RP112 100 WATT COMBO.

Regortteggel61

Good Morning, I have a RP112 100 watt  with a dubious past. Looking inside its a GP1 board and it appears to have a component missing. Looking to the right of the mains transformer there is a bank of 3 fuses, directly beneath that there is a black link and below that is were the component is missing and has been replaced by a piece of wire. Looking at a video of the same amp it appears to be a round fuse soldered link or could it be a thermal switch . This is a UK version, could anybody please help me with what that component is, many thanks.

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Wed, 07/02/2025 - 11:51

Yes.  Most likely a Thermal Switch.  Check the schematic for RPs in Downloads and Resources. -mgriffin

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Thu, 07/03/2025 - 04:35

Hi Mike, I have looked on the schematic for GP1 board but could not see anything, but must admit I am not an expert at that. The amp side of the connection goes to pin 7 on the valve base, I have not seen this on the other amps we have. I have bought another one today with a blown mains transformer which will be collected on the 15th, seller going on holiday, so at least will have something to look at. Many thanks for your time.

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Fri, 07/04/2025 - 14:01

The thermal switch shows as a SPST switch connected to the low side of the power  transformer primary side.  The letters BLK appears next to the switch on the schematic.  Also, clearer Power Supply Schematics are at the end of the pdf file.  Scroll down to see them. -mgriffin

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Fri, 07/04/2025 - 21:11

Hi Mike, found thermal fuses , but on the video showing this component clearly, it is marked up 50 volt 8 amps, one side connected to the two green and yellow wires from the transformer and  the other to pin 7 on both valves, I thought at first it was a fuse but thank you for pointing out the thermal connection on the schematic, but the problem now is what to replace it with, as the thermal fuses are governed by selected temperatures so what would be the danger temperature for it to trip. I have just looked up BLK  and its relation to  thermal switches apparently it denotes the operating temperature but I could not find what that is. the solid link situated above this component also looks like a safety link as its connected to the 2 green wires on the transformer and pin 2 on the valve base where the diode and ceramic disc are connected, what to do next is the question. Just found BLK denotes 72 to 75 degrees does this sound about right to you.

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Wed, 07/16/2025 - 14:26

I think BLK only refers to the wire color Black.  Just like BL is Blue.  R/BLK is Red & Black wire.  Anyway, I'm not sure what the temperature spec of the thermal switch is.  I would guess 75 - 100 C.  Newark Electronics has a very large selection.  Take a look.  -mgriffin  

 https://www.newark.com/c/sensors-transducers/sensors/temperature-sensor…

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Tue, 07/15/2025 - 11:26

Pin 7 on the valve base is the 6Vac input for the tube filament (heater).  It was conveniently left out of the GP1 schematic.  Scroll down the file and check the GP3A schematic.  Also, scroll down more to see the power supply schematics. -mgriffin

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Fri, 07/04/2025 - 11:15

Hi Mike, just found a video of the mystery part, looks like a large round glass fuse with wide flat solder legs, but more important to the side of it , is a label saying 50volts 8amp,  any ideas, thanks Rog.

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Tue, 07/15/2025 - 11:35

50V voltage rating seems low but it may work.  I did a search on 100-65-250 Thermal Switch and many beam lead items showed up.     -mgriffin

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Tue, 07/15/2025 - 22:05

Good Morning Mike, is there any chance you could send me a link to what you found, I have run the same headed search ,but only came up with discussions on transformer replacements, many thanks for your help once again, regards Rog..

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Wed, 07/16/2025 - 14:28

Anyway, I'm not sure what the temperature spec of the thermal switch is.  I would guess 75 - 100 C.  Also 250Vac and 2Amp minimum rating.  Newark Electronics has a very large selection.  Take a look.  -mgriffin  

 https://www.newark.com/c/sensors-transducers/sensors/temperature-sensor

https://www.google.com/search?client=firefox-b-1-d&q=100-65+thermal+switch

 

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Thu, 07/17/2025 - 05:59

Hi Mike, I have another RP112 100 delivered today with a blown mains transformer, luckily the part we have been debating is still in this one, it is a fuse, clearly marked on the outside 50 volts 8 amps and also marked on the chassis, tried to upload photos  but site will not accept jpg extention . 

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Fri, 07/18/2025 - 03:17

Hi Mike, this is the component which we have been discussing, its marked on the side of the cap 50v 8amp, so looks like a fuse, but what do you replace that with at 50 volts.

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Sat, 07/19/2025 - 01:04

Many Thanks Mike, looks like we are getting somewhere, Just got to find a supplier for just a few.

Full Name
Mike Griffin
Music Man Equipment
MM 112-RD-65

Member for

11 years 4 months

mgriffin155 Tue, 07/22/2025 - 09:49

BTW: On closer examination, those are "one shot" thermal fuses.  In other words, they do not reset after they cool down.  Can you try again to post a picture of the OEM part?  If that doesn't work, can you send a picture to my email address?  

Here is another place to look. https://www.digikey.com/en/products/filter/thermal-cutoffs-thermal-fuses/146    -mgriffin

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Tue, 07/22/2025 - 10:44

Thanks Mike on holiday away at the moment, was able to order the other 9amp 50v fuses 5 off from another supplier, what is your email

Many Thanks

Full Name
ROGER LEGGETT
Music Man Equipment
Music Man 2 x 10 65.
Music Man 4 x 10 65
Music Man RD50 1 X 10
Music Man 1 X 12 Extension cabinet.
Music Man HD150 Reverb head
Music Man 412 GS cabinet
2 x Fender Silverface 100 watt Twin Reverbs.
2 x Fender Silverface 135 watt Twin Reverbs.
1 x Sound city Concorde.
2 x Wem Dominator 50 watt.
1 x Wen Dominator Bass
1 x Wem Mk1 Audiomaster.
1 x Wem Mk2 Audiomaster
1 x Marshall JCM 800 100 watt head.
1 x Marshall JCM 800 50 watt head
1 x Marshall JTM 45 head.
1 x Marshall 4 x 12 A.
1 x Marshall 4 x 12 b
1 x Marshall 2 x 12 Vintage.

Member for

3 years 1 month

Regortteggel61 Thu, 07/24/2025 - 01:21

Morning Mike, I have posted photos on the Facebook Music Man group for the missing part.