I Finally Fried My Marshall

LLL

LLL

New member
LOL It was inevitable.

I have, for years, ran it dimed (or at 8,9 on vol); typically into a load box and tapping the signal via line out.

Popped HT fuse and 120Hz hum. Once, popped mains fuse.

So now, troubleshooting... have me a lightbulb current limiter, multimeter, spare can caps, taking measurements (drain those caps first!).

Could be a blown OT, choke or both... I'm already past the "easy check" part of troubleshooting (tubes, etc).

We'll see.

I'm not freaked out because I built the thing, and I needed to get back into the guts after a handful of years (last modding session) to re-familiarize myself with the circuit.

I'm actually going even deeper as I learn how to conclusively test the OT to see if it's good (6.3v filament transformer test), choke test, maybe ever PT test, etc..

Learning is good.
 
Re: I Finally Fried My Marshall

Blown OT's are rare, so I am thinking the odds are in your favor here.

Please update us with what you find.
 
Re: I Finally Fried My Marshall

Out of curiosity, what is a choke and what does it do?

Sent from my Alcatel_5044C using Tapatalk
 
Re: I Finally Fried My Marshall

It can be as simple as a blown electrolytic cap... It would smell. Does it?

Late 60's Marshall's were having OT and PT issues, sure but the new ones are ok I think. So I don't think it's the OT or the choke... In fact, does the choke ever blow?

Good luck finding the cause man. I hope the diagnosis would be fast and the cure easy.

B
 
Re: I Finally Fried My Marshall

a choke is a small transformer that smooths out the power supply
 
Re: I Finally Fried My Marshall

Just buy ten of them and plug into the next one. I hear that’s how Eddie did it. ;-)
 
Re: I Finally Fried My Marshall

When I ran my deluxe reverb reissue on 8 into an attenuator a lot, one time it blew a screen grid resistor. Symptoms were it was blowing fuses and sounding horrible and weak when another fuse was popped in and eventually just hummed and blew fuses immediately until i got that resistor replaced. Fortunately it was a cheap, easy fix. I hope your amp is up and running soon without a lot of trouble!
 
Re: I Finally Fried My Marshall

So far, checking the OT using the 6.3VAC filament tranny (just using the taps off the PT in the amp - e.g. heaters, which are 6.3VAC) + lightbulb current limiter test, looks like OT is shot. One lead from 6.3VAC FT to secondary tap (4,8, or 16ohm - any works), other lead from 6.3VAC FT to OT common/ground. Lightbulb lit up like a christmas tree... meaning a short.

I previously checked OT resistance on the leads and that didn't look good, so the above test is a 100% guaranteed reading.

Checked voltages on PT too and that looks good.

BTW, if you're a DIYer like myself, and don't want to throw $$$ away buying up new fuses for a broken amp that eats fuses (while troubleshooting), I highly recommend the lightbulb current limiter. It will never send too high a current through your amp (thus blowing fuses). Here's how you build one:

https://robrobinette.com/5e3_Modifications.htm#Light_Bulb_Current_Limiter

Cost ya maybe $10 bucks max.
 
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Re: I Finally Fried My Marshall

:arg: That stinks.

This is only the third no load or non-lightning strike blown OT I am aware of.

Great advice on the lightbulb current limiter.
 
Re: I Finally Fried My Marshall

JMP/HBE said:
U have to be smarter than the amp if you want it to last.
Click to expand...

The amp will last forever, because I know tube amp building and repair (Marshalls, specifically).

I jumped on the DIY wagon back in the early 2Ks... it's a great feeling knowing that if something breaks, or if I want to customize it, I don't have to bring it in to anybody - I can do it myself.

And, the tone was definitely worth it. :headbang:
 
Re: I Finally Fried My Marshall

LLL said:
The amp will last forever, because I know tube amp building and repair (Marshalls, specifically).

I jumped on the DIY wagon back in the early 2Ks... it's a great feeling knowing that if something breaks, or if I want to customize it, I don't have to bring it in to anybody - I can do it myself.

And, the tone was definitely worth it. :headbang:
Click to expand...
Sez the guy that blows up amps. Lips service is cheap & free.
I judge people by their actions. I don't believe a word you say.
Scary part is you do.
 
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Re: I Finally Fried My Marshall

JMP/HBE said:
Sez the guy that blows up amps. Lips service is cheap & free.
I judge people by their actions. I don't believe a word you say.
Scary part is you do.
Click to expand...

And how would you even be able to determine if someone knows Marshall amps?

After all, you have to take your amps in to someone else for modding and repair... :33:


I'm a guy that blew up one amp. Ever. After a decade+ of running my Marshall into a dummy load; usually dimed.

It's my amp, and I'll do what I want to it. Shush.

https://forum.seymourduncan.com/showthread.php?324666-Surgery-Time!-(JTM45-Modding-Content)
 
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