[Amps] HB Amp Parts, Values & Sources?

rlm r at somis.org
Thu Sep 11 12:46:41 EDT 2003

>A couple parts questions for a small home-brew (2x) GI-7B triode hf amp
>project I'm thinking about, please???  
><1> Plate Bypass Capacitor
>I've noticed values ranging from 1000pf up to 5000pf (2 x 2500pf) for
>the Plate Bypass Capacitor in several amp designs...  This works out to
>a reactance of from 88.42 ohms at 1.8-MHz for 1000pf, to 17.68 ohms for
€  under 20-ohms is a fair bypass.

>What is the best value for this bypass capacitor or does it depend on
>which tube(s) you're using and all of the 'network' impedances you're
>working with...
><2> Plate Bypass Capacitor
>What types of capacitors can I use for the Plate Bypass Capacitor??? 
>I've seen door knob ceramics as well as disc ceramics being used... 

€  discs work ok. 

> I
>noticed in the 4CX1600B project in my 2001 Handbook that the author
>specifies two 2500pf 10kv ceramic door knobs, Newark #46F5253, but when
>I looked up that Newark part it was a 2500pf 10kv disc ceramic (z5u)... 
>Is this another typo' in that particular article???
>Anyone have a good source for 2000pf 10kv door knob z5u ceramic parts???
><3> Plate RF Choke
>I noticed in that same 4CX1600B project in the handbook that the author
>purchased a Plate RF Choke from Command Technologies...  I'd like to run
>this amplifier on 160 through 10, including WARC bands, and I'd like to
>make sure the choke I end up with isn't resonant near any of those
>frequencies...  Any recommendations, sources, prices???

€  I would roll my own and park the resonances with a dipmeter.  Details 
on HV-RFCs are on my Web site under "Amplifiers".
><4> Filament Choke
>Hopefully there's nothing real exotic here...  Two GI-7B tube filaments
>will run 12.6vac at 4.0amps...  I suspect a bifilar wound choke is the
>best way to go 

€  true

>and if I could get one designed for 5.0 or 6.0 amps,
>instead of 30.0 amps (grin), I suspect it would be physically much
>smaller than a 30.0 amp choke...  Recommendations, sources, prices??? 
€  solenoid would be my choice;  #18 Cu woiuld do.
>I'm sure I'll have plenty of questions if I decide to start the
>I'm thinking about a custom Hypersil transformer with 820vac @ 1.0amp
>CCS for the plate supply (doubler)...  I looked at 1640vac @ 0.5amp but
>the transformer ends up being quite a bit larger for the same VA
>rating...  Is this because of the voltage breakdown spec' of the
>transformer windings, or something like that???

€  Using the same amplifier tube/s, a HV transformer - for FWB service 
requires more paper than a transformer for FWD service.   Since less 
paper leaves room for more Cu, the FWD transformer can be more compact.  
The tradeoff with a FWD is that it won't work with a resonant-choke 
>I ordered tubes (they're "cheap") and I'm anxious to start machining
>sockets...  Though, I'm still not certain about starting the full-blown
>I apologize for the long-winded note and I appreciate the collective
>wisdom represented here on "the list"...
>Very 73, Mike - K8LH (Westland, MI)...

More information about the Amps mailing list