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 > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 15th Nov 2004, 11:00 pm   #1
Colin
Heptode
 
Colin's Avatar
 
Join Date: Jun 2004
Location: Ilkley, West Yorkshire, UK.
Posts: 656
Default Mullard High Speed Valve Tester

I've just tried to get my recently acquired Mullard high speed valve tester up and running and have run into a few problems.

The version of the tester I have dates from the mid 50's and it's the earlier version with the Mains Adjust switch below the Selector switch on the front panel. The later ones had a slightly different layout with the Mains adjustment switch on the left above four horizontal push buttons. I think they were pretty similar otherwise.

It hadn't been used for around twenty years or so but the old chap that had it tried it to see if it still worked just prior to me picking it up. He said it was working okay but did nothing more than wait for the spot to appear on the CRT.

I've replaced all the caps and reformed a few electrolytics that looked as though they had been replaced at some time. They all checked out okay. I used switch cleaner on all the switches (and preset control pots) and carefully cleaned the Gate Switch that 'reads' the paxolin cards.

On powering up the spot appears on the CRT (although it appears as a small circle) but I can't calibrate it as described in the setup instructions. The mains adjust procedure doesn't seem to work as the 'spot' can't be positioned on the dotted line in the middle of the green band. The mains adjust switch doesnt seem to have any effect.

The other calibration routines (Reject & HT test) can't be completed either.

Has anyone any experience of this valve tester? All suggestions welcome.

Thanks
Colin
__________________
Colin Armstrong
Colin is offline  
Old 16th Nov 2004, 9:31 pm   #2
pingpangpow
Guest
 
Posts: n/a
Default Re: Mullard High Speed Valve Tester

Hello, I had the same problems with my Mullard High Speed valve tester (have a look at my post under the heading of 'Mullard High Speed' dated July 19th in this Test Equipment forum). However, I was seeing a 'comet' on the CRT instead of a dot. I replaced all the caps and this helped with the dot image but I still couldn't perform the set-up tests. The dot would not align when I altered the Mains Adjust and it didn't pass the HT or reject test. As I was about to condemn it to valve tester heaven I removed the chassis from the case one last time and noticed that two wires had come off their connections on the transformer. These wires are quite stiff and they weren't flapping around so it was very hard to spot amongst all the other wires in that area and they also rubbed against the side of the case so it was most probably me that knocked them off their connections whilst pulling and pushing the chassis in and out of the case. The wires were the EL37 heater wires so it might be worth checking those wire connections to the transformer and, if intact, check the EL37 itself. Since reconnectinmg the wires it works fine! Hope this is of some use!
 
Old 16th Nov 2004, 9:38 pm   #3
Paul Stenning
Administrator
 
Paul Stenning's Avatar
 
Join Date: Dec 2002
Location: Cardiff
Posts: 9,060
Default Re: Mullard High Speed Valve Tester

I have the later model (with the horizontal row of buttons).

To get this working correctly I needed to change all the non-electrolytic caps. Someone had changed them in the past with metal-cased types (the ones that look rather like electrolytics) which looked fine, but they were all leaky to some extent. However you've already done this, so it's not that.

Are you sure the electrolytics are OK? They may not be leaky, but they could be low capacitance. Ripple could cause the spot to appear as a line or circle as you describe.

I guess the next stage is to check resistors in case they have gone high.

Good luck with it!
__________________

Paul Stenning
Forum Admin/Owner and BVWS Webmaster
Paul Stenning is offline  
Old 17th Nov 2004, 1:55 pm   #4
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Mullard High Speed Valve Tester

Hi Gents, I would concur with Paul, there are several hi-stab resistors in the reject etc circuits that may well have drifted over the years. The setting pots themselves can get dirty and lastly the neon ref could be on the way out.

Ed
Ed_Dinning is offline  
Old 19th Nov 2004, 12:14 am   #5
Colin
Heptode
 
Colin's Avatar
 
Join Date: Jun 2004
Location: Ilkley, West Yorkshire, UK.
Posts: 656
Default Re: Mullard High Speed Valve Tester

Thanks for the advice.

I've changed all the caps and apart from a couple of NOS they are all new. The NOS ones are a couple of 8uf items that check out okay. I've used them in place of the two 4uf caps (C3 & C4) in the EY51 smoothing circuit. They were the best I had available at the time. Do you think the higher value might have something to do with producing the circle rather than the spot?

The main problem seems to be around the EZ90 and the 85A2 part of the circuit. There should be -200v on the junction of R56 & R55 (I have -40v) and -85v on the anode of the A5A2 (I have -45v). All the resistors in that area check out reasonably close to their rated values but R56 (4k7 2W) is running very hot and has become seriously discoloured. There is c.23mA on this part of the circuit and the voltage before the resistor is -147v and -40v after it. I haven't replaced it as its value is within spec.

I removed the neon voltage reference valve 85A2 but this made no difference to the voltage readings. The two Electrolytics in that part of the circuit (C8 & C9) have been replaced with new 450v components.

There is -210v AC at the cathode of the EZ90 and only -165v at the anode.

Can anyone suggest what the voltage readings should be at these points in the circuit, and the possible cause of the 4K7 resistor getting hot. (It's actual value is just over 4K9)

Thanks
Colin
__________________
Colin Armstrong
Colin is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:45 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 - 2023, Paul Stenning.