Bottlehead Forum

General Category => Technical topics => Topic started by: Len on November 30, 2009, 08:07:02 AM

Title: Is it possible to cascade 2 halves of dual dht, direct coupled?
Post by: Len on November 30, 2009, 08:07:02 AM

Hi all,

Is it possible to direct couple two halves of a dual dht triode, as shown in the sketch?

If so, how does one handle the cathode loading resistors? Do we go from right to left, battery plus to minus with the resistor coming off minus (minus being the center tap), and then plus of the other battery now being the center tap, then minus with the other resistor now being minus?

That doesn't seem to work, since they would both see both resistors.

Help (please)!

Title: Re: Is it possible to cascade 2 halves of dual dht, direct coupled?
Post by: Paul Joppa on November 30, 2009, 08:46:27 AM

Pretty strange but possible in theory...

Since the first stage plate must be held positive with respect to the cathode, the second stage grid would also be positive. So the second stage is running in Class A2 and drawing significant grid current. Assuming the second stage grid is designed for A2 operation (i.e. has the ability to dissipate the heat generated) this would work. The second stage grid has a low resistance  now, which will reduce the gain of the first stage, probably by a large amount. It may not have much gain, but it will be nonlinear as heck!  :^)  (Grid current is notoriously nonlinear...)

Title: Re: Is it possible to cascade 2 halves of dual dht, direct coupled?
Post by: Len on November 30, 2009, 09:04:01 AM

Quote from: Paul Joppa on November 30, 2009, 08:46:27 AM

It ... will be nonlinear as heck!  :^) 

Thanks for the reply, and for enlightening me.

It was worth a shot :-(