Avo TT537 and Avo Valve Tester MK4 - UK Vintage Radio Repair and Restoration Discussion Forum

fixitfixit · 16th Mar 2014, 5:43 pm

Hi
Does anyone have an idea of the value of a TT537 AVO transistor tester.
I have been using the meter out of this as a temporary measure. to be able to use my Avo mark 4 valve tester. The meter will not calibrate because it is a 50 micro amp meter with 2.4k resistance, which according to the internet is a Taylor Model 50 meter, even though if says AVO behind the glass.
I have had communications with Gary Tempest, who designed the op amp option to drive an alternate meter. Gary was most helpful on advice and I thank him for his help.
The other option I could do is fit a Simpson 25 micro amp 1960 ohm Taut-Band meter, part number 0395,1 from Routeco at Derby for £90.20 with a 3 week waiting time.
I also have a Taylor 85a multimete,r and a Taylor 45a Valve tester, both these have a 400 type meter which I can find no info on but may be OK to drive with the op amp circuit.
Thanxs
Fixitfixit

Radio Wrangler · 17th Mar 2014, 12:50 am

Ah, you've not checked through this the group. Last week I spotted a Simpson 25uA meter on sale somewhat cheaper than that!

https://www.vintage-radio.net/forum/...192#post667192

I bought a TT537 at the G-QRP convention for, I think £20 and found the meter coil open circuit, with windings visibly fused. I've got it going with a wrong movement in and I've not yet made a scale. If you're selling the TT537 or just the meter alone, I may be interested.

David

fixitfixit · 21st Mar 2014, 2:33 pm

Hi David
What movement have you used as a replacement for your meter?
I am using a movement now out of a Taylor 85A universal meter in the valve tester. it has a 40 micro amp and says type 400 through the glass. I have not been able to find any info on this meter.
The meter out of the TT537 fits the AVO MK4 better physically but is a 50 mico amp meter. I have now reassembled the unit but are undecided as to what to do next.
The link you sent to the Simpson meter is not the meter that is a recognised replacement in the MK4 which is a 03951 and is £90.
I think this is the best option. just need to raise some cash towards buying a new meter and then the TT537 can go.
Steve

mark-jacobs · 22nd Mar 2014, 6:53 am

You can use a movement out of a AVO CT446. The length of the needle is a few mm shorter than in your valve tester, but the movement sensitivity and meter resistance is the same for the ones I have checked. Almost all the older AVO meters I have checked are down 5-10% of full scale due to loss of magnetism, I apply 30uA and adjust the swamp bar to get the correct full scale reading. One required an additional pole magnetic.

You would need to swap out the meter scale, they are interchangeable with the CT446 meter. JACMusic also sells a replacement meter for the MkIV or check at herts meter if they still do repairs or movement replacements. The 25uA Simpson meters do come up on the US eBay infrequently.

http://www.hertsmeter.com/.
http://www.jacmusic.com/Tube-testers...ex-AVO-Mk4.htm
https://www.vintage-radio.net/forum/...ad.php?t=75413
http://www.ebay.co.uk/itm/AVO-CT446-...item20e19b625b

Radio Wrangler · 22nd Mar 2014, 8:33 am

If you're going to swap the meter, then I'd suggest putting in a nice robust 1mA movement and adding a little mains transformer and a floating opamp.

That way you don't have to worry about vulnerable meters.

I bought a number of new boxed Ernest Turner and Sifam meters with all sorts of weird scales at the Kelso rally in the 80's. It turned out that some of them had very sensitive movements. Quite a few of them got given away to people making the QRP dual-directional power meter design I did (cough) years ago.

As a kid I bought a VCM MKII with my birthday money in about 1967. It lasted several years but the meter coil failed. It was a fracture of the wire going to the inside of the coil, it wasn't overcooked. So that was the end of that machine, though its parts featured in a lot of homebrew gear afterwards.

I find a little Taylor 45D works perfectly for checking that valves will work in old radios. I'd sort of like an AVO again but it wouldn't do anything for me that I can't already do. If I wanted to get serious, say for really measuring valve characteristics, or for matching pairs of power valves, I wouldn't use any of the available testers, I'd design something to run the things up to full power, and automatically plot characteristic curves. The AVO VCMs are beautiful bits of kit but they do embody a number of short-cuts that I don't like.

