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D&A pdx-400 ssb delay


Best I can remember was to find a 10uf or 22uf (can't remember which) electrolytic cap on the tie strip where the keying transistor was mounted. This cap would have one lead connected to one leg of the keying transistor. The other lead was just soldered to the tie strip lug. A wire you install from this lug to the "SSB" switch, and a wire from the other lug of the switch to ground was what would restore that feature.

Been too long. But that's just the tip of the iceberg.

D&A assumed that this model would be used on AM. The SSB switch quiets the relay chatter, but the driver tubes tend to burn up when running SSB. There is no fixed bias on the driver tubes, and without the carrier from an AM signal, they will overheat, burn up the driver plate choke and the four driver tubes. Same thing happens when you run AM with the carrier turned down.

Unless you install fixed bias on the four driver tubes. That takes care of this problem.

Putting a SWR meter between the radio and the amplifier's 'radio' socket will often reveal a really-high SWR reading. The PDX was made in a handful of versions, and they all have the driver's input side wired differently.

If you see a 4-to-1 SWR on the amplifier's input when it's keyed, use caution with the radio you use to drive it. Some radios will handle this just fine. Other radios will blow a final.

73
 
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Thanks...sounds like ill have to do alot of work in order to not burn this thing up. Maybe when i get a better understanding of how to work on this stuff ill try to change the bias...can you explain what bias is...ive been trying to find info on the different kinds but i just see really complicated theory and get nothing. Thank for the help
 
Thanks...sounds like ill have to do alot of work in order to not burn this thing up. Maybe when i get a better understanding of how to work on this stuff ill try to change the bias...can you explain what bias is...ive been trying to find info on the different kinds but i just see really complicated theory and get nothing. Thank for the help
Thanks...sounds like ill have to do alot of work in order to not burn this thing up. Maybe when i get a better understanding of how to work on this stuff ill try to change the bias...can you explain what bias is...ive been trying to find info on the different kinds but i just see really complicated theory and get nothing. Thank for the help
How can i make a fixed bias????
 

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