The AM Forum

Hello all,
Would a stancor A-3894 125 watt mod transformer work better than the original in a Valiant II?
Thanks,
Don W9BHI

My guess is if it will fit, yes.  Use the connections table

http://www.k7jrl.com/pub/manuals/transformers/MSTANCOR/stancor1.htm

to figure out the right connections.

Al

The Stancor 3894 should work FB.  It depends on how you connect it.  All those multi-match xfmrs have a step-up ratio from the whole primary to the whole secondary.  The Valiant has 3 6146s in the final.  I would think you'll be using the parallel connections on the secondary and maybe not loaded the finals to the max.

You can call either side of the xfmr the primary.  I would think you should use the higher impedance side in parallel for the secondary and then use the ENTIRE primary on the modulators.

I would start with that set-up and see how it works.

I THINK the higher impedance side are the 7-12 connections.  The lower impedance side being 1-6.

You should check this as I may have it backwards.

Fred

I would configure the taps for less step-down than what the stock transfomer uses, maybe about a 2:1 impedance ratio (1.4:1 turns  ratio) or even up to a 1.2:1 turns ratio.  I believe the Valiant is one of those rigs that intentionally have too much step-down in the mod transformer, in a half-vast attempt to limit the modulation to less than 100% in order to prevent overmodulation, but which produce precisely the same kind of distortion and splatter as overmodulation, when the modulator tubes are driven to saturation, thus flat-topping the peaks.

I hooked one of those to my Valiant 'bout 30 years ago. I recall that it was a tight squeeze.  I would say that it was a small improvement over stock iron.   But, not a real big change by itself.  Things got much better when I changed the 6146 modulator to 811A's and redesigned the audio driver.  It may be worthwhile to use one as part of a more comprehensive modulator revamp.

Wish I still had the Valiant.  It was my first decent AM transmitter.