The AM Forum

Ive been thinking of upgrading the 2x 250TH RF deck with a bit more grunt and push a pair of 304TL's somewhat hard.

I dont have any chimneys to try to see what sort of clearance is available for the grid tit.

Any ideas?

Carl
KM1H

I have never seen chimneys used on 304 tubes. If they even exist they certainly would be unobtainium. A larger version of the open fans used in the KW desk would be appropriate.
Skip

I've never heard of a chimney for that tube either.

I believe the 304TL is designed to dissipate heat partly through radiation (e.g. like and infra-red space heater ) and it seems like a chimney would decrease the efficiency of radiation.

Might do more harm than good.

I dont think Eimac made any chimneys for that family of tubes. They b space heaters, mon. suck the air over and out.

Here is my new modulator with 304TLs.  Cant wait to get it up and running!  W0VMC did a hell of a job.

Here is a company making a Super expensive 304 TL amp for audio.  No chimneys.  He even has the schematic listed.  I think I can build a 304 amp for about $1000.  MIght not have the Iron this amp has but sure would look nice and sound nice.

http://www.alumrocktech.com/amplifier.shtml

Here is another amp that does have Chimneys.   If you go to Yahoo and click the images tab, Type in 304TL, There are lots of pictures of with and without chimneys.  I dont think they are needed and I dont see any reference from Eimac for them.   

What a Great tube!

C

Robert did a terrific job on that thing- What a work of art.

The 304 is designed *not* to need a chimney at full dissipation.

304s are made from Nonex glass (non-expanding, similar to Pyrex) which can take a great deal of heat. They are designed to be space heaters.

So cooling the glass envelope isn't an issue, but cooling the seals is important.

I run mine bright yellow from time to time and had only one go bad over 17 years- Got gassy.

If you push the things, the seals *are* an issue. You absolutely need to use heat-dissipating grid and plate connectors and use the elevated Johnson ceramic socket. Then blow a lot of air sideways past the tube, the grid and plate connectors and the base pins, which can get so hot they'll unsolder themselves. I use a stack of two high-speed muffin fans next to each tube.

Notice the inch of tube clearance in the Johnson sockets. That's so air can circulate around the base pins. Don't use a conventional in-chassis ceramic tube socket.

There is someone advertising finned aluminum 304 connectors in ER.

Thanks Bill.   Neat info on the 304.   I really enjoyed talking to you the other night.  I was on my Globe king 500.  You sure had a nice signal to AZ!

Clark

they only want $85,000 for the Alumarock unit.   ::)

Piffle!

Yeah.. People will pay it. I dont blame him.   I worked that same amp out with Hammond Iron.  Its under $1000 in parts with an estimated $200 for the chassis.  It wont look like his and wont be nearly as nice.  But it might be a cool amp to sit in the living room and play music!   

I have a feeling that if I chrome plated it and put glass everywhere, It would pull $5000 to $10,000 on ebay.. LOL


Clark

Im aware that a chimney wasnt available, Eimac didnt figure that out that method until the 4-400A and 4-1000A in the late 40's. The question was which one fits?  I'll just have to dig out the 70's full size Eimac catalog and do some measuring. Obvious choices are the 3-400Z, 3-500Z, and 4-400.

As far as cooling, a chimney and forced air is always a more efficient way of removing heat and in the direction you want than a fan which manages to heat up the complete RF deck as in a SB-220, LK-500, etc.

I'll probably use a stock socket submounted in a slightly oversize hole to get air right on the ceramic base and glass area and also punch several holes in the chassis for the remainder off the glass area and to reduce back pressure. In the past Ive kept 4-1000A's happy that way when using the Italian sockets. Treat the 304 as a 4-400A for blower cfm requirements which should keep pins and seals happy. Ive Eimac radiators on the modulator which is flat mounted and has a small muffin fan blowing on the socket  Will order the Chinese clones for the RF deck which work nice on the HK-354's.

Carl
KM1H

I am putting some Sk 406 chimneys up on ebay today or tomorrow.  Not using them on my Transmitter. 

Clark

CArl, fellow antenna nut K1-Jumpin' Jiminy used replacement Coleman lantern glass for chimneys on a 4X1 rig.  I recall a discussion about it - give a search in this forum and it should come up.

 A good glass worker could fabricate one or modify an existing chimney. The principle of laminar air flow is often under-rated and may work well in this application.

My tho'ts:

I have a big collection of handbooks especially the older ones of 304 vintage and none of them show using a chimney.  However, I like the idea of a low velocity air flow up around the bottle(s).  Maybe pressurize the bottom of the chassis and have the air flowgently around the 304TL via 1/4" holes around the perimeter - just enough to get some air flow going.  I wouldn't encourage very much volume as the glass would be seeing a temperature differential which might be bad for seals  etc.  The key here is "gently."

BTW, where does one find fil xfmrs for a pair of these bottles these days?

Al

5 or 10 volt transformers are common items in catalogs like Newark. Mine is a transformer from a junked 12 VDC 20 A power supply.

Look up Robert. W0vmc  Everytime I need a part he always has it and its a good price.  I have purchased all kinds of transformer and parts from him over the last two years.

Clark

http://w0vmc.com/

Various industrial transformers with 10-15V secondaries and lots of amps show up at surplus dealers and Epay real cheap. They do not have a CT so you need a couple of resistors. Use a small variac to set the voltage a hair low at the socket. I think I paid $10 or $15 for a 40A @ 11.5V.

Bill Orr had a great article in QST back in the 60's that went over chimney air flow, CFM, and all that good stuff. No need to reinvent the wheel.

Carl
KM1H

Thanks for the info.  I'll have to look at my Q Streets in that era to check for that article.  I have a couple 304TL's -- just don't know what to do with them.  The legal limit AM rig is slated to have 813's in it.

Al