There are so many 813 resource in China ( NOS and factory new ) that I'm
designing 2x813 GG amplifier
73!Hsu.
----- Original Message -----
From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
To: "Diane & Edward Swynar" <deswynar@xplornet.ca>; <amps@contesting.com>
Sent: Tuesday, March 29, 2011 3:51 AM
Subject: Re: [Amps] Homebrew is back..
> Good 813s are often hard to find on the market since most used ones have been
> abused.
> Other possibilities are 4 parallel 4CX250Bs with 50 ohm load resistor on the
> untuned input or
> a 200 ohm with a 1:2 turns ratio transformer.
> I really like the 4-1000A in GG but it is a bit bigger and uses much higher
> plate voltage.
>
> Instead of 813's a good possibility and rather cheap are 4-125As or 6155.
> Same plate dissipation
> and work well in gg as well. On Ebay usually very cheap new because
> practically on radios use them
> and even better yet the same sockets will allow an easy upgrade to 4-250A,
> 4-400A or even 3-500Z tubes.
> If you use over rated parts you can migrate to higher power very quickly
> using these tubes.
> Also, some are not aware that 4-250A and 4-400A tubes have the same
> electrical characteristics except the
> 4-400A has higher plate dissipation due to the fins added to the plate.
>
> 73
> Bill wa4lav
>
> ________________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf Of
> Diane & Edward Swynar [deswynar@xplornet.ca]
> Sent: Monday, March 28, 2011 4:34 PM
> To: Roger (sub1)
> Cc: amps@contesting.com
> Subject: Re: [Amps] Homebrew is back..
>
> Hi Roger,
>
> Nice note---thanks!
>
> Yes, the 813 has cost advantages, alright---but you have to jump through
> some hoops in order to make them "play" on 15- and 10-meters efficiently,
> because of the high interelectrode output capacitance of them (ex. on
> 10-meters, a paralleled pair display a total of, I believe, 28-pfd., which
> is actually more than the plate tuning capacitor value needed on that
> band!).
>
> Makes you wonder how that fellow you mentioned got away with FOUR in
> parallel! (maybe his was strictly a low-band design...?).
>
> What I did here with mine is employ a 25-uh. 1/4" edge-wound copper ribbon
> variable inductor as a pi tank coil...and I incorporated a rugged ceramic
> Centralab "bandswitch" that allows me to REMOVE the plate tuning cap out of
> the circuit entirely. I then RESONATE the final tank on 15- and 10-meters by
> varying the "L", and using the high interelectorode "C" as a "built-in"
> capacitor.
>
> For 10-meters, though, there's another step that needs to be taken: I switch
> in a 0.3-uh. silver-plated 1/8" copper coil in series with the paralleled
> plates, to act as an RF transformer of sorts. It's all detailed in my 1985
> ARRL HANDBOOK, which references the issue of QST that the idea came out
> of...
>
> It's a bit of an exercise, to be sure, but the work-out entails one's GRAY
> matter, and NOT one's pocketbook! Hi Hi. I think it's worth it.
>
> ~73~ de Eddy VE3CUI - VE3XZ
>
>
> *******************************************
>
>
> ----- Original Message -----
> From: "Roger (sub1)" <sub1@rogerhalstead.com>
> To: "Diane & Edward Swynar" <deswynar@xplornet.ca>
> Cc: <amps@contesting.com>
> Sent: Monday, March 28, 2011 2:04 PM
> Subject: Re: [Amps] Homebrew is back..
>
>
>> On 3/28/2011 3:38 PM, Diane & Edward Swynar wrote:
>> > Hi Roger et al,
>> >
>> > I use a pair of 813s in parallel grounded-grid service here in my
> homebrewed
>> > KW amplifier, and---I'm blushing as I type this!---but I have NEVER EVER
>> > purchased any of the jugs that are in it, or the spares that I have
> here,
>> > brand new...
>> >
>>
>> I forgot the old 813. I have 3 of them up on the shelf and keep looking
>> for more.
>> I used to run the "old legal limit" with a pair of them as you
>> describe. I ran into a guy on 40 a while back who claimed he could get
>> 2400 PEP out of 4 of them. I don't know if his amp was a monoband or
>> covered all of the HF bands.
>>
>> I see the GS-31 (1KW), GI-46 (1KW), and little GI-7B are at reasonable
>> prices and seem popular. With the removable anode coolers on this
>> series and the popularity of converting the old Dentron MLA2500B to a
>> pair of GI-7Bs that no one has machined a transverse version of the
>> cooler to make them even more compatible with the old 8875s I think they
>> used.
>>
>> > They are all either Hamfest finds, or freebies from friends.
>> >
>> > Life's far too short to pay-off a retiree's ransom for new& exotic
>> > tubes---
>>
>> AMEN!
>>
>> > and I have yet to hear anyone at the DX end of my QSOs asking me (or
>> > expressing any care whatsoever) which tube(s) I might be using! Hi Hi
>>
>> There does seem to be a lot of interest in what tube(s) are in homebrew
>> amps though.
>>
>> 73
>>
>> Roger (K8RI)
>>
>>
>> > ~73~ de Eddy VE3CUI - VE3XZ
>> >
>> >
>> > **********************************************
>> >
>> > ----- Original Message -----
>> > From: "Roger (sub1)"<sub1@rogerhalstead.com>
>> > To:<amps@contesting.com>
>> > Sent: Monday, March 28, 2011 1:11 PM
>> > Subject: Re: [Amps] Homebrew is back..
>> >
>>
>>
>
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