More Junk For The Shack

[Chris P.]

Picked up some stuff this past weekend. Maybe I'll get on AM this winter more than last year. (twice)

Homebrew pair of 4-400A grounded grid. It's going to need some work, but I think this may work nicely with a low power rig like a DX-40 modified for pure screen modulation. The power supply only makes 1400V, but that shouldn't be too hard fix.

[Chris P.]

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[Chris P.]

This one will need quite a bit of work. That 4X1 was really jammed in there. Not even any room for a chimney.

[KA0HCP]

Great haul there!  The possibilities are endless...

[w8khk]

That is some of the most beautiful junk I have ever seen.  You will be the channel master when you get it up and running.  Can you spell "STRAP?"

[KL7OF]

That is an interesting parasitic suppresor on the 4X1...  Turn those 4-400s into a modulator and the 4x1 is the final...  Nice find!!

[K1JJ]

This one will need quite a bit of work. That 4X1 was really jammed in there. Not even any room for a chimney.

Hi Chris,

They look reasonably well constructed.

Yep, right now it appears there is no air at all on the 4X1 amp. That tube would cook its seals in linear service.  A chimney is so important to longevity if they are run hard.  But as you said, it will take a lot of parts movement to fit a glass chimney in there.


The 4-400A rig looks like it would survive since it has both a fan below and above. However, the upper fan is blowing air only on one side which will allow the blind side of the tubes to run very hot.  I've found that if a chimney cannot be used, then blowing air directly down from the top, with a muffin fan mounted above each tube, will give a nice balanced air flow. It is against the normal "heat rises up" rule, but it does work better than from the side.  I cool my triple 4D32 PDM rig this way and I can put my hand on the tube glass after a transmission, no problem.   Even with the top fans, another fan blowing pressurized  air thru the bottom 4-400A seals is still required, of course.

BTW, I have run temperature tests with an IR gun on the tube glass while running the tube hard. With the muffin fan mounted directly above the tube, I measured both pushing air down hard on the tube and sucking air up out of the cabinet.  The cabinet itself had adequate ventilation holes and the back was open for good air flow.  The direct down air method by FAR showed the coolest glass.  Nothing beats a blast of air directly hitting a surface vs: a general area breeze.


Good luck with the projects!

T

[Chris P.]

Thanks guys.

I played with the 4-400a rig some, and yes the tubes do get noticeably hotter on the side away from the fan. I'll trying mounting some fans above and see how that works.

[WBear2GCR]

The image 4818 shows a blower mounted internally... where does it exit??
Guessing it does not exit.


That blower ought to be sufficient to cool the tubes, assuming that it is blowing into a more or less sealed compartment and there are EXIT holes that push the air up through the chassis over the tube envelope.

Or assuming an "air system socket", through the tube base into the chimney... Eimac has the proper directions and specs.

Fyi, you can make ur own chimneys from glass Mayo jars or Coleman lantern glass (they just fit, if you get the right ones.

Btw, and fwiw, the tank components seem a bit small and light for the power level... not sure that this makes 80m properly or not...

                      _-_-

[steve_qix]

I've definitely seen the 4-xxxx series of tubes run without a chimney.  The chassis was pressurized, and sufficient air came up around the sockets that the tubes were kept cool.  Radiating plate caps also helped.

This was an RCA BTA1-R broadcast transmitter, by the way.

Always wondered if the shape of the tube created a low pressure area right at the tube itself, keeping the air on the tube.  It worked, that's for sure.

Regards,

Steve

[K1JJ]

Shotgun vs: rifle approach....    Using a glass chimney has the advantage. It forces the air to follow the contour of the tube within 1/2".  The top plate cap seal is just as important as the bottom seals. The chimney allows the same air to hug the tube's  curved top and direct some air past the top seal and radiating plate cap.  

Eimac recommends a chimney, but anything will "work"  if enough air is blown and directed in the proper places. A chimney is most efficient, cheap insurance, simple  and does the job right with the least amount of air and noise.

A 4X1, when properly cooled, can dissipate upwards of 1500 watts, even though it is rated at 1KW. This level requires the cooling to be right. Linear service is a killer. There's a lot of 4X1's at the flea markets with brown temp paint lettering. If the cooling is poor and we must run the tube at reduced power, why bother? Might as well use a smaller tube like a 4-400A and cool it well.    
  
Why JS it and skimp?       The price of a chimney is 1/10th or less the price of a good tube.

After losing a few glass and external anode tubes due to inadequate cooling over the decades, I am fanatical about keeping things cool. I use temperature kiln probes and alarms monitoring every amplifier.  With chimneys and robust air flow, the exit air temps rarely get above 130F on the five amplifiers.  (or 4X1 modulators)

T

[ka4koe]

Congratulations!! Looks great!

