[Hammarlund] : Tube shields and heat

Mon Sep 29 18:02:17 EDT 2014

I have been using a couple of Variacs and bucking transformers. They work
quite well. Line voltage here is very constant although lately we have been
experiencing some frequent blackouts. The bucking transformers were made
from 12VAC 3A transformers from RS. 1960s Hammarlunds are rated for 125VAC
operation so I don't use them on 110VAC. Line voltage here monitored during
the day is never above 120VAC.

Guido Santacana KP4FAR

On Monday, September 29, 2014, Bob Camp <kb8tq at n1k.org> wrote:
>
> Hi
>
> Most of these radios were designed in an era of 105 to 110V AC line
voltage. We still call it “110” today, even though it probably is 118 to
124V. For some parts power does indeed follow voltage squared. That can be
good or bad depending on what you are up against. A simple autotransformer
based on a 12V filament transformer will fix the problem without a lot of
crazy effort.
>
> Bob
>
> On Sep 29, 2014, at 6:37 AM, Guido Santacana <gsantacanav at gmail.com>
wrote:
>
> > Lowering line input voltage readily works. I have all of my older tube
gear
> > running on 110VAC. Heat output was reduced and I noticed it more on my
SX28
> > audio output tubes.
> >
> > 73s
> >
> > Guido Santacana KP4FAR
> >
> > On Saturday, September 27, 2014, manualman at juno.com <manualman at juno.com>
> > wrote:
> >
> >> I have tube receivers here that have been running for 50 years with
their
> >> silver shields in place. Never had a crap-out due to heat-related tube
> >> stress. I would suspect if you really want to reduce tube heat stress,
> >> drop your filament voltage down by 10% or drop the input line voltage
to
> >> 110 or 105 volts.
> >>
> >> I also recall back in the "good old days" of doing a receiver alignment
> >> with all the tube shield off. Of course after completing the
alignment, I
> >> realized the shields were off so I put them back in place. For fun and
> >> giggles I rechecked the oscillator and IF alignments and found all the
> >> adjustments had to be touched up to some degree.
> >>
> >> Personally, I'll side with the original designers; they had tube
shields
> >> on certain tubes for whatever reason, so my shields will stay in place
as
> >> they came from the factory. I'm probably not smarter then they were.
> >>
> >> Pete, wa2cwa
> >>
> >> On Sat, 27 Sep 2014 15:19:55 -0700 "Kenneth G. Gordon"
> >> <kgordon2006 at frontier.com <javascript:;>> writes:
> >>> On 27 Sep 2014 at 17:24, Bill wrote:
> >>>
> >>>> All this redesign of tube shields, make me wonder why the
> >>> engineers that
> >>>> designed them didn't think of some of these tips...OR they
> >>> designed them to
> >>>> work in the way they do. Bill W2CQ
> >>>
> >>> I suspect that the reasons are several: first of all, I still
> >>> believe the shields
> >>> were added to prevent radiation, RF, either from an external source
> >>> (a big
> >>> transmitter in the same room) from effecting certain circuits in the
> >>> receiver, or
> >>> to prevent RF-radiation from certain circuits in the receiver from
> >>> causing
> >>> other outside effects.
> >>>
> >>> The heat problem was not considered, or if it was, it was considered
> >>> to be
> >>> minor, especially in a military situation in which (supposedly)
> >>> maintenance
> >>> was ongoing and organized, and tubes were bought by the millions.
> >>>
> >>> Secondly, much of the information and data on the effects of heat in
> >>> tubes
> >>> and how it shortens their lives came about AFTER the earlier types
> >>> of
> >>> shields were designed and implemented.
> >>>
> >>> As soon as the heat issues became better known, the military had
> >>> heat-reducing shields manufactured and used: i.e., the so-called
> >>> IERC tube
> >>> shields.
> >>>
> >>> After all, there is a pretty constant improvement in knowledge and
> >>> understanding of many things. Heat in tubes is probably one of
> >>> those.
> >>>
> >>> We come along much later and need some way to reduce the heat in
> >>> tubes,
> >>> thus increasing their life expectancy, since those tubes are
> >>> becoming more
> >>> difficult to find, since many haven't been made in many years.
> >>>
> >>> And, most of us cannot find, or if we do happen to find, cannot
> >>> afford, IERC
> >>> tube shields.
> >>>
> >>> Therefore, we do what we can to at least mitigate the problem.
> >>>
> >>> I believe it was Eimac who first did some extensive testing of
> >>> tube-life versus
> >>> heat (and filament voltage) and published their findings long after
> >>> the earlier
> >>> tube shields were designed....which were designed for the sole
> >>> purpose of
> >>> cutting down on radiation, RF, effects.
> >>>
> >>> Anyway, that's the way I see it, and it is worth exactly what you
> >>> paid for it.
> >>>
> >>> Ken W7EKB
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> >>
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