[AMRadio] Heath Apache symptoms

Peter Markavage manualman at juno.com
Wed Jan 7 13:52:56 EST 2009

As pointed out in another post, check the clamp circuit adjustments. For
grid drive, check the grid meter resistor (5.55 ohms) and/or use an
outboard meter to verify your Apache grid reading. Weak finals can also
cause plate current to creep. Check your low voltage supply section.

Pete, wa2cwa

On Wed, 7 Jan 2009 04:03:16 -0800 (PST) John King <k5pgw at yahoo.com>
> 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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