I’m pretty sorted!
65 JTM45 original
Then my builds:
66 45/100 JH clone
18w Trem 2x12
18w TMB EF86 1x12
Cabs are key too:
If I had to add to another I’d grab my sons 1992/2203 2 in 1 with 6550s but he would put up a fight. Regarding other originals...
The coupling caps are original and date the amp to early 77 (I had a JMP50 Model 1987 with them and it ripped!).
They work very well and I have had no issues with them, others have commented that they can be mechanically fragile if you throw the board around (why would you) and I would certainly...
Yes it is
Quick way to tell is of there is 300k on cathode follower plate supply
This has a 'new' 100k which means it may have been converted but the V1 cathode components look original so may be just replaced part
The wiring around the jacks is typical 2203/4 cascaded type
I’ve had a couple of 1970 amps (one was presented here couple of years ago) that used UPM50 Iskras -specifically 220k and couple of other values. But it is a bit like the Hystabs and Bumblebee vs long skinny Pihers around 64/65 in Marshall’s.
Pretty sure I sent a link to Al (aka Whazzagroover) in Italy.
He sells full and short length Pihers. The short ones are perfect for Marshall turret boards and cheaper. I’ll find the link again. I have only a few of those value Iskras and would have difficulty replacing them. The guy in Sweden...
I guess they are going with what works - works!
It often surprises me that very experienced people are not clued in about the layout/history spec of really classic amps (Uncle Doug's JTM45 video was another example). Not worrying about filter caps that are working 100% does not surprise or...
They do crop up reasonably frequently but most vendors are aware of value now and less of them are embarrassed to ask silly money.
As Matthews Guitars pointed out the best chance is a radio ham (or their estate) having a clear out.
Summary: late 67 Bass/lead or organ originally
Replaced switches and lamp
Replaced filter caps and boas caps
Added screen resistors and grid resistors
Output coupling caps replaced 0.1uF to 0.022uF
Added 0.68uF cap over V2a cathode
Replaced output tube sockets
So partly modded to lead spec but...
AFAIK the -139 is 3.4k primary and the -213 is more like 4k. I've had a couple but not measured them , n fact just remembered - I may have one in a 50w PA in a cupboard so can scope it/measure when I get chance.
LCRs, F&Ts and Dalys are all the same size and fit in 35mm clamps.
Like scottster I found that the ARS are of slightly smaller diameter and need a couple of wraps of insulating tape to get them snug (I have a blue that is the same colour so if you trim it to size you cannot tell).
I like the parts supplied by Valvestorm to the old Metro specs. Best quality and you can follow the build instruction links on the Valvestorm site. Looks like the Heyboer transformers are the only ones to get (either generic or Marstran)
It’s not quite ‘open the box and paint by numbers’...