Collins 32V-2 power Modification

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Mike/W8BAC:
I want to limit my 32V-2 to about 120 mills @ 600 volts input so I can run it into a 10 db amp. It has been suggested to me to use a voltage divider on the screen of the 4D32 rather than lowering the plate voltage. This will allow the modulators more head room.

Have any of you done this? Also I'm wondering if any audio mods are needed. Thanks in advance

Mike

W2VW:
Quote from: Mike/W8BAC

I want to limit my 32V-2 to about 120 mills @ 600 volts input so I can run it into a 10 db amp. It has been suggested to me to use a voltage divider on the screen of the 4D32 rather than lowering the plate voltage. This will allow the modulators more head room.

Have any of you done this? Also I'm wondering if any audio mods are needed. Thanks in advance

Mike


The way to wind up with more modulator headroom is to lower the plate and screen Voltages. If you just lower the screen Voltage then you will draw less plate current (still at high Voltage). This will change the plate load and modulating impedance. Your mod iron will no longer present the modulators with the same load impedance. Same for the output tank.
Try to maintain the same ratio of plate Voltage to Plate current when reducing power. The rig will load up pretty much the same way and you will have better modulation.

Mike/W8BAC:
I did a Google Search and came up with this WA1HLR audio mod for a 32V-3. A quick look at the V-2 schematic shows it to be almost identical. I'll give it some thought. http://www.amwindow.org/tech/htm/32v.htm

Someone has to have invented this wheel already. It would be nice to come up with a proven power reduction layout. Thanks for the advice Dave.

W2VW:
What you really want when running this thing into a linear is continuous power adjustability. Not just reduction either. You want a way to be able to run your exciter power up while tuning the amplifier. An outboard D.C. supply just for the final would be ideal. The best way to adjust the linear properly is to drive it with enough carrier power to make the amp put out it's rated max P.E.P. Of course you will want to do this quickly. You then reduce carrier drive to 1/4 or even less depending on percentage of positive modulation. You said the amplifier was capable of 10db. If you want to run max legal power then you will be driving it with 37.5 Watts carrier (assuming 100% positive modulation). Your peaks will be roughly 1500 Watts P.E.P. out. Ideally, you'd want to drive the amp with 150 Watts while quickly tuning it for max. You can do the same thing with a few other methods but this one works best. I'm assuming (yes I've seen the old odd couple re-runs) that your amp is closer to 13 db which puts you right in the ballpark as far as exciter max out.

Steve W8TOW:
Mike, I did the "HLR" af mods to my 32V3 and you hear how that sounds.
I also built solid state plug in rectifier replacements, added some new caps and the such...

As for reducing power, I echo the issue of reduction of B+ and Plate Current results in a change of the Class C load Z for the modulators (& MOD iron)
not something I suggest in doing...
I so run my 32V3 at 100 mA on low B+ tap, BUT in my case, the modulation trany is driving a 500 ohm load to the driver iron of my higher power Class B  mod deck and the 4D32 is driving the Class C RF deck...(thus the mod iron has no B+ going thru the secondary).... :cool:

vri 73 steve w8tow

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