Driver Iron Specs

[KC4VWU]

Does anyone know the specs on a 20D89 driver transformer, which I believe is a Thordarson #? I can't find any info on the net about it. It's installed in my V II and it appears to be the only part in question in the audio chain. There have been a few caps changed, but are equivalents of the stock values.

Phil

[Steve - WB3HUZ]

Are you looking to replace it or just interested to know? The stock driver tranny in the Viking is pretty crummy. I've never seen the specs but if you can replace it with a larger/better one, go for it.

[N3DRB The Derb]

the stock driver xfmr is crap. it can only take 10 ma b4 it blows up. I'm looking for h specs for you, post if I find em. I do know thats a single plate to PP grids and I bet it's got something around a 2:1 ratio.

The 6au6 mic amp can be directly changed to a 6ah6 if you want more gain. The 6au6 driving the 807's is the weak link along with the stock driver transformer. be glad it's gone. a 6C4 would be loads better, a 12B4 better yet.

[KC4VWU]

 I think it has been replaced; but I'm not 100% sure. The part # given in the manual is SNC 1503. The #stamped on this one is 20D89 which sounds like a Thordarson part #. It also says 3 to 2 or 2 to 3 ratio: it's center tapped on both sides so I guess it can be used as step up or step down. One brown, one blue lead with red CT (on primary side now) and 2 green with black CT on secondary. I'm jut trying to figure if it is worth keeping or chunk it and get the Hammond replacement?
 

[N3DRB The Derb]

its worth keeping, probably better than the newer replacement as long as the ratios are what you need to have.

it is a thordarson unit - still looking for info. Thordarson had so many damn part numbers , seems like they changed them every year.

[k4kyv]

Take that crappy driver xfmr apart and re-stack the laminations like a power transformer, without the gap in the core.  Then use about a 1 mfd coupling capacitor off the plate of the driver to feed the transformer.  Feed the driver tube plate voltage through a resistor.  Experiment with 10k to 30K to see what gives best performance, and make sure the wattage of the resistor is sufficient.  Return the +HV via the new plate resistor to the same high voltage source that feeds the final, instead of to the medium voltage source as in the stock circuit.  The voltage drop in the plate resistor from +HV should bring the plate voltage at the driver tube back to near normal.

That mod will make a tremendous difference in the audio, even if the rest of the modulator remains stock.  I did it to the Ranger I once used, and  helped N4IBF(SK) install it in his Valiant.  In both cases, coupling capacitors in preceding stages were increased in value, and the improvement in the audio was well beyond expectations.

[WA1HZK]

Get rid of the driver transformer totally. Just rewire the rig for the phase splitter. That's the first mod most guys do to these old Johnson rigs. Just look in the transmitters - Mods section of this site.
Keith
WA1HZK