Easiest AM modulator mod for 50-200 watt classic transmitters

[K1DEU]

Ken W2DTC has the complete article here  http://w2dtc.com/w2dtc-hi-fi-viking-ii-page.htm

I am guided Hammond will be raising price on the 1642SE around or just before March 17

Searching for current prices they vary between $250 and nearly $350

Radio Daze Victor, NY sells the necessary Hammond Classic 1642SE  28 pound gapped (single ended) transformer for $250 and Hammond drop ships it UPS from Buffalo, NY inexpensively to us in the US

    http://www.radiodaze.com/

There are many good solid state Public Address, Musician and Automobile 90 watt RMS Audio Amplifiers which can feed this xfmr.   73, John

note; It was ordered Monday morning and arrived UPS Thursday afternoon from Buffalo, NY area.

[WBear2GCR]

Presumably, once one goes and outboards one's modiron one can then do a modified Heising set up, pooting the gapped choke either in place of the existing mod xfmr, or outboard, or maybe even using the secondary of the existing mod iron as a choke (?an idea here?) which then will permit the use of a somewhat more available and possibly less expensive P-P audio output transformer run in reverse?

Although large (>100watt) audio output iron still tends to be expensive these days, this might open up more options for some...


         _-_-wonky built two goobered chattering relays

[ka3zlr]

Nice Find. Thanks for Bringing this in here...

Yes it does Bear. This shud be put into Forums System Archive Transmitters at the very top of the list.

[Rob K2CU]

Tim had a description for using an old TV power supply transformer for this task. A bit of work, but if you have one lying around, why buy one when you can build it out of something else. See:

http://www.amwindow.org/tech/htm/tvtomod.htm


Rob - K2CU

[K1DEU]

Bear; yes the 1642SE is a gapped (unbalanced DC) audio transformer ready to carry up to 300 ma. through its secondary. So it's a complete modulation transformer as far as its secondary and its ready to be fed 4 ohm audio from a mono or bridged stereo audio amplifier.

Yes as you aptly point out to save money we could use a normal audio output transformer (they are cross laminated) for audio duty accompanied by a DC choke and cap to carry the unbalanced DC current from the HV supply to the Plates/screens of the RF final.

http://hamelectronics.com/k1deu/pages/ham/transmitters/am/pages/using_audio_reactor.htm


       Since 1988 I have used a variation of this in my DX-100. Where a 30 Watt Dynaco audio output transformer is overkill to modulate my DX-100 over 150% positive going. My DX-100 runs 200 watts carrier output and makes about 1150 watts PeP modulating using this schematic with a 30 watt Dynaco audio out put transformer, octal socket 36LW6's, 2 in the final and two in the modulator with everything all on board.
http://hamelectronics.com/k1deu/pages/ham/transmitters/am/pages/modulation_power_mods.htm

Another lesser option is to take a large audio output transformer, remove the cross lamination pattern and re-assemble it in the gapped mode for it's original primary to carry the DC to our RF final. Carrying constant unbalanced DC requires so many gapped laminates (the same EI pattern symmetrically laid on top of each other) its not funny!  Look at at the size and number of laminates (with a gap) that a 200 ma. DC Choke requires. 

     60 Cycle laminations (like a power transformer or pole pig) for modulation aren't very good at 3,000 cycles up. Well at least 50+ years ago in 1957 people could understand my external Push Pull 6L6 public address amplifier through a B+W TV power transformer plate/screen modulating my DX-35. But nice thin Audio crossed, laminations with 20 Db. of negative feed back, would be prefered.

But for proper frequency response, when we try to save money, using a Hi-Fi audio output transformer and DC Choke  we should really use DC Chokes with thin audio laminations for good audio high frequency response. When we do this the DC Choke is properly called a Audio Reactor. The low audio corner is determined by the inductance, which would be used at 120 cycles with a DC Choke. The Expensive single ended SE and SEA Transformers are thin "M" laminations. The losses in thick lamination DC Chokes used for audio reactors can be easily over come with negative feedback but now we must enter the external audio amplifier to accomplish this !  Hmmm wonder if Hammond makes some inexpensive high inductance, high current, thin laminated audio reactors?

