UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Reply
 
Thread Tools
Old 16th Jun 2012, 9:14 am   #681
Dekatron
Octode
 
Dekatron's Avatar
 
Join Date: May 2009
Location: Linkoping, Sweden
Posts: 1,478
Default Re: The "Sussex" Homebrew Valve Tester.

Colin, those rotary switches will probably work just fine, especially since they look almost like the ones used in the Taylor 45D / 45D2 Valve Testers, see the pictures below!

The only problems that I have experienced with these are that the centre piece of the plastic wheel collects a lot of dust where the shaft turns in the PCB, it is almost impossible to get the dust and dirt out of there since the four rivets keep the pieces tight together. I had to soak them in warm water with hand washing liquid and the rinse them under hot water and lastly blow them dry as well as using air pressure to blow out the dust that had accumulated over the years.

On the Taylor 45D and 45D2 these switches were mounted flat so all dust and debris fell straight down landing on the roatating shaft. A much better way of mounting them is tilted on a front panel, that way the dust will fall down inside the panel and not land on the rotating shaft!
Attached Thumbnails
Click image for larger version

Name:	sw-1.jpg
Views:	380
Size:	107.3 KB
ID:	67699   Click image for larger version

Name:	sw-2.jpg
Views:	351
Size:	83.6 KB
ID:	67700  
__________________
Martin, Sweden
Dekatron is offline   Reply With Quote
Old 10th Jul 2012, 10:13 am   #682
Peter_C64
Retired Dormant Member
 
Join Date: Jul 2012
Location: Sofia, Bulgaria
Posts: 15
Default Re: The "Sussex" Homebrew Valve Tester.

Hello to all,

I've read this thread with interest and decided to build one of those valve testers. So I started collecting the parts.

I have a question about the DPM's - the ones currently available need 9-12V power supply (AC or DC). Will they work with 6V AC only?

Thank you,

Peter

Last edited by Station X; 10th Jul 2012 at 10:18 am. Reason: Forum rule compliance.
Peter_C64 is offline   Reply With Quote
Old 10th Jul 2012, 10:00 pm   #683
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,296
Default Re: The "Sussex" Homebrew Valve Tester.

Hi Peter, yes, they will work with 6v ac, provided that it is rectified (bridge rect best) and a resevoir cap is used to smooth the DC, you will then get 6.3v times sqrt 2 ; about 9v.
Note that each DMP must be operated from its own supply which must not be connected to ground or common.

Ed
Ed_Dinning is offline   Reply With Quote
Old 11th Jul 2012, 10:03 am   #684
Peter_C64
Retired Dormant Member
 
Join Date: Jul 2012
Location: Sofia, Bulgaria
Posts: 15
Default Re: The "Sussex" Homebrew Valve Tester.

Thank you for the reply. I think there is already a bridge rectifier and a cap on the board otherwise how it will work with AC power supply? Maybe they have just given same numbers for AC and DC.

Peter
Peter_C64 is offline   Reply With Quote
Old 11th Jul 2012, 2:13 pm   #685
RF Burn
Hexode
 
RF Burn's Avatar
 
Join Date: Apr 2008
Location: Ramsgate, Kent, UK.
Posts: 252
Default Re: The "Sussex" Homebrew Valve Tester.

You are correct Peter, they are designed for AC or DC supplies and they have bridge rectifier/capacitor on-board. The ones that I have will operate from 6 Volts AC as this gives (as Ed says) about 9 Volts DC for the electronics after rectification (which is the minimum DC voltage supply specified anyway)

Adrian
RF Burn is offline   Reply With Quote
Old 21st Jul 2012, 4:48 pm   #686
timohaveri
Pentode
 
Join Date: Sep 2007
Location: Parkano, Finland
Posts: 133
Default Re: The "Sussex" Homebrew Valve Tester.

Regarding the reported inaccuracies of the AC meter, how about using something like this:

http://www.linear.com/product/LTC1968

Would this chip together with a DC panel meter produce better results?

Timo
timohaveri is offline   Reply With Quote
Old 21st Jul 2012, 8:40 pm   #687
timohaveri
Pentode
 
Join Date: Sep 2007
Location: Parkano, Finland
Posts: 133
Default Re: The "Sussex" Homebrew Valve Tester.

I've done a little more research and it seems that the LTC1966, 67 and 68 chips would work really well in this kind of an application. I'm quite sure that the blue LED digital AC panel meters from Ebay are optimized for 50 or 60 Hz use so they are not that good with a few kHz inputs. The price of the chip alone is about the same than the Ebay meter so nothing of that quality can be inside the meters. An LTC chip together with a 200 mA DC meter would probably produce very accurate results. I would be interested in hearing the results if someone is going to try this. My Sussex is still in the planning stages because of time constraints so I'm not going to be able to try it anytime soon myself.

