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|8/11/1999 7:42 PM|
||larger tube & output in Single-Ended amps?|
I was wondering about how big (in terms of power output) can one make in a single-ended amp design? (in practical terms)
I'm still gearing up to basically make a Fender Princeton clone (single-ended with an 6V6GT power tube), and reading about the advantages & disadvantage of single-ended vs push-pull (such as the point that in a push-pull design you have "crossover distortion") and I rather like the idea of the SE style... anyway, at some later stage, I'll want to think about building a higher power amp for live use (for when I play well enough ,grin>). So, would it be possible to build an SE amp that puts out say 30 to 40 watts? or more? What output tube would I need to use?
Is this another rediculous idea?
|8/11/1999 8:50 PM|
Try a Hammond 1640SE output transformer with a parallel pair of 6550s. Maybe even EL34s or KT90s.
|8/11/1999 9:20 PM|
First off, understand that "single-ended"
doesn't necessarily mean "single-tube".
You can build a single-ended amp that
uses two or more tubes in parallel in
the output stage. In fact if I recall
correctly, there's a 50W SE amp design
that uses 4 6550s in Kevin O'Connor's
Principles of Power. You could certainly
start by looking at that. And if you
want to get crazy, you can either use even
more tubes or big transmitting tubes, and
get over 100W. The biggest problem will
be finding an output transformer that is
designed for single-ended operation at that
power level. You'd probably have to have
it custom made, it would be expensive (several
hundred dollars) and it would weigh a lot.
(Kevin's design uses a stock Hammond, which
is about as big as they get, and costs around
As far as crossover distortion, it does
not exist in push-pull class A amps, either
(it's eliminated by class A operation, not
by being single-ended). What you get a lot
of from an SE amp (especially a guitar amp)
is even-order harmonic distortion. In a
push-pull amp, the even harmonics tend to
cancel. I think that's really where most of
the tonal differences lie.
Also keep in mind that SE amps are more prone
to hum that PP types, because there's no
common mode cancellation happening. In other
words, you'll want a lot of supply filtering
and maybe a DC filament supply if you want a
really quiet amp.
If you want your small-amp sound at higher
volumes, mike your Princeton clone and run
it into the PA. Much easier.
|8/11/1999 9:21 PM|
Sorry about that... it kept saying
|8/11/1999 9:37 PM|
Jeez Reid, really trying to get your point across, aren't you??
Kidding around aside, spot on about the post, though. Interestingly enough, I have a Hammond 1640SE that is rated 50W. This is a rare beast, since Hammond, for some reason not completely disclosed, de-rated the tranny soon after I purchased mine to 25W. Perhaps they were saturating to hell with 50W of flux @ 30Hz? That's completely plausible.
The best thing about that 1640SE is the DC idle current that's allowed--200 mA. You won't find another production SE tranny ANYWHERE with that kind of flux capacity.
The downside is the very low primary Z (1K25), and low primary L, which is <10H if I remember correctly. This means paralleled tubes are necessary.
There was a Japanese guy I saw who used a Svetlana 3cx300 "hockey puck" tube to drive a 1640SE. He seemed to like it quite a bit for home HIFI use. He went with the Hammond for its DC current capacity.
I think you could still get an honest 50W, especially in the guitar range of frequencies, from a 1640SE, which are a little under 100 from Angela Instruments. When I bought mine from them it was 142. Damn. It DOES say 50W though.
If you want to get even more SE power, you can get a couple of them and stack their secondaries. Or you could get a custom SE traffo wound, for big bucks.
|8/12/1999 6:01 PM|
Maybe 3 paralleled KT90s would drive this thing? That should get you close to 50 Watts. For driving the paralleled grid load, maybe a CF would be in order.
|8/12/1999 8:07 PM|
Completely agree here. But I'd try to steer around those KT90's, since they are NOS now.
Probably best to go with three KT88's or 6550's. The low impedance of the tranny means high B+ isn't necessary, or desired, so 6550's would probably be best in terms of cost.
You COULD parallel three SV811-3's or 811-10's for the DHT sound... that might sound really good.
One of these days I'll get around to doing something with that iron.
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