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Messages - craig

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Hi all - fixing a Peterson suitcase and my unit plays/powers up, etc, but there is a pretty significant buzz and I think I traced it to a problem with the -36v as I don't get a correct reading either on the bridge rectifier or the molex connector for -36. I get the 24v and +36v, but 378.??? where -36v should be. Any thoughts? Thanks!

Hey guys. I have a 73 suitcase that keeps blowing the main power amp fuse. I've unplugged the preamp, and the modules, and can't spot anything visually. Could something on the regulator board be causing it to blow? It looks like the 100uf and the 10uf caps were replaced. Maybe a hack job? Thanks!

Is there a bias resistor on this for the output transistors? Anyone?? Thanks!

Hi all. I have a master satellite speaker that I'm trying to get up and running. Actually, it is up, and it is running, but it distorts. I've got 33v going to the preamp and I've done some work to it.

Replaced both output transistors with Motorola MJ15003
replaced all (3) filter caps with 5000uf 100v caps (one cap is on preamp board/external amp assembly)
replaced R16 - 44r (2x22r resistors in series) 2 watt resistors with one 50r 3 watt resistor.
replaced R8 with 100r 5w resistor
replaced C4 - 80uf 75v cap with 100uf 100v cap
replaced C13 - 5uf 50v cap with same

The amp is loud...really loud and distorted. Any thoughts?

Found it. Bad cap on the regulator board.

Hi all. I'm working on a 73 suitcase that had been in storage for a while. I'm having an issue with the power amp. I get the 36v +/- (actually 40) but am only getting 15v instead of 24v. Would this be a 24v regulator issue? Diodes? It's been recapped (not by me) and stays powered fine, just not getting the right amount of v at that output. Thanks everyone!


Just wanted to say thanks. I made the reg. board and installed it last week and it works great. Excellent suggestion.


Thanks so much for your reply. I'm going to do just that, with the 1a Recom. Just to clarify, the 820r goes across the output only (not from v+ output to ground like the 10uf caps in the datasheet (which I'm going to adhere to)), as well as the 10uf ceramic? BTW - here's a picture of my 76 suitcase. I've had it now for (gulp) 20 years, and did the sparkle tolex about 15 years ago. Thanks again!

Hey all - I want to add some diy effects to my suitcase behind the rail and was thinking about powering them by tapping into the 24v going into the preamp. I tried a 9v regulator (7809) and while the voltage was 9v coming out, it got too hot so I took it out. Would one of these work well? Would I also need to re-regulate the 24v going into the preamp? Any other suggestions? Thanks!

Yeah, that's my plan. I need to dig in, but I didn't know if anyone had any experiences like this so I could perhaps get a little help.

So I've done some work to it, but need help. The amp came in with a fried resistor, and some damage to the Pcb. The preamp/external outs work fine, it's the master amp that's the problem. Now I get sound out of the Master amp, but it's low level and distorted. Here's what I've done so far:

Replaced both output transistors with Motorola MJ15003
replaced all (3) filter caps with 5000uf 100v caps (one cap is on preamp board/external amp assembly)
replaced R16 - 44r (2x22r resistors in series) 2 watt resistors with one 47r 3 watt resistor (I tested the old resistors out of circuit - one was 39r and one was 29r for a total of 68r. Both had markings of 22r)
replaced burnt resistor (some unknown 1w resistor next to C4) with 100r 5w resistor
replaced C4 - 80uf 75v cap with 100uf 100v cap
replaced C13 - 5uf 50v cap with same

Where could the low level/distortion be coming from? I'm thinking I have an incorrect resistor value somewhere (maybe due to the new output transistors?), or it's not biased correctly. Is the potentiometer R1 a bias pot? I had this problem on a peterson module once and it wound up being a wrong resistor value.  Any help would be much appreciated. Thanks!

Thanks Tim. Yeah, a 1w resistor...fried. Somebody had worked on this amp before I got to it and done it a disservice.

I thought so, and it's close, but there are no 10w resistors anywhere on the board (as they are in the schematic) among other things.

I opened her up and there's a bunch of fried components, burnt PCB. I'm having trouble id'ing the fried resistor. No markings that I can read, and I can't find it on the schematic. It's a 1w

Actually, to clarify, I do hear a slight buzz, so there is sound, but I don't get sound from the piano to the master speaker cab.

Hi all. I just got a sattelite system w/88. Seems pretty clean, but I'm not getting any sound out of the master. The two preamp outs work fine, the slave out (and the slave itself) works fine, but no sound from the master itself. I'm getting 32v to the preamp and everything looks ok inside, speakers are plugged in, can hear a little buzz/crackle, a very normal amount to my ears, but no sound from the piano to the speakers. Any ideas? Thanks everyone!

