[AMRadio] Heath Apache symptoms

John King k5pgw at yahoo.com
Wed Jan 7 07:03:16 EST 2009

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   


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