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bst 14th November 2006 10:11 PM

Octal tubes for 7695-style matrix amp?
I'm getting ready to build one of Steve Bench's matrix amps. In particular, I'm looking at this one:

However, I'd prefer to use octal tubes instead of the 6GU5 input and 7695 output tubes. I've found a likely candidate for the output tube - a 50FE5. I'd like suggestions for the input, though; I'll consider almost anything, as long as it's octal.

Steve has several intriguing variants on his site, and diyparadise has a neat version of the Darling here:

As always, comments, personal experiences, and specific suggestions are greatly appreciated.

mitwrong 15th November 2006 12:58 AM


I think you use 6gu5 is not advised. It's only designed for application other than audio. You can check from age to now, no amp. manufacturer use this tube for audio.

If you want to use Octal 8 type tube, there's a lot of. It depends what type of sound u want, what type of music to be perform, string, pop, classics or ----?

Provide us more info so that we can make suggestions.

:bigeyes: :bigeyes: :smash: :smash: :smash:


bst 15th November 2006 01:34 AM


Thanks for your reply. I agree that the 6GU5 was not originally designed for audio, but Steve Bench has used it successfully for an input tube in several different topologies (e.g. his 'No R, No C' amp).

In fact, there are many tubes which were never intended for use as audio signal tubes which turned out to be very good performers in audio circuits. The 6AS7/6080 was intended for use as a voltage regulator, but makes a good OTL power tube. Virtually any TV deflection amplifier makes a good audio output tube, and most computer switching tubes turned out to be very nice input tubes. No one would've ever suspected how nice a 1626 would sound until people started playing with the Darling amplifiers.

That's part of the fun, and the challenge, of experimenting with tubes; getting away from the same old thing and trying something new.

To answer your question, I'm just experimenting with the matrix circuit right now, not looking for a completed system for my final listening room. I'd hope that the amp would yield clean and accurate reproduction at modest levels with classical, blues, or pre-1980 rock. I might even try to turn this into a dedicated headphone amp.

It'll probably undergo all manner of tweaks and insults before, or if, I ever try to build a final finished version.

mitwrong 15th November 2006 08:52 AM

You are right, 6AS7 has been used in audio, and 6080 was not.
Many manufacturer Like David Berning used 6JN6 in EA230 amp. which was designed in RF TV applications.

If you are using tubes that is not intended for audio, than you have to check out the EG-IP curve, and select the most linear part and make your design, first set the DC parameter, then AC parameter. DC parameter means you set the tube working on the linear district, AC parameter means you set the RC coupling for the desired frequencies range. Don't forget the heart of the amp. are the output transformers.

6N14N is RUSSIAN version, 6P14P is CHINESE version

Wish you good luck and successfully.

:bigeyes: :bigeyes: :smash: :smash: :smash:


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