[Collins] IERC type tube shields
Herschel McCullough
w5mc at austin.rr.com
Sat Jul 3 12:45:44 EDT 2004
Thank you Pete, very informative..and long thought about and bantered
around, but seldom so well defined or referenced..
mac/mc
----- Original Message -----
From: "pete wokoun, sr." <pwokoun at hotmail.com>
To: <collins at mailman.qth.net>
Sent: Saturday, July 03, 2004 2:37 AM
Subject: [Collins] IERC type tube shields
> I can provide this info in a .pdf file if anyone wants it that way.
> I'll soon stick it in my website for future reference:
> www.qsl.net/kh6grt
>
> More than you ever wanted to know about heat-dissipating tube
> shield mil specs...but just the item for those *HOT* 6BF5s in
> Collins equipment.
> (You may need to change your font type to a constant-spacing
> one like Courier for the tables to line up properly.)
>
> MIL SPEC HEAT-DISSIPATING TUBE SHIELDS
> by Pete Wokoun Sr., KH6GRT (6/2004)
>
> We all have heard the benefits of using International Electronic
> Research Corp (IERC) type heat-dissipating shields in the R390A
> and other equipments to reduce tube operating temperatures.
> However, I haven't seen any information on just how how
> much they actually reduce the temperatures. Collins did some
> temperature studies but I haven't been able to find a copy of
> their study, possibly called service bulletin 303. I don't know
> if that study included heat dissipating shields. Searching
> thru the mil specs that these shields were made to I finally
> found some definitive temperature reduction figures. The specs
> are all in degrees C; they have been converted to degrees F in
> this presentation.
>
> The mil spec heat-dissipating shields designated for retrofitting
> to existing equipment come from three mil specs: MIL-S-9372(USAF),
> MIL-S-19786(NAVY), and MIL-S-24251. These shields are designed
> to replace the shiny, nickel plated JAN types. Mil-S-9372 was an
> Air Force spec and MS24233, its mil standard for retrofit shields,
> was implemented January, 1958. MIL-S-19786 was a Navy spec and
> its amendment for retrofit shields was implemented May, 1964.
> Both these specs were cancelled in 1968 and replaced by mil spec
> MIL-S-24251 which covered all branches of the service and was
> implemented March, 1967. Shields made to any of these specs will
> have the mil spec part number on them. Here are those mil spec
> part numbers cross referenced to the well-known IERC numbers:
>
> SIZE IERC # MIL-S-9372 MIL-S-19786 MIL-S-24251
> ------------ ------ ---------- ----------- -----------
> Short 7 pin 5015B MS24233-1 S0761*V00 M24251/6-1
> Med 7 pin 5020B MS24233-2 S0762*V00 M24251/6-2
> Tall 7 pin 5025B MS24233-3 S0765*V00 M24251/6-3
> Short 9 pin 6015B MS24233-4 S0966*V00 M24251/6-4
> Med 9 pin 6020B MS24233-5 S0967*V00 M24251/6-5
> Tall 9 pin 6025B MS24233-6 S0968*V00 M24251/6-6
> Ex-Tall 9 pin 6027B MS24233-7 --- M24251/6-7
> *(X or C)
>
> All the above sizes except the short and ex-tall 9 pin ones are used
> in the R390A. You can get information on how many of which ones on
> many web sites. The IERC numbers are normally used when searching
> for these shields. If someone other than IERC made them, they may
> only have the mil spec number and some other model number. I have
> some made by Waterbury Pressed Metal Company (WPM in the table below)
> that are this way. One I have made by Cinch Connector Company does
> carry the IERC number. I found documentation that the Atlee Corp
> also may have produced some of these shields. Their different model
> numbers are noted in the table below and cross referenced to the
> IERC numbers:
>
> SIZE IERC # WPM # ATLEE #
> --------- ------ -------- --------
> Short 7 pin 5015B RS-215-1 A10041-1
> Med 7 pin 5020B RS-215-2 A10041-2
> Tall 7 pin 5025B RS-215-3 A10041-3
> Short 9 pin 6015B RS-216-1 A10042-1
> Med 9 pin 6020B RS-216-2 A10042-2
> Tall 9 pin 6025B RS-216-3 A10042-3
> Ex-Tall 9 pin 6027B -- ---
>
> BTW, I noticed the last two digits in the IERC number correspond
> to their height in decimal inches. For example, the 5015 is
> 1.5 inches high, 5025 is 2.5 inches high, etc. Anyone know if
> the 50 and 60 designate anything?
>
> Physically, from ones I have seen, the shield inserts (the part
> that contacts the tube) are of two types: a multi-sided cylinder
> (5-sided for 7 pin tubes and 6-sided for 9 pin tubes) or a round
> insert with a multitude of 1/16 inch fingers. I found both types
> on shields from both the -9372 and -24251 mil specs. The multi-sided
> inserts have an open top between the insert and outer shell whereas
> the mini-fingered insert has a top closed. I personally have not
> seen or heard about any shields that have the MIL-S-19786 markings.
>
> Shields made to MIL-S-9372(USAF) (MS24233) were qualified to
> reduce the surface temperature of a test 'slug' by 36 degrees F,
> minimum (a 10-11% reduction). The test 'slug' was an alumimum piece
> shaped like a tube with an internal heater and 3 imbedded
> thermocouples. This 'slug' was heated up to 338 to 356 degrees F
> when the shield was applied. The average reading for all
> thermocouples had to be at least 36 degrees F less than the starting
> temperature. How well this test 'slug' with its greater thermal
> mass related to actual tubes I don't know.
