker is OLD.

[blaise]

yah its old. but it works great .
i replaced 3 resistors, 2 caps, and 1 preamp xister.
works beautifully. quiet and loud, with super edgy fuzz tones.
thanks everyone for the help.
originally paid 80.00 bucks, invested 6.00 more.
and i got a nice OLD amp. great for playing black sabbath tunes.
i still need a footswitch for the dist. circuit. probably just make one.

[load]

I just bought this amp. I looked in it and i think that some things aren't right. Could anzbodz please send me schematic for this amp? it would be very helpful.

Thanks

[Enzo]

Try customerservice@peavey.com