Jim Thomson wrote:
> I have a buddy with TWO MLA-2500's..... and both now with flat/bad tubes.
>
> I believe one of them has a tuned input, and the 2nd one does not.
>
> Is the tube really unavailable ?
If you are asking if they are still in production, they are not. They
are occasionally available on e-bay where you pays your money and takes
your chances. There are a pair of supposedly unused ones with less than
a day to go on there right now for $599 which for a pair, if good, is a
reasonable price.
> If so, what are his options ?
Modify?
> What other tube[s] can be retrofitted ?
>
>
The 8873 (conduction cooled), 8874 (axial cooled and 400 watts
dissipation) , and 8875 (transverse cooled stock tubes) are idential
electrically and pin wise. The 8873 and 8875 are no longer in
production. the 8874 is, but there are two problems. They are expensive
and would require a different cooling arrangement with considerably more
air than the MLA stock configuration can provide.
> What is the easiest retrofit available ?
Probably the GI7B although I don't think it runs as much power as the
the 8875s did and I am not familiar with the IM products from that
tube. The plate dissipation is 350 watts or 700 watts for a pair which
with good efficiency would be enough for the legal limit. I don't recall
seeing conversions running over about 1 KW which is still a healthy
signal for a pair of tubes that cost about $35 each.
You need some one more familiar with the tube than I to come up with a
real figure on what to expect for output.
The conversion is pretty much straight forward, the amps AND tubes are
cheap, so to me it's an attractive conversions, but whether there is any
one who will do it for him at what he considers a reasonable price?
OTOH it's likely the GI7Bs will not remain so cheap and readily
available forever.
I'm sure, sooner or later some one will come up with specifics for the
conversion such as power out and the IM products (quality of the
resulting signal)
73
Roger (K8RI)
> Does anybody do these retrofits as a sideline ??
>
> later... Jim VE7RF
>
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