Hi!
I just was thinking, its normal practice to use SS diodes in a clipping stage. Does anyone know if someone, sometime have made a tube diode bridge clipping stage?
That should work right, or not? If not, why?
Seems like it would be easy enough to implement in a tube amp if it worked.
Quote from: Banjan73 on June 29, 2020, 01:06:53 PM
Hi!
I just was thinking, its normal practice to use SS diodes in a clipping stage. Does anyone know if someone, sometime have made a tube diode bridge clipping stage?
That should work right, or not? If not, why?
Yes some of the prominent amp companies have done so. One notable is Fender's Performer 1000. It uses an all solid state design with a 12AX7 wired as a 2 diodes.
You need to set up the heater voltage, plus a positive and negative bias voltage for the anode and cathode. The bias voltage sets the clipping for the tube diode. I have only seen them used in anti-parallel.
Merlin's Spark Gap uses two EB91 diodes for clipping in an otherwise TS-like overdrive.
Cool.
I thought I had a revolutionary idea here, but I guess there is nothing new under the sun ;D ;D
That spark gap was absolutely supernice!!
There are lot of triodes that have 1 or 2 diodes in the package, don't know if they are usable as they may have a common anode.
The 6BN8 has a triode and two diodes with all electrodes independent of each other. The triode has a ยต of 70 so it is equivalent to the triode in a 6AT6 in that respect but has higher transconductance and lower plate resistance than a 6AT6 triode.
> I guess there is nothing new under the sun
(https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1960/06/page16/fig1.jpg)
BTW, ignore what I said about the Spark Gap being "TS-like". That's my appalling memory talking. :icon_rolleyes: It's a pair of opamp clipping sections that you might find in lots of circuits (in many variations), one of which may or may not be a TS. Back to bed...
Just something to add. For a 12AX7, you need 150mA@12V (or 300mA@6V) just for the tube heaters. A single TS-like circuit draws about 7mA@12V, so a single TS-like circuit with 12AX7 as clipping diodes draws as much current as about 22 solid state TS-like circuit. Also, there's the huge price difference between a 12AX7 and a pair of 1N4148.
A tube as clipping diodes may sound good? Probably. May sound different than a regular diode clipping? Don't know. It worths the extra current and price? Well, it depends on the answer of the last question. But imo there are better uses for a tube.