Peavey session 400 (210 Watts) Capacitor Problem!

[Chitownrocker]

Hi All,

This is my first post,and I am an layman when it comes to electronics so please be gentle. I have a Peavey musician series 400 (210 Watts) b series amp,that is having issues.I will be replacing the 6000uf 45 wv caps and the differential transistors & two other transistors.

here are the peavey part numbers

Capacitors Stock 70320120
modified 70320136 If I modifiy it

Differential transistors 70400761
misc transistors 70466530/70466533 old numbers
30466531/30466533 new numbers

I just would like some opinions on what to do with this amp. I've serched and seen some of the other post here. And I wondering about what other parts I should change and or about using the 70320136 capacitor. I was told if modified it would have better bass and tighter notes (I.E Attack). So any help from you guys would be greatly appricated.

Thanks and God bless... Doug

Also i will post a couple pics!!! or try too (lol) 100_1897 is the capacitor

[Chitownrocker]

heres the last one (lol)

Sorry for all the pics,just wanted to cover all the bases. Doug

[Enzo]

Not sure what you mean about modifying the cap.

6000uf at 45v is not a standard value. Even back then I don't recall that as common. Modern caps run off the standard number series, so 6800uf might be a lot easier to find. And forget 45v, I'd be looking for 50v or 63v as more common. I have no idea what the newer PV part number refers to, you gave no description. Peavey is sending out a lot of 4700uf/63v caps to replace the old 5000uf/55v caps used in many models. For all I know they could be refering you to those.

But the two caps are mounted in clamps and not on the board, so anything that remotely meets the specs and can be mounted in a clamp should work.

As to the transistors, you didn't state what issues you were dealing with. The 761 pair should both be the same, whatever you use. They can be replaced with 2N5400, 2N5401. They do need to be high voltage types. You have about 80v of rail across this amp, and the diffy pair can see most of that.

The 6530 and similar numbers are common modern types 6530 is MPS6530, 6533 is MPS6533, and so on. Not sure where you are using those.


These are sturdy old solid state amps, they are what they are. Replacing those 30 year old filter caps is a good idea alright. There are a few smaller electrolytics on the board as well, you might update them too.

Your front panel is the preamp section, is yours all transistor? I see about 18 small transistors on the drawing, yes? Two input jacks, volume bas treble mids plus mid shift. reverb and trem. if that describes yours, I recommend you swap out all the small electrolytics on that panel too. There are like 7 or 8 little 2uf caps that get leaky. There are a few other caps on there. Fresh caps there will really wake up the sound.

[Chitownrocker]

Enzo to the rescue!!!

Enzo,

Thanks so much for the quick reply,I've seen some of your help with others,well done my friend. Ok so keep in mind I'm a layman when it comes to Electronics,anyway.

I had talked with Grant (service tech at Peavey) He recommened changing the item numbers I mentioned.The picture of the black peavey Capacitor I posted is the one installed now, Grant had said the original one's were silver,but I have no idea myself,but he gave me two choices the stock replacement70320120 or the 70320136 which will give the amp better bass and tighter responce (attack) also he said that alot of times the differential transistors go bad so he also recommended repalcing those and the 30466531 and the 30466533.

I forgot to as Grant the specs on the caps sorry.

thanks for the tips on the part numbers and the capacitors.

You had said "There are a few smaller electrolytics on the board as well, you might update them too." is there a way with the docs i posted you could mark which ones your recommending replacing.

Yes the front panel is transistor. I will snap a picture tomarrow,and If you could also let me know which ones to replace.

Again please forgive me,but I'm still learning,and I'm bi-polar so its a little harder for me.Also how do I go about dis-charging the capacitors,so I don't get toasted (lol). Again thanks so much for anything you can help with.

Doug

[Enzo]

The diffy pair might go bad from time to time, but me personally, I wouldn;t change them if they are working. They made it this far.

The part numbers on the caps are not descriptive. I suspect he offered two different values. The larger one will tighten up the bass somewhat... potentially. COuld be the diffference between 4700uf and 6800uf perhaps. It won't be like night and day though.

The smaller caps? Photo 100-1885, far upper left, the black cylinrical part and far right the grey part. I think there are a couple more. The electrolytic caps all look like those. The schematic might say 50uf/50v and the part on your board might say instead 47uf/50v. Don;t worry, they are the right parts. get within 20%.

Once it is off a couple minutes the caps are discharged. ALWAYS work with the amp unplugged from the wall unless taking readings. You can Always set your meter to DC volts and measure if any voltage is in the caps. A few volts won;t bother you.

I have no way to point out all the little 2uf caps, but they are probably black, and should have 2uf or maybe 2.2uf printed right on them. The ones that are not 2uf will look like the extra ones on the power amp, but smaller still. probably.

[Chitownrocker]

Now where getting somewhere!!!

Enzo,

Sweet... I will get out the Grampa glasses (lol), and the schematics and check it out. Oh BTW I forgot to say what the amp was doing...

When i first recieved it the pic where my fingers pointing at the back of the board that part, the screws where loose and one pin was disconnected,so rushing to fire this baby up, i hurriedly pushed it in,and didnt check good enough,wrapped a piece of foil around the fuse (bad idea i know) left the power switch on and plugged it in.

When i did it started to smoke and fry the wires from the capacitors back to the poweramp. So i dis-connected it and pulled out that part my finger was pointing too (straightened out the pins) pushed them back in and then tightened the screws back up.

when i fired it up, all was good for about 4-5 minutes i guess then the speakers started to crackle a little it got worse when i increased the main volume then after a while some popping and then kinda a sharp snap then hum and no output.

when hum was present i disconnected the speaker jack and reinserting it would give spark (way too much voltage) Grant from peavey said it sounded like the differental transistors.

but if i replace the big capacitors on the power supply and all the parts he and you recommend i should be good to go, Yes???

Oh and Enzo again thanks so much for all your time, I appricate it very much.

Doug