Restoration For '68 JMP Super PA 100 watt

[deliturko]

Hi guys,

Need help for restoring this beauty Power trans. is not the original one, cap board looks not good and phase invertor can cap is not wired, you will see 3 extra caps on bias circuit and also it has a additional cap wired on the main board near the 32 uf dual cap.This amp looks good but with your help it will be pretty nice again

My idea is, split cathode for one side an add some other things on the 67-68 circuits and I'll leave the other side untouched.

Since its a super Pa which I dont have any opinions about 2 days before but it looks similar to 100 watt superleads.I have checked the layouts pre, power amp and cap board wiring is same with brige rectifier.I've decided to use Metro Amp Drake 1203-80 transformer for replacement.Is that ok ?

There is nothing on output trans, what is it Drake 2" or Dagnall ?

Anyway these are the pictures
Minimass looks really tiny in here













Mustards look so nice

No bias pot on it and yellow dudes are 47 uf 350V caps


It's serial number is SP/20527

deliturko

[908ssp]

Well I have a 45 watt Super PA and it is a terrific sounding amp. I would not mod it if I were you. I'd repair it for sure make it has stock as possible. The Metro PT is a good one so is the Marstran both of those have a more vintage vibe than the MM transformer. I play mine with an a/b box feeding one channel at ten and the other channel at 6. I use a treble booster, fuzz or distortion pedals in from to get any extra gain I might need and the PA works assume for that. Any mods on old amps like that detract from the value and the Mojo in my opinion. Get a Metro kit if you want to try your hand at modding.

[deliturko]

Well, you are right about moding a vintage amp.But it has 2 identical channels per side Anyway at first I have to repair it

What are your suggestions for filter board caps ? 100 uf and 32 uf seems to be standart on layouts for its era.
I'm going to change cables, sockets,power trans, switches,pilot lamp, pots/knobs list goes on...

[VelvetGeorge]

Well, you do have some work to do. But I wouldn't change anything that doesn't need to be replaced, at first.

These might help:

http://metroamp.com/wiki/index.php/Cate ... is_Layouts" onclick="window.open(this.href);return false;

http://www.amparchives.com/album/Marsha ... index.html" onclick="window.open(this.href);return false;



George

[deliturko]

Thanks George you are the best

[neikeel]

Well, you are right about moding a vintage amp.But it has 2 identical channels per side Anyway at first I have to repair it

What are your suggestions for filter board caps ? 100 uf and 32 uf seems to be standart on layouts for its era.
I'm going to change cables, sockets,power trans, switches,pilot lamp, pots/knobs list goes on...

Are the switches, lamp, pots and knobs wrecked? They all look to be original parts. If not broken I would purely replace what is broken or cannot be repaired.
A bulgin looks neater than the kettle socket too.
It would look like yours was 100+100 in series on mains and 32+32 in series on screens. It looks very similar to my Superlead which has a Hunts 16+32 for the PI.

Pics of mine are here (its clone is there too ) part way through restoration:

http://forum.metroamp.com/viewtopic.php ... ad#p182871

It dates to second quarter of 1968 (mustards and pot dates). It even has the 47pF Murata ceramic cap in the PI like yours.

Pre restoration pics are here:

http://forum.metroamp.com/viewtopic.php ... ad#p133868

[deliturko]

Hey thanks for the photos

Can cap is 16+32 Hunts too, and switches look bad but still working, pilot light is a Fender type lamp hanging over there original light's red glass still there also.Pots needs cleaning or replacement I dont know.Amp's main problem is the power trans, sockets,and electrolytics.2 knobs missing and rest are not good looking and of course lots of rust on some areas.

More pictures










Now making parts list.

[neikeel]

Your OT is Dagnall C1998

The PT should be a Dagnall T2562. George had a short run of these made up (I had x2, one for the blown one in my origianal and one for the clone). Not sure if he has any left. His Drake 1203-80 will certainly do the job admirably, just does not have the copper shielding that the Dagnall does.

[deliturko]

Hey guys,

Today I found these in a local shop Mustards are 0.15 uf 400V ( mostly NOS but used ones available) Can I use them instead of 0.1s in Marshall circuit? Btw most of the resistors are 2 watt CC and everything cost me just 20$ with 10 percent discount And I'm going to buy 30 more mustards tomorrow





Now I just need new Power trans and some nice electrolytics then I will start to work on the amp.

DT

[neikeel]

You can use those 400v mustards but if the others ain't broke..........................

The 0.1 looks like 160v - only place you can use that is on the presence pot.

I would clean and test what you have first.

I suppose you might have an issue with that warning lamp

[deliturko]

You are right, 0.1 is 160V.

Today I removed the cap board and preamp board for cleaning.Preamp is ok.I won't change anything.Unfortunately power tube sockets are dead.Pots are still fine no replacement needed.


DT

[deliturko]

Hi,

I have a question, how about Hammond power transformer model 290HX for replacement ?

[deliturko]

Hi,

Finally amp is ready for testing here are the pics.

















Mods; split cathode for channel 1 and 2, shared for 3 and 4. 500pf cap added on mixer resistors, filtering on screens now 32uf.New 6V pilot light and switches.Cathode bypass cap on V3.I also changed all tube sockets.

[deliturko]

Hi,

Today I've tried the amp,there are some problems;

One of the 1 ohm 1 watt metal oxide resistor(V6) was burned, I checked the bias voltage it was about 80ma
I set the bias about 35ma, my plate voltage was 470V and screens were 450V and put an alligator clip on pin 1 of V6 for the grounding.After that it worked, all channels and controls were operational.After five minutes I wanted to crank it up when I set the volume over 4 I heard loud crackling noise (on both channels) That was realy annoying.

Any idea about the problem ?

[uiovbged332]

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