Solid state modulator, and TV xformer...?

[kf6pqt]

Ok, with this in the back of my mind:

http://www.amwindow.org/tech/htm/tvtomod2.htm

How would I hook up this heising scheme if I were just gonna hook up a solid state stereo amp as my modulator? Or is this just totally yellow-tastic and not worth doing? Or do I just need to build a tube driver stage in between? What happens when ya hook a ss stereo output to some 811a grids? 

I'd just be modulating an Eico 720... at first!

Thanks and 73,
Jason kf6pqt

[w1guh]

"What happens when ya hook a ss stereo output to some 811a grids?  "

I did something like this with a Valient.  I put an interstage transformer between a solid-state guitar amp and the grids of the modulator tubes.  Worked fine, except that on 40 and above the SS amp didn't really like the RF.

[The Slab Bacon]

Use a good beefy push pull outpoot transfoma hooked up backwards to drive class b grids with a ss amp. if you have enough scrote in the ss amp you may be able to use an even more strapping transfoma hooked backwards to directly modulate the final.

1 "rule of thumb" to keep in mind mudulating audio power must equal 1/2 the dc input to the final to make 100% modualtion. And a little better scenario that gives you a little more headroom for mod peaks is to have a modulator with an audio outpoot equal to or a little better than the carrier outpoot of the final.

                                                                     the Slab Bacon

[kf6pqt]

Slab, are you saying this?"

SS audio amp + audio trans + mod tubes + TV trans + cap + heising choke

?? I need that extra xformer as a buffer?

Ok, bear in mind, I now have a dozen or so hefty TV transformers... (and their chassis full of TV parts) only a few puny TV and record player audio xformers... the only mod xformer I have is a little thing for pp 6v6's that came out of (ok, still within) a BC-625... you know, WWII 2m AM thing with a pair of those funny tubes...

Now, with the old TV's I scored, I also got a record player with a working amp... makes a decent little guitar amp! 1x 12ax7 x2 50c5... (makes a hell of a buzz until you plug in the ac plug the right way, yikes!) to be honest, i don't recall seeing an output trans in there, if so, its puny as heck. Also have a meaty-looking late 70's SS stereo that is expendable.

That, and I've got several 12ax7's, 6v6's, 6aq5's, (even a pair of 6k6gt's...)  pair of 6L6GC's that I need to test, 4 new chinese 811a's with ceramic sockets and caps, a BUNCH of 1625s...

Now, with that laundry list, what sort of modulator can I build? (quick and dirty OR nice..)  I prefer the "modified heising" arrangement listed in the article, cuz at this time I simply dont have time right now to mod one of my TV transformers into gapped-core deal, and having a cap between the mod and the TX b+ just sounds nice and safe.

Thanks and 73,
Jason kf6pqt

[The Slab Bacon]

Jason,
         If your ss amp is big enough you dont need any modder tubes at all.
If not it is like this:

 ss amp > small p/p outpoot transfoma backwards > class B mod triodes > big assed mod transfoma > rf final.    Heising reactor is optional.
 
                                               OR

big assed ss amp > big assed outpoot transfoma backwards > rf final
Heising reactor is optional

I hope this helps, it is very doable if needed.

 oh, also you might be able to ues a big assed tv transfoma as a modder with a big ss amp if you pipe the low-Z output of big ss amp into the filament winding of the tv transfoma and use the B+ winding to mod the HV to the final tube. I dont think anyone has tried it this way, but it just might work!

                                                                             The Slab Bacon

[kf6pqt]

Huh, ok... now, assuming option 2...

big assed ss amp > big assed outpoot transfoma backwards > rf final

I don't have the bigass audio xformer... would I hook up my TV xformer, audio to the 120v side, and the plate b+ to the HV side? or opposite?

Or does the use of a TV xformer always have to follow the timtron method?

Thanks!
Jason

[The Slab Bacon]

Huh, ok... now, assuming option 2...
big assed ss amp > big assed outpoot transfoma backwards > rf final
I don't have the bigass audio xformer... would I hook up my TV xformer, audio to the 120v side, and the plate b+ to the HV side? or opposite?
Or does the use of a TV xformer always have to follow the timtron method?
Thanks!
Jason

The 120v primary of the tv transfoma would prolly be too high of a Z to pipe the 4 or 8ohm audio into, that is why I said to try using the filament winding for the audio inpoot FROM the big assed ss amp. I dont know if anyone has tried it, But I think it will work. After all necessity is the mother of invention!
                       
                                                                      The Slab bacon

[kf6pqt]

Aha! You added that after I replied! 

oh, also you might be able to ues a big assed tv transfoma as a modder with a big ss amp if you pipe the low-Z output of big ss amp into the filament winding of the tv transfoma and use the B+ winding to mod the HV to the final tube. I dont think anyone has tried it this way, but it just might work!

I will be the first to try it then!

Thanks again,
Jason kf6pqt

[Steve - WB3HUZ]

big assed ss amp > big assed outpoot transfoma backwards > rf final
Heising reactor is optional

In my experience, it's not optional. The audio transmformer (it's normal primary, that you would be using a the secondary in this application) is not designed to handle unbalanced DC. So a reactor/heising choke is needed.  Any 50 watt amp will easily modulate your Eico 720.

The TV transformer mod by Timtron is for use with tube modulators.

Yes, filament trannys have been used as modulation trannies with a solid state amp. So work bettee than others. Generally, it's the HF response that suffers.

[W2VW]

Crest 4001 bridged 1400 watts RMS, T368 plate transformer 110 primary fed by Crest to 1/2 secondary center tap grounded, end termional through 10 kv oil filled cap, BC-610 final fed B+ through several Wilcox chokes. Experiment of the month for August 1994. Worked WB3HUZ, tore it apart, moved to another house. Filament xfmrs might be OK choices for single digit audio sources. It's easy to test with resistors as simulated class C final loads.

[kf6pqt]

That leads into my next question, how to determine the value required for the coupling cap?

Thanks again,
Jason

[W2VW]

A couple mfd max for typical class C finals. Check the search function here. Plenty of discussion archived.

[Steve - WB3HUZ]

Go big on the choke and small on the cap (2 uF) for best impulse response.

[kf6pqt]

Now, all I have in the way of chokes are the "medium sized" ones I've pulled out of the TV... unknown values. I have a cheapy digital L-C meter, but something tells me it'll be no use in determining how many henries these things are... don't remember what, maybe my lack of experience with the meter.

Anyway, just series a bunch of these chokes and see what sounds best?

Thanks so much, I'm learning a lot with this, and its helping a bunch of other stuff make sense too!

Thanks again,
Jason kf6pqt