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RE: Transformers - Rp - Anode Voltage

Posted by Michael Samra (D) on March 16, 2015 at 11:34:46

In Reply to: Transformers - Rp - Anode Voltage posted by Triode_Kingdom on March 15, 2015 at 21:10:56:

"First, this is not an issue of insufficient drive."

Actually it is a question of drive as well with the 6P3Se. You are comparing this to a 6L6gb which would be fair however,the 6P3Se tubes are somewhat lower dissipation when driven under the conditions you are experimenting with.Increasing bias current doesn't really increase power much but it should lower distortion a bit.

This implies the 6P3S-E is also not a good sub for EL-34s, at least not in circuits that similarly use a low-Z transformer.

Nobody disputes that.It is never a perfect replacement but it works provided you have at least 400v on the plate and have at least a 5k impedance with sufficient drive.Some EL34 circuits have this capability such as Bob Latino's amps and the AES six pack amps.

Now,try and match up the best pair of 6P3Se tubes that you can and run them in a circuit like the W5m and let me know what you find..The W5s have about 11k impedance but they also have enough drive to get the job done and the B+ is running around 390v plate to cathode.
Bottom line,you do lose some power with the 6P3Se but the fact that you can run them so much harder,that can be an advantage in some circuits. When I look at the data on the 7355,it takes about 22% less drive than a 6L6gc so I'm actually shocked that you got those good of numbers. Did you modify the driver circuit when you converted this amp to fixed bias?

Jack,since you have fixed bias in that HK amp,try and see you can red plate the 6P3Se by dropping the bias at G1. You will notice that it's quite difficult in comparison to a regular 6L6gc so that tells me if you have the capability to run the tubes into a higher impedance with sufficient drive,you can get pretty good numbers..

Take a look at this. I did modify this Scott 280 but notice the B+ on the tubes and this is also a fixed bias amp. This simply shows the fact that you can run the hell out of these tubes and you almost have to get the absolute best numbers.

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

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Edits: 03/16/15 03/16/15

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