[VHFcontesting] 3cx800a 222 amp

[David Pruett]

The details for removing the grid collet fingers are shown in the ARRL 
UHF/Microwave Projects Manual, Volume 1 for the K1FO single and dual 
tube 432 MHz 3CX800 amps, and the 432 MHz 8938 amp.  Not sure how this 
would relate to K8RYU's original question in a 222 MHz application, but 
at least the illustrations clearly show the grid fingers and describe 
how to break these off.

73, Dave/K8CC


On 10/20/2015 4:37 PM, Dave Olean wrote:
>
> 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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