Recent JTM45 Build

[Gaz]

How did you set the sweep to only be only 10ma? Thanks.

[ToneMerc]

How did you set the sweep to only be only 10ma? Thanks.

It's just two pots in series wired as variable resistors to ground after a 56k bias resistor. The board trimmer which is connected directly to ground fine tunes the range of the external pot. Also, normally on the front end of the bias circuit you will see a 220k or 180k resistor, I split the difference and used 200k. It's combination that worked out well with the 355V bias tap.

I chose this scheme as a solderless method to bias up the JJ 6V6 to current KT66s. It worked out perfectly because depending upon how the pots are adjusted the total range of the supply gets just positive enough to bias up the JJ 6V6 at 78-81% and negative enough to bias up a Chinese KT66 at 79%. I currently have those GT HP's at set at 70% plate dissipation.

TM

[RevD]

Beautiful build. And your right, not a gain monster and are darker sounding than most people realize, that said its still my favorite Marshall and yours is exceptional, nice work man. Very clever with the bias circuitry too!

Regards,

RD

[Gaz]

How did you set the sweep to only be only 10ma? Thanks.

It's just two pots in series wired as variable resistors to ground after a 56k bias resistor. The board trimmer which is connected directly to ground fine tunes the range of the external pot. Also, normally on the front end of the bias circuit you will see a 220k or 180k resistor, I split the difference and used 200k. It's combination that worked out well with the 355V bias tap.

I chose this scheme as a solderless method to bias up the JJ 6V6 to current KT66s. It worked out perfectly because depending upon how the pots are adjusted the total range of the supply gets just positive enough to bias up the JJ 6V6 at 78-81% and negative enough to bias up a Chinese KT66 at 79%. I currently have those GT HP's at set at 70% plate dissipation.

TM

Thanks a lot for the explanation!

[ampmike]

Beutiful 45 build,Stunning,!!!!!!!!!! MIKEY

[Roe]

this is the real thing

[ToneMerc]

Thanks guys!

Roe,
I have a set of Brian's trannies and whenever my faceplate shows up from Sparky, I'm going to get started on a BlackFlag.

Mike

[67plexi]

Nice job Mike, I have a old 1966 Jtm45 Park Marshall. The NOS. tubes will kill your bank account. I think Marshall used old leftover parts 1963-1965
to build the Parks. I also have a park-75 it has a jtm-45 preamp board.

[tubeswell]

I never intended to use NOS Mustards

I like using them. I've still got a few dozen 22nF ones, but no 100nFs. Have you got any spare 100nFs?

[loctal]

WOW! very nice.

watch craigs list for an old heathkit w5 amp. I have found very good KT66's on amps even with blown transformers.

[andy_wreck_fan]

Very very nice build

is that SteveUK on amp garage or is there a page of his where I could check those awesome faceplate?

[ToneMerc]

He's on eBay you can search for seller Steve025uk. He currently has a listing: Marshall Style JTM45 Plexiglass Gold Faceplate

His latest panels now include brushed alum and they cost half as what I paid back earlier in the year. I have one of the newer ones, the quality of the paint is just as good, although I prefer the Arial font over the London tube font.

TM

[ToneMerc]

this is the real thing

Roe, here's the real thing. It's a shame it's missing the original small leather handle and the small gray cabinet feet.


http://cgi.ebay.com/1964-65-Marshall-JT ... 3cb05e249c

[Structo]

Wow, that's a rare one.

Even the soldiers are untouched!

Don't ask don't tell!

Really, though that is nice. Not $18K nice but nice nonetheless.