Marshall 1987 50 Watt Head Frying Bacon
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- เผยแพร่เมื่อ 27 ส.ค. 2024
- Marshall 1987 50 watt head. This amp came in to the workshop very noisy. After checking for dodgy plate resistors, a very unpleasant surprise was found up on lifting the PC Board. The amp is a 2002 reissue and is in fantastic condition for it's age.
One of the best amp of all times. Great soud .
Hola Miguel. Sí, son un gran amplificador de sonido. Gracias por mirar y cuidarse.
Sounds so sweet, nice job!
Thanks Ron.
Awesome playing! It sounds really good!
Hello Mickey, thank you. Take care.
That was tricky finding wrong value resistor on bias..and it wasnt a mistake
Hope all the caps in my amps over 20 years last better..
Good stuff
Hello Paul. Yes, can't think why it would have the wrong resistor in it. Thanks for watching and take care.
dont have to worry about loosing that calculator! great video.
Hello. Yes, I still manage to loose it sometimes though. Thanks for watching and take care.
This bacon-frying amp wants to play on the breakfast-cooking section of "Alan's Psychedelic Breakfast" !
О, Pink Floyd!
Ha Ha Ha. Yes it certainly had the right sound for that
The pots and can caps probably have date codes.
Hello, I should have said in the video that this is the 1987X which is the later one. Sorry for that. So made in the 2000s. Thanks for watching and take care.
Great repair job Martyn.. That looked a bit tricky.. Fancy that resistor in the bias circuit being the wrong value ? Some nice playing at the end..
Martyn's country pickin' could hold it's own with any of the Nashville-based session cats! As for the bias resistor being a poor value for that circuit, you would think that Marshall would have used turrets just for the bias resistor so it could be more easily changed without pulling the entire circuit board. After all, they used turrets for some (not all) of the wiring-harness hookups...
Hello Pete. Thanks. Yes, was a bit odd. Might try and research it.
Thank you. How I would love to be in Nashville. Yes I have often thought that turrets would be good in those situations. Maybe on day I should try and install some. I am sure it could be done on a PC board.
@@vintageguitaramp_guitarteacher I appreciate good country style guitar playing but what passes for country music these days is pretty sad. I always remember what Chet Atkins said when somebody asked him to define "the Nashville sound": he reached into his pocket and jingled some loose change in there and said "that's the Nashville sound" . I actually live in New England but my guess is that you'd be happier in Memphis then in Nashville. I know I would. I'm a fan of blues and blues based rock and there's not so much of that in Nashville these days but there definitely is in Memphis. Have you ever heard John Hiatt's song "let's go to Memphis in the meantime" ? " Sure I like country music, and I like mandolins/ But right now I need a Telecaster through a Vibrolux turned up to 10..."
My Marshall 2203X has the same R28 resistor problem. It biases the EL34s too cold. I'm thinking Marshall at the time wanted the tubes to run cold to keep them from failing too early.
Hello Zack. Since I have put this video out I have found out that a lot of people have found the same problem. You could be right. Or it could have a production error. Maybe someone from Marshall or who has worked for Marshall will come up with an answer will come up. It's annoying though because the amps sounds poor with cold bias. And to change the resistor properly you really have to take the board out. Have you swapped the resistor in yours?
In larger speakers, it sounds more like a storm on the seafront lol.
Hello Gary. That's a pretty good description. I didn't any chips or Seagulls in the back though. lol. Thanks for watching and take care.
What does the VR2 trimpot do?Does it change the sound if you turn it up or down?Thank you.
Hello Peter. It's a hum balance trim pot for the filaments. It does not affect the sound in any way. Thanks for watching and take care.
the two little blue and white pots on the right side of board vr1 vr2 those are the bias adj? alot of these they make self biasing
Hello. One is for bias and the other is a hum balance pot for the heaters.
👍👍👍
gracias miguel Cuidarse
What is the 2nd trim pot for? The circuit for the bias supply and electrical location of the trim pot is also a little weird, because normally the takeoff point for the bias voltage would be in between the final bias- dropping resistor and the trimpot, with the resistor to ground and the trimpot above it..... The only advantage I can see to the way it was done here is because if the trimmer failed, the output tube grids would see full bias voltage and the tubes would run cold but would still function, as opposed to totally losing bias voltage and having the tubes go into thermal runaway, turn cherry red and blow up.
Without looking at the schematic, could the second trim pot be an "output tubes matching" pot like Fender used in some of their amps? My first though was each output tube had it's own bias trim pot. If this were my amp, I would probably have installed a lower value resistor and increased the trim pot with a higher value one to allow for a greater range of bias adjustment in the future when new output tubes are needed.
It's a hum balance trim pot for the filaments. Thanks for watching
@@vintageguitaramp_guitarteacher Thanks for that info. I couldn't find that exact schematic. The earlier models I found schematics for used a 47K ohm resistor, not the 56K in the bias circuit. My 1976 Fender Super Twin Reverb amp has both a hum balance and output tubes matching pot (on the rear panel), but no bias adjustment pot anywhere.
Hello Michael. Here is the schematic I found: www.thetubestore.com/lib/thetubestore/schematics/Marshall/Marshall-Plexi-Superlead-Reissue-50W-1987X-Schematic.pdf
It says it's a 2002 under the barcode.
Yes, I realized after I did the filming. I am a bit of a plank sometimes. Thanks for watching and take care.
Of that were my amp I'd just shift the fx return board and put in some nice heyco plugs.
Yes, my thoughts exactly. A good idea. Thanks for watching and take care.
I have repaired a many Marshall amp...and just about every copy or original has that stupid 50mfd/50mfd cap under the freaking board. come on you botique amp designers...stop putting that cap where I cant replace it!
Hello, yes a real pain. Thanks for watching and take care.