[Hammarlund] : Tube shields and heat

Mon Sep 29 13:33:44 EDT 2014

Hello All,

Thought I would throw in my 2 cents..  my long experience with tubes tells me it is generally unlikely that the tubes crap out, short, etc...but amplifier tubes are a bit different.. I have a Collins R-392 receiver that is in a closed shell and it gets really hot.. especially that audio output tube..so I pull it an inch or 2 out of the case just to give some insurance.. recently got a Navy FRR-26 tube receiver,(BTW does anyone have a manual for this thing?)  covers 2 - 8 Mhz.. made by KAAR.. nice build.. has socketed electrolytic cans, now someone was thinking about service there.. but it also is totally enclosed in a sealed up case.. I tested all the tubes.. I think all were the W version, Heavy duty, the only bad tube, and it was definitely bad, was that 6AQ5 audio output.. I have seen this before, that tube runs hot ..replaced and unit working great again.. I plan on drilling a few holes in the top and side to allow for ventilation and I have a small 3 inch fan mounted on the top now.. maybe it just went out for other reasons, but some insurance is a good thing.. OH..and BTW.. as far as finding tubes.. the R-392 with its 26 volt filament tubes.. difficult to find all of them.. and not pay through the nose for them..

73, Tim  K8WBL

> From: kb8tq at n1k.org
> Date: Mon, 29 Sep 2014 07:14:41 -0400
> To: gsantacanav at gmail.com
> CC: hammarlund at mailman.qth.net
> Subject: Re: [Hammarlund] : Tube shields and heat
> 
> 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
> >>> ______________________________________________________________
> >>> Hammarlund mailing list
> >>> Home: http://mailman.qth.net/mailman/listinfo/hammarlund
> >>> Help: http://mailman.qth.net/mmfaq.htm
> >>> Post: mailto:Hammarlund at mailman.qth.net <javascript:;>
> >>> 
> >>> List Administrator: Duane Fischer, W8DBF
> >>> ** For Assistance: dfischer at usol.com **
> >>> 
> >>> 
> >>> This list hosted by: http://www.qsl.net
> >>> Please help support this email list: http://www.qsl.net/donate.html
> >>> 
> >> 
> >> ______________________________________________________________
> >> Hammarlund mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/hammarlund
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:Hammarlund at mailman.qth.net <javascript:;>
> >> 
> >> List Administrator: Duane Fischer, W8DBF
> >> ** For Assistance: dfischer at usol.com **
> >> 
> >> 
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >> 
> > ______________________________________________________________
> > Hammarlund mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/hammarlund
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:Hammarlund at mailman.qth.net
> > 
> > List Administrator: Duane Fischer, W8DBF
> > ** For Assistance: dfischer at usol.com **
> > 
> > 
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> 
> ______________________________________________________________
> Hammarlund mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hammarlund
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Hammarlund at mailman.qth.net
> 
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
> 
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html