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Old 5th March 2012, 05:12 PM   #211
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Location: Eureka, CA
Originally Posted by smoking-amp View Post
What happens to the voltage (series connection) between the Op Amps during a signal swing? Is it tracking the output?
Are you looking at the power supply connection that goes through the IC1B symbol? Both op amps are powered by the same +/- 12V offsets from the Q3 and Q4 sources.This tracks the output less the voltage drop across R4. R5
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Old 5th March 2012, 05:31 PM   #212
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Oh, I see now. All in one chip. Of course.
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Old 7th March 2012, 05:07 AM   #213
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Originally Posted by Michael Koster View Post
Funny you bring this up. I'm building a hybrid consisting of a SET stage with a true current boosting push-pull output stage.

The main ideas are:

Current is shared between the output stage and the SET stage by a ratio of 20:1 by virtue of the 20:1 ratio between R6 and R4,R5. This reflects the 250R OPT primary impedance back to the triode node at R1,R17 as 5K ohms.

The triode actually sees 10K plate load due to the 50/50 current sharing of the anti-triode Q5.

The output stage operates in class AB.

The idea is that the amp behaves just like a 20W SET into the real loudspeaker load, based on reflecting a constant % of the load current back to the triode plate while the output voltage nearly exactly follows the triode plate voltage.
Well, I was asking for a much more elementary reason. I'm building my first pp power amplifier - a transformer input differential circuit using video pentodes (cuz I got 'em) direct coupled to 2A3s . The drivers are loaded with Wavebourn's SVCS (The strange looking icons with ccs discs and the sine wave between) and the cathode circuit is like the cap coupled one that Shoog used on his EL84 amp.

I don't really understand them yet but I've always been interested in what you guys have been doing with the anti-triode and when I saw your schematic and realized I was assembling most of the parts anyway I thought it might be easy enough to get the op-amps and try it out somewhere along the way.
The idea of getting a single ended signature with one tube @ twice the power is appealing when thinking of tubes like the 45 or 10, but I haven't seen much in the way of subjective comments from people who have actually built and listened to them.
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Old 8th April 2017, 05:19 AM   #214
Shef is offline Shef  Canada
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Several points confirmed experimentally while half-year torturing of this particular design:
- with using a single CCS in output stage you are risking your 2A3s way too much. If one is accidentally pulled out (or heater is not up) - the second one goes to the spiritual world (of garbage bin) quick. Make the CCS' separate;
- hence, a differential stage better be the first stage, with a common CCS;
- actually, instead of the separate CCS in output stage 2 x Zener/resistor/cap work way better (cooler on temp and sonically sweeter);
- btw, 2 x 1400 uF is not any better than 2 x 14 uF, so just replace both with a single non-polar 20-50-100 uF - will be well sufficient.
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