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4X150A tube




 
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Author Topic: 4X150A tube  (Read 1077 times)
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W4AMV
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« on: December 18, 2017, 11:26:05 AM »

Good day and Happy Holiday.

Looking at a hybrid Tx build, solid state exciter and a 4X150A output.
The tubes have been in the collection box for some time. Tarnished silver
but look like they can clean up. Heater continuity present and checking
for internal shorts.

Is there a method of bringing these tubes initially on line?


And is it necessary to use the free air flow socket?

I have read folks have used standard Loctal sockets as long as free air flow is available.

Plan is to run a single tube at 100 W with plate V at 1kV. Thanks! Alan 
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WBear2GCR
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« Reply #1 on: December 18, 2017, 04:44:19 PM »

What are we talking here??
A linear on the output side of a low power transmitter?
Or, the final in a plate modulated rig? Or a screen modulated rig?

These tubes need airflow.
They're designed to cool via the fins.
At reduced power they need less airflow.
Regardless of the socket, IF air flows up via a pressurized chassis (or sub chassis)
there needs to be a means of directing the flow up, past the tube pins and through
not over the plate.

This is not too difficult, and all sorts of stuff can be used as a chimney, including PVC, glass,
ceramic, etc... and since it is small, pretty easy to make even with hand tools if it is PVC or
other plastic...

As far as "gettering" the tubes, I'm no expert, but I'd expect that running the filaments and
maybe bringing the tube up at low voltage, but some current, creating heat inside would be
sufficient. Check Eimac's recommendations online. And look at what people have said online
about other ceramic tubes.

I see these sockets at hamfests quite often.
Should be available online like epay too.
Probably someone here has an extra and can send you one...

But seems kind of a waste of a good high voltage tube to run it at such a low power and low
voltage to make 100 watts, plus the extra work to put air through it. A pair of 6146s will do
the same job, as will a 4D32, etc.,etc...
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W4AMV
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« Reply #2 on: December 18, 2017, 05:28:58 PM »

Hi Bear, thanks for the reply.

The transmitter design goal is compact size with the low level stage(s) solid state. About 5- 10 W out to drive the 4X150A to 100+ W. The mode is CW. So the power dissipation level is significantly eased. I would run these class C probably grounded grid(s) and the motivation in using them is simple... I have a bunch of them. What I don't have is the appropriate air-system socket. So I was contemplating being a bit clever here and see if fabrication of a SIMPLE socket that would provide a scheme for forcing air under the base of the tube up towards the radial fin would be possible. Again since this is CW, perhaps I can get away with an air flow scheme that is less than ideal. The built in screen bypass and all the other aspects of the special socket I would have to address.  By the way, these are not cermic but do have a glass seal which can be compromised without sufficient air flow. Apparently just lightning the tube up with no applied HV is risky without proper air flow. Although this is second hand information and not stated in the Eimac notes I have read.
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KD6VXI
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« Reply #3 on: December 18, 2017, 06:09:21 PM »

Simple.  If the chassis is enclosed.

Run a piece of silicon pipe or tube from the anode to a collet on the inside of the top of the chassis. No other open holes in the top side of the chassis. 

Pressurize the top of the chassis.  Now, all cool air will flow around the glass, up through the external anode, and you are almost golden.

You'll also need cooling air across the base pins. Something like a muffin fan should work.

--Shane
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W2PFY
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« Reply #4 on: December 18, 2017, 11:48:53 PM »

I see those sockets on eBay quite often and for not a lot of money, they have the screen bypass built in and they also come with a ceramic chimney. I used to run the 4X150D which is the 26.5 volt filament and had no problems as long as the small blower was blown into an airtight chassis. 

https://www.ebay.com/sch/i.html?_nkw=4X+150+TUBE+SOCKET&_in_kw=1&_ex_kw=&_sacat=0&_udlo=&_udhi=&_ftrt=901&_ftrv=1&_sabdlo=&_sabdhi=&_samilow=&_samihi=&_sadis=15&_stpos=12204&_sargn=-1%26saslc%3D1&_salic=1&_sop=10&_dmd=1&_ipg=200

There is one on there for $25.00 with the chimney.
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WD8BIL
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« Reply #5 on: December 19, 2017, 10:08:04 AM »

Datasheet attached.

