Hi Pwr Mod Iron--without a reactor

[k7yoo]

I have some nice mod transformers in the 2.5--5KW range that were designed for use with reactors. What would be the disadvantage of using them at reduced power without the reactors? I was thinking a 50% de-rating would be sufficient. As long as there is no core saturation or current overload I don't see how fidelity would be affected.
Skip

[k4kyv]

Why don't you try them and see?  I would expect that it would take more than 50% derating though.  A 2.5 kw unit should run ok at 500 watts.  If the laminations are interlaced, it doesn't take much DC to saturate the core.

[flintstone mop]

What a nice blessing to have several mod transformers! Can't beat the b'cast transformers.
Fred

[WQ9E]

Skip,

I will be interested in the results of your experience as I have the modulation transformer from a 5KW Westinghouse transmitter that also was used with a reactor.  I haven't found any suitable reactors except from P. Dahl.

73, Rodger WQ9E

[k7yoo]

Looks like it is time to get out the clip leads and do some testing. I will keep the forum posted on the results.
Skip

[Bacon, WA3WDR]

This might be a place to apply the unbalanced modulator tube idea, using two tubes in parallel for the positive peaks and running high resting current on them, and maybe lower resting current on the negative-side modulator tube, to reduce the DC imbalance in the transformer core.  Then drive the two parallel tubes with half of the drive given to the negative tube, and polarize the audio waveform appropriately.

I sometimes wonder if a core could be magnetized, or if a magnet could be built into it or coupled to it, such that the modulated stage DC would balance out its DC field.

[Ian VK3KRI]

I sometimes wonder if a core could be magnetized, or if a magnet could be built into it or coupled to it, such that the modulated stage DC would balance out its DC field.

If you have a spare winding, you can run current through it to balance the DC in the core. BUT you need to make sure it doesn't act as a shorted winding by adding enough 'L' or 'R' in series.
                                                                                        Ian VK3KRI

[WBear2GCR]

This might be a place to apply the unbalanced modulator tube idea, using two tubes in parallel for the positive peaks and running high resting current on them, and maybe lower resting current on the negative-side modulator tube, to reduce the DC imbalance in the transformer core.  Then drive the two parallel tubes with half of the drive given to the negative tube, and polarize the audio waveform appropriately.
<snip>

If you run two tubes in parallel with extra quiescent current, ur more in to class A on that side, with double the current of a single class A tube, and no more positive swing than a class B tube. Actually because ur into class A and the positive side conducts into the negative as well, maybe you'd get more negative peaks than positive?!?

BUT, you could bias one tube in normal class A or AB, and the second tube more like class B, or actually closer to class C, so that as the drive goes up, the second tube "comes to life"... or something like that...  there's an audio amp design that used a triode and a screen grid tube together in a similar set up...

                     

           _-_-bear

[Bacon, WA3WDR]

A single-ended Class A modulator on the 'negative' side would balance the DC even better, but it would be awfully inefficient.  I was looking for a compromise that would extend the unbalanced-DC capability just enough.

Maybe the high-efficiency class B series modulator design should be used instead, eliminating the mod transformer altogether.