Also have a Super PA amp and looking for some info

Ned B

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Nice amp!...And it has the RS potted military PT!.. @Ned B . She's had some changes but it's in good shape for an amp from around April 1966. It looks like someone did a little re-voicing for the individual channels. Some of the changes I noticed are:
The cathode cap for V1 has been replaced.

Someone added a bypass cap (can't make out the value) for the 270K summing resistors for channels 1 & 2.
The preamp coupling capacitors for channels 3 & 4 have been changed to what looks like 0.1uF instead of the usual 0.022uF.

The cathode follower 100K resistor has been replaced.

The preamp filter cap has been replaced with a dual section cap. Original would have been a 16uF/450Vdc. Also someone added an addition 10K/1w B+ voltage dropping resistor at this filter cap.

The bias circuit has been updated with a slider trim pot and at least one bias cap has been changed at one point.
An additional 32uF/450Vdc filter cap was add.

Looks like the diodes & 0.05uF/1000Vdc cap for the rectifier circuit changed at some point. They look like IR diodes but typically around this time frame they were using metal cased Mullards.

The On/Off switch has been replaced.

Not sure why the OT has R/S 207-330 written on it...To me it looks like a Drake 1202-84 which would be period correct. Looks like someone moved the Yellow 8-ohm tap wire from the Selector to the speaker jacks....

The choke looks like a replacement.
This is 6657 that I use to own. Really regret letting this go. Note the thick Vox front panel strip.
 

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Matthews Guitars

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Fixing broken lexan pretty much isn't a thing. You either live with the panel as it is or you get a replacement.

Actually someone with the right gold paint MIGHT be able to touch up missing or delaminated gold on the panel, if it's loose and can be removed from the chassis without damage.

For me to complete the design work to make JTM100 Mark IV Super PA front panels, I need some accurate dimensional data on the hole locations.
 

neikeel

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The RS PT has dual taps, 350-0-350 and 425-0-425. IIRC the dual OT has 540v on the plates of the KT66s but I really ought to check my notes (if I can find them!)
 

KevNukes

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I’m happy to work on it for free if Kev pays for parts and gets it to me.
Hi Neikeel, I can't work out how to send you a message, but I'd be interested in chatting about this. Several people have encouraged me to take up your offer. Seems like a nice honest bunch here! I wonder if I can add my email address... [email protected]. Perhaps we can talk further.
 

KevNukes

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Sweet. Its difficult to value in non-working condition. It will always be at least the value of both transformers.

What band did you play in?
The band I was in back then was called Savage. We were only kids, 16. We used to rehearse next door to Iron Maiden. If things had been different I might have had my own plane :D I'm still playing in a semi-pro way. My current band is NUKLI and we play at lots of small festivals. I haven't got the stamina to lug huge Marshall amps around these days. I'm afraid I've gone to the dark side of amp modelling! Shall I get my coat :D
 

Matthews Guitars

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To send a private message, click on the member's name under his icon on the left side of the screen, and then click on "Start conversation".

Unless you'd settle for a mere 2000 US dollars for that amp, which is all I can justify spending at this time, and I know others here would offer more for it, I withdraw from vying to buy this amp from you. I limit myself to buying not more than one vintage Marshall a week and I've already bought one this week! :cool:

I'd like it but I'm just not the best possible buyer for it. It's too rich for my bank account.
 


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