* 4X150A_D.pdf (571.96 KB - downloaded 18 times.)
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W4AMV
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« Reply #6 on: December 19, 2017, 01:14:02 PM »

Thanks for all the replies. The notion to try this was somewhat prompted from this article in HR Dec 75.
The idea of trying a loctal socket with suitable mounting with FREE but not forced air flow may be a stretch.
He used the appropriate socket but no forced air based on what he observed at Eimac. Alan


* 4X150_amp.jpg (248.7 KB, 708x887 - viewed 111 times.)
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w4bfs
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« Reply #7 on: December 19, 2017, 03:11:20 PM »

ok the 'golf ball' tube .... before you obligate too far be sure to hi-pot test the tubes to guard against partial vacuum ... should be good to 3 kV
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KI4YAN
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« Reply #8 on: December 20, 2017, 01:12:29 PM »

Also, these tubes are not designed to run in grounded grid mode-they must be grid driven.

http://ethw.org/w/images/c/c0/Eimac_tube_notes.pdf
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W4AMV
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« Reply #9 on: December 20, 2017, 01:54:10 PM »

Yes, I saw the Eimac note and it is another point that needs checked before I consider this approach. Despite the original authors success. One technique is to add some bias to screen and control grid. But of course, that detracts from the compactness.

The Hi-POT test is also a good idea, however, if I have a partial seal fracture that I cannot see, I expect when I bring the filament up slowly, the tube under test is going to fail pretty quick.  I am going to start there first.
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WBear2GCR
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« Reply #10 on: December 20, 2017, 09:01:47 PM »

I'm going to speculate that the circuit shown is "within tolerance" because of the reduced plate current and so
the screen current is similarly reduced... as compared to running the usual 2kV+ on the plates.

Still the idea of putting a screen supply in while grounding it via a capacitor has some merit.

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« Reply #11 on: December 20, 2017, 09:02:49 PM »

Treat it like a 4cx250.

--Shane
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WD8BIL
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« Reply #12 on: December 21, 2017, 10:59:25 AM »

A series of holes drilled around the socket, use a chimney and mount a fan directly under the socket on the chassis bottom.
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W4AMV
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« Reply #13 on: December 21, 2017, 12:53:10 PM »

A series of holes drilled around the socket, use a chimney and mount a fan directly under the socket on the chassis bottom.

Yes, that was my thought. Although if I can find the Eimac or Johnson equivalent  socket at a reasonable price, that would be nice. Applied filament V to all the tubes in the collection. No issues. Seals are fine and the heaters are operational. I had a good size muffin fan running over the tube bottom side, tube sitting on its radiator. Place a finger on the bottom side ceramic base and lightly warm. However, cut the air flow down a bit and the base can get uncomfortably  warm. How the author managed to be comfortable with no forced air is still a bit worrisome. Have to see.
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WBear2GCR
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« Reply #14 on: December 31, 2017, 07:44:42 PM »

I may have some spare sockets... email or PM me...

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Patrick J. / KD5OEI
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« Reply #15 on: January 01, 2018, 09:56:29 AM »

I can see using no anode cooling if the power is very low. Running it with no cooling at all on the base is may really shorten the life of the tube. The power is 6V@2.6A. They have large cathodes for their tiny size and very close spacing of the elements. The grid is extremely delicate and not designed for current, but some Eimac data shows a grid current of 1mA. As it is in the circuit where there could be grid current.

I don't disbelieve the article. It's a great practical experiment. If there were a way to find out the cathode temperature and adjust the heater current to maintain that under no-cooling conditions, it would be a possible aid. The author used a resistor to reduce the filament power probably to do that or to reduce it even below 'normal' as he said or implied. It would be interesting to know the heater voltage and current under normal circumstances and then see what it is in that circuit. A clue toward running the 4X150 without cooling. The cooler cathode would produce less current but how much is really wanted? Just if running it cool then don't 'saturate' the cathode or it might be damaged or stripped as they say?

If it's wanted to getter or hipot it, might be best to use base and anode cooling for that just to make sure it's in good shape.

Correction - data sheet with some control grid input etc. I must be having an off day!

* 4X150-A.pdf (382.44 KB - downloaded 5 times.)
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« Reply #16 on: January 01, 2018, 12:01:33 PM »

It would be interesting to see the imd output of that amp.



Especially with the grid resistor kicked in.

--Shane
KD6VXI
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