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Author Topic: Power supply for T-195B Advice Please.  (Read 2355 times)
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Edward Cain
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« on: April 21, 2014, 04:20:04 PM »


   I want to build a dedicated power supply for my T-195B using parts that I have on hand.
   For those not familiar with this Tx, it is the model that uses solid state for HV rather than a dynamotor and requires approx. 28 Vdc at 42 amps during transmit and 9 amps during standby.

   Based on the parts I have, I want to build a choke input supply.

   The parts I have are as follows:

   117 V input/ 32 V output at 48 amps Antek toroidal transformer

   2.5 mH at 51 amp choke

   Lots of computer grade caps in the 50-75 volt range and 15,000-40,000 uF range

   A bunch of 15 ohm, 95 watt wire wound resistors

   My initial concerns are:

   How much capacitance to use after the choke

and

   Is it practicable to use the 9 amp standby current draw as part of the “bleeder” current necessary to maintain critical inductance for the 2.5 mH choke. (My arithmetic tells me I will need approx. 13 amps ‘bleeder” current).

Thanks,
Ed/KJ4JST
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KA2DZT
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« Reply #1 on: April 21, 2014, 04:59:55 PM »

9 amps standby current should be enough bleeder current.  With a 2.5mH choke and 9 amps there shouldn't be much of a voltage rise on standby from what the voltage would drop to on transmit.  You'll have to build the supply and do some testing.

Fred
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Edward Cain
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« Reply #2 on: April 23, 2014, 11:12:03 AM »

Thanks for the reply, Fred. I may give that a try. Any thoughts on capacitance for an L type filter?

Ed
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WB6NVH
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« Reply #3 on: April 23, 2014, 05:20:41 PM »

I have seen this type of "brute force" AC power supply for the T-195B series end quickly in failure of one or both of the T-195 internal power supplies.  The germanium transistors are not tolerant of spikes or higher than nominal voltage at the input and they will live up to their nickname "three legged fuse."

It would take one huge transformer to go from idle to full load without first sagging and then shooting up in output when the transmitter is unkeyed.  A solid state regulator solves this issue (more or less) but you still need some serious current capacity.  In a vehicle the battery absorbs spikes and surges.

Maybe if you have a big enough transformer it will work, but I am skeptical.  Something like the PP-4763 DC regulated supply used with the GRC-106 should run a T-195B but only if the transmitter has both fully solid state supply units.

Just for reference, a bunch of T-195's went thrugh depot overhaul in the mid 1960's and emerged with whatever power supplies were plucked out of the bins.  That means a "B" could have dynamotors or the original solid state supplies while a no-suffix could have both solid state units or only one, and so forth.  These went to foreign militaries, mainly, but some were surplused by DRMO in the early 1990's and seem to have wound up mainly at a surplus dealer in Pennsylvania. 
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Geoff Fors
Monterey, California
WU2D
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CW is just a narrower version of AM


« Reply #4 on: April 23, 2014, 07:09:01 PM »

That transformer would work with a bridge and big cap and a bank of 3055's in old buzzard 1970's style 723 regulator fashion.

I have used this LC style of power supply on my ART13 and ARC-2 and the autotunes work nicely. Regulation can be better than 2V out of 28V with a decent transformer.

I am convinced that if you removed the turns from a big old core and wound your own choke, you could get an L network with a more modest bleed to work. But I would try it with a dummy load for testing the best bleed and definitely would use a big variac on the primary.

A big old 30V, 50W zener would be a good transient suppressor.
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