One more link: http://www.extremecircuits.net/2010/...converter.html
timohaveri is offline   Reply With Quote
Old 6th Aug 2012, 7:05 pm   #688
n_r_muir
Hexode
 
n_r_muir's Avatar
 
Join Date: Jul 2007
Location: Edinburgh, UK.
Posts: 344
Default Re: The "Sussex" Homebrew Valve Tester.

Hi,

Are any PC boards still available for this project?

Ross
n_r_muir is offline   Reply With Quote
Old 8th Aug 2012, 3:50 pm   #689
Peter_C64
Retired Dormant Member
 
Join Date: Jul 2012
Location: Sofia, Bulgaria
Posts: 15
Default Re: The "Sussex" Homebrew Valve Tester.

Hello stoned6,
I am also new here. I have sourced most of the parts but I'm still waiting for the DMM's to come from China.

I will use a transformer from an old radio with a 250V secondary - I'm going to rewind the other secondaries (the transformer is not potted so it's easy to dissasemble it). Have to make the PCB's too.

Are you going to use LTC1968 RMS to DC convertor? I have already ordered a200mV AC DMM so I will build the tester with it and may change it later if it's not accurate.

I'm also may try the oscillator proposed by Les Carpenter.

I will be glad to see how your build goes - we can post pictures and ideas when there is a progress.

Peter
Peter_C64 is offline   Reply With Quote
Old 8th Aug 2012, 4:39 pm   #690
stoned6
Triode
 
Join Date: Nov 2010
Location: Dorchester, Dorset.
Posts: 11
Default Re: The "Sussex" Homebrew Valve Tester.

Hello to everyone,

Firstly, I must congratulate the late Mike Rowes as the original instigator of the project, and Les Top Cap for his excellent handbook made available to all. I read the thread from beginning to end and was inspired by all the members who contributed to the project.

I am rather late coming to this excellent thread -I wanted to know if members are still building the Sussex Valve Tester?

I am also building the tester but with a few changes and additions, in particular to the area of GM measurements and am using a DC 200mV DPM (as suggested by other forum members)with RMS TO DC convertor, together with a fully differential amp input to increase the 1KHz signal level and reduce common mode interference problems. This way allows the use of a power supply for the GM DPM which is not flapping about at a high voltage.

I am also using a 8038 function generator chip to obtain a more stable 1KHz 100mV test signal.

Also, to further help improve this area of measurement, I am using regulated DC heater supplies, up to about 30V DC.
There are 7 DPM,s in my version, so I had to make a transformer with 7 isolated supplies.

I have built my own instrument case for the tester, and also made my own transformers.
All the circuits on are on stripboard and I am at present putting it all together.
Forum members will be aware of the moment I first switch on as the National Grid will dip for a few seconds...

Any other ideas and improvements from the obviously talented forum members would always be welcome.
I would post a few pictures if I only knew how to! My electronics is good but my Computer skills and emails and attachents etc, is not yet up to par.

Karl
stoned6 is offline   Reply With Quote
Old 9th Aug 2012, 2:50 pm   #691
stoned6
Triode
 
Join Date: Nov 2010
Location: Dorchester, Dorset.
Posts: 11
Default Re: The "Sussex" Homebrew Valve Tester.

Hello Peter,

Yes, I will use a simple RMS to DC convertor and use a 200Mv DC meter instead of the AC type.
The RMS to DC convertor is just a good quality dual 8 pin op-amp with a few extra components, preceded by a differential amplifier with a gain of 10 to boost the 1KHz signal.
The input to the differential amplifier will be 2 capacitors from the 10 ohm sampling resistor and this method will remove the requirement to have the meters power supply flapping about at a high voltage. The differential amplifier will help to remove common mode noise i.e. 50/100 Hz power supply induced noise and give some gain for the RMS to DC convertor to work with.
I have built this part and seems to work very well, but of course I have not yet assembled the complete valve tester...

I also have wound my own transformers, which is just as well, as I needed 7 separate windings just for the 7 meters I will be using!
So I made up 3 separate smaller transformers to get all the windings I needed.
I also wound an extra 15V-0-15V winding for the op amps power supplies - the wire for this can be very thin as we only need a few mA for this circuit.

I have built the instrument case myself - from 3mm thick aluminium equal angle and 1.5mm and 2mm sheet - it is very sturdy.

