JTM-45 build recommendations

[dehughes]

Hey all,

Long time, no build. The last ones I built (one Vox-ish, the other something unusual...) turned out pretty well, and I just sold my "big amp" (a killer Germino Classic 45...) and want to replace it with my own creation...of the same ilk. Yes, I know, silly to sell a perfectly good amp from a great builder to go and then make one of your own, but I'm brave (or stupid....take your pick).

Anyway, I'm going to do a JTM-45...probably with a Mojo chassis...and probably with either terminal or turret strips (a fan of Hiwatt and such, admittedly). Probably go with a 320-0-320-ish PT, a Radio Spares OT, and a 3Hy choke (all from Heyboer). Already ordered the Sozo caps...have a bunch of wire and resistors lying around.

Just looking for recommendations/suggestions/words of advice/things to avoid from you all who have gone before.

Thanks!

[dehughes]

Oh, and it will be running either a 4x12 Marshal cab with Heritage G12Ms, or a 2x12 with Alnico Blues. I like options.

[Stevem]

I would up the screen resistors to 1k just in case your every want to pop in EL34s and also along with that wire pin 1 to pin 8.
I also think that the stock 40uf of filtering is too light before the choke, and since you will likely have to stack two filters to get a 600 volt rating I would stack up two 220uf filters or at least two that end you up with about 80uf

[matt h]

(deleted)

[dehughes]

Very nice...thank you both. I am a fan of lower filtering in general.

[ToneMerc]

I prefer the lower filtering and 3H choke in the JTM45, with slightly softer voltages you might try 5H or 7H choke as well.

TM

[dehughes]

Excellent...thank you.

I'm guessing a 320-0-320 PT would get me close to 410v on the plates of your average KT66 pair in a JTM-45, yes? I want to keep the voltages reasonable so I can run new production KT66s and 5881s without fear of meltdown...

[ToneMerc]

Excellent...thank you.

I'm guessing a 320-0-320 PT would get me close to 410v on the plates of your average KT66 pair in a JTM-45, yes? I want to keep the voltages reasonable so I can run new production KT66s and 5881s without fear of meltdown...

320 should do it I would think.

TM

[dehughes]

Thanks. I'd like to retain the option of running 5881s, while at the same time keeping the voltage high enough to do a KT66 right.

[Roe]

I prefer voltages around 440v and the 6k6 primary of the RS OT. Also I like the flying resistor (although I've reduced mine from 1k to 470R). Good 5881s will probably work fine in a jtm45 with the flying resistor (1k shared screen resistor plus 470R individual resistors)

I prefer the 352-114 3h choke

[Bob S]

All of the above is great advice.
I like diode rectification with a 80uF or larger reservoir. 80-32-16-16-16uf works really good for my ears.
400vdc B+ or less even works great too. The Heyboer or Pacific TW Express PT is a good candidate - lots of power on tap. The Express OT isn't too shabby either.

[dehughes]

Thanks guys....much appreciated.