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.

Closed Thread
 
Thread Tools
Old 19th May 2020, 3:04 pm   #1
retailer
Heptode
 
Join Date: May 2005
Location: Adelaide, South Australia
Posts: 541
Default Another Home Built Valve Tester

I have come very close to the end of my home built valve/tube tester project and though I would share with other forum members, it is heavily based on the RAT tube tester as designed by Steve Bench, I know the Sussex tester has been extremely popular on this forum with many forum members building their own interpretations, the RAT tester operates in a slightly different way. The Sussex follows the tried and proven fixed bias way of setting up the valve for testing, the RAT tester uses valve self bias, I guess similar to the way that a cathode biased valve sets it's own bias voltage. A few of the US made Hickok tube testers have the option of fixed or self bias - I read through the Hickok 539B user manual and it does not have a lot to say about this feature only a short paragraph on how to use it and how to select the best cathode bias resistor, but no explanation on why and when to use.
The RAT tester uses a variable constant current sink rather than a set of bias resistors, a current limited variable negative voltage is applied to the cathode and the valve sets its own bias. In practice - once the valve has warmed up, the negative voltage on the cathode is increased until the bias voltage reaches the data book value, anode current and Gm are shown on meters, if the anode current or Gm fall short as is often the case with used valves, increasing the cathode negative voltage will increase the anode current and bias voltage will be seen to drop.

I tried to keep the switching to a minimum and simplified the filament continuity check by using a current transformer to activate a front panel LED once a filament current of over 40mA is detected, sensitive enough for even 1.4v battery valves, the output of the current transformer is also taken to a pair of banana sockets where I can measure filament current, I scaled the current transformer load resistor so a voltage of 100mV ac equates to 100mA filament current. The digital panel meter (200mV AC) I had lined up as the Gm meter proved to be quite non linear at the low end of the scale and after trying various options I settled on a moving coil meter driven by an AC to DC opamp meter amplifier. There is no shorts test apart from a H/K short LED indicator, in practice with current limited to 50mA max I can see from the volt and screen meter activity if something is not right the meters will dip suddenly, I have the option of switching to a 100mA limit if needed. The RAT tester circuit provides for measuring Mu (triodes only) as well as Gm, I made provision for it on the pcb but haven't included the switching so only Gm can be measured.

The photos are of various stages in construction, I made and re-made some things a few times, just about all of the electronics, pcb's etc are mounted on the front panel, and a small chassis that mounts on the rear of the front panel, a 4 pin and 9 pin connector take the various AC voltages to the electronics and an 11 pin connector takes the various dc etc voltages to the valve sockets on the top panel. The front row of valve sockets are hard wired for most common audio valves - no need to set switches, and a row of thumb wheel switches sets up the voltages for the sockets at the rear, I've copied AVO switch wiring layout so I can use the AVO data manual for switch settings.

I've made a short 5min some what amateurish video posted it on youtube showing the operation of the tester it can be seen here if interested:-

https://youtu.be/Imsj8aT4JGo
Attached Thumbnails
Click image for larger version

Name:	Circuit.jpg
Views:	237
Size:	70.0 KB
ID:	206218   Click image for larger version

Name:	Pic 1.jpg
Views:	221
Size:	85.9 KB
ID:	206219   Click image for larger version

Name:	Pic 2.jpg
Views:	216
Size:	68.4 KB
ID:	206220   Click image for larger version

Name:	Pic 3.jpg
Views:	235
Size:	69.7 KB
ID:	206221   Click image for larger version

Name:	Pic 4.jpg
Views:	233
Size:	65.0 KB
ID:	206222  

retailer is offline  
Old 19th May 2020, 5:52 pm   #2
Electronpusher0
Nonode
 
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,288
Default Re: Another Home Built Valve Tester

Very impressive! A good selection of valve bases as well.
I will have to study the self bias system used.

Peter
Electronpusher0 is offline  
Old 19th May 2020, 6:06 pm   #3
CambridgeWorks
Nonode
 
CambridgeWorks's Avatar
 
Join Date: Jun 2010
Location: Spalding, Peterborough, Cambridgeshire, UK.
Posts: 2,851
Default Re: Another Home Built Valve Tester

I do like the idea of several B9A bases for your common valves. The Marconi gm meter looks the part and has a nice long, clear scale. Well done!
Rob
__________________
Apprehension creeping like a tube train up your spine - Cymbaline. Film More soundtrack - Pink Floyd
CambridgeWorks is offline  
Old 20th May 2020, 3:35 am   #4
joebog1
Banned
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
Default Re: Another Home Built Valve Tester

Excellent work !!!! Your movie is not amateur at all !! I would love to see your power supply circuitry at a decent size. I would suggest you are similar in occupation to myself. Mostly badly neglected guitar amps, with some new Hi-Fi stuff on the side. Your idea of pre wired "switchless" sockets is excellent too.

All in all, I love it.

Joe
joebog1 is offline  
Old 20th May 2020, 8:23 am   #5
Ted Kendall
Dekatron
 
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,658
Default Re: Another Home Built Valve Tester

Nice-looking bit of kit as well - knobs and case matched, clear panel marking. Really liked the changeover switch for double triodes. And the video is just the way I like them, too - straightforward visuals, good sense spoken, and no irrelevant background music.
Ted Kendall is offline  
Old 20th May 2020, 11:57 am   #6
retailer
Heptode
 
Join Date: May 2005
Location: Adelaide, South Australia
Posts: 541
Default Re: Another Home Built Valve Tester

Thank you for all the nice comments it is much appreciated.

Joe: a larger (I hope) pic of the circuit I redrew in KiCad prior to making the pcb, the Steve Bench original can be found here http://www.triodeel.com/tester.htm I think the name RAT tester comes from the "old" style pre-Facebook social media news group name Rec.Audio.Tubes, I believe Steve Bench was a frequent contributor, so I think this circuit has been around for a good number of years. If you have trouble seeing it I can email you the KiCad file, I have noticed that the image upload part of the forum has a habit of resizing images, the uploaded image was 216 KB it is now 81KB.
Attached Thumbnails
Click image for larger version

Name:	Circuit larger.jpg
Views:	138
Size:	81.2 KB
ID:	206279  
retailer is offline  
Old 28th May 2020, 2:06 am   #7
retailer
Heptode
 
Join Date: May 2005
Location: Adelaide, South Australia
Posts: 541
Default Re: Another Home Built Valve Tester

Joe- zip file that I could not work how to attach to a PM
Attached Files
File Type: zip Power supply.zip (59.6 KB, 85 views)
retailer is offline  
Old 28th May 2020, 3:14 am   #8
Bazz4CQJ
Dekatron
 
Bazz4CQJ's Avatar
 
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,924
Default Re: Another Home Built Valve Tester

That is one sweet piece of kit! Of course, during lockdown, I've been exercising by carrying my Avo VCM from one room to another .

B
__________________
Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.
Bazz4CQJ is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 7:12 am.


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 - 2023, Paul Stenning.