I think it might fit, just about, There is about 73mm clearance from the
tops of the 8874's to the cabinet of the 78. The 8877 measures about
43mm taller than the tiny 8874. so there would still be a good bit of
clearance.
Reworking the plenum would seem a reasonable requirement. This could be
made larger also by removing the stock blower and mounting something
more appropriate on the rear of the cabinet. Suitably designing the
plenum should allow for a 50mm x 50mm or similar sized opening. Even
quite a large blower should not protrude above cabinet height. A
toroidal filament transformer might go where the removed blower was and
allow nice short leads.
The HT is woefully short however but there seems enough current for
overall power. People who have done the conversion to 3CX800's say they
can get plenty of power so perhaps a doubler from 2000 to 4000 volts at
appropriately reduced current might not be such a bad compromise.
However this is all quite a bit of work for a tube which, yet again, is
becoming somewhat precious. Replacement 8874's can still be had, just,
at around US$1500 for the 3, 3CX800's at around US$1000 a pair and
8877's at circa US$500-800 (*) depending on source. Not outrageous but
not pocket fluff either. Still there are no tubes which can achieve this
degree of performance and likely available for the next 50 years at
US$50 a piece (**).
The 3CX3000A7 is indeed an interesting choice though I think that really
is too big for the 76/78 chassis without a top hat. Given how many 76/78
amplifiers are out there that could be otherwise consigned to the B.E.R.
pile it might not be such a big deal. Taller custom front panel and a
taller custom wrap around top cover, an extra 100mm might be enough. Re
designed plenum and external blower. Voltage doubler on the power supply
which might be sufficient power for 1500 watts SSB service or a custom
transformer to take account of the increased space from the taller cabinet.
It might be easier than a full home brew since a lot of the parts are in
place but still probably beyond the average US extra class ham these days.
I have a Henry 2k console that is a bit of a semi basket case. The
3CX3000A7 might be a tempting retrofit. It is the Classic Export version
so has the super HD transformer. But at 9 inches high the Henry is still
too short for such a tube. The cabinet butchery required would seem a
bit extreme.
Martin, HS0ZED
(*) Based on prices I have been able to source, YMMV.
(**) Not that I've been able to identify, YMMV.
On 07/11/2019 08:46, Alek Petkovic wrote:
A taller cabinet and I would suggest a heftier blower.
73, Alek.
VK6APK
On 7/11/2019 5:48 AM, Steve London wrote:
Okay....I'll be stupid....
Besides the filament voltage and socket, what else would it take to
convert something like a 3 tube Alpha 76 to a single 8877 ? Seems
like the output Z is in the right ballpark.
73,
Steve, N2IC
On 11/06/2019 02:26 PM, Jim wrote:
Agreed! 8877 is one the the BEST tubes for ham radio.
LOTS of them out there and available. Hams bought many of them for
spares that never got used; Because the 8877 was such a robust tube.
Most 8877 tubes got babied... Except for contesting... But there is
testimonial from K3LR's large and busy contest station below. So
even in a contesting environment, the 8877 goes STRONG!
8877/3CX1500A7 hard to beat!
Thanks
73
Jim W7RY
On 11/5/2019 8:34 PM, Tim Duffy wrote:
Hello Jim,
I agree - the 8877 - 3CX1500 is a VERY good Ham Radio tube. I have
several in service here at K3LR that are 30 years plus years old.
18 amplifiers here using 8877s that make 1500 watts output RTTY
with high TX duty cycle - no problem - all the way to 220 MHz!
The 8877 is an excellent engineered tube for amateur radio - easy
to build amplifiers with the 3CX1500A7.
73
Tim K3LR
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of MU
4CX250B
Sent: Tuesday, November 5, 2019 9:12 PM
To: Carl
Cc: amps@contesting.com
Subject: Re: [Amps] GS35B Amps Common Problem / few more comments
You may be a bit harsh, Carl! I’ve lost two 8877s in the past half
century or so, and it was my fault both times. The first was when I
stupidly let the filament voltage drop way below specs, and the second
was when the blower on my Alpha 9500 failed and I didn’t notice for
two weeks. My workhorse homebrew amp, built in the 1970s, has an Eimac
8877 with a 1978 date code. Still full output, 4300V on the anode.
73,
Jim w8zr
Sent from my iPhone
The 8877 is a fragile short life wannabee befitting an oxide
cathode tube
Carl
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