Marshall voltage chart ?

[10thTx]

Can anyone verify whether this is an accurate chart for Marshall amps? OR ………. can someone offer a voltage chart for a 50w Marshall amp?

Thanks, 10thtx

[martin manning]

I think it’s legit. I believe that is part of a document describing the various Marshall amp circuits, separating them into generalized preamp and power amp circuits.

[10thTx]

Thanks, Martin!

With respect, 10thtx

[Roe]

the voltage on the 50w models decreased from ca 450v to 370v

[Stevem]

370 volts or so sounds like the output from hot biased JTM 45 PT , not a 50 water!

[martin manning]

I believe those are JMP/early JCM period, late ‘70’s.

[Roe]

370 volts or so sounds like the output from hot biased JTM 45 PT , not a 50 water!

No, the 70s amps had those low voltages. A healty 45 should have 440-450v

[pdf64]

I think that chart is a snapshot in time of the standard for Marshall production AT THAT TIME.
Hence it is not universally valid.
My guess is that it was issued ~73-74, as that coincides with lower HT '50 watters' and the 200 watt still being in production.
Such '50 watters' only put out around 30 watts clean.
By the later JMP, and certainly the JCM era, most 50 watters were back to full power with a HT ~450V, see http://scumbackspeakers.com/specs/jcm800powerspecs.jpg

[martin manning]

There were low-and high-voltage JCM800 50W. See: https://www.thegearpage.net/board/index ... s.1567598/ The transition seems to have occurred around 1980-1981

[pdf64]

Thanks, learn something new everyday
The latest low voltage 2204 / 1987 I've come across was '77, and an acquaintance had an early JCM800 2204 which was up around 450V HT, so I guess I jumped to the wrong conclusion
I wonder if more of the low voltage ones went over to North America, as they should lead to a longer tube life?

[Roe]

I any case, Marshall seems to have used the same dropper resistors on the high and low voltage amps. The former has much higher voltages even in the preamp as a result. Often the low voltage amps sound better if you raise the preamp voltages by reducing the values of the dropper resistors (e.g. 10k+8.2k)

[Reeltarded]

As an aside, those transitional amps.

Ooof

[Reeltarded]

Also, the Majors went 6550 and were out of production about a year later. I am unsure what we are looking at. It's later than 72 and earlier than 74.. but not 73. Is this a compilation of charts for internal use that someone scanned together or something?

Dig the 620 on the KTs. On wall voltage here.. that dream is a nightmare. Out of my four the middlest one was WAY crazy.

[pdf64]

Also, the Majors went 6550 and were out of production about a year later. I am unsure what we are looking at. It's later than 72 and earlier than 74.. but not 73. Is this a compilation of charts for internal use that someone scanned together or something?

Dig the 620 on the KTs. On wall voltage here.. that dream is a nightmare. Out of my four the middlest one was WAY crazy.

Bear in mind that the charts may have been intended for service / repair purposes, as well as new production testing; I think that Marshall have always undertaken that work for their amps. So it could have contained historic info for obsolete amps.
The doc that's in the public domain may not be the whole picture, may well be just a selection of what was available even when it was issued.

[Reeltarded]

Right. After I posted and looked at the saved image I only then noticed the weird setup with CA7s and GZ 50 setup. That was 435v on my JTM 50 transitional period amp. It's charts from 67 through whenever and whatever that amp they are describing was.. maybe an Artist model? Dont recall a model with voltages like that and a tube rectifier.