The AM Forum

Photos of the rf goodies removed and cleaned (roller inductor needs some more love) from teh rf deck skippy sent me.  :D National MB-50 input tank in FB shape not pictured.

the old buzzard Cardwell cap is a XG-110-XS. I gather it's 110pf, but does anyone have a Cardwell book they could look in and give me the finer details?

What's the group consensus on the roller inductor? Skip sez 200 watts or so, which looks abt right but second opinions are always good. I think these will wind up being my tank circuit for a 1 hole HK257B rf deck to go into the small rack. Drillage and blastage & punchage to commence shortly. If this roller could stand more power, I'd just punch 2 holes and go.

As soon as I get the punch for the 4-400's I'll hit some holes n mount some sockets, likewise.

If there was a Drool emoticon, I'd use it! WOW!

What do you mean 200 watts?  Is that input or output?  Did the cap come from the same piece of equipment?  Was the equipment they came from  commercial or private vintage?  What is the size of the coil (diameter) and wire gauge?  Just curious about all of this.

well, its a 3" coil, and its ww 2 stuff. It came out of a BC-375 (?) not being a military guy, I dont know much about it. wire size looks to me to be around 14 gauge solid, and it came out of a homebrew rf deck someone made that used a 4-125. so did the cap. I know it wud be FB for 200+ watts or so, but maybe someone here has actually used one n can advise abt the safe non crap out power level.

went out and looked a bit - it tuned a 211 operating at 1000 volts@220 ma. So, 220 watts inpoot as installed. looks like a 1 hole roller.

With all that, I would say you would be safe up to 300 watts Derb.  Even the Globe King which has 350 watts out only used #16 wire for their tank on 80 and 160.  The 20-10 meter section is #14 or so silver plated.  What you have should easily handle a 4-400 at full output with 2-2.5 KV on the plate. 

Just be sure that slider bar is clean and put just a dab of Nolox on it.  Not much.

I dunno, that seems a bit optimistic. :o If it could handle 350 watts I'd consider it a victory. cant a 4-400 hit around 600+ watts with about 2200?

Derb,

I've seen output inductors made of similar gauge wire used up to the 1200 - 1400 PEP level.

This is, however, on the upper bands, but on  MUCH smaller diameter coils, so YMMV, and a bunch of other acronyms.

--Shane
 

And thanks for the video of Don and his shack....  Not NEARLY as old buzzardly in video as that crabby picture he uses on here :)  Makes me actually want to try working him now :)  Full size 160 Mmmm

Well do you plan to have 600 watts out?  I know some people design for 600 and only use 300 but what is your goal?  If you are going for 600 watts, get some #12 or 10 silver plated wire and rewind that coil.  It should not be difficult to do.  With those holes in the ceramic form you will have better than ususal cooling.

My Dentron MT 3000 tuner uses coil stock with #16 wire as does many other RF generators for that power level (350 watts).  Since that inductor was for the military use, you can be sure the fudge factor is at minimum 2:1.   A quick look at the specs shows the manual suggest 350 ma. with 1 KV.  So, using 50% efficiency then you have 150 watts out.  You should be real comfortable with 300 watts on the thing. 

But you need to decide if you want to have more than 600 watts on the 4-400.  I should ask why?  300-350 watts is enough and you can do that with this thing.

200 watts carrier 1 KW PEP and it will run hot above 40 meters.
The tank in my class e final is 1/8 inch silver plated and runs quite hot at 1200 watts carrier.

well, I'm trying to make all my parts fit the best way possible.

I have a hankering to use the H&K tubes first, basically 200 watts a bottle. from 200 to 400 was enough of a difference to want the advice of others.  ;)

Frank,

Is that Strap or wire?  And I'd be really interested to know the difference, if you've played with it, between strap and wire.

Contemplating my tuna, and what would be best... I'll have to order it fresh, in either case.  I'm leaning towards strap, just because..

--Shane

1/8 inch tubing. I've used both strap and tubing. All about surface area

I am going to use the identical coil at 1300 - 1600 VDC and 180 to 230 ma. for 234 to 360 watts input.  Compared to the the B&W 299 series inductors (rated at 500 watts, 16 ga wire and a solid ceramic cylinder) I think it will work just fine. I hope!

Hey, I'm just starting to learn about this stuff myself--the bread slicer cap looks like it might be useful as a tune cap but for load you gonna need more range right?  somewhere around 300 or 400 pF?  Looks like you don't have to worry about the voltage on the slicer  :D

Rob

yeah, the rig as it was built used a stack of fixed value hi voltage micas all 2500 volt working; 7 of them that he would switch in or out with a rotary switch to adjust the loading. So it had no variable loading cap.

Those caps are much more valuable to me for use as HV bypass (like bypassing the R175A) and HV blocking units (keeping DC offa the tuning junk) and I have 3 or 4 caps good for loading. They are spaced typical BCL spacing, might not be enough. My first rig had full HV on the tuning cap and the coil.  :o At least this one wont have that going on.

My rigs have never been known for their innovative safety features. I think transmitting tubes and such are things of beauty, like good sets of boobies - they should never be covered up or hidden from view.  ;D

Derb, Should be great for 300 watts on  160, 80 and maybe 40, but the rotary contact is potentially the greater problem , especially over time ... dead spots, arcing, etc. so you really don't want to overload it.

Might be fun to find the sweet spots,Q wise , etc. and then duplicate the dia. , wire size in a new coil and make permanent taps to a bandswitch.

I'll bet you can find a beefier roatary coil somewhere.

The BC-375 was rated at 50 W; of course that was into any antenna you could throw over a tree.  Shows plate voltage source at 1100 VDC with low voltage at 425 VDC.  I agree with the above comments concerning how much power it should handle under 'normal' utilization. 

Definately a major DROOL FACTOR ;D.  Did you have to clean up that inductor and if so, how'd you do it?

Al

Yup Tim,
That's how you make the monkey schwang
More Volts!!!
Phred

re the roller cleaning : dishwasher. the ceramic was almost black before.

Dang!  That dishwasher is sure powerful medicine!!