Re: The "Sussex" Homebrew Valve Tester.
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D12 and D14 are shown the wrong way round on the board layouts. I have placed amended sketches into my handbook on:- http://homepage.ntlworld.com/lez/Sus...%20version.doc Many thanks for the feedback, Les |
Re: The "Sussex" Homebrew Valve Tester.
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Re: The "Sussex" Homebrew Valve Tester.
Page 11 doesn't have any text apart from the component lists.
The Document is about a Commercial - Philips - Valve Tester, which is hardly the context of the current Thread nor the Poster's comments on his own unit. Is he saying that he did the same and it worked? Alan |
Re: The "Sussex" Homebrew Valve Tester.
It's the right link and it is Fig 11. Quoting F. Langford Smith, p1283, Radio Designer's Handbook available as free download here;
http://www.tubebooks.org/technical_books_online.htm "Parasitic oscillations often occur at frequencies of the order of 100MHz with leads from valve sockets forming resonant circuits, and with a feedback path provided by a few pF of capacitance between plate and grid circuits." Placing a capacitor between control grid and earth, but remote from the socket, won't eliminate parasitics under all operating conditions because there is still a good lead length. The 100R resistors and 270pF capacitors soldered right on each of the valve pins do. It's normal design practice to use grid stoppers soldered as close as possible to g1 and g2 (and in extreme cases to anode) socket pins but this isn't possible here. Proof of concept can be tested before committing, by testing, for example, an EF183 or EF184 and soldering just three RC pairs with short leads to g1, g2 and a (pins 2 and 8 and 7) of the B9A socket base. They should have no effect on DC voltages used during leak testing etc. or on your 1KHz test signal but I confess that I haven't fully studied the design. Values aren't critical and cheap 5% 1W resistors and 1000V 220pF ceramic capacitors would suffice. On my curve tracer design, there were extreme current and voltage surges, or constant current effects on the XY recorder without these in place when testing EF183, though I could successfully trace ECC82 characteristics. My first thoughts were to build an adapter with 240R stopper resistors soldered close to each pin with small switches to short out those not required. A clumsy solution. Then I came across this thread researching other options. I continued, wondering how it was done historically and came across the simple Philips design. Tried proof of concept, and it worked. Regards, Bob |
Re: The "Sussex" Homebrew Valve Tester.
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Re: The "Sussex" Homebrew Valve Tester.
.... and Post #505 answers my question. It was copied from a Commercial Design and it did work in the home-brew version.
Alan |
Re: The "Sussex" Homebrew Valve Tester.
WOW!
I stumbled on this incredible project about a week ago, but it seems that I'm a little more than a year behind. Sure have some catching up to do! I've read almost 400 of the posts and am getting geared up to build this thing, but hope that I haven't missed the boat on getting a transformer and PCBs. I even read that someone talked about getting a few kits together, but I assume that time has passed beyond that idea. I don't yet have PM credentials, but would like to get a post up that I'd like to get a transformer (USA version) and PCBs if they are still out there. Someday I'll be a big kid and will be able to send PMs. Thanks, Ed |
Re: The "Sussex" Homebrew Valve Tester.
Welcome to the forums. You are now a big kid.
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Re: The "Sussex" Homebrew Valve Tester.
Hi Ed, transformers still available, PM sent.
Ed |
Re: The "Sussex" Homebrew Valve Tester.
Hello Ed, I'm interested in the transformer, could you please send me a pm with the details?
Also, is there a pcb available as well? Many thanks Alejandro |
Re: The "Sussex" Homebrew Valve Tester.
Alejandro
Martin probably has some PCBs left, look through the earlier postings Mike |
Re: The "Sussex" Homebrew Valve Tester.
Hi Mike,
Many thanks for your response and great work by the way! I've been testing my valves with a breadboarded simple voltage regulator, CCS and driving the grid with an audio oscillator to measure GM. Recently I saw the RAT tester and started modifying the circuit with some enhancements and changes. I also got a set of LCD meters from eBay which are sourced by 8-12V AC/DC. Question: does each one of the meter need a separate floating supply to ensure there is no loop currents across them to avoid burning? Thanks for the help Cheers, Ale |
Re: The "Sussex" Homebrew Valve Tester.
Hi Ale, PM sent.
Yes, the meters need seperate supplies in this application. My transformer covers heater voltages from 4 to 12.6; the US version with a 110v primary also has a 2.5 v heater tap for the power triodes that were popular there. It would make for a very bulky and costly transformer if I included all heater voltages up to 110v, so it is suggested that you use an external power supply for the odd values. Ed |
Re: The "Sussex" Homebrew Valve Tester.
