Thank you Dave !! Now thats the kind of affordable fix I needed to
know about.
Incidentally, whatever is up with my Herc II relay, its not stuck all
the time. It will work OK for quite a while before it quits. Or it
completely refuses to work at all from switch-on. There's no pattern.
The last 2-3 days it has not quit at all (!) This was fortunate
because it gave me contacts with E4 (Palestine) on 12, 17, 30, 40 and
80. (The 40m inverted V dipole does good sometimes .. :-)
One minor point. The transient protection diode in my Herc II is
not wired directly across the relay terminals. Its on the PC board, so
if I just swap the relay leads over, I do not need to swap the diode
over as well (one leg is grounded).
I have seen recommendations to install a capacitor across the vacuum
relay coil, value unknown. Photos I have seen suggest its probably
only an RF bypass capacitor, maybe 1000 pf. TT don't fit such a
capacitor in the Herc II. I guess it would do no harm to add a small
ceramic capacitor whilst swapping the leads over. The only use for it
that I can see is to minimise RF heading back down the (unshielded)
leads to the control board.
Finally, as for replacing the relay with a surplus one, this is more
feasible for a tube amplifier where you might expect to find a much
higher driving voltage - the trick to speeding up relays is to hit
them with a higher than normal voltage, through a current limiting
resistor. This has featured in at least one QST article on a QSK
linear conversion. In the Herc II, no such high voltage is readily
available. If your fix fails because the relay is totalled, the
answer is to bite the bullet and get a new 12v relay. Or experiment
with a cheap 5-6v open frame relay and a limiting resistor, in the
hope of speeding up the closure to under 5ms.
Off to warm the soldering iron ... Thanks again everyone.
John G3JAG
On 24-Feb-99 Dave Bowker wrote:
> Here's an old trick I have used to "repair" sticking vacuum relays
> in
> airborne military and government equipment for the past 30+ years.
> Although prescribed as "temporary repair", I have found it to be
> "long-term" repair in a majority of cases. There will be some
> relays that
> just can't be "repaired" in this fashion.
>
> SIMPLY REVERSE THE WIRING TO THE RELAY!
>
> In Ten-Tec amplifiers the relay coil transient protection diode is
> physically placed across the relay coil terminals, so you will have
> to
> reverse the diode as well.
>
> I have had a Ten-Tec Titan-I amp for approximately 5 years and it
> developed
> the sticking relay symptom about a year ago. I performed the above
> surgery
> immediately and it is still performing flawlessly after an
> estimated
> half-million or more cycles.
>
> 73, Dave, K1FK
> Fort Kent, ME
----------------------------------
E-Mail: patents@dx0man.prestel.co.uk
To: <tentec@contesting.com>
Date: 25-Feb-99
Time: 09:07:21
John Crux
Consultant in product forgery - Asia and
Africa
----------------------------------
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