1973 Marshall 50W Servicing, Need Help!

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Rocksy
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1973 Marshall 50W Servicing, Need Help!

Post by Rocksy » Mon Feb 03, 2020 12:42 pm

Hey Guys, I'm working on re-caping a 1973 50-watt Marshall amp.

I don't have a lot of experience working on vintage Marshalls, and I wanted to ask for assistance identifying this particular model so I can find the appropriate schematic.

-Does anyone know what components in this amp are non-original?
(The orange drop caps look odd, and two of the three cap cans are the "Tab" type)

-Also, any advice on what type of caps I should use to replace the old ones I pulled out with?
Can I replace the "Tab" type caps with more standard ones that fit in a clamp?
(Was planning on replacing all three cap cans, and the three electrolytic ones on the board)

Thanks!!

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neikeel
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Re: 1973 Marshall 50W Servicing, Need Help!

Post by neikeel » Tue Feb 04, 2020 2:32 am

The board is amazingly all original except for the rectifier diodes and the snubber caps (Orange drops)

The best caps are F&T or ARS manufactured 50/50uF @ 500v. You will need 6 off

https://valvestorm.com/Products/Compone ... ectrolytic

If you use modern UF4007 diodes (or even better(UF5408) for the rectifer (I would lay out more conventionally) then you can remover the snubbers completely.

https://valvestorm.com/Products/Compone ... Rectifiers

Any issues post back :thumbsup:
Neil

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neikeel
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Re: 1973 Marshall 50W Servicing, Need Help!

Post by neikeel » Tue Feb 04, 2020 2:32 am

The board is amazingly all original except for the rectifier diodes and the snubber caps (Orange drops)

The best caps are F&T or ARS manufactured 50/50uF @ 500v. You will need 3 off

https://valvestorm.com/Products/Compone ... ectrolytic

If you use modern UF4007 diodes (or even better(UF5408) for the rectifer (I would lay out more conventionally) then you can remover the snubbers completely.

https://valvestorm.com/Products/Compone ... Rectifiers

Any issues post back :thumbsup:
Neil

Rocksy
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Re: 1973 Marshall 50W Servicing, Need Help!

Post by Rocksy » Wed Feb 05, 2020 2:59 am

neikeel wrote:
Tue Feb 04, 2020 2:32 am
The board is amazingly all original except for the rectifier diodes and the snubber caps (Orange drops)

The best caps are F&T or ARS manufactured 50/50uF @ 500v. You will need 3 off

https://valvestorm.com/Products/Compone ... ectrolytic

If you use modern UF4007 diodes (or even better(UF5408) for the rectifer (I would lay out more conventionally) then you can remover the snubbers completely.

https://valvestorm.com/Products/Compone ... Rectifiers

Any issues post back :thumbsup:
Thanks so much for the advice!
I have a few more questions for you.

What is the benefit of rebuilding the rectification circuit?

Do you know what the single orange drop cap by the "Polarity Switch" is for?

Do you know where I can find the schematic for this particular amp?
(is this the correct layout? http://www.ceriatone.com/ceriatone/wp-c ... 0-Lead.jpg)
Could I copy the rectifier circuit from that layout?

Thanks!!

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wdelaney72
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Re: 1973 Marshall 50W Servicing, Need Help!

Post by wdelaney72 » Wed Feb 05, 2020 12:56 pm

That's the "Death Cab". The polarity switch is not necessary if you convert the input power cord to a 3-prong. I'd strongly recommend making this conversion.

I'm going to guess that modern day diodes do not require the caps, which is why they could be removed.

that's an impressive amp....nice to see one so pure, unhacked.
Walter

"There's no great thing in being a soloist. I think the hardest thing is to play together with a lot of people, and do it right." - Angus Young, 1984

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neikeel
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Re: 1973 Marshall 50W Servicing, Need Help!

Post by neikeel » Sat Feb 08, 2020 4:22 pm

Only issue I see is the replaced PT (why do people cut corners like removing the grommets where wires go through the chassis).
Re: the diodes it is just my OCD (I get over it - mostly) as I like to see things neat and tidy and that installation is totally random!
If you are ever in need I have and original PT for that amp (bear in mind I am in the UK so financially tricky!)
Neil

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