There are other changes and mods that I have introduced into the valve tester to make it more versatile for my needs.
If anyone is interested, I will of course, post these changes, and when I understand how to attach pictures, I will do so.

The transformer you are going to rewind...have you tested the turns ratio before you take it apart? Or are going to rewire the whole thing, including the mains input winding?

I have used a ICL8038 function generator chip for the 1KHz test signal - it is very stable.
I am using DC for the heater supplies - fixed 3V, 4V, 5V, and 6.3V, and a variable 0V to about 28V option, and an option for external DC heater inputs.
A DC/DC convertor is used for the heater supply, and with two switched 12V AC secondary windings, plus another relay, I can get a very efficient and versatile heater circuit.
Will you also using DC for heaters? I think it will help to reduce interference when making GM measurements.
The HT supplies for anode and screen, I have modified a bit to enable me to use multi-turn pots instead of the fixed switched values - this seems to work very well and there is now a separate meter for anode and screen voltages.

But basically, the general design is as per Mike's and Les' - I am very indebted to them both, and for all the other members contributions...I think it is a super project and if I hadn't stumbled onto this excellent forum, I would not have had the idea or compulsion to build my own valve tester...

Peter, when do you think you will start building your version of the Sussex?

If you are interested, or indeed if any forum members are interested, I will gladly post any information on my Sussex build.

Karl
stoned6 is offline   Reply With Quote
Old 9th Aug 2012, 4:51 pm   #692
stoned6
Triode
 
Join Date: Nov 2010
Location: Dorchester, Dorset.
Posts: 11
Default Re: The "Sussex" Homebrew Valve Tester.

Peter,

Just an update.
I have studied the data sheet on your suggestion of the LTC1967 and, well, what a lovely little chip!
The only drawback that I can see, apart from being SMT, is the rather high output impedance (50K) so we need to look at that aspect. Working into a 1M meter input impedance will reduce the accuracy somewhat.
Otherwise, a nice chip, and only about £5.00 or so. I am going to get one from RS and have a closer look at it, but I will use my present discrete set up for the RMS to DC at the moment, because I have used it many times for other projects.

Do you have equipment for making SMT PCB's? Or indeed any PCB's? I do not have facilities for making my own PCB's yet, but I have designed many PCB's in the past using Easy-PC15.

Karl
stoned6 is offline   Reply With Quote
Old 10th Aug 2012, 5:27 pm   #693
Peter_C64
Retired Dormant Member
 
Join Date: Jul 2012
Location: Sofia, Bulgaria
Posts: 15
Default Re: The "Sussex" Homebrew Valve Tester.

Hi Karl,

The transformer from the radio has the turns numbers printed on its label. I'm going to keep the primary and the high voltage secondary, so it's an easy modification.

Why do you think it's necessary to use DC heaters - because the heater wires can not be twisted and kept away from the signal wires?

The LTC1966-68 chips were suggested by timohaveri. I also checked the datasheets of these chips - LTC1968 has the lowest output impedance of the three (12.5 kOhm). There is also written that if the input impedance of the DMM is 10 MOhm that will increase the gain error from 0.1% to 0.125% which is not too much. But if the impedance of the DMM is 1M the error will be 1.25% - in that case we can add a buffer at the output of LTC1968.

I will try to make the PCB's with the method of transfering laser printer toner to the board. I will make a test first to see if it's possible to make the SMD part that way. There are adapters for MSOP-08 case but they cost almost as much as the chip itself.

It will be interesting for me to see some pictures of your build and the schematic of the oscillator. It's easy to attach files and pictures - when posting a reply use "Go Advanced" option and there you will see the attachments button in the toolbar.

Peter
Peter_C64 is offline   Reply With Quote
Old 11th Aug 2012, 8:41 am   #694
stoned6
Triode
 
Join Date: Nov 2010
Location: Dorchester, Dorset.
Posts: 11
Default Re: The "Sussex" Homebrew Valve Tester.

Peter,

LTC1967 - This one was the only type stocked by RS, I have ordered one from them.
Many of the DPM modules I have used from China have input impedances of 1M ohm, indeed I have used some with input impedances of 100K!
I will check the 200mV types that I will be using. But you are right, we can easily work around the high output impedance.

So, you have a transformer with the turns ratio marked on the actual transformer!
Now, DC for heaters - most quality valve amps use DC for the valve heaters to keep noise and hum pick-up to a minimum, which is want we want to do for the valve tester.
But the main reason I am using DC is that I can easily control, and vary, the voltages to the heaters - this is very useful for valves with odd heater voltages, eg radio and television valves, and it allows me the ability to reduce the heater voltages by, say 10%, to test the emission changes - this is a good way to test for weak valves. So, I have both heater voltage and current displayed on my tester.
I wish I could put my circuits onto PCB's.

