[AMRadio] Heath Apache symptoms

[Mike Sawyer]

Hmmm, as an Apache man my self, 9 chances out of 10 I would say check out in 
and around that clamp tube. It almost sounds directly related to heat, (Ip 
goes up the longer the radio is keyed). Might be some bad R's. When you find 
it, post your findings here since I for one would be very interested.
Mod-U-Lator,
Mike(y)
W3SLK
----- Original Message ----- 
From: "John King" <k5pgw at yahoo.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, January 07, 2009 7:03 AM
Subject: [AMRadio] Heath Apache symptoms


Hello, fellow AM folks! I would like to hear from those intimately familiar 
with the Heath Apache.

I think my Apache needs some TLC. It is working and gets good reports on 
strength and audio, however:

I note that when keyed up, after loading and dipping the finals, that the 
plate current starts out lower than the tune up and then starts creeping up. 
My experience over 50 years as a Ham has convinced me that creeping plate 
current is usually a sign of screens in the final tubes going bad. In fact I 
once had a Hallicrafters HT 32B that had creeping plate current when the 
6146 tube screens began  going bad. In fact, if I didn't increase the bias 
on the tubes, they would eventually "run away" and self destruct. The finals 
in my Apache do not "run away" they just go from lower current at tune up 
and rise to slightly more current than at tune up.

I think that my grid drive is also marginal because it takes all the 
available grid drive to set it at the rated and desired level of drive. The 
drive control must be at extreme maximum, fully clockwise. This could be 
related to "creeping plate current". What do you think?

In addition, I note some downward movement of the plate current of the final 
amplifier upon modulation. Lack of grid drive may cause this problem if I 
remember correctly. In addition, I seem to feel that over coupling of the 
output of the final tank circuit might also contribute to the downward 
modulation? I recently replaced the 6AQ5 clamper tube but did not readjust 
the circuit after replacement.

I would like some input from you who have the knowledge and experience to 
discuss these symptoms. I want to have this discussion before I start trying 
to wrestle this Green Monster out of its' cabinet. I am not as strong as I 
was when I became a Novice over 50 years ago. Before you laugh, let me say 
that if you are LUCKY, maybe you will live to get WEAK!! Hi!! HI!! You may 
address this issue off the reflector if you prefer. I don't want to bore the 
other members with a topic that may not be of interest to them. After all, 
the majority of hams feel that AM is a relic of the past. I enjoy AM, SSB 
and CW. Thanks in advance and 73, John, K5PGW