David

16th Mar 2014, 5:43 pm	#1
fixitfixit Diode Join Date: Mar 2014 Location: Nottingham, UK. Posts: 3	Avo TT537 and Avo Valve Tester MK4 Hi Does anyone have an idea of the value of a TT537 AVO transistor tester. I have been using the meter out of this as a temporary measure. to be able to use my Avo mark 4 valve tester. The meter will not calibrate because it is a 50 micro amp meter with 2.4k resistance, which according to the internet is a Taylor Model 50 meter, even though if says AVO behind the glass. I have had communications with Gary Tempest, who designed the op amp option to drive an alternate meter. Gary was most helpful on advice and I thank him for his help. The other option I could do is fit a Simpson 25 micro amp 1960 ohm Taut-Band meter, part number 0395,1 from Routeco at Derby for £90.20 with a 3 week waiting time. I also have a Taylor 85a multimete,r and a Taylor 45a Valve tester, both these have a 400 type meter which I can find no info on but may be OK to drive with the op amp circuit. Thanxs Fixitfixit

17th Mar 2014, 12:50 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,857	Re: Avo TT537 and Avo Valve Tester MK4 Ah, you've not checked through this the group. Last week I spotted a Simpson 25uA meter on sale somewhat cheaper than that! https://www.vintage-radio.net/forum/...192#post667192 I bought a TT537 at the G-QRP convention for, I think £20 and found the meter coil open circuit, with windings visibly fused. I've got it going with a wrong movement in and I've not yet made a scale. If you're selling the TT537 or just the meter alone, I may be interested. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

21st Mar 2014, 2:33 pm	#3
fixitfixit Diode Join Date: Mar 2014 Location: Nottingham, UK. Posts: 3	Re: Avo TT537 and Avo Valve Tester MK4 Hi David What movement have you used as a replacement for your meter? I am using a movement now out of a Taylor 85A universal meter in the valve tester. it has a 40 micro amp and says type 400 through the glass. I have not been able to find any info on this meter. The meter out of the TT537 fits the AVO MK4 better physically but is a 50 mico amp meter. I have now reassembled the unit but are undecided as to what to do next. The link you sent to the Simpson meter is not the meter that is a recognised replacement in the MK4 which is a 03951 and is £90. I think this is the best option. just need to raise some cash towards buying a new meter and then the TT537 can go. Steve

22nd Mar 2014, 6:53 am	#4
mark-jacobs Triode Join Date: Dec 2009 Location: Tucson, Arizona, USA. Posts: 44	Re: Avo TT537 and Avo Valve Tester MK4 You can use a movement out of a AVO CT446. The length of the needle is a few mm shorter than in your valve tester, but the movement sensitivity and meter resistance is the same for the ones I have checked. Almost all the older AVO meters I have checked are down 5-10% of full scale due to loss of magnetism, I apply 30uA and adjust the swamp bar to get the correct full scale reading. One required an additional pole magnetic. You would need to swap out the meter scale, they are interchangeable with the CT446 meter. JACMusic also sells a replacement meter for the MkIV or check at herts meter if they still do repairs or movement replacements. The 25uA Simpson meters do come up on the US eBay infrequently. http://www.hertsmeter.com/. http://www.jacmusic.com/Tube-testers...ex-AVO-Mk4.htm https://www.vintage-radio.net/forum/...ad.php?t=75413 http://www.ebay.co.uk/itm/AVO-CT446-...item20e19b625b

22nd Mar 2014, 8:33 am	#5
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,857	Re: Avo TT537 and Avo Valve Tester MK4 If you're going to swap the meter, then I'd suggest putting in a nice robust 1mA movement and adding a little mains transformer and a floating opamp. That way you don't have to worry about vulnerable meters. I bought a number of new boxed Ernest Turner and Sifam meters with all sorts of weird scales at the Kelso rally in the 80's. It turned out that some of them had very sensitive movements. Quite a few of them got given away to people making the QRP dual-directional power meter design I did (cough) years ago. As a kid I bought a VCM MKII with my birthday money in about 1967. It lasted several years but the meter coil failed. It was a fracture of the wire going to the inside of the coil, it wasn't overcooked. So that was the end of that machine, though its parts featured in a lot of homebrew gear afterwards. I find a little Taylor 45D works perfectly for checking that valves will work in old radios. I'd sort of like an AVO again but it wouldn't do anything for me that I can't already do. If I wanted to get serious, say for really measuring valve characteristics, or for matching pairs of power valves, I wouldn't use any of the available testers, I'd design something to run the things up to full power, and automatically plot characteristic curves. The AVO VCMs are beautiful bits of kit but they do embody a number of short-cuts that I don't like. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done