Actually -
The problems with the filaments of the 3-500z tubes
were NOT confined to the SB220 amps vack in the 1960
and 70 era. The problem also occurred in the Drake
L-4B amps.
The solder would literally melt out of the filament
pins on the tube.
A change in sockets did NOT resolve the problem.
EIMAC eventually admitted that there may have been a
bad run on the tubes and agreed to repair the base of
all the 3-500 tubes we were having a problem with.
The fix (removing the base and re-soldering with a
silver solder, resolved the problem.
73,
Jay/AF2C
--- Martin Sole <msole@loxinfo.co.th> wrote:
> I wonder, would it so happen that the mounting holes
> for the SK-410
> might just be the same as those for the Johnson 275?
> I think real
> sockets might have made it on to my list for the
> Henry rebuild file.
>
> It does sound like the less than ideal Johnson style
> sockets coupled
> with the Phenolic base ring on later 3-500Z's might
> well lead to a
> situation in some amps that produces less than ideal
> amounts of air over
> the tubes. Since my ambient everyday shack
> temperature runs around 30C I
> need all the help I can get.
>
> Martin, HS0ZED
>
>
>
>
> Robert B. Bonner wrote:
> > Martin, Terry, Group,
> >
> > Good morning guys. Like I have mentioned before
> when I was back at the RADIO
> > SHOP (Drake Collins Kenwood, Yaesu etc factory
> service) while in college in
> > the late 70's I had to perform surgery on a lot of
> SB-220's.
> >
> > History Lession:
> >
> > The Johnson sockets had been designed for the
> 4-65, 4-125 and not even the
> > 4-250 sized tubes let alone the 4-400's. Since
> the 3-400 and 3-500 plugged
> > in directly many ham manufacturers cut corners and
> put the $5 sockets in
> > instead of the much more expensive aluminum Eimac
> airsystem sockets for the
> > 4-400 or the fancy less expensive SK-410's.
> >
> > The original Drake L4's had Sk-410's the L4B the
> Johnson sockets, cheapo.
> >
> > Well the amplifiers where where air blew sideways
> across the tubes and pins
> > instead of through the sockets or didn?t have
> enough airflow due to NOISE
> > CONCERNS developed a syndrome.
> >
> > Somewhere along there we also got the 1500W output
> increase. These two amps
> > were 2KW PEP input amps. When operated at balls
> out power the TUBES didn?t
> > cool adequately and got hot enough to either melt
> the solder out of the tube
> > pins, or take the temper out of the socket
> retainers which then caused a
> > high-z situation that melted the pin solder on the
> filaments.
> >
> > THE PHENOLIC Pin holder base Eimac put on the
> 3-500Z was there to stabilize
> > the pins and ad some cooling flow if this
> situation arose. (Cheap fix)
> >
> > However in the normal air system socket base it
> blocked the airflow
> > slightly.
> >
> > Syndrome Fix:
> >
> > If you are resoldering pins in 3-500's bases, you
> have to be very careful to
> > not melt the tube base seal.
> >
> > I did this by heating the removed larger pins with
> a torch in an old tube
> > socket and setting a tube with clean and fluxed
> pins into solder bath filled
> > pins and allowing to cool. If you have a lot of
> repairs a steel fixture
> > could be machined to effect the repairs.
> >
> > It has been noted here that the spring clips can
> be individually replaced on
> > the sockets, I preferred to replace the whole now
> $20 socket.
> >
> > You guys are right on it.
> >
> > BOB DD
> >
> > -----Original Message-----
> > From: amps-bounces@contesting.com
> [mailto:amps-bounces@contesting.com] On
> > Behalf Of Martin Sole
> > Sent: Tuesday, February 06, 2007 5:13 AM
> > To: terry@g4amt.com
> > Cc: amps@contesting.com
> > Subject: Re: [Amps] 3-500z - intermittent filament
> >
> > Hi Terry,
> >
> > I think you have experienced one or more not
> uncommon problems with a
> > number of 3-500 amplifiers. The re-soldering of
> tubes base pins is a
> > common sight and though highly inappropriate I
> think most that I have
> > seen have been done with regular soft solder
> rather than something with
> > a much higher melting point. If you consider that
> something melted the
> > original 'filler' then it indicates a whole lotta
> heat, either through
> > inappropriate use or insufficient cooling for
> whatever reason.
> >
> > There is another point to consider as well, I
> think. The tube bases get
> > pretty hot, even in normal, reasonably cooled use.
> Over the years this
> > heating and cooling of the base contacts may well
> lead to them becoming
> > minutely distorted. I have found cases where I
> believe this has caused
> > the very problem you mention, the contact becomes
> sufficiently high
> > resistance to prevent the heater kicking in. On
> the Johnson 275 series
> > sockets, I think, you can remove the spring clip
> that holds the two
> > parts of the contact together and bend it to
> provide a firmer contact. I
> > did that on my Henry 2K which was doing what you
> have indicated and it
> > has been fine ever since.
> >
> > I think it might also be useful to measure the
> voltage at the pins of
> > the tube. This means putting your voltmeter on the
> tube pins NOT the
> > base contacts. If you think about it the 3-500
> series want 5 volts +/-
> > 0.25 at 14.6A, so just a little R in the base
> connections could see that
> > fall below spec. My Henry promptly delivered
> several hundred watts more
> > once the heaters pins were at operating volts
> rather than just the base
> > contacts.
> >
> > Martin, HS0ZED
> >
> >
> >
> > terry@g4amt.com wrote:
> >
> >> My TL922 is mis-behaving with one tube operating
> intermittently. Symptoms
> >> were of open circuit filament but valve tested ok
> with ohm-meter and
> >>
> > worked
> >
> >> when refitted. Next power up, tube failed to
> work. jump soldered link wire
> >>
> >
> >
> >> to pins across bases to rule out base
> connections. Tube worked when pin
> >>
> > and
> >
> >> base `encouraged` with screwdriver.
> >> Looks as though previous owner has attempted to
> resolder the filament pins
> >>
> >
> >
> >> and I suspect a dry joint (?) within one or both
> filament pins.
> >> Is it safe to re-solder the pins ? Anything else
> suspicious I should be
> >> looking for ?
> >>
> >> Many thanks
> >>
> >> Terry
> >>
> >> _______________________________________________
> >> Amps mailing list
> >> Amps@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/amps
> >>
> >>
>
=== message truncated ===
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