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 <[email protected]> writes: > 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 ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body.
