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Old 23rd May 2017, 9:13 pm   #1421
Station X
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Default Re: The "Sussex" Homebrew Valve Tester.

I think this may have been covered before:-

https://www.vintage-radio.net/forum/...&postcount=282
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Old 24th May 2017, 9:41 pm   #1422
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Default Re: The "Sussex" Homebrew Valve Tester.

The X-Ray diagram referred to in post 282 shows the cathode of D6 connected to the junction of R19 and R20. This is, as reported not as shown on the circuit diagram. However in my oscillator complete stability is obtained by connecting D6 the wrong way round according to the circuit diagram, the cathode should be connected to the junction of R19 and R20 with the anode connected to C6 and R17. The purpose of this diode has always puzzled me because it is not needed in the conventional phase shift oscillator. I would be interested to know the results obtained by other builders if they reverse this diode, i.e. place it the opposite way round to the circuit diagram.
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Old 24th May 2017, 11:42 pm   #1423
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Default Re: The "Sussex" Homebrew Valve Tester.

I ran the circuit through LTSpice.

With the diode with the anode to the resistor divider R19/R20 VR1 had to be set below 100 Ohm for the oscillator to start to oscillate.

With the diode with the cathode to the resistor divider I had to set VR1 at lower than 18 Ohms for the oscillator to start to oscillate.

Now, LTSpice isn't perfect but it shows an important thing here, you get a greater trim interval for RV1 when using the diode with the anode connected to the resistor divider than when used the other way around.

This might not be the case in the real world but it shows that the circuit works with the diode either way but with somewhat different settings of VR1.

I made some more tests as I saw that the oscillator produced a somewhat clipped top, like has been shown in oscilloscope pictures in this thread, by lowering R16 from 100k to 68k (or even 56k) I got a much nicer looking sine wave signal, all other component values like in the original circuit diagram. Now this might vary in the real circuit as it depends on the transistors used (hfe), but if you get a clipped sine wave signal then try to change (probably lowering) R16 - this will of course have to be checked with an oscilloscope. It also meant that the output signal from TR7 was looking a lot better with equal positive and negative peak voltage levels.

I've read that the diode is there for amplitude stabilization, but never seen any real description of how it actually works. It made only small differences in LTSpice but the center voltage on the collector of TR6 was better centered with the diode like in the circuit diagram with its anode to R19/R20.

/Martin
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Old 25th May 2017, 9:53 am   #1424
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Default Re: The "Sussex" Homebrew Valve Tester.

Basically I agree with your comments. In my case I did find that the output from TR6 was a pure sine wave after the modification but clipping occurred in TR7. A reduction in the value of R21 cured this and the scope now shows a pure sine wave. Initially I made the mistake of setting the 100mV using the scope, completely forgetting that it reads peak to peak and not RMS - senior moment!
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Old 25th May 2017, 2:23 pm   #1425
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Default Re: The "Sussex" Homebrew Valve Tester.

Here are two pictures of my interpretation of the Sussex VT1. The PCB boards are home made and most parts sourced from my collection of stored parts (or junk as my wife prefers to call it). The case is made with a base and back of wood, the end panels are polythene, sourced from kitchen chopping boards and the aluminium panel is covered with sticky back plastic.
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Old 26th May 2017, 8:54 am   #1426
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Default Re: The "Sussex" Homebrew Valve Tester.

Looks good Barry. Many happy hours testing your valves now.
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Old 7th Jun 2017, 7:38 am   #1427
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi, Does anyone know if Ed Dinning is still doing the transformers. I've emailed him a couple of times but no reply.

Is he OK? Is he on holiday maybe?

Regards

Simon
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Old 7th Jun 2017, 7:51 am   #1428
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Default Re: The "Sussex" Homebrew Valve Tester.

He checked in at 9.14AM yesterday and posted on 1st, 2nd, 3rd June.
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Old 7th Jun 2017, 8:01 am   #1429
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by Barryg4 View Post
Here are two pictures of my interpretation of the Sussex VT1.
It gladdens the heart and pleases the eye to see homebrew projects built to such a high standard, and from 're-purposed' materials, and that you made the PCBs too. I've no doubt that it looks just as neat and tidy 'under the bonnet'!
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Old 8th Jun 2017, 8:20 pm   #1430
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Simon, yes I'm still about, I've sent you a PM with my e-mail address.

