Hi Richard!
> Not sure how much was pre-existing, how much was me :)
R. Measures wrote:
> Kevin -- Parasites are not brought about by operator error
<unless you include the operator error at the time of purchase! HI!>
Yeah, I've been reading old posts about parasitics in this amp design.
Interesting stuff.
Seems like there's a number of deficiencies in the design, well documented
here and elsewhere.
Found out more why the T/R relay seems to stick on, allowing RF out, even if
in STBY or the keying cable is disconnected.
-The T/R relay toggles off when I power off.
-It sticks on after the first time RY (key) is shorted to gnd.
It's odd: seems the relay coil must have a slightly resistive path to
ground somewhere
(other than the normal path thru RLY) to allow enough current to hold
the relay in.
Not enough to pull the relaty back if I then push it manually ..but
enough to hold it ...
so it sticks after the first time RY is shorted to gnd.
I'm thinking there's a path back thru the grid circuit somewhere, that
creates the circuit to ground,
.... that if that's true...maybe this is also keeping the bias from cutoff,
so the amp "works" even though the STBY/OPER switch is in standby.
I'm going to start with ruling out a failure in the relay...see if the
path back to the
bias resistor is needed to hold the relay in, or whether there might be
an internal short or something.
I guess I just have to disconnect some components and ohm out some stuff.
I'm wondering if the adjustable 30 ohm 10 watt bias resistor might be
shorted in some way.
So the list of problems so far is:
1) 10 meter band switch connection blown at two places
2) T/R relay stays in T, after the first keying with RLY
3) bias cutoff doesn't seem to work: amp works on 80/40/20/15 while in STBY
4) burning on the plate choke coils
Won't be able to look more till next weekend.
I think I'm going to attempt to repair the 10 meter bandswitch with a
piece of soldered copper strip,
like the repair that was done at the 80m position. Looks funky but seems
to work.
-Kevin
KE6RAD
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