Hi,
I found my way to this thread (a year late, it would seem) as a result of my request for a reasonably priced valve tester on the "wanted" section. WOW! What can I say, you guys have really mapped it all out. I have not yet found the neccessary twenty hours to read all the posts, but am really interested. Are the Transformers and PCB's still available? Parts lists? Wiring diagrams?And from whom? Thanks, Barry PS. Sorry if all these questions have been asked before |
Re: The "Sussex" Homebrew Valve Tester.
Hello all,
I'm a newbie to this Forum as well. I understand from reading some of the previous posts by 'swordholder' that the pcb might still be available from "Martin"? Much obliged if Martin can please indicate if this is so..many thanks... |
Re: The "Sussex" Homebrew Valve Tester.
Hi,
Has anyone considered using thumbwheel switches (either edge wheel or pushbutton) instead of the 9 pin selector switches? They would seem to be closer to the AVO style selector and would take up far less panel space. Most of the ones I have looked at, have poor current switching ability (200mA) but at 1Amp current carrying capacity seem to be up to the job. As I recall the rotary switches are also poor at current switching. Here is a link, NOTE: the decimal switch, not the BCD coded version. http://www.farnell.com/datasheets/310077.pdf Barry |
Re: The "Sussex" Homebrew Valve Tester.
11 undrilled PCBs left (plus 2 reserved) at £10 ea. including UK post.
(Plus £1 for EU or £3 for the rest of the world.) I have also built 10 (including mine!) PCBs up, but not tested them yet, price TBA. |
Re: The "Sussex" Homebrew Valve Tester.
I am intending to try thumbwheel switches in my version of this tester.
But I have hunted out some huge thumbwheels to help with both current carrying and high voltage requirements. The main thing is not to expect the switches to be moved when carrying current. I never move the Avo tester switches when a valve is being tested anyway. PM me if you want to try this option as I had to buy a large batch and have quite a lot spare. I could easily make up a 9-way set for you! (PS Avo photos coming soon as requested) regards Jeremy |
Re: The "Sussex" Homebrew Valve Tester.
Hi Gents, Sussex transformers wound as required, £65 including UK postage. I also have a version with a US (110V) primary available.
Ed |
Re: The "Sussex" Homebrew Valve Tester.
All my spare thumbwheels now gone - that was quick!
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Re: The "Sussex" Homebrew Valve Tester.
Hi,
I know I am simply showing my ignorance, but I have to ask :-[ I understand that the three meters need to have a separate power supply from the circuit they are measuring. But would it be possible to run all three meters from a single supply so long as it was isolated from the rest of the circuit ? If not, could anyone explain to me just why not ? ??? Thanks in advance ! |
Re: The "Sussex" Homebrew Valve Tester.
No. The meters' supplies need to be isolated from one another, because they are not all referenced to the same "ground".
The grid voltage meter is referenced to the cathode, but the anode current and gain meters are in series with the anode supply. |
Re: The "Sussex" Homebrew Valve Tester.
Hi AJS,
I'm still working on my Sussex - are you indicating that each meter needs it own power supply?? Regards Rob |
Re: The "Sussex" Homebrew Valve Tester.
Rob,
Each meter needs its own supply, Eds transformer has 3 separate 6v windings, one for each meter Regards Mike |
Re: The "Sussex" Homebrew Valve Tester.
Hi Gents, the meter windings on my transformer are white insulated wire and are tri-filar wound so they all see the same voltage and are well insulated from each other. The lead-outs have either 1, 2 , or no knots in them for ID.
Ed |
Re: The "Sussex" Homebrew Valve Tester.
Thanks Ed,
This is a timely reminder that I should finish what I started and complete my tester! Regards Rob |
Re: The "Sussex" Homebrew Valve Tester.
3 Attachment(s)
Here's a few pictures of my Sussex testing a 40 year old Dynaco branded ECC83. Some valves just seem to go for ever!
The case is from an old subwoofer amplifier which had lost its side panels, so I made the curved wooden side pieces as a nod to the Avo MkIV. A big thanks to everyone who helped simply through your posts to this forum and especially to Mike (swordholder) for sharing his original project.:thumbsup: Gordon |
Re: The "Sussex" Homebrew Valve Tester.
