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Unexpectedly good EL84 amp
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Old 17th June 2019, 08:28 PM   #141
Lingwendil is online now Lingwendil  United States
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Quote:
Originally Posted by chede View Post
Lingwendil,

what would be the reason for running the Concertina hotter than John Broskie had set it ?

Would the main benefit be the evenly distributed DC current through both halves of the 6N1P ? And would the benefit of that again be the more even wear on the two halves of the tube ? Or does it have something to do with the drive capability of the Concertina ?

If it's just for more even tube wear, my approach would be to set up the tubes for the respective channels in mirror-like fashion - in one channel, the Concertina would be on the left half of the tube; in the other channel, it would be on the right half. That way, I could swap the tubes between sides from time to time and even out the wear.

When I look at the data sheet of both the 6N1P and 6N1P-EV, for example the inter-electrode capacitances, the two halves look pretty symmetric to me - anything that would speak against this approach ?

I am slowly gathering parts for building this amp ... just got 100 pieces of 30k 2W 1% metal film resistors, so it would be no problem to try out 30k as well as 15k (by paralleling two 30k) on the Concertina ...

Also, I plan to buffer the B+ for each 6N1P with a 35 uF MKP cap per channel, so I am not terribly afraid of "non-constant" AC current draw ...

Best regards,
Claas
I would mainly do it to keep each half at similar DC conditions for wear, along with slightly (theoretically) better drive capability... No real delbreaker to run as shown though. Your idea for mirrored channels and rotating is a good one, and what I do on most point-to-point builds anyway, not likely to make a huge difference, but gives a good warm-and-fuzzy feeling
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Old 28th June 2019, 12:12 PM   #142
Bas Horneman is offline Bas Horneman  Netherlands
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I liked the Tubecad EL84 so much. That I built a 6P1P version for my son. Obviously with lower voltages. red led this time where I had the schottkey last...under the first 6n1p.
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Old 28th June 2019, 03:32 PM   #143
Lingwendil is online now Lingwendil  United States
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Lovely

I really need to grab a few 6P1P at some point while they're still cheap.
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Old 4th July 2019, 04:20 PM   #144
mashaffer is offline mashaffer  United States
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If one were to rework it for 12A_7 family of tubes I suppose the AT7 would be the closest in gm and mu but it is not so linear. If doing a stereo amp one could use a more linear tube for the VAS and the AT7 for the PI as it seems nearly ideal for that possition. Perhaps the AY7 or AX7 for the first possition as both are pretty linear. The AY7 has an advantage in biasing for. Grid input headroom and of requiring smaller plate load.
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Old 4th July 2019, 06:22 PM   #145
Lingwendil is online now Lingwendil  United States
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AY7 or a DW7 may be a decent choice.
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Old 6th July 2019, 04:39 PM   #146
mashaffer is offline mashaffer  United States
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Would you estimate the TCJ first stage gain to be around 10?
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Old 6th July 2019, 06:07 PM   #147
Lingwendil is online now Lingwendil  United States
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With a cathode resistor that isn't bypassed I think it's around ~20 or so, I have to check my notes.
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Old 7th July 2019, 01:52 AM   #148
kodabmx is offline kodabmx  Canada
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Unexpectedly good EL84 amp
Quote:
Originally Posted by Lingwendil View Post
Lovely

I really need to grab a few 6P1P at some point while they're still cheap.
I found these.
6P1P-EV Lot of 10Pcs Russian Audio Output Tubes OTK Stamp new industrial box | eBay

The price was $1 per tube when I bought a bunch of them... Now over $3!

I think I'll keep the 30 or so I have left and sell them when they go for $10 a piece

These are only $1.50 USD each if you get 50. 6P1P-EV / 6AQ5 / EL90 tube (new in paper) - Vacuum tubes - Tubes-Store.com
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Old 16th August 2019, 02:22 PM   #149
Hilko Peter is offline Hilko Peter  Sweden
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Many times one reads that the 6N1P is equivalent to the E88CC except for the filament current. Would the E88CC work in this setup without needing to change anything? I now use the 6N1P and I find my power transformer getting pretty hot (max 4.5A@6.3Vac) so reducing the filament current would probably help. I use led bias in the first stage.

Thanks!
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Old 16th August 2019, 03:14 PM   #150
Bas Horneman is offline Bas Horneman  Netherlands
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Yes you can use it without changing anything.
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