"I think" the GI-7B would be an easy tube to convert to transverse
cooling to replace the no longer available Eimac tubes in the
MLA-2500s. The coolers are easily replaced by removing a single screw.
A lathe and mill could easily build custom radiators. It'd be a simple,
straight forward conversion. IM products?
73, Roger (K8RI)
On 12/27/2017 Wednesday 9:59 PM, Stan Gammons wrote:
How does one go about identifying what mfg made the Russian tubes? The
GI-7BT's I have have purple ceramic. They have some marking on them,
but no mfg name.
One of these days I'll get around to building the amp using the pair
of GI-7BT's...
73
Stan
KM4HQE
On 12/27/2017 08:46 PM, Jim W7RY wrote:
They were probably Burle brand? They were famous for pink ceramic.
RCA made a few too.
73
Jim W7RY
-----Original Message----- From: Alek Petkovic
Sent: Wednesday, December 27, 2017 8:42 PM
To: AMPS
Subject: Re: [Amps] Life of tubes in ham service
On 28/12/2017 8:21 AM, Carl wrote:
I have used a scope to monitor filament voltage on a large number of
commercial amps and have yet to see one where the filament
transformer or winding does not do an excellent job of limiting inrush.
If the HV hasnt been recapped with over 25-30 uF total that
transformer or winding is also a good inrush limiter also offering
switch protection..
If spending money is of no concern then by all means buy whatever
keeps you happy amd hope you do a very good job installing it..
Any old tube, today or in the future should be brought up on a
Variac to be sure it hasnt gone partially to air which will not show
up initially on a glass envelope. NOS US built 3-500Z's are already
becoming scarce as are 4-400A's which can often be easily adapted.
The 4-250A can be used at reduced power at the same voltages as the
only difference is the anode construction; the PL-175A also shows up
at times as well as various 4 digit numbers for the others.
IF OK then bring the filament, plus HV up slowly to about 1200V and
look for the telltale glow of outgassing. Do notkey the amp and
never with RF at this stage. With amps using the old CW/SSB switch
about 1800-2000V in the CW position is the norm and if the gas is
not excessive it will not cause an internal arc.
In all amps I highly suggest a HV surge, aka glitch, resistor sizeed
to limit fault current to a safe level and allowing fuses or
breakers to blow. A 25 Ohm 50W Vitreous Enamel resistor is the ONLY
choice I suggest (25W on SB-200, AL80's power level is fine) as it
will absorb the high current without self destructing as does sand
type or other cheap substitutes.
Ceramic/metal tubes are not immune to outgassing but that is limited
to a small variety...at least this year. Id be worried about Russian
and Chinese offerings.
The technicians at the now defunct Coastal Shipping station, VIP, here
in Western Australia, said that the finest 4CX250/350 type tubes they
ever used, were the purple ceramic Russian ones. The best life and
lowest leakage. At the time, they were not easy to get but they said
they were miles better, in all respects, that the Eimac versions.
I've not had any personal experiences to confirm or dispute their
findings.
73, Alek.
VK6APK
Philips and other mainline EU tubes seem excellent IMO but I havent
tested enough types to be 100% sure.
There are several ways to regetter a tube which is a different
subject I have detailed many times over many decades..Perhaps
someone has preserved a file.
Carl
KM1H
Amp service since 1964
----- Original Message ----- From: "Leigh Turner"
<invertech@frontierisp.net.au>
To: "'Rob Atkinson'" <ranchorobbo@gmail.com>
Cc: "'AMPS'" <amps@contesting.com>
Sent: Tuesday, December 26, 2017 5:27 PM
Subject: Re: [Amps] Life of tubes in ham service
Rob, I concur with your succinct sentiments here about transmitting
tubes.
The only proviso I would make is the inclusion of a soft-start
mechanism on
the filaments to bring them up slowly in a controlled manner at
initial
switch-on; and ensure the filament voltage as measured at the
socket pins is
tightly within manufacturer's specification.
73
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Rob
Atkinson
Sent: Wednesday, 27 December 2017 3:45 AM
To: amps@contesting.com
Subject: Re: [Amps] NXP 65V LDMOS 1K80H-1800W
"What happens when they quit making tubes?"
For some tube types that happened decades ago. But you can still find
plenty of good 810s etc. decades later.
In other words, what happens when no tube of any type is made?
Answer: Not much, except prices may go up.
What happens when tubes no longer exist?
Not our problem because we'll all be SK.
Why are you so flippant?
Because millions of tubes have been made and for ham use, a pair of
3-500Zs (to use them as an example), will outlast all of us _if they
are treated properly_.
That's the rub. Broadcasters wear out tubes because they run them day
and night non-stop for a year or two and they lose emission.
Hams don't do that. The only time a tube wears out in a ham rig is
when hambone abuses it, usually by running too much plate current or
grid current.
Most common is the single 3-500 "Kilowatt amp" that pisses away 3-500s
every 3 years or so. A certain manufacturer should get a medal from
the Chinese company making 3-500s these days.
If you know how to run your tubes, they'll be running after you are in
the ground.
73
Rob
K5UJ
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
---
This email has been checked for viruses by AVG.
http://www.avg.com
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
--
Roger (K8RI)
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|