10th Nov 2011, 10:09 am | #601 |
Nonode
Join Date: Mar 2008
Location: Virginia Water, Surrey, UK.
Posts: 2,877
|
Re: The "Sussex" Homebrew Valve Tester.
I have had quite a few PM enquiries recently about sourcing thumbwheel switches.
I got mine from Electrovalue, a fine place for odds and sods of surplus stuff. But I cleaned him out and he says he definitely has no more. The ones I had made up only 3 or 4 sets. All I have left is a lot of end-cheeks! For reference they are about 2.25" square and have very wide-spaced tracks on the pcb. The action is rather jerky and stiff but at least they click positively into place. I have yet to test them on higher heater currents but they look fairly meaty. For anyone new to thumbwheel switches it's worth noting that virtually all currently available (surplus) switches are BCD coded (binary, 4-contact) not decimal, which is useless. Make sure you see a full set of 10 contacts on the back, plus common. Contacts marked 1,2,4,8 instead of 1,2,3,4... are a giveaway of the BCD type. If I find a good source of big switches I will post here. All the best Jeremy
__________________
Jeremy, G8MLK, BVWTVM Friend, VMARS, BVWS Secretary. www.pamphonic.co.uk www.bttt.org.uk |
10th Nov 2011, 1:46 pm | #602 |
Nonode
Join Date: Jun 2005
Location: Western Lake District, Cumbria (CA20) - UK
Posts: 2,136
|
Re: The "Sussex" Homebrew Valve Tester.
These from RS should be OK. Bit pricey though.
Bear in mind that the ratings are for make or break under load. Presumably you are going to set the switches up off load as with the AVO VCMs. The current rating isn't so important under those circumstances.
__________________
Brian |
16th Nov 2011, 11:56 pm | #603 |
Pentode
Join Date: Feb 2007
Location: South Yorkshire, UK.
Posts: 134
|
Re: The "Sussex" Homebrew Valve Tester.
Herewith a first attempt at producing numbered skirts and background plates for DIY rotary valve pin function selector switches. The diameter of the skirt is about 28mm and the plan is to print them onto OHP transparency material and them laminate them for a bit more rigidity before finally cutting them out and supergluing them to the underside of suitable control knobs.
Alan Last edited by a_strong; 17th Nov 2011 at 12:01 am. Reason: To correct typo |
17th Nov 2011, 6:46 pm | #604 |
Pentode
Join Date: Feb 2007
Location: South Yorkshire, UK.
Posts: 134
|
Re: The "Sussex" Homebrew Valve Tester.
Hi all - egg on face time, spot the deliberate mistake. Back to the drawing board!
Alan |
21st Nov 2011, 6:44 pm | #605 |
Hexode
Join Date: Aug 2010
Location: nr. Hannover, Germany
Posts: 372
|
Re: The "Sussex" Homebrew Valve Tester.
I have just stumbled onto this thread. What a marvellous project - thanks to all involved. Another example of what a fine community we have here.
I was in the process of building another design, but after reading this thread (took best part of yesterday evening ) have binned the idea and will go for the "Sussex". However, I would like to use the stage I have already bulit - the heater supply. I have the following questions: 1. Are there any reasons for not using a DC heater supply - my circuit will supply up to 2.5A DC? 2. Can you give me an idea where to obtain the DPM's - the links mentioneD in the thread all seem to be dead and as there are so many types of DPM on offer I would like to make sure I buy the correct types. Thanks guys Eddie |
22nd Nov 2011, 8:24 am | #606 |
Rest in Peace
Join Date: Aug 2009
Location: East Preston, Sussex
Posts: 162
|
Re: The "Sussex" Homebrew Valve Tester.
Eddie,
I dont see any reason why DC could not be used for the heaters, I didn't originally use it for obvous reasons, cost size etc. Re the DPMs I found these http://myworld.ebay.co.uk/ithingsonl...id=p4340.l2559 although I havent used them, they shoud be OK Mike |
22nd Nov 2011, 11:35 am | #607 |
Hexode
Join Date: Apr 2008
Location: Ramsgate, Kent, UK.
Posts: 252
|
Re: The "Sussex" Homebrew Valve Tester.
Eddie,
I have used this source for my Sussex DPMs http://stores.ebay.co.uk/1stincity-U...=p4634.c0.m322 All the ranges needed for the Sussex VT are available. Adrian |
22nd Nov 2011, 11:45 am | #608 |
Pentode
Join Date: Feb 2007
Location: South Yorkshire, UK.
Posts: 134
|
Re: The "Sussex" Homebrew Valve Tester.
I have just bought four meters from http://stores.ebay.co.uk/Asia-Engineer?_rdc=1.
If you are buying more than one meter Email the seller (Giorgio) for a price for the lot, rather than ordering them individually. I saved a bob or two. Postage can be a bit slow. Although they were despatched straight away mine took three weeks to arrive. Alan |
22nd Nov 2011, 9:08 pm | #609 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
|
Re: The "Sussex" Homebrew Valve Tester.
Hi Eddie, make sure you have 3 seperate and isolated supplies for the DPM's, or you will have shorts between the tester supplies.
Ed |
25th Nov 2011, 1:40 pm | #610 |
Triode
Join Date: Mar 2009
Location: Cambridge, Cambs. UK.
Posts: 34
|
Re: The "Sussex" Homebrew Valve Tester.
