The AM Forum

There is a catch however ::)

http://www.prismnet.com/~nielw/T368F/

Carl

Wow.  If I lived closer, I'd drive up there and pick the stuff up.  Does the $200 price include a place to put it after you get it home?

Damn, why are these deals alwaysl all the way across the country when gasoline is $3.50 a gallon ???

60 miles for me (and I own a truck) and I have a reasonable bid in for it...you'll notice that it says highest bid OVER $200!

Finally something close; most of you guys live in the NE and don't have too far to drive for those "come and get it" deals. It was a 2,000 mile round trip to pick up the Gates near Denver.

The VHF set that goes with it can pair up with my NDB transmitter. Both beautiful pieces of gear that are, sadly, mostly good for parts.

:( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :(

Yow !  
I hope you didn't mean to include the T-368 as "mostly good for parts."

If you can't afford the trip because gas is $3.50/gal versus $2.35, you couldn't afford the transmitter anyway.  :)

I always wondered why they used a black, steel chimney for the 4-400A that blocked the radiant heat dissipation, considering radiant heat along with pressurized convection is part of the cooling for that tube. Probably something to do with shrapnel and bullets.

I used to have a junker T-368 RF deck back in 1975. See that long strip next to the 4-400A? I made a little more room to the right and sandwitched in FOUR 4-400A's in GG parallel, with four pressurized glass chimneys - creating a nice linear amp. That was when I was living in a tiny buffet 10 unit apartment building in urban Denver and received an eviction notice. It stated: Eviction for "interfering with neighbors' TVs and radios, having a puppy [Yaz I] and for drilling sounds at 2AM in the morning."   ;D

T

those bastards!   ::)

Nikoli Tesla never got evicted for experimenting!

;D

I removed the 'Best Offer' part yesterday when I listed it in the For Sale section because it wasn't clear in Niel's ad whether that was for the T-368 or the TUQ. Since there was no price attached to the T-368 part of the ad and only 'preference given to...' followed by the TUQ and Best over $200, it seems to say best offer over $200 on the TUQ, which I'd agree is more useful as a curiosity or parts donor, maybe a museum piece for a CAA display.

Outside of the T-3 appears a bit grungy but looks like it would clean up well. Inside looks pretty nice. Should make someone a good AM transmitter.


Actually I think it has to do with more effective cooling for long key down periods Tom, like RTTY service perhaps. Think of the shiny shields used in a lot of rigs that were later replaced with the IERC black type, complete with heat-dissipating inserts. Somewhere there's a report showing the difference in cooling efficiencies of the different types over bare bulb. The IERC type could actually cool a tube better than leaving it exposed. No doubt a heat sink approach. The chimney effect for the blower certain increases this, funneling air past it at a decent rate.

I think Bill 'HG did some research on this some years back and published the results in ER. Can't remember if that's where I saw the comparison chart or not.

wouldn't the black help to absorb some of the heat and the shiny ones would want to reflect it?

Interesting take, Todd. I don't know the answer.  So, you feel a black, aluminum shield [heatsink effect] around the glass tube may be better than a glass chimney that will let the excess heat/light pass thru ?   Maybe someone has some hard data on this.  I usually keep the glass clean to enhance the effect, but never considered metal shields.

Actually, it might be cheaper to make an aluminum chimney rather than a glass one, so wonder why the manufacturing companies don't do it for glass 3-500Z's, etc?  External anode tubes would be an exception since they don't depend on radiant heat and use solid chimneys.

Anyone know the story?

T

Absolutely not!  :o

The TUQ and the NDB transmitter I already own are the parts units. They are really nice looking pieces, and if some museum wanted them that's where they would go. They are full of really high grade parts and the plug-in racks on the NDB should be good for a great old buzzard transmitter, just not in the 200-400 kc band.

A few years ago, a guy had a TUQ that he had moved from 120 mHz down to 75m.I am sure he rebuilt all the tuned circuits.I have a picture of it , but it shows the front view.

http://www.amwindow.org/tech/htm/irec.htm

A pair of 4-65s mod-ed by a pair of 809s!

