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WA2P

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13.8 volt power supply recommendations Mar 20th 2013, 03:19 5 900 on 12/3/14
Transistor switch using negative base voltage Jan 2nd 2013, 04:43 10 897 on 3/1/13

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Topic Author Posted On
13.8 volt power supply recommendations WA2P on 20/3/13
Hello all,
I will be purchasing a Yaesu FTdx3000 transceiver soon, and will be needing a 13.8 volt power supply. I've been looking for a suitable supply, but so far haven't found any with really good reviews. I would prefer a linear supply, and would appreciate the names of companies I could look at. Specific model names would be great as well. Thanks for any suggestions.
Pat Ciferri (WA2P)
Transistor switch using negative base voltage WA2P on 3/1/13
Thanks, thats the most promising lead I've seen. Maybe the -49 volt value isn't as sacred as the manual suggests.

There's one other symptom I forgot to mention before. At one point, I removed ALL of the tubes except the finals and the two power supply rectifiers and the voltage regulator 0A2. The finals STILL glowed as orange as before! Of course, increasing the voltage with the bias adjustment pot made the glow disapear. Maybe it needs to be neutralized...

Pat (WA2P)
Transistor switch using negative base voltage WA2P on 3/1/13
I wish this was only a cosmetic change to reduce power consumption. Unfortunately, the original issue is that when the rig is turned on, no matter if in standby, operate, CW, SSB, or AM, the finals glow orange all the time. The rig transmits fine, it's just that the finals are going to fail if something isn't done to cut them off. If the idling current was not so high and the tubes wouldn't overheat, I wouldn't worry about it.

I've posted to the Hallicrafters Users Group forums, and the consensus was that the bias should be more negative when not transmitting. That's led me to searching for a bias modification solution since the finals will fail if nothing is done.

Thanks for everyone's input, I appreciate it. I'll check out the AM forum next. As an aside, if anyone would like the "joy" of looking at the rig and is within reasonable driving distance from Poughkeepsie, I'd like to hear from you... HI

Thanks - Pat (WA2P)
Transistor switch using negative base voltage WA2P on 3/1/13
Thanks for the lead to the AM Fone forum; I will check it out. Before I do, I would like your opinion on a possible solution.

From looking at the schematic again and measuring voltages in the bias supply, I've found that it produces -130 volts before going to the components, primarily an 18K resistor, that regulate it down to the required -49 volts for the entire rig. The control grids on the 6146 finals are connected to that voltage, and the output from the driver is fed there also via a capacitor in it's plate circuit.

Am I on the right track in saying that I could remove the current bias connection to the 6146's grids, duplicate the few components required to get to generate -49 volts, and use a bias switch to bypass the new 18K resistor to put the full -130 volts on the 6146 grids to cut them off? If so, can I also tap into the plate circuit from the driver, via a capacitor, to control the bias switch so the resistor is not bypassed when transmitting? I would think that by modifying only the line that goes to the 6146 grids, the chances of damaging the rig would be small.

Assuming I'm correct, I would look for an article on how bias switches work to begin with, since I currently can't figure it out from looking at the QST articles.

Thanks, Pat Ciferri (WA2P)
Transistor switch using negative base voltage WA2P on 3/1/13
Thanks for the link to the QST articles. I've looked them over, but I can't figure out how the circuits shown would fit into my HT-32. The rig uses -49 volts for bias everywhere, and the -49 volts are on the control grids of the 6146's. I know I have to disconnect the current bias line from the grids and then switch between -49 volts when transmitting and a larger negative voltage when idling, and that I have to add a new bias supply to the rig to provide the higher negative voltage.

Unfortunately, I have to admit that I have little technical circuit knowledge, and can't figure out how to adapt one of the designs from the QST articles to work with my rig. I would very much appreciate some assistance in coming up with an appropriate circuit as I know I could easily do something to damage the rig.

Thanks, Pat Ciferri (WA2P)

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