Mod Iron Taps

[Todd, KA1KAQ]

Once upon a time, I knew a little bit about this stuff. Now.......eh, not so much.

The CTC transformer from the KW-1 has two sets of taps, 18000 ohms P-to-P, or 12000. 18000 is suggested by the manual to be the most efficient, giving 'the same level of audio at lower input' or such. Something like:

Modulating to 100% w/sine-wave carrier (no voice) 350 ma for the 18000 taps, 410ma for the 12000.

But somehow I remember the 12000 taps 'sound better', fuller audio, better peaks, or ? Uncle Ed  WA3PUN was very clear about it when we discussed mods(shh) in 1990: USE THE 12000 TAPS, IGNORE THE MANUAL.

No doubt a simple answer awaits, and I'm not ashamed to admit I'm still (re)learning a lot of this. Fuller Audio/Less Efficient, Thinner Audio/More Efficient makes some basic sense, but I'm missing the bigger point here. If 18000 is just as good sounding and more efficient, why bother with the 12000 tap at all?

[WA1GFZ]

The higher Z will give you better lows since the transformer inductance is higher but it could reduce high end response due to extra inductance and leakage inductance. Also the power to the final will reflect different loads on the mudulators. So if you really push the final the lower tap may work better.
Put a scope on da signal and ax around to see how it should be.

[Todd, KA1KAQ]

I think I was under a mistaken impression, that this mod iron was made for this transmitter and not an 'off the shelf' generic model. The same transformer (small insulators) was used in the early Johnson Viking KWs and later changed to much larger insulators covering the sides. Appears to be the same frame and laminations, and makes a FB sub. Only problem is the spark gap - the Johnson version won't fit into the Collins cabinet due to the larger/longer insulators.

Based on the above, it made no sense why Collins or anyone else would pay for an additional winding if it wasn't intended to be used. Maybe Skip can add some comments since he's had these things turned inside-out over the years. K7Y-O-O.

[k4kyv]

The higher Z will give you better lows since the transformer inductance is higher but it could reduce high end response due to extra inductance and leakage inductance. Also the power to the final will reflect different loads on the mudulators.

You will get better positive peak capability using the 12K taps.  With the 18K taps, the modulator will probably just barely be capable of modulating 100% if even quite that much. The transformer will have more step-down using the high-Z primary than with the lower one. 

Since the secondary winding will be working into the same load impedance, I wouldn't think there would be a great difference in frequency response between the two sets of taps.

OTOH, the modulators will operate at higher efficiency using the 18K taps.  At the same power level, the modulator tubes will run cooler.  But for voice modulation that shouldn't be a problem.

I believe this is an off-the-shelf unit, not custom built for the KW-1.

I would recommend the 12K taps.

[Opcom]

Once upon a time, I knew a little bit about this stuff. Now.......eh, not so much.

The CTC transformer from the KW-1 has two sets of taps, 18000 ohms P-to-P, or 12000. 18000 is suggested by the manual to be the most efficient, giving 'the same level of audio at lower input' or such. Something like:

Modulating to 100% w/sine-wave carrier (no voice) 350 ma for the 18000 taps, 410ma for the 12000.

But somehow I remember the 12000 taps 'sound better', fuller audio, better peaks, or ? Uncle Ed  WA3PUN was very clear about it when we discussed mods(shh) in 1990: USE THE 12000 TAPS, IGNORE THE MANUAL.

No doubt a simple answer awaits, and I'm not ashamed to admit I'm still (re)learning a lot of this. Fuller Audio/Less Efficient, Thinner Audio/More Efficient makes some basic sense, but I'm missing the bigger point here. If 18000 is just as good sounding and more efficient, why bother with the 12000 tap at all?

what you just said about the taps.. Do you have a coupla goode pictures of that iron please? I think I have one sitting here. It says 890 watts on it IIRC and I'd like to ID it to know what toobs and volts to best use. Also, a 60H modulation reactor weighing about 120-150 lbs came with it.