Modulation Transformer

[N4LTA]

No - don't worry about send the thread on a tangent. I'd like to see some of the experts jump in.

pat

[N2DTS]

It always works a LOT better to have way more audio power than you need.
Things are much cleaner that way, and you dont have any problem getting well over 100% positive modulation.

I like as much audio power as rf output power as a rule of thumb.

On the other hand, some guys on the air lower the modulation percentage for a better cleaner sound.
I dont agree with that, I like 90% neg modulation and the positive peaks can go wherever they want, that usually sounds good.

Excessive positive modulation can distort in the detector on the receive side, and very few people have gear that handles that well, so I suppose that would sound loud but semi-crappy in most shacks.

If you pay attention to the 1500 watt pep rule, I wonder if there is much difference at the far end if you run 250 watts carrier and 1500 watts pep, or 500 watts of carrier and 1500 watts pep???

Anyone ever run tests of this? What sounds better? What works better?


I cant say I am a big fan of the S series iron, special crap for hams is what I thought it stood for, different from the well made commercial stuff.
Even the commercial CVM 5 mod transformer is not very good, although it is good for the power.

Brett

[KE6DF]

While we are discussing UTC modulation transformers, I have often wondered about the concept that if one takes a modulation transformer designed to support DC on the secondary (like the CVM or S series), that one can deploy these transformers in a modified heising arrangement and then run them at 3 times the power.

So, by that theory, a CVM-4, with it's 300w rating and gapped core, could put out 900 watts of audio if the DC was run through a heising reactor?

This sounds way too high to me. Perhaps moving the DC off would give some kind of a boost to the 300 watt rating, but three times?

One of the reasons I question this is the 260W spec for the LS-67 transformer from the same vendor weighs more than the CVM-4, is designed with no gap for use with a heising reactor. And it is only spec-ed at 260W??

That three times number doesn't seem to add up.

If people said 20% more or something like that, it would sound more reasonable.

[N4LTA]

The DC on the core takes a lot of core capacity that can't be used for modulation. If you look at the Hammond SE transformers - the 75 watts one is  as large as the 280 watt push pull transformer.

As an example the largest Hammond SE 1642SE is rated 75 watts and weighs 28 pounds

The largest Push pull transformer is rated 280 watts and weighs 28 pounds

One has 300 Ma DC on the core and one has no net DC - That a difference of 370%  - so the three times may very well be true.

Pat
N4LTA

[Steve - WB3HUZ]

Saturation is one thing, but more power means more current and potentially more voltage. I'd look at the voltage specs on the CVM unit before cranking up the power.

[N4LTA]

I found the specs on the Hammond 2220 transformer. It was a "professional series" transformer with ceramic standoffs and mica insulation. I would bet it would do fine with a modulation reactor at 300 watts or so.

It weighs 28 pounds.

BTW KM1H - Toroid Corp just called me and said they could not build a reactor with a 2500 volt rating. The engineering guy said they did not have a meter that could measure 50h. That was somewhat of a surprise.

[KD6VXI]

So, by that theory, a CVM-4, with it's 300w rating and gapped core, could put out 900 watts of audio if the DC was run through a heising reactor?

This sounds way too high to me. Perhaps moving the DC off would give some kind of a boost to the 300 watt rating, but three times?

I believe it's the diff between ICAS and CCS, as well.  Three times, for slightly greater than SSB duty cycle. 

I did play with removing DC from solid state amplifiers broadband xformers.  It DID help, and efficiency went up.  SO, I would tend to agree... From what I remember, I got about 20 percent more power, PEP, out of a circuit when removing DC from the xformer.

--Shane

[flintstone mop]

If you pay attention to the 1500 watt pep rule, I wonder if there is much difference at the far end if you run 250 watts carrier and 1500 watts pep, or 500 watts of carrier and 1500 watts pep???

Anyone ever run tests of this? What sounds better? What works better?



Brett

It takes 6dB to make an S-meter move one increment, so I guess the difference from 250W carrier and  a 500W carrier would not make much difference.

But an interesting thing was brought to my attention about the P.E.P thing. You could have a 1KW carrier and only modulate for a P.E.P. of 1500 watts. Hows about those apples???

FRED

[KM1H]

Tube specs were quoting theoretical power and not the actual power to the load. They also did not include distortion power.

QST articles regularly stated to run substantially more than half the RF input and even quoted mod iron losses as around 20%.

Heck, Im running 304TL's to modulate 250TH's as well as a four pack of 813's. We wont discuss what reaches the antenna but be certain its fully modulated.

Clipping the highs isnt going to do anything for the peak power of male human voice as its already falling off at 3 kc. The true power is in the lows. Cheap iron already kills the lows so if you have limited power put it into "communications" audio until you can score the right iron. Dont get carried away with lots of processing either with cheap iron, it doesnt like the high average power. If people tell you the audio sounds restricted just tell them its a Collins

Im using a wet 7500W mod xfmr with the 304TL's, no worry about saturating but Id still like to find something that doesnt need a cherry picker to move. Dont laugh...it was cheap!
All the shaping is done at low level ( 150-3500cps) and with just a pi-net splatter filter at high level. I can easily go 150% on the positives and see nothing nasty on the spectrum analyzer.

Before that I was using 810's and a 600W xfmr to modulate the 250TH's and even at 900W RF input I couldnt get the clean processed levels I wanted. Thats now with the 2 x HK-354 RF deck which is running at 600W and works fine.

In the late 50's I had the classic PP 250TH's with 810's and didnt know then what I was missing until I tried duplicating it a few years ago. And went thru a big awakening and actually read the old articles with understanding this time around.

Carl
KM1H