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Old 23rd Feb 2020, 3:24 am   #1
retailer
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Default Tennis Ball Triode Testing

Has anyone had the nerve to test one of these - it is a STC 4104D tennis ball type triode, while I'm not sure if it is from 1920's or later I believe it is one of the earlier ones as it has a metal base, the tips of the pins have a yellow metal coating, could it be gold ? - the filament is ok so and all of the internals are clearly visible and I can't see any signs of a short so it should be operational, the glass is slightly tinted so I'm assuming it has had some use - but I am a bit hesitant to hook it up to my valve tester, no socket for it so I'll have to use flying leads, should I take any precautions or just hook it up and see ?
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Old 23rd Feb 2020, 3:55 pm   #2
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Default Re: Tennis Ball Triode Testing

Found this on the National Valve Museum site:

http://www.r-type.org/exhib/acl0004.htm

Appears to have been used for telephone repeaters
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Old 23rd Feb 2020, 5:09 pm   #3
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Default Re: Tennis Ball Triode Testing

Strangely an STC 4104 is also a microphone :-

https://www.canford.co.uk/Products/9...MICROPHONE-Lip

Now made by Coles.
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Old 23rd Feb 2020, 5:23 pm   #4
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Default Re: Tennis Ball Triode Testing

My take is if you want to use it, use it in a radio, if I had one I would build a radio especially for it, I would enjoy using such a thing for the history.

Otherwise leave it be for the next custodian.
 
Old 24th Feb 2020, 11:32 am   #5
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Default Re: Tennis Ball Triode Testing

Hello Retailer,
The valvebase looks rather like an oversize B4. If you have an old gash B4 valve lying around - use it's base to make an adaptor. If your valve's pins are slightly larger then perhaps the pin sockets out of an old American UX valve holder might fit. Refit(Araldite) these pins into a circular piece of paxolin, at the correct spacing, then connect to the B4 base(more araldite), & away you go.
One needs to treat these old(nigh-on 100 years old) valves very carefully. Preferably securely upright in a valve tester or adaptor box, not lying loose on a workbench just connected with crock-clip leads.
Several years ago I had to do something similar with a much larger 1930's STC4212D.

Regards, David
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Old 24th Feb 2020, 3:58 pm   #6
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Default Re: Tennis Ball Triode Testing

I'm not 100% certain but I think it plugs into a UX4 bayonet socket, the pin spacing/pitch is the same as an 80 rectifier, the filament pins are however a smaller diameter and may or may not make contact with the socket, the tips of the pins are I think faced with gold (or at least it looks like gold) so the pins are meant to make contact on the tips and not the sides. I before I do anything with it I'll either make or buy the correct socket - as you say best thing to do - minimise chances of knocking something over and breaking it. I do have another one that is still in storage - I believe it is new and never used it is still in it's original box that has been marked as "spare" plus a bunch of STC and and WE triodes that I believe were used in telephone repeater equipment. Back when I picked them up they were quite cheap a large carton of them was $50 and I thought I overpaid at the time - I had big plans for the ultimate SET amplifier but 20yrs later I've done nothing with them.
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Old 24th Feb 2020, 6:06 pm   #7
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Default Re: Tennis Ball Triode Testing

The interior design of the valve really brings home the American practice of calling the anode the 'plate'.
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Old 25th Feb 2020, 11:41 am   #8
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Default Re: Tennis Ball Triode Testing

Retailer, if you have some decent boxed NOS STC valves from the 20's/30's, then if they test out fine(no reason why they shouldn't), the might be worth a lot of money. If my STC 4212 experience is anything to go by.
Some members of the Audiophile fraternity have been paying top dollar for rare 20's/30's Triodes, particularly the powerful ones. Big brass bases & unique shapes are desired to enhance retro Stereo & Quad amplifiers, so I'm told.

Regards, David
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Old 25th Feb 2020, 3:47 pm   #9
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Default Re: Tennis Ball Triode Testing

I spent a few hours at the workbench and came up with this, looks a bit agricultural but works, I think the correct socket is either a UY4 or UX4. I have WE and STC valve data pdf's and the data is a bit conflicting the STC book gives 60mA as the max anode current and the WE book gives 25mA as the average anode current, both books give 190v as the max anode voltage various sources around the internet give anode currents from 12mA up to 50mA not wanting to push things I decided on 25mA and 160v, this came up easily, bias voltage was around -35v, Gm of around 1.2mA/V. I could easily get the anode current up to 35mA and could have gone higher but didn't.

This was a pleasant surprise as my tester does not have a 4v filament setting (STC = 4v, WE = 4.5V which is right ?) so I used the closest which is 3v, with only 75% or so filament voltage I would have expected the valve to struggle to reach 25mA anode current, amazing - I did not really expect this from a valve that is close 100yrs old.
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Old 25th Feb 2020, 5:12 pm   #10
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Default Re: Tennis Ball Triode Testing

I think you've done an excellent job. 'Specially with the flat stable base. What I would suggest, and it would give you a reference(and a selling point, should you wish to flog it), and be a reference for other Forum folk or Australian vintage radio chums - would be to draw up its Gm graph. Say - using Va of 160V & a stepped range of -ve Vg from -45V to -30V in 1V steps, but limiting Ia to a max of 50mA. If it looks OK, then maybe you could try a family of curves - say one at Va at 150V & another at 180V. Again limit Ia to 50mA, and don't linger more than a couple of seconds at that value, to be on the safe side.
This is what STC used to do back in the day in their valve data manuals. I've a 1940's one somewhere, so will look it out & see if your 4104D is in it. I find these lovely old Triodes fascinating, much better than testing predictable KT66's etc.

Regards, David
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Old 26th Feb 2020, 11:52 am   #11
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Default Re: Tennis Ball Triode Testing

The STC 4104D datasheet is accessible from the r-type.org link in post#2.
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Old 26th Feb 2020, 3:51 pm   #12
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Default Re: Tennis Ball Triode Testing

Here is some STC valve base info from my 1940 Ref Book. Dave
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Old 28th Feb 2020, 3:49 am   #13
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Default Re: Tennis Ball Triode Testing

I saw the data sheets on r-type.org - I also have seen a number on various internet sites and they do not always agree 100% it was the filament I was concerned about not sure how tolerant of over voltage early filaments are, one source gives 4v and another gives 4.5v in the end it was my tester that decided for me as it has no 4v setting which is why I went for the nearest at 3v.

The correct socket according to the Western Electric data sheet is either a 100L or 100R western electric socket I located a pair on the 'bay for an eye watering AU$1200, I've seen these at car boot sales in the past and never bothered with them, now that I know I'll probably never see another.
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Old 28th Feb 2020, 11:24 am   #14
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Default Re: Tennis Ball Triode Testing

Perhaps if you make a big dollar sale you could buy a posh house out in Morphett Bay. Regards, David
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