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Modulator power supply schematic




 
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N4LTA
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« Reply #25 on: July 17, 2020, 03:50:25 PM »

I'll be your first customer.

Pat
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N4LTA
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« Reply #26 on: July 19, 2020, 07:54:21 PM »

Got a good bit done this weekend on the modulator. Got most of the punching complete , all components mounted , the heater wiring done and the VR tube screen supply done.

The VR tubes are running at 25 mA and are regulating at 307 volts which is probably close enough to the 807 designed screen voltage of 300. The 100uA meter on the front panel is calibrated in volts x 10 and it is working well as shown in the photo. (the supply is not connected to the screen) There is a front panel switch to switch it from screens to plates.

The plate supply is now 784 volts, which is too high. I have a 47K bleeder but is does not pull sufficient current to get the 10H choke to drop the voltage to the desihn value of 680-700 volts.
Th ezero signal plate current will add another 35-40 mA and that should be enough current to get the choke to reduce the voltage to get me close. I am assuming this is OK and that I don't need to install a smaller resistance bleeder. The voltage should drop when the modulator is keyed.

The two other meters read 0-30 mA for the screens and 0-300 mA for the plates. Expected plate current is approximately 150 mA.

I need to wire the two 807s and the 12AU7 and build the bias supply.

Pat
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WD5JKO
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« Reply #27 on: July 19, 2020, 09:02:05 PM »


The plate supply is now 784 volts, which is too high. I have a 47K bleeder but is does not pull sufficient current to get the 10H choke to drop the voltage to the desihn value of 680-700 volts.

Quote

Pat,

   Take a look at what I did in post 3 of this thread. I positioned the 2nd choke such that it passed both the HV and LV supply current to ground. This brought the HV B+ down a bunch. As I recall, it was about 560v as I show it, or 750v the usual way. The regulation was very good as well. The return side choke can be less inductance, but must be rated for higher current.

YMMV

Looks nice!

Jim
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