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I don’t have a schematic but it’s likely to be very similar or identical to the Marshall 2144.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Does the Marshall 2144 have reverb & boost? EDIT: Yes it does. Got it now.
Rob
Either way, this amp never had a Marshall equivalent. As stated above it's almost certainly based on the 2144, but this amp is a 1x12 combo.
Many Parks were simply Marshalls with slightly changed cosmetics, panel hole/control positions, control names (but usually not functions) etc, but some were a bit more different including the 75W and 150W models with KT88s, and most of the ones with boost and reverb - but they were all fundamentally based on Marshall circuits and components.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
The 1210 Rockhead which Steve Grindrod designed around 79 has a plate driven tone stack and a post phase inverter master volume which has 2 sets of coupling caps. Quite a radical design for the times. Some argue that the tone stack is cold and hard compared to normal Marshall circuits but tbh I quite like it. It’s been done I many other high end amps like Dumble for example.
I got a reply today from Joanna at Marshall with information about the speaker and also attaching Steve Grindrod's hand drawn schematic of the Park Model 1239 dated 17th January 1980.
I have trawled the internet looking for this schematic to no avail and it seems Marshall had one all the while.
Great service from Marshall.
If anyone wants a copy of the schematic, drop me a PM with your email. I have JPG and PDF versions now.
Rob.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
It would be good to hear your thoughts about how it differs, or is similar to a Marshall.
Cheers,
Rob
I’m now looking at the amp itself and trying to decide how far to go. It works fine, as it should, but it’s a little bright. I think I removed the treble bleed cap off the input gain pot on my last one, so I’ll probably do that again.
If yes to any of those, re-cap it.
If no to all, then personally I wouldn't - yet. But be aware that it will need doing eventually - sooner or later, and quite likely sooner.
My current record holder for an amp with original caps which showed no signs of problems at all - no hum, no physical leakage, no measurable electrical leakage - is 65 years old. But they could fail tomorrow, and in an amp without really effective fusing (which is most, especially any without an HT fuse) there is a risk to other components, including the PT.
Do you feel lucky, punk?
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
No, not professionally, maybe only a gig a month.
No, it doesn’t hum.
No physical sign of leaking or bubbling, but I don’t have the ability to test them.
No other work required, the mains tranny is already an old replacement.
Hmmmm.
A couple more questions.
The schematic shows a mains fuse at 1amp, the back panel says 2 amp? Should I go 2amp? The one currently there is 3 amp.
Also the schematic shows an internal fuse on the board at 500ma. It has a 2amp in there. Given that the schematic and back panel differ for the mains fuse, what do you think the internal fuse should be?
Cheers,
Rob
HT: no more than 500mA for a 50W amp. Depending on where it is in the circuit you might possibly need a T, but usually an F is fine.
I would probably leave the caps for now. By the late 70s they were becoming much more durable, it's really when you get back to the dark blue Erie/Daly ones or even older plain aluminium ones that it's almost essential to change them.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Rob
One last question. I feel like I’m pestering you now.
Would you add 1k 5w screen grid resistors? It doesn’t have any, which I find odd.
I haven’t done this stuff for years. I think I can just move both wires from pin 4 to pin 6 and then put the resistor between 4 and 6. Am I right?
Rob
Yes, that's how to do it.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein