[Amps] FL-2100B Failure

[Will Matney]

I'll try to help with some more explanation below.


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.

The old carbon comps change resistance over time.

>
> 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.

If that dont work, he could find a friend with a TV or computer repair shop
who has a degaussing coil. 1-2 passes through it would cure his problems.
They want an arm and a leg to buy one now so borrowing ones use is the idea
for a single use.


>
>   -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

Correct,
Residual magnetism is the magnetism left after the coils field collapses.
The iron can become magnetized if the coil was dropped out at the wrong
place in the sine wave of the coils input current. It can be worse in a DC
relay coil. This can be in combination with a weak armature spring not
having enough strength to pull it away. It's the same thing as wrapping a
nail with a bunch of wire and putting a DC current to it. There's always
some magnetism left after the coils current is removed. I think I'd check
the spring too.

>
> 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.

I agree with Rich, seen it more than once.

>
> 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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Best, 

Will


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