What's the best type of cap to use for RF bypassing, other things being equal?

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N3DRB The Derb:
Steve, is there a distrib for these that will sell direct, or can you point me to a dealer that will? They sound every good.

Q: will paralleling bypasses to a desired value point further reduce ESR? Likewise, will providing a 8 lane rf highway in the form of soldered silver strap on the chassis side reduce ESR? I would assume such things are much more critical on FETS, but I'd rather apply the best to anything I do in the shack. I have a couple of months time to get everything ready. Once the static is gone I have to make up for lost time operating and I dont want to have to go back inside the gear after each piece is done.

I've really lost a lot of tech knowledge over the last 5 years. I'm sure it shows in various ways but I'd rather just admit I don't know. my experiences has left my memories more like a block of swiss cheese, there's some things that used to be there that are now just holes with nothing.  very common thing after brain surgery and radiation.

steve_qix:
For Tube transmitters, the 100C or 100E series of capacitors are probably overkill !!  Unless you have an unusual situation (like Tempest or something like that), standard bypassing will probably work just fine.

I like using a few different value capacitors in parallel for serious bypassing of high current circuitry.  This puts several self-resonances in parallel, and can eliminate it.  This is very good practice for high current situations, but can also help stabilize amplifiers, and provide a more consistant reference point.  Anywhere where low impedance shows up, such as tube cathodes or heaters, a few capacitors in parallel works nicely to keep these at RF ground.

With some VHF MOSFET drivers, I've seen 10 different value capacitors in parallel used as a bypass !!  These are 50 ampere drivers looking into a .02uF load operating at 60mHz.  Nothing you're doing here - I used it as an example.

Of course, tube circuitry is very forgiving  ;)  I've used .001uF disk ceramic capacitors for bypassing tube cathodes in high power amplifiers (not a good idea, but I did it).  If I used the same caps in the bypasses for a 500 watt class E rig, they would melt down.  I have had orange drops explode in single-capacitor bypass applications in my early class E rigs.  Now, I use 3 of them in parallel (all different values), and everything runs nice and cool.  It really is something to see what high current will do to a "good" capacitor  :D

Regards,

Steve

w3jn:
Steve makes a good point - depends a lot on the impedance of the circuit.  A relatively high impedance circuit - the ESR of the cap isn't gonna make hardly any difference.  A very low impedance circuit, say class E rig, well, you need really good caps and very short leads and several in parallel.

The best caps are of course chip caps, having no leads.  You can get relatively high voltage chip caps (several KV, IIRC, in the latest Allied catalog) but of course they're really not suited to tube type point-to-point wiring.

Disc caps are prolly the best for tube bypassing, but not so great for coupling the final to the tank as they don't have a lot of current capability.

N3DRB The Derb:
I have a crap load of parts coming in for the Gonsets.  the one thing I'm missing is a pair of decent plate chokes. I have to rebuild the second amp to match the first. I keep going back and forth as to if I should try again with the bandswitch. I'm leaning heavy to say F that. it's too weak.

I think I am going to hardwire the tank for 75, put a hole plug where the bandswitch knob used to be. and test into the termaline for loading and wire one or both of the fixed padders in place so it loads as needed into 50 ohms.

tired of f'ing with it. make em make power on 75 and b done. 1000ma's on those 572b's and then drop the drive down apply audio and swing the monky. 225 carrier. put up the W7FG antenna and get on.

Update: I just ordered 2 new plate chokes custom wound from Frontier Engineering offa ebay @ 36 each delivered. I aint playin now.  8)

http://stores.ebay.com/Frontier-RF-Products

WA1GFZ:
Many TNX John. I used some of those blue caps you gave me on a project at work.
DDX

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