[W3GMS]

I would start out by pressurizing the bottom and see how much air you can get around the tube.  Collect the data and then you will know what you need to do. 

If your really in trouble air wise, here is something that will do the trick 

Lots of great parts and it will be fun to see what you can do with the least amount of work vs. RF output!  If you not happy, then use the parts and go to  a larger chassis with a slightly different layout. Then again, even though its more work, a class C final is a great way to go for an old buzzardly type of transmitter! 

Its all about tradeoffs!

Joe, GMS

[Chris P.]

The blower underneath is blowing into a sealed compartment below the tubes, but its kind of weak and very little air is making its way through the socket. The tank is definitely going to need some work. No output on 80 or 20, and the 15 and 10 meter positions aren't even hooked up. I think it would be safe to say this one was never used. Hopefully that will change soon

[W3GMS]

Look for air leaks or a blower that does not hold up to back pressure.  As has been discussed and you know the importance of good air flow. 

You should be able to do a practical feasibility test on it under operating conditions to see how its going to fly.  Then you can go back and clean things up.  No use doing that if it does not meet your preliminary criteria. 

Joe, GMS     

[Opcom]

Refer to the tube manual and dig out the ol' manometer. The 4-1000 is going to take a bit of pressure because the socket offers some resistance. The book ought show how much.

[WBear2GCR]

Ummm... nothing will make it through the sockets unless it is an air system socket.
So, pull one or both tubes, and look. Turn on the blower and see what sort of air is moving or not.

One way to solve the problem is to mount a "real" blower externally, perhaps on the rear of the unit, or even via a short hose/pipe (smooth wall) flexible or not to the back of the chassis...

The other thing is that for the blower under the chassis to work, it has to not be in a sealed chassis too!

Obvious stuff, but it seems to me that the original builder was not quite up to speed in certain ways.

Again, I question if the tank is up to the task power/voltage wise or if it will reach the low bands at all. Looks to me like 10m size stuff. Fwiw. (anyone else with me on this?)

Plenty of room for larger tank parts, just have to make some "adjustments" to the layout.

[Chris P.]

That was going to be my next question. Is it possible to adequately cool a 4-400A in a non air socket if a strong blower is used below and a fan above? I think the builder used this article as a guide for construction. http://mikea.ath.cx/eimac/eimac01.pdf The construction article starts on page 17 of the PDF.

Note how the article suggests cooling the tubes. I wouldn't think that would be enough even for sideband service.

[Opcom]

I guess it's your turn for 'somebody keeps dropping of all this junk'. Those are great acquisitions! don't let them be the last!

[Chris P.]

Well I haven't done anything with the amps. Got sidetracked, and now more junk showed up the other week.

[KB2WIG]

C,

It's up to us, the AM community, to help rescue our history.

Chris, I'm willing to do my part. Please send me the latest collection, along with that lollypop in the bed. If we all stand together, they can't pull us apart.

Do it for the children.

klc

[w8khk]

Well I haven't done anything with the amps. Got sidetracked, and now more junk showed up the other week.

That Hallicrafters HT-33A is a real find.  It has a Penta PL172A tube.  I have seen various ratings on this tube, most specify 1000 watts, although others specify 1500 watts dissipation.  I restored one a few years ago, it runs great.  The fan is rather quiet, two speeds.  I run low speed on sideband, and high speed on the heavy duty modes.  I replaced the 866A rectifier tubes with 3B28s.  Also had to replace all the bleeder an dropping resistors in the screen regulator circuits.  THe PL172 is a pentode, grid driven, requires very little power in for full output.  It is a heavy beast, with a plate choke and HV oil cap.  Properly restored and cared for, it should serve you for a long, long time.  The only caution is it is very HEAVY.  Get help moving it.  Also, the  interlock switch in the cover functions on the primary side of the transformer.  Use your Jesus Stick before poking around inside, over 3000 volts!   Congratulations!

[Chris P.]

Thanks. The HT-33A turned out to be better than I first thought. I was told it sat in a couple inches of water years ago, so I wasn't expecting much. I warmed the HV transformer for a while in case there was any residual moisture, and then lit the filament only for several hours. The bias supply still needs some preventive maintence but so far everything seems to be behaving. I was excited to find the PL-172 was good! I'm looking forward to getting this stuff on the air.

[N2DTS]

You don't need air on the tubes unless you are going to run things at their limits.
Look at the Collins 30K1, no fans, the globe king 500 had a fan but it did not really do anything.

Some tubes might need it, but 4-125/250/400's seem to get by without it unless you are pushing things to the maximum.

They should have air flow for convection cooling or some sort of gentle quiet fan, loud fans or blowers are no fun at all.

[DMOD]

We should not call it junk.

i think "Classic Electronics" would be more appropriate.  

Looking at the guage of the sheetmetal, these builders were serious.