[VHFcontesting] 3cx800a 222 amp

[Dave Olean]

Hi Bill et al.
The one I remember was the grid collet for the 8938 on 432. It needed a 
slight bit of inductance for best neutralization.  I remember that Steve 
figured it out, although the amplifier worked fine without it, you would see 
some drifting in the power output, no doubt due to some regeneration in the 
grid crcuit. After removing a small number of fingers from the grounded 
collet, the amplifier was much more stable as far as power output went. When 
I got the tube initially, W6PO indicated that it had flunked the stable 
power output test and was rejected for an order to the Swiss gov't. The 
tubes were for remote unattended sites where the tubes would normally be off 
until required and then had to reach full power from a cold start. Bob 
indicated that with use the tube would probably improve and be just fine. I 
did see power drift, which improved, but, by removing teeth from the finger 
stock, it got really stable. Now I do not notice much drift at all. I think 
Steve removed every fourth finger. I could always take the 432 KW apart and 
look at the grid ring!

Dave K1WHS

----- Original Message ----- 
From: "Bill Olson" <callbill at hotmail.com>
To: "terry price" <w8zn54 at verizon.net>; "VHF Contest Reflector" 
<vhfcontesting at contesting.com>
Sent: Tuesday, October 20, 2015 4:48 PM
Subject: Re: [VHFcontesting] 3cx800a 222 amp


> yeah, duh, I was talking about the grid collet!! so where I said "cathode 
> connection" was just me being stupid, what I MEANT was I seem to remember 
> there needed to be just a little inductance in the grid connection, so 
> with homebrew collets you had to diddle with the number of fingers a 
> little..
>
> bill
>
>
>
>> From: w8zn54 at verizon.net
>> To: callbill at hotmail.com; vhfcontesting at contesting.com
>> Date: Tue, 20 Oct 2015 12:39:16 -0400
>> Subject: Re: [VHFcontesting] 3cx800a 222 amp
>>
>> I've built several 3CX800A7 222 amps and the cathode circuit that was 
>> used
>> on the 8874 version was the same. The plate line changed.
>>
>> Terry - W8ZN
>>
>> -----Original Message-----
>> From: VHFcontesting [mailto:vhfcontesting-bounces at contesting.com] On 
>> Behalf
>> Of Bill Olson
>> Sent: Tuesday, October 20, 2015 12:00 PM
>> To: VHF Contest Reflector
>> Subject: Re: [VHFcontesting] 3cx800a 222 amp
>>
>> Ralph, I'm really straining my brain here, but I seem to remember these
>> triodes wanted a little inductance in the cathode connection to 
>> "neutralize"
>> them. I remember with an 8874 on 220 back 35 or 40 years ago I build a 
>> home
>> made grid collet with finger stock.. The finger stock was in a solid ring 
>> at
>> first but in order to make the thing work I had to keep bending fingers 
>> away
>> from the grid ring on the tube.. That's all I remember, don't have that 
>> amp
>> any more..
>>
>> Steve, W1SMS, now owns and runs Lunar Link, I'm sure he has the info you
>> want..
>>
>> bill, k1DY
>>
>> > Date: Tue, 20 Oct 2015 11:23:01 -0400
>> > From: mathenyr at marietta.edu
>> > To: vhfcontesting at contesting.com
>> > Subject: [VHFcontesting] 3cx800a 222 amp
>> >
>> >
>> >
>> > I remember reading that there was a K1FO 222 amp using a single
>> > 3xc800a7 tube.  I have tired to get such an amp to behave without
>> > success...cathode circuit problems.
>> >
>> > Does anyone know if the K1FO amp description was ever published?  Does
>> > anybody have one of the amps who could send me a copy of a manual or
>> > perhaps photos??
>> >
>> > Also looking for a proper grid collet for the thing...
>> > Eimac 720359 ...  anybody know a source?   The grid collet
>> > may be my problem, but I am on my second "hamstyle" version and
>> > getting frustrated.
>> >
>> > The 2M version of the thing worked first try....
>> >
>> > Thanks..
>> >
>> > de K8RYU
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