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Old 14th January 2013, 01:25 PM   #401
cotdt is offline cotdt  United States
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300V should be fine... they tend to use conservative max ratings for long life.
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Old 14th January 2013, 02:48 PM   #402
Pano is offline Pano  United States
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Thanks, I'll see what I can do with the PSU. As the DCR of the OPT is about 340R, there isn't much voltage drop at the anode. Easy to drop it at the input stage, not so easy at the output stage.
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Old 14th January 2013, 03:00 PM   #403
iko is offline iko  Canada
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Pano, you might want to throw in a tube rectifier if you haven't already. The voltage drop will help a bit. Also, consider a choke input ripple filter, instead of the capacitor input.
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Old 14th January 2013, 04:32 PM   #404
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I would use 250V Zener string and one source follower. Huge gain per buck.
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Old 14th January 2013, 05:21 PM   #405
Pano is offline Pano  United States
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Or I could make a gyrator/CCS out of some of the big depletion mode Mosfets I've got.
I am using a 6BY5G tube rectifier - a TV damping diode. I will get a choke in there ASAP. Thought I had one on hand, but seems not.
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Old 14th January 2013, 05:52 PM   #406
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Quote:
Originally Posted by regal View Post
Thanks for cleaning up my skimpy schematic, but 150V B+ is much too low.

Good operating point for this tube is 200-230V 30mA.

So that means you have a B+ of about 275V for the first tube with the CCS or gyrator, then use an extra RC to give the 200V B+ for the second tube.

I have 4 of the 4p1l's and am determined to build this when I finish this DAC B.S. But I am on the fence between Grados, Senns, and Orthos. So something to keep in mind when you buy your transformer is you might not want to be tied down to only a 300 ohm tap.



Also to add confusion if you read the ecp article linked above about parafeed, you will really get frustrated cause finding a permalloy core custom para-feed transformer is impossible.

A high quality permalloy 5k:300+32 parafeed OPT would be a real nice to have for preamp builders because it would give a nice headphone output. Kill two birds with one stone.
Can I use only one SSHV2 to power all four tubes? if yes have I to adjust SSHV2 to 140mA?
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Last edited by merlin el mago; 14th January 2013 at 06:01 PM.
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Old 14th January 2013, 06:00 PM   #407
stajo is offline stajo  Sweden
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Quote:
Originally Posted by merlin el mago View Post
Can I use only one SSHV2 to power all four tubes? if yes have I to adjust SSHV2 to 1440mA?
SSHV2 is good for about 100 mA
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Old 14th January 2013, 06:05 PM   #408
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Quote:
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SSHV2 is good for about 100 mA
Yes max current 100mA, so I will need two SSHV2 one for each channel, but the question is can I do it like the last attached pic?
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Old 15th January 2013, 12:20 PM   #409
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Anatolij,

How this gyrator will works in real life with 4P1L in pentode mode?
Sorry, I have no experience with the practical application of gyrator.

Thanks,
Rajko
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Old 15th January 2013, 04:05 PM   #410
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Hi Rajko;

I have no practical experience in loading pentodes on gyrators. :-)

But I believe that you will definitely need negative feedback, otherwise amplification will be excessive and frequency dependent. Like in opamps, where VAS stage is loaded on CCS.
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