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Old 30th Jan 2013, 1:22 pm   #761
ColinTheAmpMan1
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Default Re: The "Sussex" Homebrew Valve Tester.

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Originally Posted by Pamphonica View Post
If anyone wants ferrite beads to put on all the leads right next to the valve bases, to stop oscillations, I have a few(!) available.
Hi All,
I am desperately trying to assemble all of the parts to make my own Sussex VT1 and was trying to decide what valve-bases would be useful to have. I got onto the thought of top-cap leads. It made me wonder if the length of such leads should be as short as practicable and if, in fact, they should also be fitted with ferrite beads to stop oscillations. Any thoughts? What did AVO, Hickok and Taylor do about top-cap leads?
Regards, Colin.
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Old 30th Jan 2013, 2:51 pm   #762
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Default Re: The "Sussex" Homebrew Valve Tester.

Colin, you should use ferrite beads on top cap leads, AVO and many others did so just for the reason to stop oscillations. Place it as close as possible to the clip at the top.

You will probably also benefit from more ferrite beads in the wiring, have a look at the AVO patent on how they stopped oscillations by putting the wiring between the valve sockets in a loop with ferrite beads distributed on strategic places along the wiring. The wiring was then tapped at one point where the roller selector was connected to it and then the wiring went from the roller selector to the valve tester electronics. The patent can be found here: https://www.vintage-radio.net/forum/...ad.php?t=86837 and is numbered GB735865A. the tapping point would then be where your rotary switches would be connected to the wiring loops. AVO used ferrite beads on the wires closest to teh roller selector switch so you should put ferrites on your rotary switches there too.

The "dampening resistance" AVO speaks of were in fact just standard resistors with a value from 75 Ohm up to 120 Ohm, and in some case higher resistances, used by AVO in the Mk I & II valve testers, these resistors were later replaced by ferrites in the Mk III & IV valve testers.

The beauty with the resistance in the loop is that it is not seen as a resistance by the low frequency heater voltage just because it is connected in a loop, both ends of the resistor are shorted by the wiring which means that full current is delivered to the valve heater. But at high frequencies (unwanted oscillations) the wire acts as both a coil (inductance) and a capacitor and together with the resistance (ferrite or resistor) it all then acts as a dampening solution effectively stopping most oscillations, not all but most.

So it seems like a combination of resistors and ferrite beads would stop more oscillations than just one or the other - perhaps something to test by someone? I definately know that either ferrites or resistors is not enough to stop oscillations with all valves, but a combination of them stops oscillations for some valves.

Modern automatic computerised valve testers have this problem since they use wiring that is not connected in loops (some do though) which means that you have to build a socket adapter for each troublesome valve that you want to test just because the pins are not in the same place for another valve, you can imagine what it would do to put a 4.7K grid stopper resistor in the heater connection.

/Martin
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Old 1st Feb 2013, 12:19 am   #763
ColinTheAmpMan1
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Martin,

Do I take it that you are suggesting that using the "loop" method with a low-value resistor incorporated in the "loop" and putting ferrites at the valve holders and other strategic places would be a good idea? The AVO patent only refers to the "loop circuit with damping resistor" improvement; nothing about ferrites.

While your information is appreciated, I am still a little confused. It seems that valve-bases with the same number of pins should be put into their own loops. While I can see the logic in that, would it cause any problem if a 7-pin base was included with the eight-pins, or would it be best if separate loops were made. I suppose this wouldn't be a problem with separate loops for 7-pin, 8-pin and 9-pin bases, but including a 5-pin (UX5 for 807s) now gets us to four loops. This seems a little tricky to me.

Regards, Colin.
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Old 1st Feb 2013, 1:45 am   #764
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Default Re: The "Sussex" Homebrew Valve Tester.

Colin, at low frequencies an ordinary resistor works just as you will think of a resistor, but at high frequencies the ferrite works as a "resistor" too (more complicated than just a resistor but that is the anology).

AVO used ordinary resistors (and also some capacitors) in their first models and then went on to use ferrites only in their latest models - so ferrites only will work for most cases.

AVO only says that these ferrites should be placed in "strategic" places, so without a lot of high frequency measurements you can't know exactly where they should go in a new design.

But doing like in the Polish valve tester ELPO P-508 uses a ferrite at each end on each wire will probably work just fine, but you'll need a lot of ferrites then. If I remember correctly AVO used ferrites on seven, out of the nineteen, valve sockets and at the roller selector switch in the valve panel of an AVO Mk IV. You can see some photos here: http://www.fonar.com.pl/audio/fotki/..._p508/p508.htm - this Polish valve tester use the AVO roller selector switch, I am not sure if it is an original one or a copy though.

The wire loops should be of approximately equal length, just as the patent says, which means that you just let the unused wires pass by that valve socket and continue to where they should be connected. So every pin-1 should be connected to every other pin-1 and so on but the wire for pin-8 should just pass by the B7G socket, so it still hase approximately the same length as the first seven wires.

Don't forget to either isolate each ferrite bead with shrink tubing, or place them over the plastic insulation of the wire - the way AVO did, and then just make small kinks in the wire or use glue to keep them in place. The ferrites will otherwise short the wires if they touch each other.

You can have a look at Ronald Dekkers uTracer 3 manual here: http://www.dos4ever.com/uTracer3/uTracer3_con_man.pdf on page 50-52 where Ronald shows some photos of the wiring and also has written about it.

I'll be happy to answer any more questions on this but if you are interrested in knowing exactly how ferrites work and more about high frequency stuff you'll have to ask someone else that is more knowledgeble than me in those areas.
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Old 1st Feb 2013, 3:49 pm   #765
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Default Re: The "Sussex" Homebrew Valve Tester.