 73  John 

[Opcom]

This should also work on a Viking I? I think it is the same except the RF PA?

[K1DEU]

Yes Pat; the Viking 1 is basically a 200 ma. Plate current 600 volt RF final. The 1642 is Excellent for 200 to 330 ma. around 500-700 VDC RF finals and anything smaller. But,

For smaller transmitters like 140 ma. Plate current or less. 70 watt DC input or less such as Rangers, DX-60's, 20's, 35's and Zillions of others I would use the more affordable $96 Hammond 1628SEA 12 pounder. 

Radio Daze Victor, NY sells the necessary Hammond Classic 1628SEA  12 pound gapped (single ended) transformer for $96 and Hammond drop ships it UPS from Buffalo, NY inexpensively to us in the US

 http://www.radiodaze.com/

 73  John

[w1vtp]

But for proper frequency response, when we try to save money, using a Hi-Fi audio output transformer and DC Choke  we should really use DC Chokes with thin audio laminations for good audio high frequency response. When we do this the DC Choke is properly called a Audio Reactor. The low audio corner is determined by the inductance, which would be used at 120 cycles with a DC Choke. The Expensive single ended SE and SEA Transformers are thin "M" laminations. The losses in thick lamination DC Chokes used for audio reactors can be easily over come with negative feedback but now we must enter the external audio amplifier to accomplish this !  Hmmm wonder if Hammond makes some inexpensive high inductance, high current, thin laminated audio reactors?

 73  John 

Above emphasis, W1VTP

John

Paul WB2SKC and I are using the Hammond 1650P xfmr with their 100 ma 20 hy reactor in a modified Heising approach.  This will be used with an Eico 720.  I would have liked to have found a reactor with a higher current capacity as this will be right at the spec limit of the choke.  The AF will come from (in my case) a Bogen 60 watt tube PA amp.  Paul will be using a SS amp chip that will be more than adequate for the job.  We want to stick with current hardware so that others can use the same or similar approach.  I'd be open for suggestion as per your comments regarding Mod Reactors

73, Al W1VTP

[K1DEU]

Dear Al; Do you already own the 1650P and 100ma. DC choke?

For For smaller transmitters like 140 ma. Plate current or less. 70 watt DC input or less such as Rangers, DX-60's, 20's, 35's and Zillions of others I would use the more affordable $96 Hammond 1628SEA 12 pounder. 

For here is everything in one package with thin"M" laminations.  73  John

[flintstone mop]

I will attest to Tim's mod iron using a power transformer from a huge stereo amplifier using 2 5AR4's in the P.S. and 4-EL37's in the power outpoot. This conglomeration and it's Heising choke and cap make some really nice audio from my Elmac AF-67.....Out boarded, of course.

Fred

[k4kyv]

A very simple way around loss of high frequency response when using power supply types of chokes as mod reactors, is to place a small, low inductance choke in series with the top end of the mod reactor winding.  At 3000~ you need only 0.5 Henries or so of inductance in the reactor.  So, as the large reactor begins to become lossy at higher audio frequencies, the smaller reactor takes over and continues to appear as a high impedance across the modulation transformer, and isolates the larger reactor from the circuit.

[Opcom]

To predict the potential for losses at different frequencies when using a power supply type of choke, does it make sense to set a DC current through the choke and then sweep the choke with an audio power amplifier (or maybe with one of those vacuum tube regulated 0-500V/500mA power supplies suitably modified for audio) and note the choke's varying impedance, or is there more to it?
Having a pile of chokes, it is dificult to choose the best ones.

[Jim KF2SY]

John,
Audio mods aside; you said you get a 200W carrier out of a
DX100.  Maybe I missed sumptin.  Please explain.

Thanks...
Jim

Never mind John....I see said the blind man....

octal socket 36LW6's
Big azz sweep tubes, interesting.
I imagine neutralizing was a chore, do they sing correctly on 10M ?

[flintstone mop]

Hi Jim,
I like your avatar...The little banjo player from "Deliverance"........"Now lets you just drop them pants....take them right off"!!! Weeeeee Weeeeeee

Fred