On Feb 22, 2005, at 1:14 AM, Kevin Normoyle wrote:
> 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!>
>
What sort of error would cause a parasite?
> 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.
Indeed. This morning, I got an e-mail from Downunder stating that a
FL-2100 suppressor's 22-ohm suppressor-R had increased to 3560-ohms.
>
> 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.
Residual magnetism in the armature will do this. Reversing polarity to
the coil may help for the next 20-years or so.
>
> -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.
residual magnetism
>
> 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
If the burn is in certain areas only, odds are that it was VHF that did
the roasting.
>
> 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.
I have bandswitch fixed contacts.
>
> -Kevin
> KE6RAD
>
>
>
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>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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