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Well, it looks like I am going to build a Sussex, so count me in for one of the next batch!
Me too I'd take one, so count me in too.
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Old 3rd Feb 2013, 9:05 pm   #766
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Default Re: The "Sussex" Homebrew Valve Tester.

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I'll be happy to answer any more questions on this but if you are interrested in knowing exactly how ferrites work and more about high frequency stuff you'll have to ask someone else that is more knowledgeble than me in those areas.
Hi Martin,

Many thanks for this info. I don't think I am particularly bothered about how ferrites work, just so long as they do. I'm guessing that you can't really have too many. If there is one on a lead close to a valve-base terminal, then that will probably suffice, but a few more scattered around won't do any harm. I now have a much clearer idea of how the physical wiring of a reliable valve-tester should be.

It might be interesting to know if anyone has had any problems with valves oscillating while being tested on a Sussex VT1. Or maybe anyone who has experienced no problems at all, even though the loop wiring/ferrites solution wasn't used?

Regards, Colin.
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Old 3rd Feb 2013, 10:41 pm   #767
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Folks, Sussex transformers are still available and are wound to order. PM me if you need one and I'll get it wound on my return.

Ed
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Old 8th Feb 2013, 4:42 pm   #768
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Ed, I'd like a transformer doing but don't seem to be able to PM you?

Steve
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Old 8th Feb 2013, 4:46 pm   #769
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Default Re: The "Sussex" Homebrew Valve Tester.

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Well, it looks like I am going to build a Sussex, so count me in for one of the next batch!
And another

Steve
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Old 9th Feb 2013, 7:29 am   #770
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Steve, you need several posts before you can send a PM. I'll put you on the list as I'm currently on holiday at my son's. I will be winding a batch for the end of Mar. I'll PM you details later.

Best regards, Ed
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Old 14th Feb 2013, 5:45 pm   #771
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Martin,
I'm new here so cannot yet PM.
I am interested in getting a PCB, are some being done?
Cheers
Paddy
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Old 15th Feb 2013, 9:16 pm   #772
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Default Re: The "Sussex" Homebrew Valve Tester.

Yes, I finally got round to ordering 30 of Mike Rowe's original design this week.
This time they'll be machine-drilled all holes 0.7-0.8mm and HASL tinned, but again all 3 on one platen, no solder resist nor screen printing. They should be ready in a couple of weeks. (Total cost was 243.60, so 8.12 each plus postage.)
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Old 17th Feb 2013, 3:49 pm   #773
ColinTheAmpMan1
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Default Re: The "Sussex" Homebrew Valve Tester.

Martin, you have a PM.
Colin.
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Old 1st Mar 2013, 3:20 pm   #774
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Default Re: The "Sussex" Homebrew Valve Tester.

Hello Mike,

As you are prepared to send circuit of your valve tester perhaps you could send a copy to me either by e-mail or post to me here.

Thanks

Ken
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Old 1st Mar 2013, 3:50 pm   #775
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Default Re: The "Sussex" Homebrew Valve Tester.

You don't say which Mike you're refering to. If you mean Swordholder, then I'm afraid he's been dead for over a year, as evidenced by his "Rest In Peace" status.

https://www.vintage-radio.net/forum/...ad.php?t=79144

Circuits and a handbook are available via the links in post #1.
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Old 21st Mar 2013, 5:39 pm   #776
Mike Brett
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi all
I was seriously thinking of building the simple version of the valve tester posted elsewhere on this site. I am now wondering why not go the whole hog and build the Sussex valve tester. As always it is down to cost, being an O.A.P. funds are not unlimited, but I have been so impressed by others efforts that I would dearly love to have a go. Are the main parts still available , I suppose this would include the transformer and P.C B. and any other hard to find items. If someone could give me the price of these plus the rough cost of the whole project I could start the ball rolling.
Cheers Mike
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Old 21st Mar 2013, 6:10 pm   #777
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Default Re: The "Sussex" Homebrew Valve Tester.

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If someone could give me the price of these plus the rough cost of the whole project I could start the ball rolling.
I kept my own copy of the original BOM for use as a shopping list and tracked the prices. For me it came to about 250, but I did have to buy a few tools too. Case and hardware selection seem to make a big difference to the price.
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Old 23rd Mar 2013, 9:50 am   #778
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Default Re: The "Sussex" Homebrew Valve Tester.

I have taken the plunge and ordered the transformer and pcb, and am now searching my stock of parts to see what else I need to buy. With inflation everything is a bit more costly
than when the project first started ,but I would think 250 is a fair estimate at todays prices.Wish me luck.
Mike
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Old 23rd Mar 2013, 3:12 pm   #779
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi all
Normally I would put this in the wants thread but this is aimed mainly at Sussex builders.
I was going to order my resistors from Rapid but the minimum order for the specified 0.6 watt resistors is 100 each. Some I only need one of, plus I have thousands of resistors but they are all .25 watt only. Has anybody got the following ones I need in the 0.6 Watt rating they could sell me .
1 x 1R, 3 x 10R, 1 x 22R, 2 x 100R, 3 x 470R, 3 x 1K, 1 x 2k7, 12 x 10K, 2 x 15K, 4 x 30K,
1 x 100K, 6 x 150K, 1 x 300K, 1 x 470K, 1 x 820K, and 2 x 1M.
Many thanks Mike
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Old 24th Mar 2013, 5:59 am   #780
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Mike,
R27 (2K7) and R2 (120K or 100K ) are the only resistors I know of that need to be more than 0.25W.
For tolerances, R12's can be calibrated out, but R13 might be worth going to 1%.
Tolerances on R32-41 (twice!) for the Anode & Screen volts may tend to average out and it's debatable how critical the tolerances on the individual settings are anyway bearing in mind the tolerance on the zeners ZD1-7.
Best regards,
Martin.
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