[TenTec] Ameritron amp issues and looking for a Centaur

[Rick Denney]

Ed writes...

> On the B- side of the HV is a diode D16 according to the schematic
> in the metering  circuit. Its a 1N4007, make sure it isn't open.

I will do that.

> Also check the 2.5mH choke, L3 on the output of the tank circuit.

I did test it for DC continuity, and I suppose for there to be
anything else wrong there would need to be some signs of heat damage,
which I don't. If you think I should, I'll test RF through it using my
scope.

> Other than that its time to pull the tubes and check them for shorts.

I hadn't considered that, though I did inspect them for what I could
see through the glass. I will check those, too.

> Ed W3NR

> PS Don't forget that Ameritron is well known for leaving connections
> totally un-soldered or poorly done solder joints. Their QC is terrible
> to say the least.

That's why I have done so much continuity testing. Once before with
this amp, I found a poor solder joint where the coax from the load air
variable connects to the T/R relay, and it was arcing until it finally
unsoldered itself completely. I resoldered and the amp worked fine for
a long time.

This evening, I injected RF using my MFJ-259 as a source, and traced
it through the circuits with my scope. RF input makes it reliably to
the cathode inputs on the tubes, and RF output makes it reliably from
the anode connections to the output connector. The tubes were
connected and in place, so I'm wondering if they were shorted,
wouldn't my RF get shunted to ground somehow? The two sides of the
cathode aren't shorted or the filaments wouldn't light, and if the
bias input side of the anode was shorted, I would have seen big
sparks, it seems to me. Maybe it's just wishful thinking--I don't want
to have to replace those three tubes again!

This has been a real learning experience for me--I'm sorta glad my
ebay amp has had (the expected) problems--but now I'm ready to just
fix it. I will check the things you suggested. Thanks.

Rick, KR9D

---
Richard W. Denney, Jr. PE|Iteris, Inc.
Associate Vice President |107 Carpenter Dr. Ste 230 |    703.925.3819
rwd at iteris.com           |Sterling, VA 20164        |Fax 703.471.1757