4-65A Transmitter Update

[W9ZSL]

All of my iron for both supplies is Thordarson.  I'm using a T-19P59 which is used for the modulator along with a series 19 4-20 Hy NOS 300 ma swinging choke.  The PA plate iron is a T-16PO3 with another 12 Hy 19 series choke.  Both NOS.  Everything is matching and all rated at 300 ma.  I REALLY got lucky pickin' and except for the modulator plate iron, the other three pieces came in the original boxes.  The 16PO3 arrived in it's original wooden box complete with the Allied Radio sales slip and warranty card!  Sweet!

[KA2DZT]

The 16P03 is a better Thordarson plate xfmr than the 19 series iron.  The 19 series chokes are also good.  I have on the bench a 19P59 and a 19P60 that I'm repainting and improving some of the terminals.  I have no plans for them right now but maybe in the future.  I also have 4 or 5 19 series chokes.  In my HB xmtr I'm using a Thordarson 6411 plate xfmr.  It has the same ratings as the 19P59 but has much more iron in it and heavier copper. The Thordarson 4 digit part numbers predate all the iron that have a letter in the part number.  Through out their history, Thordarson made thousands of different xfmrs.  Thordarson also liked to change their part numbers every few years.  Stancor almost never change their part numbers and they made the same xfmrs year after year.  But, they did changed the construction of them through out their history.  So, some Stancor xfmrs may have the same part number but may be constructed somewhat differently.  You can tell the apprx age of the iron by the way it looks.

The 19P59 is perfect for the 811 modulators.  The class B modulators present a short duty cycle on the xfmr so it won't work up a sweat powering the modulators.

I run both my 811 modulators and the 813 final from the one 6411 xfmr.  It is only rated for 280ma but handles long winded transmissions without getting the slightest bit warm.

You may be able to run your xmtr from the one 16P03 .  Although I forgot the voltage of the 16P03,  I'll have to check my catalog.
You lucked out getting the NOS ones.
Fred

[W9ZSL]

Hi Fred!  The 16P03 is 4280 CT using the high side of the primary or 3480 using the low.  The 19P59 has dual secondaries and is 3120 and 2500 CT.  I bought it specifically for the 811A's and it should give me 1KV. Two supplies will work out fine since I have all the parts I need.  I notice your comments on the UTC iron.  My modulation transformer is a VM-3 which comes in a "G" housing (as I recall) the same as the "S" series.  It is identical to the CVM-3 except for the round can.  Mike

[KA2DZT]

The VM-3 and the CVM series mod iron are not the same as the S series.  Although, the S series mod xfmrs are widely use and should be good.  I only have one S series mod xfmr.  The VM-3 is older than the CVM series and it should be good.  The 16P03 has the tapped primary instead of the dual secondary that the 19P59 has.  The only thing you should check on the 16P03 is the voltage rating of the primary.  The early Thordarson plate xfmrs were 110VAC primaries.  Using a 110 volt primary on 125 volts may saturate the core causing it to run a little hot.  I don't remember what the 16P series plate xfmrs were rated at, 110 or 115.  Check the metal tag, it will show the primary voltage.  That rating is for the high voltage tap.  The low voltage tap can handle higher primary voltages.   As for the S series, I tested a few of the chokes and they did a poor job at filtering than most all other common chokes in that current range.  The S series plate iron are good, somewhat better than the 19 series Thordarsons.

Having said that, your 19P59 will work fine for the 811 modulators.  The 19P59 should get you 1000 volts or 1250 volts.  I would run the 811s on the higher voltage.

My HB 813/811 rig uses a Thordarson 6411 plate xfmr.  It, like the 16P, has a tapped primary.  It is only rating for 110V primary, but I run it on the low voltage tap.  The 6411 is rated like the 19P59 to give either 1000 volts DC or 1250 volts DC.  Running the low voltage tap on 120VAC gives higher than 1000VDC.  It is about 1150VDC.  My rig runs on 1500VDC both the 813 and 811s.

So, how did I get 1500VDC from a xfmr yielding only 1150VDC?  I added another 350 volt xfmr to the supply.  How did I do this?  Using a second xfmr that will yield 350 volts from the diode rectifiers (no choke no caps).  Just the xfmr and it's rectifiers,  connect the output from the diode rectifiers directly to the center tap of the secondary of the plate xfmr and it will bring up the output voltage by the 350 volts.  The current rating of the boost xfmr should be the same as the plate iron.

You can use this method with any xfmr that can handle the CT being above ground.  Your 19P and the 16P can handle it easily.  In fact, most any xfmr can handle the CT tap running above ground by a few hundred volts.  There are others that the CT must be grounded, so can't do it with those.

You can use any type xfmr for the boost.  The rectfiers can be FW or FWB.  With FW, the CT of the boost xfmr is grounded as normal.  With FWB, the negative terminal of the FWB rectifiers is grounded as normal.

If you want to lower the voltage, you can just shut off the boost xfmr and the output voltage will drop by the 350 volts.  No need to disconnect anything, just shut off or turn on the boost xfmr.  In fact, you can leave on the boost xfmr and shut off the plate xfmr and you'll only have 350 output volts.

This boost method will also work with both xfmrs using FWB rectifiers.  If the main xfmr uses FWB rectifiers, then connect the diode output of the boost xfmr to the ungrounded negative terminal of the FWB rectifiers of the main xfmr.

Fred

[W9ZSL]

I'm assuming both the CVM-3 and VM-3 have the same pin-outs?  This VM-3 has the same case as the "S" series.  Both Thordarson plate transformers are 115 volts.  I took measurements with 120 on the primaries and should have about 1900 VDC on the PA and 1 KV on the modulator which will give me a potential of about 175 watts of audio and about 228 watts input RF.

[KA2DZT]

The VM mod xfmrs are part of the same vintage PA series.  They predate the CVM mod xfmrs.  You're right they have the same case style as the S series but they are not the same.  The 125 watt CVM mod xfmr has a round case.  I'm not sure of the pin outs for the CVM mod xfmr but it is probably on line somewhere.  I may have it in my papers, I look for it.

OK on the plate xfmrs, the 115V primary should be no problem at 120 volts.  You need to use the higher plate voltage on the 811s.  With 1900 volts on the PA you'll never make 100% modulation with only 1000 volts on the modulators.

As for the pin outs,  most all these multi-tap mod xfmrs are usually made the same way.  There should be two windings on one side and two windings on the other side.  Each of the four windings usually has a tap.  This gives a total of 12 pins, six on each side.  The taps on each winding are not in the center, they're off center.  The total winding on one side is not the same total to the other side.  Meaning, there is a step-up in impedance from one side to the other.  Or reversing the xfmr there is a step-down.  Because, you're using higher plate voltage on the PA than the modulators, you'll probably need a step-up in the turns ratio.

The best way to connect the mod xfmr is to use the entire winding (no taps) on the modulator side.  The modulators should be connected to the lower impedance side of the xfmr.  You can then use the entire winding on the PA side, this will give a slight step-up in voltage swing.

Fred

[W9ZSL]

DMOD, in regard to the inrush limiter, I take it where the upper relay contact lead to R1 crosses the lower contact's lead form the black "mains" lead, there is no connection?