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

[Vic K2VCO]

The W8JI article quoted by G8TIC explains what they thought they were doing and why Tom 
thinks it's a bad idea:
<http://www.w8ji.com/vhf_stability.htm>

I'm going to make the non-controversial mods I mentioned first, like QSK, glitch r, 
soft-start, etc. and see how it works. Then I'll try grounding the grids and introducing 
negative feedback with a small resistor in series with the cathode. Some people have 
reported that they had to modify the input networks, and I want to see what the SWR to the 
exciter looks like before I change anything that might affect this.

Another question for anyone interested:

The manual says that operating CW in SSB mode is strictly forbidden and may cause 
"immediate, extensive" damage to the amplifier. Plate voltage in CW mode is only 2 kV, and 
they recommend tuning up to plate current of 650 mA. This is an input of 1300w, which 
corresponds to an output of only about 850-900 watts including fed-through power.

My question is: what components are they suggesting would be damaged by operating CW in 
SSB mode? I can think of two candidates: the plate transformer and the surprisingly 
frail-looking bandswitch.

If it is the plate transformer, I think the addition of the QSK circuit which will cut off 
the tubes in between keyed elements will significantly reduce the load on the transformer.

But what if the bandswitch simply can't take the continuous RF current?


On 8/14/2011 8:08 AM, Steve Thompson wrote:
> 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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-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/