Hi Gordon,
That's a very handsome looking tester unit you got there!... very well done indeed. What did you use for the letterings for your Sussex panel faces..did you use white 'Letraset' transfers? Regards...Gary |
Re: The "Sussex" Homebrew Valve Tester.
Gordon, congratulations! What a great job you've made of that. Want one ... :-) How did you apply the lettering?
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Re: The "Sussex" Homebrew Valve Tester.
Thanks for the kind words -yes, it is white Letraset - bit of a pain to apply, but easy to remove if you make mistake - which I did numerous times! Once on it's quite durable - I have some valve amps I built many years ago where the lettering is still in good condition. In hindsight I wish I'd used 3mm letters instead of 5mm as it's a bit congested in the centre of the case - still, as age will no doubt take its toll on my eyesight using the larger letters might be beneficial in years to come!
Gordon |
Re: The "Sussex" Homebrew Valve Tester.
Hi,
Can one of you who have already completed their tester please help. What should be the RMS value of the control grid signal 100mV or 1V? Reading through the complete thread I have found references to both values. Thanks in advance. |
Re: The "Sussex" Homebrew Valve Tester.
100mV
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Re: The "Sussex" Homebrew Valve Tester.
Thanks Top Cap,
I found your drawings and notes inspirational. I will post pictures of my tester when the darned meters turn up! |
Re: The "Sussex" Homebrew Valve Tester.
Many thanks for the compliment. I tried to explain in the notes how the 100mV signal was seen as a voltage across the 10 ohm load resistor such that the meter gave a direct reading of gm. However, writing technical notes is like writing software, one thinks everyone can understand it but only when someone tries to follow it you realise the deficiencies in ones work. I even get the same problem when sending Morse code, people come back at ridiculous high speeds (not to them) and I find it so dis-heartening to keep up that I give up. However, on this Forum, one finds everyone wiling to do whatever it takes to help someone, whatever the problem. Something that makes this Forum such a wonderful place so never be afraid to ask. Hope you have final success with your 'Sussex VT', you will find the project to have been very worthwhile.
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Re: The "Sussex" Homebrew Valve Tester.
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Peter M6XRH |
Re: The "Sussex" Homebrew Valve Tester.
Peter.
You just start to read from page 1, it is all here in this thread :-) Joe. |
Re: The "Sussex" Homebrew Valve Tester.
Hi everyone,
I'm still working on my updates and tweaks to the Sussex. Question: is there any particular reason why it wasn't added the mu meter as in the RAT tester? Les, Ed, Many thanks for your notes and help, it has really helped me a lot in making some good progress in the circuit updates. Hopefully I can etch the new PCBs and test the circuit soon... Cheers, Ale |
Re: The "Sussex" Homebrew Valve Tester.
I just bought some thumbwheel switches from Ebay (item number: 290538529383). They have only 6 segments so I bought two so that I can combine them. Do you think these will be suitable for the Sussex? The datasheet says they are rated 28 VAC or 28 VDC at 125 mA but they can handle max. 3 amps non-switching. Does the voltage rating apply in non-switching conditions? Normally you don't ever need to switch these under load. The datasheet also says that the dielectric strength is 750 VRMS so I'm hoping it'll be able to handle the anode / screen voltages as well. What do you think?
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Re: The "Sussex" Homebrew Valve Tester.
As these are used in a non-load breaking application they will probably be OK.
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Re: The "Sussex" Homebrew Valve Tester.
Hello All,
Although I havent tried them, I found these on the net http://www.sourcingmap.com/pcs-elect...-p-111670.html Looks like a very good price, maybe worth a punt if you are looking for a roller switch. Mike |
Re: The "Sussex" Homebrew Valve Tester.
