4-400A - which Chimney to use??

[Ralph]

I recently acquired a HT-45 with a 4-400A tube replacing the original 3-400. The chimney is a coleman latern glass that appears to be near the same diameter as the sk-xxx chimney (it fits the seat brackets), but without the narrow mouth at the top. No doubt the airflow is dfferent compared to that from a "real" chimney and I'm wondering if the tube cap will get the proper cooling. Does anyone have experience using a "Coleman" chimney or should I look for the "correct" replacement, and if so which one do I need for a 4-400A?? The socket is a ceramic type that allows the tube to sit flush on the chassis. The manual doesn't give any info. Any help would be appreciated.

[K1JJ]

Hi Ralph,

I've been experimenting with lantern chimneys for 813's here. Got one modulated by a pair called the "Blown 813's". Still busy wiring it, maybe 90% finsihed now.

As you said, the only difference on yours is the tapered top. The air will not hug the top of the tube and continue the same rate of air flow moving past the top... no big deal. It's really a matter of degree. If you are moving ample air past the tube in the first place, a not-so-perfect chimney will not make much difference in overall cooling. Also depends upon how hard you beat it.   Heck, some amlifiers don't use much air at all... just a fan across the glass and they survive.

BTW, my 813 chimneys, by Leitz, do have the tapered top. But I had to look at many to find them.  About $5 each.

Don't worry about the tapered top air flow at all. As long as the glass hugs the tube in a reasonable manner and there is a good, balanced air coming out of the top, it's FB.
Big finned heat caps for the plate caps helps too.

BTW, notice the air holes cut in the chassis. This makes a HUGE diffence in air flow. I do the same thing for my 4-1000A's. It increases air flow perhaps 200% over using just the air holes in the socket. There appears to still be ample flow through the pin area, dispite the altered air re-routing. The fan seems to simply push much more air with less restriction. I use about twelve, 1/2" holes in a circle, right to the edge of the glass chimney on all of my projects.

73,
Tom, K1JJ

Big Pics - these are early pictures - most of the work is finished at this point -
http://home.comcast.net/~k1jj/wsb/html/view.cgi-photo.html--SiteID-2536768.html
http://home.comcast.net/~k1jj/wsb/html/view.cgi-photo.html--SiteID-2536765.html

4X1 X 833'A's   - notice the air holes:
http://home.comcast.net/~k1jj/wsb/media/254120/site1099.jpg

Blown 813 X 813's:

 

[w3jn]

Is that transformer painted Safety Yellow so you don't bark your knee on it in the dark, T 

[K1JJ]

Is that transformer painted Safety Yellow so you don't bark your knee on it in the dark, T 

 

Well, John, the real story is that I lent that mod transformer to a buddy who used it for six months. When it left it looked pretty rough... rusty, etc.  When it came back, well, look at it!  I'll probably leave it that way just to add character to the rig. I spent a day painting all of the other transformers black or gray for the various rigs, but left that one alone.

If you look at my current avatar, you'll see I have no taste anyway.

I've gotta take some new shots. The six rigs are really coming along and almost finished except for supply wiring, etc. The three tube-glass AM rigs are gonna be under plexiglass for full viewing. The sterile steel  linears are all in racks, of course... who cares to see them anyway?

What you been working on?

T

[w3jn]

I completely rebuilt a Hallicrafters SX-11, re-did the front panel, etc.... now that's the main RX for the garage station.

The Vortex generously donated the PS out of the Kelvinator Kilowatt (or was it the Coca Cola Kilowatt) for my 4X1 leenyar, but I haven't gotten to tearing it down yet.  It's too big right now for what I need for the leenyar, but it has a bunch of Fine Business iron indeed.  My son helped me lift it outta the trunk of the car, and he was in awe 

Been working on converting a SOB-400 to HIHIHIFI AM auuuuuuidio.

A Hallicrafters HT-20 somehow made it into the shack and I'll be working on that as time permits also.

Look forward to hearing alla them thar rigs on the air, T!!

73 John

[WA1GFZ]

Jonh,
Get rid of the 1n270 germanmaniuma diodes in the balanced modulator. they are very unstable when you bias them on. Tried it once on my sob401.
Man have not turned that rig on in almost 25 years.

[WBear2GCR]

I posted to the Technical section one very decent and almost free solution for 4-400 or 3-500 chimneys!!

hint: Mayonaise jars...

       

               _-_-WBear2GCR