Hi Mike, et. al:
The amplifier you are describing is similar in power and voltage to the
SB-200, but using different type of triodes.
#3 I would go to RF Parts for the plate choke: about $24.00 for a choke
rated up to 4KV at 1+ amps. It is the one Ameritron uses in their AL1200 +
AL1500 amps. Mine is noted to have a resonance only at 12 MHz, but also has
a resonance at 16 MHz. No problem, as the resonance is sharp enough to not
bother 14 or 18 MHz.
#1 I assume you mean plate coupling capacitor. Usually about 2000 pfd
does the job down to 160, although Dentron used only 1000 pfd in the MLA2500
amplifiers. I think you have choices, and since you will have only about
2KV on the tubes, a pair of 1000 pfd doorknob capacitors at 5KV will do.
Alternately you can use maybe 4 disc ceramics, 500 pfd at 6 KV in parallel.
These are also in the R F Parts catalog. The disc ceramics are about $2
each and the door knobs are about $15 each. If you look at the new Ten Tec
Titan III amplifier web site you will see a circuit board with disc ceramic
capacitors in parallel for coupling the RF from the plates to the plate tank
circuit, so TenTec has gone the disc ceramic route to keep price down. R F
Parts also shows an Erie ceramic door knob: 1900 pf at 15KV for about $16.
if you want to avoid paralleling components. Maybe that is the best choice.
#2 For plate choke bypass capacitor use a couple of the 1000 pf at 6 KV
or 1500 pf at 3800 volts - about $2.00 each in the R F Parts catalog. At
160 meters, if you have too much grid current at proper resonance, add
another disc ceramic or two.
I hope this helps. 73, George K8GG
----- Original Message -----
From: "Mike, K8LH" <k8lh@kramerairtool.com>
To: <amps@contesting.com>
Sent: Thursday, September 11, 2003 3:59 AM
Subject: [Amps] HB Amp Parts, Values & Sources?
>
> Gentlemen:
>
> 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
> 5000pf...
>
> 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... 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???
>
> <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 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???
> Toroidal???
>
> ---------------
>
> I'm sure I'll have plenty of questions if I decide to start the
> project...
>
> 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???
>
> 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
> project...
>
> I apologize for the long-winded note and I appreciate the collective
> wisdom represented here on "the list"...
>
> Very 73, Mike - K8LH (Westland, MI)...
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>
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