I take my transmitting tube tester to hamfest and test tubes before I
buy them.
People have brought me tubes they have purchased to test as well.
Many of the 813's that I tested not been so good. Just about all of them are
WWII surplus. If they are unused they usually are good but used ones are
often bad either
gassey or have low emission.
My first large amplifier was a pair of 813's GG zero bias around 1965.
New cheap tubes were available then. I later changed it to a
pair of 250TH in Grounded Grid with some bias. Both worked well driven
by my modified for AB1 homebrew 6146B CW transmitter driven by a
CE-20A.
After that I scaled down to a pair of 4CX250Bs in AB1.
Same exciter.
Now have a HB 4-1000A amp, a Thunderbold, Desk KW and
30S1. I want to get back to building higher power RF stuff but have
too many other things that need to be done.
>
>
> At 04:02 PM 3/28/2011 -0400, you wrote:
>>Use Google.. you'll find all the 813s you want... I just did and found a
>>bunch with prices that vary from $25 to $455....
>>
>>Wa3gin
>>
>>-----Original Message-----
>>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>>Behalf Of Fuqua, Bill L
>>Sent: Monday, March 28, 2011 3:51 PM
>>To: Diane & Edward Swynar; amps@contesting.com
>>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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