Amp porn - safe for work

[billyz]

Jelle may be right.
This one is probably worth more as is with it's original electrolytics if working.

[gui_tarzan]

I would not be changing resistors just because they have drifted. They would have to be open or noisy. Probably change the power supply caps and bias supply caps. Might be all it needs to be reliable and sounding good. This is amp is quite valuable if authentic, I would be for preservation of as many original parts as possible.

I see nothing wrong with changing parts if they are WAY out of spec, and I agree with you that no more work should go into this than absolutely necessary, but I get the feeling the owner wants it to work and who am I to say "no, it's too valuable"? I have verified that it is authentic and is a true 1964 model, but if the man wants to play it it needs to work.

I'm not a shotgun-replacer. I'll only replace what has to be replaced but the last thing anyone wants is to for this thing to fry if I don't. He will get the original, bad parts back. I do that for everyone I do work for.

[crbowman]

That is a beauty! I don't know that I've ever seen a Marshall with flying heater wiring.

[gui_tarzan]

So what's the power supply look like? Should be 32u, choke, 32u, 8k2, 16u, 10k, 16u or something like that? Is the reservoir 32u+16u now?

Yes.

[martin manning]

Do you mean yes that's what the power supply components look like or yes the reservoir (first filter) is 32+16 (=48u)? I was thinking the 32u can on top of the chassis is the one connected to the rectifier.

[gui_tarzan]

Ok, the top can has a slightly larger gauge wire connecting to the standby switch so the top can is the reservoir. The wires are bundled so tightly and the wire sizes are so close together I'll have to spend some time mapping some of them out with a continuity tester just so I know where they go.

[gui_tarzan]

Every single resistor checks out within tolerance. How often does THAT happen on an amp this old??? I like it!

[KellyBass]

Every single resistor checks out within tolerance. How often does THAT happen on an amp this old??? I like it!

Almost never!

What a great amp!

[shane]

As regards the flying heater wiring, its unusual for Marshall, at least the ones I've come across.
Also most of the Marshalls I've seen have had Red and Black heater wires.
Plus those tube sockets look rather new, so maybe they've been replaced at some time and had new heater wires.
Damn nice amp though!!!!

Cheers
Shane

[cbass]

Man what a sweet amp . I don't think all carbon comps are created equal . I've seen old amps where they were all within 10% . ivevseen old amps where nearly every resistor was 50% or more off. I've never seen an old Marshall before. They sure don't make em like that anymore.

[gui_tarzan]

Ken Underwood, one of the original Marshall employees is discussing it with us on another forum. He said it could have been a late '64 or early '65 based on the way the heater wires were twisted and that RS had a very large stockpile of caps and such at that time, so it could have been carryover inventory. Either way it's awesome.

I am going to try to reform the original caps before I change them. The more I thought about it, the better idea it seemed to be.

[billyz]

Ken Underwood, one of the original Marshall employees is discussing it with us on another forum. He said it could have been a late '64 or early '65 based on the way the heater wires were twisted and that RS had a very large stockpile of caps and such at that time, so it could have been carryover inventory. Either way it's awesome.

I am going to try to reform the original caps before I change them. The more I thought about it, the better idea it seemed to be.

I just reformed the original caps in a 71 50w. I am not typically a cap reformer, but this one was just too clean and new looking. It has been working well now for over a month. Very quiet and strong sounding.

[gui_tarzan]

Which procedure did you use? I've seen several different explanations online.

[gui_tarzan]

As regards the flying heater wiring, its unusual for Marshall, at least the ones I've come across.
Also most of the Marshalls I've seen have had Red and Black heater wires.
Plus those tube sockets look rather new, so maybe they've been replaced at some time and had new heater wires.
Damn nice amp though!!!!

Cheers
Shane

They appear to be original. I don't think anything in this has been touched since it was built. It looks like a very few solder joints have been re-touched but nothing changed.

[billyz]

Which procedure did you use? I've seen several different explanations online.

I don't think it did it the approved way. I used a light bulb limiter with various wattage bulbs and the voltage tap switch on the amp itself. At first I had no tubes installed. As the voltages were adjusted higher I installed the tubes. I made a chart and watched the voltages stabilize before moving higher each step. I did it over three days. I usually form them individually with my it-28. But not wanting to unsolder them from the amp did not allow for that option.
I have seen some folk use resistors to limit the current only.