[Boatanchors] EF Johnson thunderbolt

[KA2PTE]

Yep, I believe some or all the issue was the neutralizing cap C2, I 
inspected it the other night
and heres what the inside of the stationary section looked like:

https://www.mediafire.com/view/u4e6nqk0tj872ql/c2.jpg/file

the movable center piece also had some kind of gunk on part of it which was 
coming between the 2
electrodes of the cap. The aluminum as also really dusty and dulled, so I 
brightened it up inside and out with
scotchbrite and used some sandpaper to deburr the pits the zorching made.

I am fairly certain there was enough buildup to alter the capacitance spec 
which is like 2-11pF.

It seems to be the same as this Johnson  N250:
https://www.ebay.com/itm/EF-Johnson-N250-High-Voltage-Neutralizing-Capacitor-2-9-12-pF-NOS-w-Box-/184497035511

Which is all good, however in case there's more to it, and this worstens 
things, and the choke smokes faster, I rather be prepared.


--
Steve Hearns
KA2PTE



----- Original Message ----- 
From: "Rob Atkinson" <ranchorobbo at gmail.com>
To: "KA2PTE" <ka2pte at 3950.net>
Cc: "Boat Anchors List" <boatanchors at mailman.qth.net>
Sent: Sunday, July 04, 2021 12:32 PM
Subject: Re: [Boatanchors] EF Johnson thunderbolt


> You need to find out what's causing the oscillation and shut it down
> instead of running through chokes.  One idea is to make sure ground
> bonds to chassis are all low resistance, i.e. around 1/2 ohm.
>
> 73
> Rob
> K5UJ
>
> On Sun, Jul 4, 2021 at 10:21 AM KA2PTE <ka2pte at 3950.net> wrote:
>>
>> Curious if by chance anyone has any of the 2.5mH RF chokes used in this 
>> amp?
>> L8,9 and 10 are all the same.
>> https://www.mediafire.com/view/4mu4pddwi7vacxu/L8.jpg/file
>>
>> I got some new ones at RF parts.com, but am on my last one as I have a
>> parasitic osc from tuned grid to plate happening that is eating these up.
>>
>> --
>> Steve Hearns
>> KA2PTE
>