Hi all,
Bit late to the party but going to build this as and when can get all the parts. I have a HRO that is feeling poorly and a couple other sets could do with some attention and testing the valves is required. The simple bit I guess was the 3 DVM and they are on order from HK already as I was buying a couple for a separate meter project. Daft question but has anyone compiled a BOM with item numbers from Farnell et al? I have seem a few 'lists' but not the item numbers. 72 Dom M1KTA |
1st Dec 2011, 2:36 pm | #611 |
Triode
Join Date: Mar 2009
Location: Cambridge, Cambs. UK.
Posts: 34
|
Re: The "Sussex" Homebrew Valve Tester.
Hi Mike et al,
All parts (except DVM and transformer) arrived (Rapid supplied), with an additional eBay purchase. Also I was sent a pair of PCBS and will hand one to another interested party. Will probably start to melt solder on this before next weekend. 72 Dom M1KTA Last edited by Station X; 1st Dec 2011 at 3:51 pm. Reason: Disguised reference to eBay removed. |
4th Dec 2011, 8:27 pm | #612 |
Retired Dormant Member
Join Date: Jan 2010
Location: Harrow, London, UK.
Posts: 78
|
Re: The "Sussex" Homebrew Valve Tester.
I'm 're-engineering' my VT-1 to get rid of my rats nest of cables.
Will be three, maybe four PCB's. One for the switch network, one front panel, one main PCB and perhaps a valve socket PCB. I've finished the layout of the front panel PCB (moved some of the main board components to this PCB to simplify wiring. I've also finished the switch matrix PCB. I'm using Phoenix connectors for board interconnects. Next up is the main PCB. I'll post some images when I get further on with this. Andy |
5th Dec 2011, 7:31 pm | #613 |
Hexode
Join Date: Aug 2010
Location: nr. Hannover, Germany
Posts: 372
|
Re: The "Sussex" Homebrew Valve Tester.
Hi all,
I'm a bit unclear as to the measurement of Gm. Am I correct in assuming that a) the level of audio-signal injected into the grid circuit is fairly critical and should be a stable 100mV rms? b) the audio frequency is not that critical. What is the nominal frequency of the Sussex phase-shift oscillator? Next question, how does the gas test work? Thanks guys. Eddie King |
6th Dec 2011, 9:54 am | #614 |
Pentode
Join Date: Feb 2007
Location: South Yorkshire, UK.
Posts: 134
|
Re: The "Sussex" Homebrew Valve Tester.
HI Eddie - Les (Top Cap) has kindly produced an excellent document summarising the Sussex design. This can be found at post #502 which should appear on page 26.
He says this about the GM test. Start quote: "Gm is a measurement of gain and is in fact the change in Anode current (mA) from a change in Grid voltage (V). In the Sussex we apply 0.1V to the grid of the valve under test and measure the change in Anode current across a 10 Ohm resistor R12. Let us assume a valve under test has a gain of 25, if we were using 1V as a grid voltage we would expect a change in Anode current of 25mA and therefore there would be 250mV developed across R12. But as we are using 0.1V signal then the voltage developed will be a tenth of this i.e. 25.0mV. This figure is what will be displayed on the front panel Gm meter. Due to failures encountered with this meter under fault conditions, for example if the Anode supply FET goes short circuit, a protection diode placed across R12 is being trialled. The diode has a forward turn on voltage of 600mV approximately so should not affect the 100mV max expected in normal use. Whether a simple diode on its own will be sufficient has yet to be proven!" End quote. If you cannot find the Les's document I can email it to you if you send me a personal message. Regards - Alan G3WXI |
6th Dec 2011, 11:25 am | #615 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,288
|
Re: The "Sussex" Homebrew Valve Tester.
__________________
Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
10th Dec 2011, 1:28 pm | #616 |
Retired Dormant Member
Join Date: Jan 2010
Location: Harrow, London, UK.
Posts: 78
|
Re: The "Sussex" Homebrew Valve Tester.
I've been a busy bunny
This is what I've done so far...... I know it'll need a few tweaks but I want to finish a board for the valve base interconnects after which I'll sit them all side by side and do a net check against the circuit. Andy |
11th Dec 2011, 12:37 am | #617 |
Retired Dormant Member
Join Date: Jun 2009
Location: East Coast, Singapore
Posts: 16
|
Re: The "Sussex" Homebrew Valve Tester.
Looking great !
Should enable a very neat and compact build. I'll be interested in a set if you decide to do a run of these. |
11th Dec 2011, 4:25 am | #618 |
Heptode
Join Date: Jan 2004
Location: Stockport, Greater Manchester, UK.
Posts: 827
|
Re: The "Sussex" Homebrew Valve Tester.
Hi Andy,
Congratulations: They look an excellent enhancement to the project. (And come with near-perfect timing as I have only 2 of the batch of 50 to the original design left.) |
13th Dec 2011, 4:25 pm | #619 |
Hexode
Join Date: Apr 2008
Location: Ramsgate, Kent, UK.
Posts: 252
|
Re: The "Sussex" Homebrew Valve Tester.
Andy,
Nice work, however, do check the track/track/pin spacing on those boards, there look to be some pretty close bits on there considering the high voltages that are in use. Adrian |
13th Dec 2011, 5:11 pm | #620 |
Retired Dormant Member
Join Date: Jan 2010
Location: Harrow, London, UK.
Posts: 78
|
Re: The "Sussex" Homebrew Valve Tester.
Adrian
Yes, I've set my routing rules for a minimum 0.8mm track spacing. Isn't this enough? Andy |