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?
>>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|