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Old 7th June 2012, 04:57 AM   #1
TheGimp is offline TheGimp  United States
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Default 6DX8/ECL84/6F3P Baby Huey

I've posted previously in the "EL84 Baby Huey" thread that I thought the 6DX8 aka ECL84 aka 6F3P would make a nice Baby Huey.

I figured I'd start a new thread as I build this amp, based on the triode/pentode combo video device (which is also listed by Miniwatt as an audio amp).

I've been simulating it off and on for a while, and finally got a chance to pull out the tube-lab and breadboard something.

If I flog it, I can get 14W out with slight red plate on one tube. I could probably hand select tubes to run at 14W.

Dialing it back I get 10W without problems at 66% red plate dissipation (still greater than spec).

I switched to a speaker with You Tube source from a computer, and adjusted the input LTP bias by ear and it sounds pretty good.

I'm running a GXPP10-8-10K.
300V B+
26mA bias current, fixed bias.
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Old 7th June 2012, 07:36 AM   #2
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Please, do keep us posted, you got at least my attention

Do you have the output pentodes connected in UL or plain pentode?
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Old 7th June 2012, 12:33 PM   #3
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Old 7th June 2012, 12:34 PM   #4
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Quite an interesting tube, 'cause it's triode is somewhere between 6SL7 and 12AT7. And cheap also: Recently I've bought a bunch of them at €2.50/pc, made by Mullard..

But 14 watts anode dissipation when the maximum dissipation is 4 watts? Wow!

Best regards!
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Old 7th June 2012, 01:28 PM   #5
TheGimp is offline TheGimp  United States
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Outputs are wired UL Mode currently.

The 14 Watts was the output at 1KHz with the plate of one output tube a dull orange that could hardly be seen with the lights on. It was evident with the lights off.

No signal dissipation was about 12W. From past testing I've done, I believe 8W plate dissipation is going to be reasonable. I'm currently running 7.8W (300V B+ at 26mA bias current).


The 6DX8 is available from ESRC in the US for $1.00ea in qty 10. The ones I'm using are Raytheon, but I think I have another brand as well as the 6F3P.
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Old 7th June 2012, 03:43 PM   #6
TheGimp is offline TheGimp  United States
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In case anyone finds this thread later on, here is the original Baby Huey thread which was the impetus for this design:

EL84 Amp - Baby Huey
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Old 7th June 2012, 04:30 PM   #7
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Quote:
Originally Posted by TheGimp View Post
I'm running a GXPP10-8-10K.
300V B+
26mA bias current, fixed bias.
That means a plate-to-plate load of 20 kOhms with UL taps at 63%?

Best regards!
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Old 7th June 2012, 05:22 PM   #8
TheGimp is offline TheGimp  United States
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The transformer is rated at 10W, 10K plate to plate , 40% UL taps single 8 Ohm output.
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Old 7th June 2012, 05:44 PM   #9
Cookj is offline Cookj  Belgium
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My understanding-
6F3P is equivalent to ECL82,
6F4P is equivalent to ECL84
6F5P is equivalent to ECL85.

Regards

John
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Old 7th June 2012, 06:25 PM   #10
TheGimp is offline TheGimp  United States
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You are correct. I confused 6F3P and 6F4P. The title should read

6DX8/ECL84/6F4P Baby Huey

If an admin would change it, it might be helpful to someone in the future.
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