|Author:||Paul Fawcett (registered user: 2924 posts )|
|Date:||Sat, Jul 21st, 2012 @ 08:29 ( . )|
On 07/20/2012 @ 19:08, John Polstra wrote :
I was thinking about how to do it with a triode, and I came up with a couple ways that should work. The easiest would be to make a normal triode amplification stage with a medium-mu tube like a 12AU7A, and then put a resistor R in series with the reverb tank. Choose the resistor so that the output impedance of the triode stage + R was 15K or so. The only thing is, the stage would need to be able to produce a pretty large voltage swing at its plate. It should be doable, though.
: Another way to do it would be to use a cascode arrangement. I would just use a MOSFET for the top half of the cascode. It would make the effective plate resistance of the triode practically infinite, and you could design the circuit almost as if you had a real pentode.
: I might beef up the article to talk about those possibilities, once I've tried them out.
The sound clip sounds really nice.
As for using a triode with a series resistance, Merlin's been there and done that: [link] In fact, I used a circuit very much like his parallel 12AU7 version (in conjunction with a 1.5K Zin tank) in my Grail amp. It works well -- the quality of the reverb is fairly similar to the one in your clip.
--* A transformerless reverb driver
7/21/2012 @ 15:35--John Polstra
7/21/2012 @ 22:06----printer2
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