It is not a question of money or to put some other types of tubes.
It is a question of using only one 3-500Z in this amplifier and what I
have to change to realise this not more !
Of course I have to change the filament transformer into a 5VAC version
because originally both 3-500Z's are in series on 12VAC !!
Regards Jean ON4AEF.
On Tue, 26 Jan 2010 14:20:24 -0800 (GMT-08:00), Colin Lamb
<k7fm@teleport.com> wrote:
> "A. A new 3-500Z costs around $150
> B. The grids are not grounded in a TL-922.
> C. I dont think there is top clearance for a 4-400"
>
> The ham raising the question was not in the US and tubes may be more
> difficult and expensive there. The fact that the writer was willing to
put
> in a new filament transformer to run one tube rather than two implied
that
> purchasing a replacement 3-500Z tube was not an option. I do not know
his
> finances, but I have been in countries where $150 is a years income for
> some.
>
> No, the grids are not grounded directly, but pins 2,3 and 4 can be
> strapped together and will work.
>
> I thought the 4-400 is the same height as the 3-500Z. I have
substituted
> directly in the SB-220 with no problem.
>
> Colin K7FM
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