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No, that's a 70's 1987 just like my '73.
That's the only version of that schematic I've seen but it's pretty damn close to a regular Plexi of which there are plenty of nice clean re-drawn versions.
Print one of those and pencil in the differences?
Mine just rips, sounds phenomenal with all Mullards tubes including EL34's I converted it to.
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Plexi just refers to amps made from around 66 to 69 that had a plexiglass front panel.
The amp circuits were basically the same with small changes made to the different models over the years.
The Plexi models fetch more money, even though my 73 model 1987 is almost identical to a 69 model 1987.
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Okay, after pulling out my Marshall amp book-
M1989 is a 50w 4 input 2 channel Organ amp, quite rare.
Both channels share the same cathode resistor and cap as the normal channel of a 1987.
Very similitude with just a few differences.
I'd love to see a picture of the cabinet.
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Originally posted by drewl View PostPlexi just refers to amps made from around 66 to 69 that had a plexiglass front panel.
The amp circuits were basically the same with small changes made to the different models over the years.
The Plexi models fetch more money, even though my 73 model 1987 is almost identical to a 69 model 1987.- Own Opinions Only -
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Originally posted by drewl View PostI'd love to see a picture of the cabinet.
Thinking the power supply filter caps were not up to par, I paralleled a 40uF 600v polarized Weber cap around a 50uF can cap. The amp's fuse blew. I still don't know why. Here's what I do know.
1. I hooked up the new cap with the correct polarity.
2. The new cap is not defective.
3. The plates in the new cap have been properly formed by slowly applying power.
4. The leads connecting the new cap were not shorted to another lead or cabinet.
5. I've been doing repairs for almost 50 years, some of them commercially.
Your thoughts are welcome.
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Originally posted by Helmholtz View PostDid you connect the additional cap to the powered circuit? If so, it would draw a huge charging current surge that may blow the fuse.
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From the schematic in your first post, which cap would be the equivalent?
Which fuse blew, mains or HT? Was it slow-blow? What value?
I know it's not your 'first rodeo', but you also said it must be 'something stupid' so we do like to ask the simple questions in case anything was overlooked. We all have those momentary lapses (of reason ).Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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Originally posted by g1 View PostFrom the schematic in your first post, which cap would be the equivalent?Which fuse blew, mains or HT? Was it slow-blow? What value?I know it's not your 'first rodeo', but you also said it must be 'something stupid' so we do like to ask the simple questions in case anything was overlooked. We all have those momentary lapses (of reason ).
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Is the bias supply still stock, ie standby mode deenergises HT AND bias?
Marshall had a decade long ‘lapse of reason’ in sending their 50 watters out like that.My band:- http://www.youtube.com/user/RedwingBand
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