Stereo class A 6+6W - 2x 6L6G 1 x 6N2P - diyAudio
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Old 26th August 2012, 09:24 PM   #1
pilovis is offline pilovis  Italy
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Default Stereo class A Ultralinear 6+6W - 2x 6L6G + 1x 6N2P

Schematic:

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Line transformer output = 250 Vac 0.3A - 6.3 Vac 3A
Diode bridge = 4 x 1N4007
Filter Cap = 2 x 100 uF 385 V
Plate voltage of 6L6G = 290 Vcc (plate <> cathode)
Grid #2 voltage of 6L6G = 240 Vcc (grid2 <> cathode)
Bias current of 6L6G = 44 mA (17.2 V @ 390 ohm 2W self bias resistor)
Audio output transformers = 3Kohm/8ohm, Grid #2 connection @ 43% of primary winding (ultralinear).

note:
6N2P =6AX7 = ECC41 = 6h2n
6N2P, 6N2PEV (6H2n, 6H2n-EB)

You can try out 6N1P = ECC88 instead of 6N2P (with less gain)
6N1P, 6N1PVI, 6N1PEV (6H1n, 6H1nBN, 6H1nEB)

6L6 = 6L6G = 6L6GT
http://hvid.it/datasheets/6L6%20RCA.pdf

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Youtube video:

Stereo Hi-Fi Tube amplifier 6L6G - YouTube

Last edited by pilovis; 27th August 2012 at 05:37 PM.
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Old 27th August 2012, 08:25 AM   #2
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Nice and simple. I can even call it too simple, I see no gridstopper resistors.
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Old 27th August 2012, 09:22 AM   #3
pilovis is offline pilovis  Italy
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Simple doesn't mean bad or incomplete .
Less components you use, less trouble you'll get.

There is no need for gridstoppers in this particular circuit, but you can use 1 Kohm resistors for that.
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Old 27th August 2012, 04:23 PM   #4
TheGimp is offline TheGimp  United States
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If you can be sure the source does not place a DC offset on the inputs you could even remove the input caps.
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Old 27th August 2012, 05:22 PM   #5
kevinkr is offline kevinkr  United States
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Never use them myself, haven't lost a tube or amp yet.. (40 + yrs)
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Old 27th August 2012, 05:27 PM   #6
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by kevinkr View Post
Never use them myself, haven't lost a tube or amp yet.. (40 + yrs)
Never used what ?
Gridstoppers or input caps?
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Old 27th August 2012, 05:44 PM   #7
TheGimp is offline TheGimp  United States
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Input Caps. They block DC from upsetting the bias on a stage. It wont destroy your input stage as it is current limited by the anode resistor.

An example of a stage that could result in anode over-dissipation would be a choke loaded input stage. If a DC bias shift occurred, the DC resistance of the choke might not be enough to limit the anode current. This could result in destruction of the tube due to excessive anode dissipation.

Grid-stop resistors help prevent pickup of RFI from radio stations, TV, etc but this is not a potential damaging source for the tube or circuit. Only causes distortion.
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Old 27th August 2012, 05:48 PM   #8
pilovis is offline pilovis  Italy
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What about a short circuit on the driver between anode and grid?
It could inject High Voltage on the preamplifier output stage, I suppose.
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Old 27th August 2012, 05:49 PM   #9
kevinkr is offline kevinkr  United States
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What the Gimp says as I was corroborating his comment..

(No input caps, but I do use grid stoppers religiously, perhaps too religiously in some instances.)
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Old 27th August 2012, 05:52 PM   #10
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by pilovis View Post
What about a short circuit on the driver between anode and grid?
It could inject High Voltage on the preamplifier output stage, I suppose.
The source impedance is usually quite high in the event of a grid to plate short except in the case of IT or choke coupling where some serious mischief could occur. I've never seen a grid to plate short in any small signal triode or pentode to date - this does not mean it can't happen. The transformer coupled output circuitry in my line stage cannot be damaged by quite large voltages as long as the current is limited (it is) - if you are using solid state gear I would recommend fitting a higher voltage output cap - this will take care of the issue without requiring an additional part in the signal path.
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