[Amps] TL-922 --> 21st century

[Carl]

They tried to copy the SB-220 who copied the Drake L-4 which used a similar 
circuit. The choke DC resistance introduces some sort of frequency dependent 
NFB but has its own problem. It was something Bill Orr forced manufacturers, 
by constantly bombarding, them to use in the 60's.

The problem with directly grounding the grids is that it now increases the 
circuit gain which can cause a borderline stable amp to take off. One way to 
help that is to add non inductive 10-15 Ohms in series with the RF drive 
right at the filament.

Another method Ive used with a particularly troublesome amp of any brand is 
to run a single 27 Ohm 1W carbon resistor to ground for each tube and bypass 
each grid pin with a .01/1KV disc plus add the series resistor at the input. 
The various 115 to 220pf micas should be removed as many are at an age that 
they are developing leakage.

Output at 100W drive will be about 100W less but stability holds on all 
bands as long as the parasitic suppressor is good. Ive detailed my way of 
dealing with that on here several times.

Carl
KM1H


----- Original Message ----- 
From: "Steve Thompson" <g8gsq72 at gmail.com>
To: <amps at contesting.com>
Sent: Sunday, August 14, 2011 11:08 AM
Subject: Re: [Amps] TL-922 --> 21st century


> I'll hazard a guess that the idea is to try and create some sort
> of resonance with the grid wires to reduce feedback at vhf.
>
> Steve
>
>> A question:
>>
>> The grids are grounded via a parallel combination of 3 220 pf capacitors, 
>> a
>> 4.7k resistor
>> and a 470 uh choke. I don't understand this. I am tempted to just strap 
>> the
>> grids to
>> ground. What were they thinking?
>>
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