[Amps] 2x813 or 2x3-500zg ?

[EP Swynar]

On 31st December, Mike wrote...

 "... I was thinking about two 813 in grounded grid configurations but now
I'm thinking why not the pair of 3-500zg from RF-parts? I newer used 3-500zg
before so I can't compare it to 813. I understand the difference in pricing
but I also know it's easy to buy matched set of 3-500zg but it's just
impossible to find matched pair of 813."


 ******************************************

 Hi Mike,

 Well, I would NOT say that it's impossible to find a matched pair of
813's --- far from it!

 I have never purchased a "new" 813 here, yet whenever I need replacements
for my 2x813 amplifier (which, BTW, happened only ONCE in 17+ years of near
daily operation!), I simply reach into my junque box collection of donated
813's / Hamfest acquistions / etc., and place them into my amplifier one at
a time, taking note of each tube's resting current (i.e. full B+ voltage
applied, no excitation)...

 I then mark the metal base shell of the tube with the current value in ma.,
and go on to the next one. I continue this until I find two that are very
close to one another. Once I find two such tubes, I'm off to the races.

 Tube brands don't matter --- it's the resting current that I find to be
critical here, a lesson that was painfully forced upon me to learn many
years ago, when I attempted to get my very first HB kilowatt on the air, a
4x811A grounded-grid set-up (have you ever seen holes in tube plates the
size of your baby finger nail...?! Hi Hi).

 ~73~ Eddy VE3CUI - VE3XZ