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Vintage threads from the first ten years

Re: 1970 Marshall SLP 1959

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6/15/2000 4:48 PM

Re: 1970 Marshall SLP 1959

Rebel,
I did notice that, but there is a transition period with JTM-45 JTM-50 and leading up to the solid state rectifier 1987 models where anything is possible. I've seen all kinds of variations. It was a very experimental period for Marshall. I agree with you though this amp may be modded..and probably is..it looks to be modded....it's a great pic, but I just cant tell from the pic what's been done here.

Peter S
Kimerik Amplifiers

6/15/2000 5:54 PM

quote:
"it's a great pic, but I just cant tell from the pic what's been done here."

The whole front end of the preamp has been rebuilt. Those resistors are obviously from another era, and the JTM-45's never had the split cathode arrangment.

6/15/2000 6:23 PM
Dave M.	Also take note of the IEC power receptacle. Hmmm, how much has been changed? -Dave M.

6/15/2000 10:23 PM

Yep no doubt some of the resistors have been replaced and the wires running to the grids have been replaced,as well as the coupling cap on the normal channel, but I remember seeing some amps around 71 or 72 that came into the shop and looked to be factory with the split cathodes....with a .68 bypass and 2.7k cathode on one side and the 820ohm resistor on the other...but still using 2 .02 coupling caps....I remember about 4 of us standing around with one of these babies on the bench scratching our heads the first time we saw it. This one here is definitely not factory though. Another thing that's odd is I've never seen a JTM45 with the solid phenolic board, everyone I've seen has been perf board, including all of the ones I've owned. They did some really strange things for a few years up until they went to the solid brown phenolic boards and got rid of the perf board.

Peter S

6/16/2000 4:12 AM

Here's a couple more observations about this Marshall.......first the bias circuit looks like it's been changed, I can't tell how or what but something......but get this one.....and this is what I mean by anything goes during this period.....It has the 8.2k first power resistor, but then it has two more 10k resistors in the rail with the extra decoupling cap. So the B+ rail is like a 50 watt Plexi(almost), not a JTM-45. A plaexi would have had the two 10k resistors in series right after the screens. The split cathode's not factory though cuz it doesn't have the extra turret. Nice Picture!

PS

6/16/2000 5:40 PM

quote:
"I remember seeing some amps around 71 or 72 that came into the shop and looked to be factory with the split cathodes...."

Marshall started building them this way in 68 or 69.

6/16/2000 5:55 PM
Peter S	No I dont mean 68 or 69 50 watters......these were JTM-45's and as near as we could tell they were built sometime in 66 or 67. I saw at least 3 of 'em during the time period between 1971 and 1974 and if they werent factory Marshall wired amps....someone did an amazing job of making them look like it. Also the weird power supply changes were rampant back then. Not very much consistency. Peter S

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