Rock Master 120 head schematic?

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Lester H
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Rock Master 120 head schematic?

Post by Lester H » Wed Sep 23, 2020 9:55 pm

I am looking for a schematic or someone with the know how to identify a resistor that has blown on the "power board" section of my amp. Based on some other amp schematics like the Road Master and VTM i'm guessing the resistor in question is a 400 ohm 10 watt based on those schematics. Its light blue and probably about an inch and half to 2 inches in length. Mine burnt in half right where the numbers were stamped on it.

if this is the correct value I have only seen possible replacement resistors as being the square, white cement type resistors. Are those a safe and correct alternative to the skinny tubular light blue resistor currently in the amp?

Any help is greatly appreciated.

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Enzo
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Re: Rock Master 120 head schematic?

Post by Enzo » Thu Sep 24, 2020 12:11 pm

A 400 ohm 10 watt resistor is a 400 ohm 10 watt resistor, I don't care if it looks like a banana.

By the way, to make it easier, a 390 ohm resistor is a perfect replacement and will be an easier value to find.

Looking for a schematic? Contact [email protected] and ask for it.


I think you are correct assuming that part, as they used the same circuit in amp after amp after amp.

And the only reason that would burn up is something shorted downstream, in all likelihood shorted power tube.

Lester H
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Re: Rock Master 120 head schematic?

Post by Lester H » Fri Sep 25, 2020 4:44 pm

Enzo wrote:
Thu Sep 24, 2020 12:11 pm

And the only reason that would burn up is something shorted downstream, in all likelihood shorted power tube.
You would be correct. I have a bad habit of not dicarding tubes and in my attempt at trying some different power tubes this happened and it dawned on me the stash I got into was ones I pulled out of another amp in which one or more were shorted out. It didn't dawn on me until I already let the smoke out of my Rock Master.....

Thank you for the reply btw!

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Enzo
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Re: Rock Master 120 head schematic?

Post by Enzo » Fri Sep 25, 2020 6:27 pm

I don't save bad parts in the shop, for just that reason. I have plenty of pulls, but they are like the good tube of a pair where one failed.

If I save parts to return to a customer - I always return all parts I remove - I cut the leads off, or bend them badly, Tubes get a giant X with a sharpie or grease pencil (china marker)on the side.
PV Rock Master.pdf
(1.09 MiB) Downloaded 18 times
It is a weekend, so here is the schematic file you want.

Lester H
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Re: Rock Master 120 head schematic?

Post by Lester H » Fri Sep 25, 2020 8:52 pm

Enzo wrote:
Fri Sep 25, 2020 6:27 pm
I don't save bad parts in the shop, for just that reason. I have plenty of pulls, but they are like the good tube of a pair where one failed.

If I save parts to return to a customer - I always return all parts I remove - I cut the leads off, or bend them badly, Tubes get a giant X with a sharpie or grease pencil (china marker)on the side.

PV Rock Master.pdf

It is a weekend, so here is the schematic file you want.
Thanks so much for that schematic! R60 is the one that blew. I checked the fuses on the power board and all of those were ok.

I found a 400 ohm 10 watt resistor on a antique amp parts site so I guess I need to get one (or two) coming. I've had that amp since 1993 but only used it occasionally but had really been enjoying it lately. My use of it always depended upon whatever band I was playing in at the time. I joined a new band earlier this year and I just found the Rock Master to be the better fit for the music we were doing.

I wish there was a little more literature about that amp as I don't think it was in production very long. It appears to be a stepping stone to the Butcher as far as I can tell.

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Enzo
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Re: Rock Master 120 head schematic?

Post by Enzo » Fri Sep 25, 2020 9:30 pm

400 ohm 10 watt need not be special. And remember, 390 ohms is valid here. In fact in years past I have occasionally orderd the 400/10 from Peavey themselves and they shipped a 390. It is only a couple percent difference.

I don't know what the Antique place wants, but Mouser - a fine old parts house - has a few choices of 400/10, a couple dollars or less.
https://www.mouser.com/Passive-Componen ... hm&FS=True

Oddly the 1% one is a couple cents cheaper than the 5% one.

Oh, did you mean ANtique Electronics Supply at tubesandmore.com ? Good place too, they are asking $1.56. Looks like same ones MOuser sells for $0.68. AES likely has other amp-specific parts you may need.

I had a Rock Master for a long time. SOld it for $150. LOUD and raw.

Lester H
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Re: Rock Master 120 head schematic?

Post by Lester H » Fri Sep 25, 2020 9:52 pm

Enzo wrote:
Fri Sep 25, 2020 9:30 pm
400 ohm 10 watt need not be special. And remember, 390 ohms is valid here. In fact in years past I have occasionally orderd the 400/10 from Peavey themselves and they shipped a 390. It is only a couple percent difference.

I don't know what the Antique place wants, but Mouser - a fine old parts house - has a few choices of 400/10, a couple dollars or less.
https://www.mouser.com/Passive-Componen ... hm&FS=True

Oddly the 1% one is a couple cents cheaper than the 5% one.

Oh, did you mean ANtique Electronics Supply at tubesandmore.com ? Good place too, they are asking $1.56. Looks like same ones MOuser sells for $0.68. AES likely has other amp-specific parts you may need.

I had a Rock Master for a long time. SOld it for $150. LOUD and raw.
Thanks for the Mouser link. I checked the 68 cent cement resistor and it has a minimum order of 10. The middle Ohmite resistor looks more like what is in the amp. Whichever way I go a couple of bucks isn't going to break the bank!

I paid $100 bucks for my RM back in ''93. It was my first tube amp. I ran a rack mount BBE preamp and an ART effects processor into it. Lots of good memories with that setup!

I tried selling it once for $75 at a yard sale. Had a couple guys looking at it but no takers. I was glad it didn't sell and never tried to sell it again. I put it away in favor of other various combo amps over the years because I only had an old oversized PV 412 cab to use it with and I got fed up with the weight and inconvenience of the cab. I eventually bought a 212 cab and it started seeing more use again at that point.

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Enzo
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Re: Rock Master 120 head schematic?

Post by Enzo » Sun Sep 27, 2020 12:49 am

I sold mine at a local guitar show. I was asking $200. Some guy early on was interested. he hung around all afternoon, and as the show was closing offered $150.

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