Marshall 1987 MK2 to 50W Bass conversion

[shocki]

I recently built a Marshall 50W Bass amp which I like a lot. It is basicly based on this layout which is an original Marshall schematic.
http://ceriatone.com/images/layoutPi...sCeriatone.jpg

Unfortunatly I sold it

I have to chance to buy a JMP MK2 50W 1987 (4 inputs, no MV, printed board, I think from 1978) though and asking myself if the circuit could be modified easily to those specs? And even it could be converted if the plate voltages and OT would be very different?
For my Marshall build I used those transformers which are exact replicas of those old transformers IGOT-JMP50 | Output Transformers | Transformers | IG Präzisions-Wickeltechnik

Thanks

[Chuck H]

The JMP' 50's had widely varying plate voltages throughout their run with some as low as 380 and others as high as 470. I think the lower voltage units were from a later era than the one you're looking at. If you could find out before buying that may help. I had two MV models with identical circuits. though years apart. Both had 420Vp. Not real high for something like a bass amp but probably alright. The OT from the actual Marshalls that I had tested out at 3200 ohms primary while all the replacements are spec'd at 3500. Not an earth shaking difference. All the 19XX Marshall 50W amps are so similar that circuit alterations to make one into another aren't even necessary.

[shocki]

Thank you. So this might be cheaper option than building one myself again. And if I don't like the sound I could replace the trannies. Power tranny ist not that expensive anyway and even the OT would not cost a fortune. Building one myself would cost about the same plus 20 hours of work

The OT from the actual Marshalls that I had tested out at 3200 ohms primary while all the replacements are spec'd at 3500.

I think it is not just about the specs but how the iron is build. But I am no expert on this.

[Chuck H]

Worth considering is that those amps are most valuable left in stock condition and should easily be worth more than the cost of parts for a scratch build.

[shocki]

I would leave it pretty much stock. Or make it at least reverseable.

[soundguruman]

A Marshall is a copy of a Fender Bassman...
with a few capacitor values changed.

It's not the transformers, really.
Change the transformers, and you will notice almost no difference at all. ("if" any)

Change the capacitors, to the Fender design...
and you will have a Fender Bassman.
(that says "Marshall" on the outside.)

OK, so a Marshall that is all original, is worth more to a collector.
Maybe you should sell the Marshall, and buy a Bass amp.

[shocki]

A Marshall is a copy of a Fender Bassman...
with a few capacitor values changed.

It's not the transformers, really.
Change the transformers, and you will notice almost no difference at all. ("if" any)

I have never done a test personally but there are all those "boutique" transformer winders out there. Like Mercury Magnetics and others. You think this is just marketing hype?

[Chuck H]

A Marshall is a copy of a Fender Bassman...
with a few capacitor values changed.

It's not the transformers, really.
Change the transformers, and you will notice almost no difference at all. ("if" any)

Just stop it. You're wrong. The purpose the OP indicated for changing transformers would be to either correct plate voltages or idealize primary impedance. Not just changing out stock units for equally rated boutique units. You replied to this with a knee jerk reaction that didn't apply. Read the damn post and try to say something relevant or stay out of it.