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I have another question. I too would like to include a diode / rectifier testing functionality into my version of the Sussex. The circuit similar to AVOs method of testing that was described here earlier seems to be the way to go. But does it really work the same way? I've been studying the AVO circuit and it basically just has a fixed resistance (700 ohms in total) in series with the valve (I assume that the capacitor can be discarded because we are using DC). In the lowest 3 ranges there is also an additional resistance added in series (18.6k/1mA, 3.6k/5mA and 600ohm/15mA). I've been doing some calculations and if I'm correct it seems that this arrangement lets the valve being overrun in some cases. On the other hand the current limiter / constant current circuit in the Sussex can apply up to full test voltage (60, 100, 175 or 225 volts depending on the range) across the valve enabling the maximum current to pass even if the valve is low in emission. For example a normal EZ80 will pass 40mA (per anode) if the voltage across it is 30V (according to the graph in the datasheet). Surely you can squeeze out that same 40mA from a weak valve by just raising the voltage? If the only goodness indicator is the anode current meter then all the good and some weak valves will show exactly the same reading which is the value of the current limit in that range. Or am I completely wrong about this? Perhaps a working solution could be achieved by combining the AVOs resistor arrangement and the current limiter? Would this still give meaningful results just with a current meter? Would it be difficult to incorporate a good/bad scale into the Sussex? It could be made for example from a multicolour LED bar graph display but how to control it? Anode current/voltage ratio? I assume it varies between valve types so it can't be easily used? I hope you can make some sense of my ramblings :-/ Timo |
Re: The "Sussex" Homebrew Valve Tester.
I looked at using these small thumbwheels as I had some "in stock", although I then found some larger ones. But they should be fine - I tested the insulation strength on mine with a modern megger and they showed no leakage at all at 1000V between adjacent sections. As long as they are not switched while carring HT or LT all should be well. But don't let them get greasy or wet!
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Re: The "Sussex" Homebrew Valve Tester.
Hi Timo
In post #266 I posted a circuit for a diode function that I am using on my Sussex. It is current limited which varies depending on range selected and the voltage across the diode varies depending on range. It is up and running, but I haven't got a low emission diode to verify that it will show it up as low emission. It is based loosely on the AVO circuit and on the higher ranges it will overload the HT transformer but as the test will be only for a brief period it is able for that short term overload. Frank |
Re: The "Sussex" Homebrew Valve Tester.
Hi Frank. It would be very helpful if you could test how that circuit works since you have already built it. I'm by no means an expert so I might be fussing over nothing. Bytheway, does the AVO show just the good/bad reading on the scale or does it show the actual current value also (when testing rectifiers)?
Here's an excerpt from a web page that I found recently (http://www.jacmusic.com/Tube-testers/): Quote:
Timo PS. I just found there are more types of those thumbwheel switches available that swordholder mentioned. The type KM2 is the smallest of them (dimensions are mentioned in the description). The bigger types might be more legible. They are also sold in Ebay for slightly lower prices. http://www.sourcingmap.com/products_...type/all/bar/1 |
Re: The "Sussex" Homebrew Valve Tester.
Hi Timo
Referring to the diagram I posted. S1d sets the Anode voltage to the diode under test and this will not change unless the current goes over the current limit which is set by S1e. The Anode current will change depending on the emission and can be read the same way as a triode or pentode. I don't know much about the AVO's the only ones I have seen were in photos. Frank |
Re: The "Sussex" Homebrew Valve Tester.
The AVO Valve Testers (AVO Mk I, II, III, IV, CT160, CT160A and VCM163) have a RED/WHITE/GREEN scale of "Goodness" for the valve rectifier tests. In the CT160 manual on page 7 you can read that this scale is made so that the GREEN zone is from 130% to 70% and the WHITE zone from 70% to 50% and the RED zone from 50% to 0%.
Then on page 8 and 9 AVO says that the design is made in such a way that the circuit will let a valve rectifier pass a current that is equal to the maximum load current for the valve. The circuit is then scaled so that a valve passing this current deflects the meter to the center of the GREEN scale. Since we know how the scale is made up from these coloured zones we could in fact read the current on the scale if there had been any lines to show it, but now we will have to make an educated guess from what we know from the percentages. Full scale deflection in fact corresponds to 135% of the current flowing through the valve at each range, with some small variation for each range except for the VCM163 which has larger deviations on some ranges. I am currently writing an article explaining all of the maths and why the components are choosen as they are inside an AVO valve tester but it is probably a few days (if not a few weeks) before I can finish it. Then you will be able to read more about it here on the forum. |
Re: The "Sussex" Homebrew Valve Tester.
Hi Martin
Thanks for explaining that, it will make it easier for me to interpret the readings I get and make them more meaning full. Frank |
Re: The "Sussex" Homebrew Valve Tester.
5 Attachment(s)
Hi,
I started late, on my build but with help from various members I think I have caught up. This is my VT1 built into an RS service case (about £29) , at just over A4 footprint it makes avery compact and portable valve tester, and works a treat. |
Re: The "Sussex" Homebrew Valve Tester.
Very nice job there, very professional presentation.
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Re: The "Sussex" Homebrew Valve Tester.
Well done a neat and compact build.
Frank |
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