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6AS7GA as push pull output?
6AS7GA as push pull output?
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Old 16th November 2018, 09:25 PM   #211
Lingwendil is offline Lingwendil  United States
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6AS7GA as push pull output?
Heresy!

Guards! Take this man away! He's lost his composure!
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Old Yesterday, 05:59 PM   #212
mr2racer is offline mr2racer  United States
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It was earlier mentioned that having a front end with a higher B+ than the output is clumsy at best. But in this case it may not be? I have a 15 amp 6.3 volt filament transformer for everything. And a 230 volt 1.09 amp power transformer for 6N13S. All I need now is a power transformer for the front end. I'm going to use the topology from the posted schematic, (LTP pair feeding another pair for the second stage) for the front end. I've found a $16 Triad isolation transformer with a dual secondary for 230 volts. I could build a voltage doubler. The idea is to have a B+ in the 500 volt range to optimize the plate resistors and the tail resistors. When I receive the new transformer I'll know what my possible B+ voltages will be. If I don't have enough gain I could substitute 6SL7GT for the current schematic's 6SN7.
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Old Yesterday, 06:07 PM   #213
mr2racer is offline mr2racer  United States
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As for the noise problems with the 6N13S? I'm wondering if those problems are the result of driving the tubes very hot, 100ma 100volt? Along with hyper efficient speakers. My speakers are only 89 db efficient. And I listen to music louder than most so if there is a small amount of noise it may be tolerable?
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Old Yesterday, 06:11 PM   #214
mr2racer is offline mr2racer  United States
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One other question. In the earlier schematic the second stage 6SN7's use a CCS as the Bias/tail. If I use the conventional bias resistors and single tail resistor in the second stage the design would still benefit from the rising falling characteristic of the LTP and the CCS approximation of the tail resistor wouldn't they?
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Old Yesterday, 06:15 PM   #215
artosalo is offline artosalo  Finland
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Quote:
As for the noise problems with the 6N13S?
This does not exist in PP-output stages, maybe in some headphone amplifiers, but I have not observed this problem ever.
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Old Yesterday, 08:18 PM   #216
Lingwendil is offline Lingwendil  United States
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6AS7GA as push pull output?
I've never encountered the noise issues that others seem to have. Maybe these tubes were gassy/improperly stored? Not sure. I've only ever used them push pull with reasonably efficient speakers and they were no worse than any other push pull amplifier build, even after several years of daily use. They're as quiet as the PSU and topology used.
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