>
> Shields made to MIL-S-19786(NAVY) were qualified using an
> instrumented glass tube called a Thermion. Apparently these were
> tube-sized things containing a heater and thermocouples. It was
> heated to its test temperature when the shield was applied. The
> shields designated for retrofit service were only required to reduce
> the temperature of the thermion between 10 and 25% (symbol 'X' in
> the tables). However, the shields worked so well they were
> qualified to the next higher reduction of 25-38% (symbol 'C' in the
> tables). Specific temperatures for this spec are as follows:
>
> Bare Bulb Shield Temp Reduction (Minimum)
> MIL-S-19786 # Test Temp (X) 10-25% (C) 25-38%
> --------------- ------------- ------------- ------------
> S0761 (short 7) 293 degrees F 27- 65 deg F 65- 99 deg F
> S0762 (med 7) 437 degrees F 41-101 deg F 101-154 deg F
> S0765 (tall 7) 455 degrees F 43-106 deg F 106-161 deg F
> S0966 (short 9) 266 degrees F 23- 59 deg F 59- 89 deg F
> S0967 (med 9) 446 degrees F 41-104 deg F 104-157 deg F
> S0968 (tall 9) 347 degrees F 32- 79 deg F 79-120 deg F
> Note: The V00 in the -19786 mil part number refers to a
> vertically mounted shield with no separate base provided.
>
> Shields made to Mil-S-24251 were qualified using actual electron
> tubes. The temperatures were measured from a thermocouple imbedded
> into the test tube's glass at its hottest spot. The hot spot
> location was determined by temperature sensitive paints. Like in
> the previous specs, the test tube was heated to its test temperature
> when the shield was applied. The shield had to reduce the bulb
> temperature by at least the amount indicated in the following table:
>
> Bare Tube Shield Temperature
> MIL-S-24251 # Test Temperature Reduction (minimum)
> ---------------------- ---------------- -------------------
> M24251/6-1 (short 7) 239 degrees F 45 degrees F (19%)
> M24251/6-2 (med 7) 419 degrees F 72 degrees F (17%)
> M24251/6-3 (tall 7) 464 degrees F 81 degrees F (17%)
> M24251/6-4 (short 9) 266 degrees F 45 degrees F (17%)
> M24251/6-5 (med 9) 437 degrees F 99 degrees F (23%)
> M24251/6-6 (tall 9) 446 degrees F 81 degrees F (18%)
> M24251/6-7 (ex-tall 9) 455 degrees F 81 degrees F (18%)
>
> Typical tube operating temperatures I expect are somewhat less
> than these test temperatures which maximized tube dissipation.
> This would lead to somewhat less than the above temperature
> reductions in actual situations. However, I think these tests
> were closer to actual conditions than the 'slugs' and Thermions
> used in previous testing.
>
> The mil spec Mil-S-24251 remains in effect today. However,
> there are no products on its qualified products list. What
> that means is no one currently makes any of these shields
> because the military doesn't have a need for any. Personally,
> I think shields made to any of these mil spec are going to
> perform similiarly because they're not all that different
> from each other.
>
> There are other types of mil spec heat-dissipating shields even
> of improved design but they are not designated for general
> backfitting into existing equipments. These shields and their
> sockets were designed from the start as an integral part of their
> equipment. As such, significant quantities to use in other
> equipments are probably not available.
>
> So, what does all this mean? Here are my thoughts: These
> temperature reductions listed that the shields had to meet are
> all minimums so actual reductions cannot be determined.
> Physically these shields seem to remain pretty much unchanged
> throughout the years; it was the mil specs that were changing.
> And mil specs are sometimes written just to document what is
> normally used and available! From the mil spec 19786 qualified
> products list the manufacturers had test data that supported
> their products qualification of 25-38% reductions in bulb
> temperatures. This range also allowed them to meet the newer
> mil spec 24251 minimum reductions. So I would venture to say
> a typical bulb temperature reduction of 20-25% is realizable
> with the heat-dissipating shields. Having a temperature
> reduction figure only leads to a further question: By
> decreasing the operating temperature of a tube by some amount,
> how much improvement in tube life does this lead to? This
> becomes harder to answer than determining how much cooler the
> tube operates. But one can generalize by saying any increase
> in tube life by lowering bulb temperature is beneficial.
>
> The most informative article I was able to find on-line which
> related tube bulb temperatures to tube life was
> pearl_tube_coolers.pdf on the www.pearl-hifi.com website.
> Although much of the website borders on the more esoteric
> nuances of high-end audio, this paper presents some of the
> earlier works done by GE and IERC on tube temperatures and
> life spans that are difficult to find these days. An example
> from an IERC study in that article: a 6AQ5(6005) tube
> operating near maximum plate dissipation has a bare bulb
> temperature almost 460 degrees F. Enclosed in a bright JAN
> shield its bulb temperature rises to 600 degrees F. With an
> IERC type B cooler installed the bulb temperature drops to
> 365 degrees F. This is a 20% drop from its bare bulb
> temperature and an 39% drop from its JAN shield temperature.
> This related to a tube survival rate after 500 operating hours
> of 35% using no shield, to less than 5% using the JAN shield,
> to over 95% still working using the IERC type B cooler.
> In another example from a GE study: From a batch of 200
> 6AQ5(6005) tubes running at 502 degrees F, 15% were still
> operational after 2500 hours. A second batch running at
> 428 degrees F, 74 degrees cooler or about a 15% reduction in
> bulb temperature, still had 90% operational after 5000 hours.
> It seems "small decreases in bulb temperatures often result
> in seemingly disproportionately large increases in tube life".
> The article is also interesting in that it touches on other
> factors like filament voltage, forced air cooling, and
> temperature gradients that also have an influence on tube life.
>
>
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