On a hunch I threw in 15r for bias with the MJ15025G's and it works great.  Just letting it run for a bit.  Thanks again for the help.

Thanks again Tim.  I tried this morning with some MJ15025G's that I'd gotten from Mouser last year and the 12r bias resistors but it distorted so I'm going to order some MJ15016s as you suggested and follow your directions.  Hopefully that will do it.  Oh, and the amp does measure just under +-31v.  Thanks again for the help!

Tim - thank you so much for the info, it's extremely helpful. I've swapped the GE for SI transistors before on Peterson suitcase modules with success (w/12 r bias resistors). I just wasn't sure, since the +- voltage on the student piano is 30v (not 35-40v like the suitcase) which transistors to use, and which ones would work/how much to bias. One question though, how do I check the offset?  Unplug the speaker and measure there?

I've had mine catch fire the middle of a gig. Not fun.

Hey all -

Helping a friend restore his Jetsons 69 piano.  He wants to replace the germanium output transistors with silicon on the amp module before they fail. It's a Peterson amp module (w/820r,270r,.47 5w resistors in the output section), but the output transistors are Delco GM 801552, not the usual ones I'm accustomed to seeing on 80w Peterson suitcases.  Has anyone had success swapping these out for Silicon ones?  Would the Vintage Vibe silicon conversion kit (matched transistors, bias resistors) that they offer for the suitcase amps work for this? Thanks!

Actually, one more thing.  I want to recap the pre-amp, but the values are different than later Peterson models (6.4 uf instead of 4.7uf, 125uf instead of 100uf, and 50uf instead of 47uf). Should I/would I be OK to sub the new values for the old ones? They're the original caps, who knows how spec they are anyway. Thanks!

Real MC - thank you for your reply, much appreciated...and helpful.

The Fender Rhodes Electric Piano / 1960's Sparkle top suitcase issues
« on: July 21, 2016, 11:38:04 AM »
Hey guys -

Still getting my teardrop sparkle top up and running. I've got the modules working fine (silicon conversion via VV), but I've got a couple of issues. I'm just not too familiar with this model and my harp output seems low compared to my Mark I. I'm getting 390 ohms resistance at the RCA jack as opposed to 1430 r for my Mark I.  I've measured some of the pickups and they all measure about 33 ohms each though they're still connected. Is this right?

Also, my power amp +35 output isn't measuring (the -25 and -35 are fine.  What would be causing that?  Thanks everyone!

Hi all.  I just picked up a late 60's Peterson Sparkle top suitcase (felt teardrops...). It came with one non-functioning amp module and one decent (but a bit noisy) one. Otherwise works fine. Having had my day to day catch fire on me in the past (during a gig, no less), I decided to convert them both to silicon power transformers and change out a few caps and resistors.  Anyway, I got the one broken one up and running and have converted the other, fine functioning module to silicon. They both work, and perform the exact same, that is, with distortion and slightly low output. Here are the components I changed ;

MJ15025G power transformer and a pair of 12 ohm 2w resistor bias resistors in place of the 2.7ks

I'm thinking I have the wrong value for the bias resistors since both modules act the exact same.  My other suitcase is a mid70's, same amp module conversions, and they work fine, even in the sparkle top for testing. Is the sparkle top amp module different than a mid 70's which would cause it to need a different bias resistor? Am I missing something?  Thanks for your help!

Hi all.  Does anyone know if the voltages match up so it'd be possible to convert an old 4 pin STRAIGHT power amp for use in a Peterson 4 pin DIN suitcase?  Is the only difference in the amps the connectors?  Thanks.

Hey thanks for the reply.  I kinda figured I was all right.  I have 2 power supplies for this and both read the exact same, but your reply made me feel a little more at ease.  Thanks!

P.s.  I have the VV video - it's great.

HI all.  I know how to check the voltages on the power supply (and the modules), and my 73 key suitcase (Peterson) runs hot.  I've adjusted it so that it is 25v, but the +/- 35 volt readings are about 39v.  How do I adjust these voltages so that I can get them to 35v?  thank you in advance.

Amps, Effects & Recording Techniques / transformer on power amp
« on: October 11, 2005, 09:01:17 PM »
hi there.  i have a 75' suitcase and one of the tranformers in the power section (there are two-one for each set of speakers) blew out yesterday.  i want to replace it but i can't find the schematic for it, and i'm not sure what the rating is for the transformer.  anyone know?

has anyone tried this?  i was wondering how/if it is possible to reroute the bass notes on my 73 suitcase so that they go to an external amp.  so basically, i'd have all the high keys go through the suitcase amp, but the bass go to a bass amp or something.  thanks


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