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Old 20th October 2003, 10:10 AM   #21
dhaen is offline dhaen  Europe
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Quote:
6688 ----el34 cathode follower ---gm70
Are you going to DC couple from the EL34 to GM70?
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Old 20th October 2003, 10:37 AM   #22
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Dhean
Yup dc coupled
read your site and steve bench site about cap coupling and A2
your information spearheaded that direction.
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Old 20th October 2003, 03:48 PM   #23
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Quote:
Originally posted by NickC
Brett
i am also going with a pentode front stage but would be a 3 stage
6688 ----el34 cathode follower ---gm70
might go with a 2 stage but power would be lower (can it sustain A2 operation?). Probably try the fame c3m or the sv83
what's the specs for 12HG7A rp,mu ?
would look at pete millet's side if he has it
Dunno about A2. Never tried to do it as a diff GM70 even at low volts had heaps of power for my requirements. My speakers are >104dB/W. About 50Wrms should be possible in A1 (PP) without much trouble.

12HG7 datasheet
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Old 20th October 2003, 04:32 PM   #24
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Brett
50 watts in A1 ? that seems alot with a 6k transformer i presume
i running 90dbs would like the extra power in A2. MOst of it will be for the learning curve of A2 anyway. I am planning with going with 12k lundalhs. Do you any way that i can reduce the output impedance, need better dampening factor, apart from using larger impedance ratio, parallel tubes but some form of feedback is allright.
Were do i buy this 12hg7?
Thanks
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Old 20th October 2003, 07:16 PM   #25
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Quote:
Originally posted by NickC
Brett
50 watts in A1 ?
It was an ottomh number but shouldn't be too far off. Lets say 40 (1dB difference) to satisfy the pedants.

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that seems alot with a 6k transformer
I never specified how, just based it on efficiencies you can expect from the tube ratings.

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i presume i running 90dbs would like the extra power in A2. MOst of it will be for the learning curve of A2 anyway.
I have no idea how much power you'll want/need in your room, but 40W would be reasonable.

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I am planning with going with 12k lundalhs. Do you any way that i can reduce the output impedance, need better dampening factor, apart from using larger impedance ratio, parallel tubes but some form of feedback is allright.
Feedback is probably the only real way. Depending on how you // the tubes and the impedance ratios chosen, you may not end up with a lower output Z, even though you'll have more power. These are your design decisions to make depending on what you want from the amp.

Quote:
Were do i buy this 12hg7?
Thanks
AES, or one of a hundred other tube vendors. It was a common tube in TV's but isn;t used much anywhere else so it's cheap and available. because not used in audio much, you may have to ask vendors as it might not be on their lists.
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