Ed
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Old 19th Jun 2017, 6:27 pm   #1431
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Default Re: The "Sussex" Homebrew Valve Tester.

I am an Italian electronic technician, interested in building a ''Sussex''.

Where I can buy all the PCB's for it?

Many thanks, Vincent.
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Old 20th Jun 2017, 12:00 pm   #1432
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Default Re: The "Sussex" Homebrew Valve Tester.

Hello Vincent and welcome.
It's a long thread, but I suggest you start at post 1308 for your query. Assuming they're still available, Martin (post 1312) is the person to contact.
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Old 20th Jun 2017, 2:12 pm   #1433
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Default Re: The "Sussex" Homebrew Valve Tester.

Ok,
thanks
many thanks.

vincent
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Old 20th Jun 2017, 4:06 pm   #1434
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi Vincent, I can also stil supply the transformers.
PM me if you want one as I only build to order now.

Ed
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Old 13th Aug 2017, 8:30 am   #1435
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Default Re: The "Sussex" Homebrew Valve Tester.

Quote:
Originally Posted by G8UWM-MildMartin View Post
I still have (28) PCBs for sale at cost (8.12 GBP).
Plus, maybe, the cost of a padded envelope, depending on whether any suitable used ones are being thrown away at work, plus the ever-increasing Royal Mail postage cost, minus the discount from using the franking machine at work, plus any applicable curency transfer or exchange fees.
Hi Martin.

Are these still available?
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Old 21st Aug 2017, 12:40 pm   #1436
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Default Re: The "Sussex" Homebrew Valve Tester.

PM sent.
I have a few of those left, but now sell the current version (as improved by Martin-Dekatron in Sweden) of the main PCB @ 5 and, if required, his design of switch PCBs @ 4 for a set of 4, plus postage.
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Old 22nd Aug 2017, 11:35 am   #1437
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Default Re: The "Sussex" Homebrew Valve Tester.

Recent information in another thread (http://www.vintage-radio.net/forum/s...d.php?t=138636) on voltage settings in the Sussex made me decide to make a small piggy board for the PCB I made some time ago, and also a new main PCB, which incorporates the necessary components for the Supertex LR8 high voltage regulator. It replaces the zener chain and components used to get the +300V bias for the Anode and Screen switches.

I've had problems with zener chains in other constructions and replaced them with the LR8 which works a lot better. Here is the datasheet for the Lr8: http://www.microchip.com/wwwproducts/en/lr8 (Microchip bought Supertex some time ago).

I'll make a small batch of these PCB and test them before I publish the PCB here. They will incorporate a part that can be broken off if you want to mount it right on top of the current PCB but that part will contain two screw holes that can be used to place it somewhere else if you are looking to modify another older main board or your own design.
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Old 22nd Aug 2017, 4:24 pm   #1438
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Default Re: The "Sussex" Homebrew Valve Tester.

Thanks Martin, I was looking into the LR8 myself at your suggestion - a small PCB would be a useful option.
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Old 22nd Aug 2017, 5:40 pm   #1439
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Default Re: The "Sussex" Homebrew Valve Tester.

I just ordered a few of the small LR8 PCBs, hopefully they'll arrive in a week or two and then I'll test one - I don't have a Sussex myself but I can build and test the PCB anyway as it is just acts as a three pin voltage regulator.
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Old 29th Aug 2017, 6:36 pm   #1440
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Default Re: The "Sussex" Homebrew Valve Tester.

Hi !

I have the project of a Sussex-like tube tester that has higher current capability to be able to test power tubes, especially those used in guitar amps such as EL34, KT88, 6V6GT etc. I left the project for a few years because I lacked time to build it, but now I'm on it again.

I have a question regarding the testing of power tubes.

Will applying a 100mVAC sinewave on the grid be enough to get a faithful reading of gm? Should I implement a sinewave level switch with according division of the signal feeding the meter ?

Thanx in advance.

Best regards

Eric
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