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Modulator power supply schematic




 
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Author Topic: Modulator power supply schematic  (Read 327 times)
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N4LTA
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« on: June 30, 2020, 03:11:50 PM »

Here is a rough sketch of what I am planning for my dual 807 modulator (Class AB1). The plate supply will be roughly 700 volts and the screens will be 300 V regulated.

Looking at a power out of approximately 60 watts  The plate transformer is a Hammond 275X and I will use the 6.3 v winding (5A) for the tube filaments.

Bias voltage for the 807 grids is variable from -27 to -35 volts.

I will steal 10 ma at 200 volt or so for the 6C4 driving a 3:1 interstage transformer (Hammond 124B)

Anything major out of place? The 807 plates pull 139mA not amps at noted.

Also is a photo of the chassis and front panel.

Thanks

Pat
N4LTA


* modulator P supply sch.jpg (84.86 KB, 640x480 - viewed 82 times.)

* modulator chassis.jpg (56.17 KB, 640x480 - viewed 36 times.)
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WD5JKO
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WD5JKO


« Reply #1 on: June 30, 2020, 03:55:02 PM »


Pat,

   With all that Hammond Iron, you must be working for them?  Tongue

The 400-0-400 tranny secondary needs a CT to be shown, and from there the LV filter attaches. The current attachment point on the FW bridge (diode anodes) should go to ground instead.

The OA3 is a 90v tube (VR90). I think you meant to put OD3 (VR150).

Looks like a fun project.

Jim
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N4LTA
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« Reply #2 on: June 30, 2020, 04:51:43 PM »

Thanks -I know better. That is one of my favorite power supply circuits also thanks for the tubes number correction. I mean't to put 0A2 as it is the miniature 7 pin 150 volt version. I am short of space.

My rememberer doesn't work as well as it used to.

I have a Hammond distributor acount still active from a while back. I can save you some money on Hammond stuff.

Pat
N4LTA
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WD5JKO
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WD5JKO


« Reply #3 on: June 30, 2020, 07:15:37 PM »

Pat,

   As a reference, I attach a schematic I used in a Central Electronics 20A. It is similar to your supply, but adds a series regulator instead of a shunt regulator, and includes an adjustable zener diode in the bias supply portion. Since I drew that circuit, I changed the LV series pass tube to a 6W6, and the error amplifier tube to a 6CB6 (the 6AH6 got a heater cathode short).

Jim


* CE_20A_QRO_Power_Supply.jpg (604.82 KB, 2448x3264 - viewed 53 times.)
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Patrick J. / KD5OEI
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« Reply #4 on: June 30, 2020, 10:55:45 PM »

When using gas regulator tubes, some designers make use of the 'jumper' inside the VR tube to interrupt the power supply via a primary relay in case the VR tube(s) are not in the socket(s) for some reason.

Keeps unregulated voltage from getting to the screens. Unfortunately does not help if the VR tube is just worn out.

Glad to see VR tubes being used though. It's the RIGHT thing to do Smiley .

An electronically regulated supply is the ne plus ultra.
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w7fox
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« Reply #5 on: July 01, 2020, 12:00:04 AM »

Pat,
The voltage to the 0d3 regulator tubes is 5 volts below the minimum recommended for reliable starting.  It will probably work anyway, but if not, I would use 720 volts instead of the center tap of the transformer.

I have a similar modulator running the same plate and screen voltages as you are.  The only difference is I am driving it in class AB2 using NPN transistor followers.  It gives more oomph than AB1.  If interested, I can provide a schematic.

73,
Fox
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K8DI
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« Reply #6 on: July 01, 2020, 07:20:21 AM »

Not sure what your design is supposed to be doing,  because it seems the screen voltage will be a large negative voltage with respect to ground. Did you mean to use separate rectifiers for it instead of a bridge?  Is this supposed to be an “economy” doubler arrangement that’s drawn wrong?

Ed
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N4LTA
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« Reply #7 on: July 01, 2020, 10:51:28 AM »

Yep, As stated above the schematic  is drawn wrong.

I initially was going to run class AB2 but couldn't find a good source for a driver. I decided to go with higher voltage on the plates and use a low cost 3:1 interstage transformer. I used one with a better core for better frequency response. I would be interested in seeing your transistor driver circuit as I have a 120 watt modulator in my future plans.

Pat
N4LTA
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w7fox
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« Reply #8 on: July 01, 2020, 04:10:20 PM »

Pat,

Sorry for the rough drawing, it was my working copy.  The driver transformer is from an ART-13 and I believe for class B modulators.  I think 1:1 primary to total secondary.  I used bipolar transistors for the drivers, but I would use MOSFETs if I did it over. 

* 807 modulator.pdf (624.76 KB - downloaded 29 times.)
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N4LTA
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« Reply #9 on: July 02, 2020, 02:02:16 PM »

Thanks for the information. It will be helpful on the next project.

Best 73,

Pat
N4LTA
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