As far as I remember you can not run 4X500´s in zero bias GG,
you will not be able to get correct ZSAC for linera operation.
4X500´s need screen and grid voltages to get correct operating
point.
4-250A or 4-400A or C is OK in SB-220. Just tie all grid pins together
and ground them directly, also you must short out the "bias"
zener diode to get correct ZSAC, maybe adjust with a string of
diodes to get correct ZSAC.
73 Jim SM2EKM
PS: Think I remember that some 4-400´s was a bit too tall for
the PA compartment lid to fit, 4-250A is never a problem.
---------------
Hsu wrote:
> Thanks Peter!
> I have got a a died TL922 as a junk,I only pay $100 for it.so I don't
> want pay for it too much.Althought the 3-500Z are made in China, but I call
> the factory, They ask me pay $500 for a matched pair!Mr.Richard L. Measures
> have mentioned in the list that 3-500Z can replace by 4-400(need some
> work),I have a pair 4-400C, but I just test them, they all died!in this
> weekend, I check my junk box, and find out some NOS Chinese FU-500Fs(same as
> 4X500A) and its socket, I just read its datasheets , I found the screen and
> grid dissipation power not too small, so,I think maybe it can work in GG and
> cathode drive.It have same volt and cureent of filament as 3-500Z.
> 73! Hsu
>
>
> ----- Original Message -----
> From: "Peter Chadwick" <g3rzp@g3rzp.wanadoo.co.uk>
> To: "Hsu" <Jbenson@sohu.co>; <amps@contesting.com>
> Sent: Sunday, July 23, 2006 7:14 PM
> Subject: Re: [Amps] 3-500Z convertion
>
>
>
>>Hsu said:
>>
>>>My TL922's 3-500Zs died,I have some 4X500As,it seems the 3-500Z can
>>>convertion by 4X500A, <
>>
>>The 4X500A is an external anode tube, so the cooling won't be right, it needs
>>a different socket, and it's a tetrode. You'd need to do soem careful
>>calculation to determine if the grid and screen dissipations would be
>>exceeded. All in all, i'd say buyin a pair of new 3-500Z is a better way to o.
>>73
>>Peter G3RZP
>>
>>
>>
>>
>>
>>========================================
>>Message Received: Jul 23 2006, 11:54 AM
>>From: "Hsu"
>>To: amps@contesting.com
>>Cc:
>>Subject: [Amps] 3-500Z convertion
>>
>>Hi, I'm a new member.My TL922's 3-500Zs died,I have some 4X500As,it seems the
>>3-500Z can convertion by 4X500A, Does anyone have this experience?Thanks in
>>advance!
>>73! Hsu
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>
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