The AM Forum

I wonder if anyone here on this board has ever worked on this model transmitter?

Does anyone have a copy of the transmitter schematic with detailed values for all the resistors and capacitors as well as a voltage chart for just the 5KW section?

There were only 12 built and what makes them unique is the screen modulation.

The 317B at WJR SN #1. Number 2 was in use until 1999 somewhere. I guess they were quite well made transmitters.

I dont know much about them, but the ones I do know about seem to have been in service just about forever, and every new one I hear about
is the same way. Continental bought out Raytheons broadcast division way back when.


http://www.oldradio.com/archives/hardware/ce.htm
http://www.rossrevenge.co.uk/tx/continental.htm

Hey thanks Derb for those posts... I thoroughly enjoyed reading those links about the Continentals and the SGM.   8)

10-4. tnx fer the qsl, I got it OK, but I haven't had any qsl cards since maybe 1988.  :-[

What am I, Chopped liver ??? ???

John/K5PRO can talk to you about those transmitters.

Thanks Jim, I'll try to locate him.

Of course not!!

Your initial inquiry to this whole affair made all of this possible! Kudos to you Terry!  I've been dreaming about someday having a broadcast transmitter.  Your NOS Westinghouse has got be an awesome presence!  My controlled carrier screen grid modulated with WC3K mods DX-60 makes really nice audio.  Of course the carrier is limited to about 12 watts max.  Does okay into my SB-200 for 100 watt carrier though.  I'd really love to have a linear that loafs at legal limit to bring out the best in the ole girl. No, I'd really like to have a broadcast transmitter!  But I'm at the "run what ya brung" stage...

Carry on!

He is a member of the AM Radio reflector and here as well.  Note under "Latest Articles" on the left is Recsues of BC Transmitters by him.

He may be busy at the moment but should show up.  If you will go to that link then to his website you can email him.

Well there are few good comments on the BB about screen modulation. I don't know if Stu, AB2EZ has anything on here about it but he has done extensive research and experimentation on the subject of screen modulation and in my estimation, has taken screen modulation to a much higher level. I think its foolish if you have a rig that's ready to be on the air for the want of mod iron,and it just sets there. I have heard AB2EZ and WA1SSJ with screen modulation and they sound excellent.  

I would like to have a rig that uses a 4CX5000 with screen modulation just to watch that plate current swing up to 2 amps with about 6000 volts on the plate. Of course I would only operate it on 27.185 where it is legal ;D ;D ;D

When I looked up " A-1 Operator " there you were. I'll catch you rappin on the Superbowl (channel 6) one day.  ;D

not to mention the Slab Bacon with his 4 x 1.

You would be THE channel master

Fred

thanks Tim for posting the web sites ... I spent several hours yesterday analyzing the 317B screen modulator .... used several 4 - 65 tubes low mu triode connected as the cathode follower to modulate both 4-5000a .... first time I had seen any of the 4-xxxx family used that way ....impressive

Does anyone know where to get a manual for the beast??

Attached is a pdf of the 4CX5000. They have the values for screen modulation on the sheet. Looks like you could get a cool (HOT) 3350 watts of good old RF from one of these tubes on mod peaks. I wonder what the idle power output would be?

Those 50 kw Continental 317 series transmitters were using screen modulated Doherty Power Amplifier stages.  When they worked right and were kept well tuned, they worked very well.  When not tuned right, they tended to "spit" at you.  I worked on both the 50kw 317 series as well as the 10kw 316 series.

Look up the Doherty amplifier theory where two PA tubes are used, one as the "carrier" tube and one as the "peak" tube, screen modulated, and the unique way they were driven, modulated, and combined.  Each of those transmitters has a small 'scope built in to them, which could be switched to sensors in several places in the RF chain so you could adjust for the proper phase shifts and drive levels from the drivers, modulators, and PA circuits.   One particular one I worked on would throw around some lightning bolts inside when agitated.  15,000 volts @ 7 amps, or so for 50kw carrier.

If you also want to, then explore a method known as Ampliphase, which RCA marketed in AM broadcast transmitters, Google that as well.  That one started with phase modulation of two RF streams, and were combined so the the quadrature part of the modulation was cancelled out in the PA stages, and only amplitude modulation was left.  That also worked quite well when adjusted properly.  If it was mistuned, it sounded horrible.

Have any of you ever come across the Gates Vanguard series of 1 kw AM transmitters?  It was a short lived run of transmitters, Vanguard One and Vanguard Two, that generated  the AM with a ring modulator diode circuit at low level, and used a 3000 or 5000 watt (I can't remember now which one) tetrode as a linear PA.  It ran something like 3000 volts at an amp, about 30% efficiency, to get the 1kw output.  Again, when it was tuned right it did sound quite good (audio specs from 30 to 16,000 Hz @ <1%THD)).  But it spun the power meter like crazy.

When we still used tubes, there was PDM, etc., all kinds of ways to eliminate heavy mod iron and still achieve reasonable PA and mains power in to RF power out.

These days, some of the newer 50kw boxes are smaller than a 250 watt box of the 40's.  And the 1kw sized transmitters almost fit in a briefcase!

73
Ted  W8IXY

I love the artical on the commercial screen grid modulated transmitters. I think (Screen grid mod ) is a very efficent and cheaper way to go, low power consumed. Has anyone ever made (modulation) modifications to a KNIGHT T150.

John W9BFO

I missed getting a Vangard II just a bit.  Used the 3000 tube in the final Class A.  Every one commented how the II looked like a jukebox and the I like a washing machine.  The I did not have the exciter and the II did, as I recall.  When I though about the power consumption, I was glad that I didn't get it.  Intersting transmitter.  I believe it was spec'd flat from 20 cycles to 20 Kc if tuned properly with less than 1% distortion.

contact Art N4JK ... his T150 sounds very good

I got to babysit a 315B years ago, the 5kW version.  The station was between owners, and needed some fill-in staff.  It never went down, so I never had to beat on it.

Doherty rigs were really efficient, regardless of what grid was modulated in the driver stages.  The modulation was not applied in the finals.

In the big mamas the 90-degree phasing networks got to be pretty large amongst the tank & output stuff.

My WECo 5Kw 405A2 final cabinet is 4X4X7, has but three tubes in it.  There is one air-variable in it that weighs over 50 lbs....

The whole thing is some 9,000 pounds.