#1
Hey guys,

Long time reader, first time poster in this forum. I am about to set off on a quest to build my own tube amplifier, and I'm almost done figuring out exactly what I want it to do.

I just have a couple questions; first off, I'm basing my design off a JTM45 (I love the Bassman sound but I want it to sound a little more rock n' roll), but I want it to run at about 30 watts. My plan is to use 6v6 power tubes rather than KT66's. I will be adding a bias control to the amp (a la George from Metroamp), so that aspect of using different tubes won't be an issue. But I understand that JTM45 plate voltage is typically somewhere around >400. I've found a few 6v6s that are rated to handle that kind of voltage, but I still can't shake the concern that at high power, I'll have tubes failing all over the place. Would a JJ 6v6 be able to stand up to that kind of plate voltage? Is there anything in the circuitry I need to modify? And would it help to just get a power transformer that is designed to push two 6v6s? I haven't bought any parts yet, still thinking about what I want.

Go easy on me, I am a blatantly ignorant person about so, so many things regarding tube amplifiers. I admit my lack of knowledge freely and submit to your superior experience and knowledge ; )

Thanks in advance!

EDIT: Before I get called a fool for "not checking," I am perfectly aware that a JJ 6v6 tube is rated to handle 440 plate voltage. I'm just concerned that there might be some aspect of the power tubes that I am forgetting and that will prevent me from simply switching out the KT66's in the design for 6v6s and biasing accordingly.
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Last edited by Denthrare at Jun 14, 2010,
#2
The JJs should be fine in the amp you describe. They are some seriously tough tubes, and it looks like you've covered all your bases. I assume you've done your impedance matching calculations so you get the right OT.

As far as a power transformer, you could probably get by with something smaller like a DR transformer, but you might want to leave yourself the option of using EL34s or KTs if the 6v6s don't sound right, or don't last very long due to the increased plate voltage.

It sounds like a cool build. Make sure to post a build thread in here for us!
#3
I think my bases are covered on the PT and OT front, since I'll be using drop-in replacements from Tube Depot which are specifically designed for a JTM45.

http://tubedepot.com/transformers.html

I'm extremely excited about this build, I'll definitely be too energetic about putting it all together to not start a thread for it!

I think my research is leading me to the realization that higher plate voltages isn't necessarily a bad thing; as I read it, it'll make the amp sound more dynamic, and it'll take pedal distortion better. I'm definitely down for that!
Tobacco Sunburst Fender Strat
(Lollar Dirty Blonde pickups)
Fulltone FatBoost
MI Audio BoostnBuff
Fulltone OCD
This1smyne "Pearl"
Wilson 10Spot II
Red Witch Phaser
Fulltone ChoralFlange
BOSS DD-7+DD-20
Tech21 RVB
'59 Bassman Reissue
#4
have u built an amp before? this sounds like a nice build. i'd want to make something like this as well. haha

check out www.angela.com for some quality hammond transformers. they have excellent selection, and they list their primary/secondary taps voltages. i recently built a custom made amp so i'm aware of where i can obtain the parts you need.
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#5
The real JTM45 has about 35-40 Watts of output. Replacing the KTs with JJ6V6s in such high-power mode won`t drag it down much. For example, going from 40 to 25 is only 3db drop of volume, which is considered unnoticable by most humans.
And besides that, since JTM45 is a clean amp, its crunch is derived from overdriving the PT and the output stage. So changing the power amp design won`t get you "that" tone.
Classic amps are examples of a strict interaction between all its parts - change one and you`ll change the tone.
I consider building the amp as is. It even will be easier, as you won`t meet all those questions about changing circuitry, voltages, tranformers etc.

Regards. Ace.