It could be done.

I'd bid on the TUQ if it were close by. That is a nice transmitting set.

I've always painted the innards of my transceivers (rf cages) with flat black.  Black will absorb infrared instead of reflect it like bare metal.  The metal does absorb the heat with paint on it.  There's indeed an improved heat transfer to metal.   Not sure on how glass compares though.  I do know one thing glass properties will influence how much infrared passes through.  It's an issue with homebrewed solar panels and efficiency.

By the same token, white reflects the heat well. If the filament transformer or other critical part has to be close to something like a 3-1000, then white is helpful.

Remember, we're talking extended duty cycle on the T-368 since it was a military brat. Many, even most probably ran RTTY at some point in their lives, some did nothing else.

For our light (in comparison) duty cycle work, I'd almost think glass would be preferred. Less restriction to air flow and the ability for the radiant heat to pass directly through. Of course, we're not banging them around in mobile service in some military vehicle with a comms shelter on back, either. Certainly not a glass-friendly environment.

I'll dig around and see if I can turn up that chart showing the temp comparisons. They were for receiver-type tubes, as I recall, but it proves the theory.

Here's a snippit off one fellow's page, Tom:

"  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"

Pete has a lot of good info on the IERC type shields in his site, including test info:

http://www.qsl.net/kh6grt/page4/shields/shields.htm

Still not the chart I was looking for, but a good start.

Vely, vely interesting.  I never would have expected those results. Intuitively you would think no heat obstruction (glass chimney)  would always be better than a metal obstruction (flat black chimney)  to get the heat away from the tube quickly.  It seems a metal barrier collects and re-radiates the heat better than air.

I wonder if this could be applied to a standard air cooled 4-1000A using a flat black aluminum chimney? They are talking about ~20% reduction in bulb temperature for the tests on minature tubes with no air cooling.

Anyway, the paragraph below from the site you listed, Todd, tells the story using our old friend, the 6AQ5 tube. The lifespans of the large samples were extended markedly with the flat black tube shield.

Thanks for the info.

T

**  Shhhhh - What's that sound? Sounds like frantic scurrying to pull out all those bright tube shields!  ;D

--------


"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."

Morning T... The military appears to have already considered your suggestion... the 4-400 in the T-3 here uses a dark aluminum chimney... the color of the chimney is consistent with some of the IERC tube shields I have here... after manufacturing, the chimney could have been left with just it's silvery mill finish or for corrosion resistance a quick Alodine dip but the military went with a much darker anodized finish... for some reason, the military thought it was worthwhile to do the extra conversion step in the manufacturing process...

The 4-400 chimney in my T-368e (1962) is anodized, a dull golden color FWIW.

The 4-125 chimneys missing...

And the 6AQ5 is almost identical to YOUR old friend, the 50C5  ;D

OUCH!!!


BTW, here's the quick start and full articles concerning this subject of tube cooling.

I'm afraid to "probe too deep" fearing finding something about using external outside cold air for cooling the big rigs. Temp gradients. I don't want any bad news.


http://www.pearl-hifi.com/03_Prod_Serv/Coolers/TubeCooler_QuickStart.pdf
http://www.pearl-hifi.com/03_Prod_Serv/Coolers/PEARL_Tube_Coolers.pdf

T

When your head is in the sand another area is exposed

Is that why I have a hard time recognizing Tom at Nearfest which is only 2 months away

Tough crowd.

In my best Arab accent:  "I fot in you face!"

"Your mother was a hamster....."

http://www.youtube.com/watch?v=R7qxqvjTbu0&feature=fvst

I just got this in Email...

"The History Center has received a donation request from the Antique Wireless Association/Museum. They've decided a donation to the AWA best fits the intent of the original donor. The T-368 is no longer available"

Sounds like a good home for both pieces!

It'll sure save me space, I've got more than enough projects, even if I live to be 100!

Except I thought the AWA was interested in real antiques, i.e. gear with wood front panels, spark transmitters, crystal receivers etc.   I don't think of a T3 as an antique.  I hope they operate it -- put it on the air and don't just let it sit in some exhibit.

Rob