The gi7b is a decently easy retrofit that nets me about 1050w-1080w
out on most I forget what it is on 160, but lower-- maybe 990? More
annoying fits can be done and keep higher output, I was recently
thinking that gu74(?) (4cx800 like russian surplus one) but haven't
really looked into how much more that would be to do-- it ceratinly
would be a case mod as well for that one, and just about anything but
the gi7b that I know of really, even if it is a light bit of body work
like the 8874's.
I have been looking for another mla 2500 to do another fit on since I
"sold" the other to a friend. (sold like one day I might get money
for it...) I really like that little amp and want one for myself
again, but I haven't seen any reasonable lately. (i have seen some
that were reasonable considering they were already fitted for a 3cx800
or such, but not stock with or without tubes)
I did also find a box that I had for that one and lost before the fit,
that says on the side "working pulls" that is not in my writing.
Pretty sure they came with one along the way and were up in the top of
that closet for years. Maybe if he wants to sell one of them I can
actually find out if those are any good hihi. I could also do the fit
as a side job since I really do like doing it, but I don't know how
quick I would be to get it back. (was only half joking about buying
one of them though for my own fit though if he wants to sell one)
-- Ryan w8cya
On Wed, Mar 3, 2010 at 1:05 AM, Roger <sub1@rogerhalstead.com> wrote:
>
>
> 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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