At 09:59 AM 9/1/2004 -0700, R.Measures wrote:
On Sep 1, 2004, at 8:22 AM, Jim Isbell wrote:
This is EXACTLY the answer I needed. The amp uses a pair of 4-125As
and the screens are at "350V - 400V" Plates at "2000V - 3000V" (but no
terminating resistor) so I guess that makes it a class AB1 linear.
Jim -- Class AB1 amplifiers always have a grid-terminating R because the
grid draws zero current. .
Not always. You don't have to have a grid-terminating resistor for AB1
there is always a parallel resistance due to the loss in the grid tank
circuit. Q= R(parallel)/ X. The tank circuit is loaded by the drive
impedance also, so it is not totally unloaded Q.
Many of the old designs were for maximum gain so that very low power
exciters could drive them. Here you can vary the drive quite a bit by
changing the link coupling.
The screen grids have several bypass caps to ground but no resistor.
A shunt resistor is needed to sink reverse screen-I. Typically, about 25%
of normal screen-I is shunted by this resistor.
The 4- series does not have problems with the negative screen current like
the 4CX series. I just checked the data sheets. It is a serious problem
with the 4CX tubes. However the bleeder is desirable to maintain regulation
if you don't have regulators.
The signal is fed to the control grids through the MB-40-L and the plate
circuit is prety normal..
Just what I needed for my vintage shack linear.
R. Measures wrote:
Jim -- If the tetrodes are being operated at roughly half of their max
screen-V rating, they are likely being run in a non-linear mode.
If they are being operated at their max. screen-V rating, and there is a
grid-terminating R, they are probably operating in Class AB1 linear service.
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|