I will post some schematics when I have them in a suitable format.

Karl
Attached Thumbnails
Click image for larger version

Name:	VT1+_1.jpg
Views:	486
Size:	76.5 KB
ID:	69649   Click image for larger version

Name:	VT1+_2.jpg
Views:	468
Size:	88.0 KB
ID:	69650   Click image for larger version

Name:	VT1+_7.jpg
Views:	490
Size:	104.2 KB
ID:	69651   Click image for larger version

Name:	VT1+_10.jpg
Views:	485
Size:	99.0 KB
ID:	69652  
stoned6 is offline   Reply With Quote
Old 13th Aug 2012, 4:00 pm   #695
Peter_C64
Retired Dormant Member
 
Join Date: Jul 2012
Location: Sofia, Bulgaria
Posts: 15
Default Re: The "Sussex" Homebrew Valve Tester.

Karl,
You have advanced a lot with your build. Did you wound all the three transformers?

I saw that Farnell have all the three types of LTC chips in stock.

These old radios were produced in government factories so the transformers usually have stamps with the turns ratios and wire diameters on them. Unfortunately in this one the heater winding is between the primary and the high voltage secondary and it won't be so easy to modify it. I will remove all the windings except the primary and will add taps to it at 5V steps in 215V-240V interval to be able to adjust the voltages.

I have to buy the materials for the PCB and will test the laser printer method.

Do you know how can we measure the input impedance of the DMM's?

Peter
Peter_C64 is offline   Reply With Quote
Old 15th Aug 2012, 8:43 am   #696
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,296
Default Re: The "Sussex" Homebrew Valve Tester.

Hi Peter, you can easily (if there is the space) wind additional turns onto your transformer on top of the other windings. These can then be connected to aid or oppose the original winding to give more or less volts out.

Ed
Ed_Dinning is offline   Reply With Quote
Old 15th Aug 2012, 10:53 am   #697
daviddeakin
Hexode
 
daviddeakin's Avatar
 
Join Date: Apr 2007
Location: W Yorks, UK.
Posts: 410
Default Re: The "Sussex" Homebrew Valve Tester.

I will confess to not having read the whole thread, but would I be right in thinking that this tester can measure gm, but does not measure mu or ra?
daviddeakin is offline   Reply With Quote
Old 15th Aug 2012, 2:06 pm   #698
Peter_C64
Retired Dormant Member
 
Join Date: Jul 2012
Location: Sofia, Bulgaria
Posts: 15
Default Re: The "Sussex" Homebrew Valve Tester.

Hi Ed,
I wanted to remove the existing heater winding to free space and wind it again with taps for all the heater voltages needed. It was not on top so I had to unwound the high voltage winding too.

Hi daviddeakin,
If we add an additional DMM to monitor the anode voltage then we can measure the anode current for two different anode voltages and calculate Ra = (delta Ea)/(delta Ia). Knowing Ra and Gm we can easily calculate µ = Gm/Ra.

Peter
Peter_C64 is offline   Reply With Quote
Old 15th Aug 2012, 5:58 pm   #699
squegging
Triode
 
squegging's Avatar
 
Join Date: Mar 2011
Location: Bristol, UK.
Posts: 44
Default Re: The "Sussex" Homebrew Valve Tester.

I am still collecting bits & pieces, progress is slow I'm afraid. However I did get some digital panel meters at £5.99 each and wondered about the calibration of the 200mV AC module. So I hooked it up to my function generator, monitoring the level with my (uncalibrated!) Maplin White Gold DMM and Tek scope. I checked it at 60 Hz and 1 kHz, both powered up from a 9V battery, and also 6.3V AC from Ed's transformer. I was quite pleased with the result (as attached), and for me the accuracy is more than adequate for this project. For some reason that escapes me, the AC powered result is better than the DC powered one. (No, the battery wasnt flat).
Attached Files
File Type: doc DPMcalibration.doc (22.0 KB, 337 views)
squegging is offline   Reply With Quote
Old 15th Aug 2012, 10:36 pm   #700
squegging
Triode
 
squegging's Avatar
 
Join Date: Mar 2011
Location: Bristol, UK.
Posts: 44
Default Re: The "Sussex" Homebrew Valve Tester.

Just occurred to me after posting the above, that the calibration error of the DPM @100mV can be calibrated out if the 100mV 1kHz grid stimulus is set up using the same DPM.
squegging is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 12:42 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2024, Paul Stenning.