Very interesting Sam. Thanks for that info.
Cheers, Alek.
On 31/08/2019 10:50 AM, Svante Nordenstrom
sm3dyu@...
[ham_amplifiers] wrote:
Hi
I have done an amp that had suffered
multiple oscillations on 10 meters and damaged the bandswitch.?
The grounding of VC1 was done according
to the article and that cured the oscillation. Amp was stable and still
is without burning bandswitch contacts.
It seems not all amps have the problem
with instability, but if the amp you are working on Alek, have arc
marks on the bandswitch, this may be the remedy.
73
Sam
HS0ZDY
?
GN, I've made some mods to 2100B, 2100Z, etc., several.
I have never made that specific mod, all amps worked fine and stable.
What I usually do is to add extra decoupling caps in plate choke base
(4400 pF extra), plus one 1000 pF before glitch resistor; 15 ohm 10 watt
glitch resistor at rectifiers pcb; increase grid caps upto 1000 pF; back
to back 1N5408 diodes (at shunt's place).
General cleaning, resolder and checking bias pcb caps and resistor
values, lube fan motors, checking SWR diodes and its compensation, etc.
You can add in parallel the extra, not used contacts at RL1 (I ask
myself why they didn't).
Don't forget to check the HV capacitors inside the tube's cage, some may
be cracked (see the attached image).
If you need extra parameters, ratings at half and full voltage, email
me.
Regards
Guillermo - LU5WE.
El 30/8/19 a las 21:18, Alek Petkovic vk6apk@...
[ham_amplifiers] escribi¨®:
> ?
>
> A local ham dropped in a Yaesu FL-2100Z amp tp me and said that he
would
> like all the PA0FRI mods done to it.
>
> See
>
> This is no big problem, as most of the mods are common sense and
they
> are what one would normally do to an amp.
>
> However, there is one mod that strikes me as odd.
>
> He suggests cutting the grounding wires on VC1, the plate tune
> capacitor, and running a thick wire or coax from the cold side of
VC1 to
> a ground point at the base of one of the 572B sockets.
>
> This seems very odd to me. I don't see how this would enhance
stability,
> having that grounding wire running all that way.
>
> Every amp I have seen or built, has the cold end of the capacitor
bonded
> to the nearest point on the chassis.
>
> Should one be doing this mod? My feeling is that it should be left
alone.
>
> Opinions appreciated.
>
> Thanks, Alek.
> VK6APK
>
> --
> From sunny Binningup
>
> Family Businesses:
> SP Electrical.
> The Velvet Fox.
> Smart Design Electrical.
> Perth Interiors.
>
>
--
From sunny Binningup
Family Businesses:
SP Electrical.
The Velvet Fox.
Smart Design Electrical.
Perth Interiors.
