Bob McGraw - K4TAX writes...
> Your initial problem was caused by a VHF parasitic oscillation that
> caused failure of the 811A's. Common faults occurring after a
> massive VHF oscillation can likely be switch damage on the input
> section or output section of the band switch. Likely you should see
> evidence of burn marks or melted contacts or maybe contacts that are
> no longer present.
The band switches all look good and test good, with both DC and RF (at
low levels from my MFJ-259) continuity through all bands. The problem
behavior is the same no matter what the position of the band switch.
> Although the 572B's have a higher plate dissipation, I don't suggest
> replacing 811A's with 572B's as there is no advantage due to power supply
> voltage and current limitations.
I didn't do it to get more power--I know that the amp is constrained
by the power supply. I did it to get graphite plates instead of
sheet-metal plates with those soft, shiny bits in the middle where I
cooked them, heh, heh.
> If you are using the N.O. relay in the Omni to place the amp into transmit,
> yes, you will experience hot switching in the amp. This is not a QSK amp
> and thus the transceiver should not be operated in the QSK mode. You will
> have to use manual PTT to accomplish RX to TX switching.
I thought of this later, and that was the reason for my question. The
only time I see the hot switching as a problem is when I use the
"Tune" button. I'm normally using the SSB mode, and as long as I don't
start talking until everything's keyed up, there shouldn't be much
signal making heat when it switches. But I was doing a lot with the
tune button during my testing. Once I get it working again, I will use
the amp-control switch on my foot switch to key the amp.
I would have thought that hot-switching would be primarily visible
with burned contacts on the T/R relay, but there's no evidence of that
and the relay works perfectly. It might have taken out a component,
but dang it there aren't that many components in an AL-811, and I've
tested many of them.
Keeps those cards and letters coming.
73, Rick, KR9D
---
Richard W. Denney, Jr. PE|Iteris, Inc.
Associate Vice President |107 Carpenter Dr. Ste 230 | 703.925.3819
rwd@iteris.com |Sterling, VA 20164 |Fax 703.471.1757
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