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Old 31st October 2010, 04:22 PM   #1
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Default EL-34 to 6P3S-E

Hi,

I have a´ pair of Sentec M30 mono amplifiers constructed
for running two EL-34 type tubes in p-p. Can I put in 6p3s-e
in place of EL-34 without to much risk ? The OPT:s primary
impedans is 6kOhm when your speaker have 8 Ohm. The
Anode voltage is about 400V.

Thank you !
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Old 31st October 2010, 06:16 PM   #2
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google it there are many questions about this, the pinout is almost the same except for the non connected pins, so you needs to watch the oringinal builder didnt use the non internally connected pins for any connection (which people often do).
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Old 31st October 2010, 08:23 PM   #3
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Compared to modern production EL34s, I'd say that the 6П3С-Е (6P3S-E, the coin-base version) is tougher and more reliable. Don't use the ordinary 6П3С though, that's a 6L6GB analogue, and only rated for 270V on the screens, 19W anode dissipation.

The bias voltage is very different though, and you will have to correct this before installing a 6П3С-Е. Measure the cathode current using those resistors in the cathode leads, then look up the bias voltage needed against the screen voltage the amp is running. Watch out though, the sample-to-sample variation on these is very wide, and your amp specifies matched pairs!

Many NOS 6П3С-Е are gassy, and you need to test for this, and monitor the tubes' cathode current for a hour or more before you're sure it's stable. A slow roast at 100 deg C for 12 hours will often fix the gas.

The 6П3С-Е will work in a EL34 socket with no connexion changes.
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Old 31st October 2010, 10:58 PM   #4
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Quote:
Originally Posted by Rod Coleman View Post
Compared to modern production EL34s, I'd say that the 6П3С-Е (6P3S-E, the coin-base version) is tougher and more reliable.
And they sound better too, at least in my amp.

jeff
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Old 1st November 2010, 02:17 PM   #5
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Quote:
Originally Posted by Rod Coleman View Post
Compared to modern production EL34s, I'd say that the 6П3С-Е (6P3S-E, the coin-base version) is tougher and more reliable. Don't use the ordinary 6П3С though, that's a 6L6GB analogue, and only rated for 270V on the screens, 19W anode dissipation.

The bias voltage is very different though, and you will have to correct this before installing a 6П3С-Е. Measure the cathode current using those resistors in the cathode leads, then look up the bias voltage needed against the screen voltage the amp is running. Watch out though, the sample-to-sample variation on these is very wide, and your amp specifies matched pairs!

Many NOS 6П3С-Е are gassy, and you need to test for this, and monitor the tubes' cathode current for a hour or more before you're sure it's stable. A slow roast at 100 deg C for 12 hours will often fix the gas.

The 6П3С-Е will work in a EL34 socket with no connexion changes.
Thank´s for your detailed answer Rod Coleman,

Any idea on which cathode current that should be the "optimal"
setting whit 6P3S-E ? EL-34 needs about 52mA "optimal"
as you can see in the drawing. Thank´s again !
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Old 1st November 2010, 02:55 PM   #6
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52mA with 400V is a shade over 20W.

6П3С-Е will withstand 20W better than a modern EL34 can. Why not start there, at 50mA? then you can compare the sound.

If you modify your bias circuit so that it can adjust between -45V to -35V, approximately, it will be OK. start at -45V and adjust until the current is correct (1.0V at the test point).

You have two adjusters, so a matched pair is not too important, despite the schematic note.
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Old 1st November 2010, 03:04 PM   #7
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Try 6П27С instead of EL34. It is better than 6П3С.
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Old 1st November 2010, 04:40 PM   #8
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Originally Posted by Wavebourn View Post
Try 6П27С instead of EL34. It is better than 6П3С.
Hi Anatolij, do you have some 6П27С? They seem very hard to find. But I agree it's a better fit for an EL34 socket, if you can find some.
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Old 1st November 2010, 04:51 PM   #9
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Originally Posted by Rod Coleman View Post
Hi Anatolij, do you have some 6П27С? They seem very hard to find. But I agree it's a better fit for an EL34 socket, if you can find some.
Unfortunately I don't have them...
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Old 1st November 2010, 05:01 PM   #10
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Neither do I, but I do have some 6P3S-E:s . . .
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