36 watt Jazz Amp

[mooreamps]

Current project ; almost done.
6 watts single-ended ; 36 watts push/pull.
two channel preamp on a footswitch, and blend-able in preamp mixed mode.
Choke driven low impedance output inverting/non-inverting 2 watt IPA
Fixed bias in both preamp channels and in the IPA when in S.E. Mode..
Electronic Volume Controls for both preamp channels.
Combination bias for power tubes...
12 inch loudspeaker for dry tones, 10 inch loudspeaker for reverb.

-g

[Chuck H]

Wow, that's realy... uh... BIG. No matter. You can put it in a hardwood furnature style cabinet. The jazz guys will eat it up.

I've done the dedicated reverb thing before. It works great. I ran my tank by filtching power off the main amps output. I don't SEE a tank in your pic so I don't know if your using one. But if you are I can tell you that running it off the main amps output and then dedicating a recovery amp and speaker works really well.

The trick, IMHO, is to market directly to jazz players in their publications. They seem to like funky quirky stuff with a different sort of design.

Some of your features seem like stuff one might do because they could rather than because they should. But if you consulted a bunch of players about what they want and the amp sounds good then it's great. Looking forward to hearing the clips.

BTW, if you wanted to try the 'run the tank off the main amp' thing I won't get wierd like you took my technology. Gibson, Hammond and others did it almost fifty years ago.

[mooreamps]

This one is going to Denver. I wanted to do the cabinet in dovetailed maple, but he said pine was good enough.. I also wanted to do a Fender style reverb, but I would have needed to have a different transformer to drive the tank. I do have a tank, it's mounted on the wall ; off camera. In exchange for the amp, he is going to do a professional video shoot and recording... The other condition was that I was able to use up most of the left over parts that I collected in doing other builds up to now.. .. I've done several power on tests with just the lead channel, and from listening to it being driven from my little black guitar, it does work ; tone being subjective of course, which is why it's going to Denver for eval...


Something else, I really like the choke driven P/I. It allows the cathodes to only ride abouts 20 volts above ground, instead of either 40's or 80's ; and the balance is not bad.

-g

[J M Fahey]

Nice build.
Congratulations.
Looking forward for that Video.

[pdf64]

What is meant by a
'Choke driven low impedance output inverting/non-inverting 2 watt IPA' ?
Based on
'I really like the choke driven P/I. It allows the cathodes to only ride abouts 20 volts above ground, instead of either 40's or 80's ; and the balance is not bad'
it may be an LTP with a choke for the tail resistor, but not sure how that fits with '2 watt IPA' part. Pete.

[mooreamps]

In Push/Pull mode, it functions like a P/I. In S.E. mode, it functions like two independent gain stages ; and it's hot-switchable. Total of 2 watts output with a driving impedance of abouts a 1000 ohms. So, guess what ? I can drop the grid leaks on the power tubes to abouts 10K .

-g

[Chuck H]

Total of 2 watts output with a driving impedance of abouts a 1000 ohms. So, guess what ? I can drop the grid leaks on the power tubes to abouts 10K

I'm confused. I do know that it's a good idea to have the lowest possible impedance at the power tube grids to avoid grid conduction under loading conditions like overdrive, and I've never achieved 1k AFAIK, and available watts would be an indicator of available current, which also AFAIK is the point behind shooting for a low impedance, but the power tube grid is still primarily a voltage dependent circuit. Honestly, the available wattage at the power tube grid doesn't impress me without a drive voltage figure to back it up. After all, if the tubes aren't overdriving (or biased into class B or some other condition that requires grid current) whats the point in the available current? Not being a dick. I'm just interested in what your doing and the positive result your getting from it as it relates to guitar amps. What kind of voltage swig can you achieve with this circuit? If it's high enough to drive the piss out of a pair of big bottles that would be great and useful.

BTW, sorry for the long sentances and all the comma's. Just trying to convey as I think.

[mooreamps]

It drops the noise floor on the power amp. I'll measure the volts on the grids tomorrow.

-g

[mooreamps]

What kind of voltage swig can you achieve with this circuit? If it's high enough to drive the piss out of a pair of big bottles that would be great and useful.

I'm getting at least a 100 volt rms swing between both plates in class A/B mode. That should be good for abouts 30 watts...

-g

[Steve Conner]

Happy new year!

Now I'm curious to know, what's an IPA?

India Pale Ale? Isopropyl alcohol? Intermediate power amp?

[mooreamps]

Happy new year!

Now I'm curious to know, what's an IPA?

India Pale Ale? Isopropyl alcohol? Intermediate power amp?

Intermediate power amp... I call it that because of it's very low driving impedance, compared to a standard P/I..

-g