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 10th Mar 2016, 10:17 pm   #21
David Simpson
Nonode
 
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,838
Default Re: Mullard HSVT 7600/4

Aye Frank, it was a toss up between V5's heater or V2/V3's as to which is the most important internal valve, calibration-wise. Also, having noted the wee range of PJL's R41's -ve voltages, made me plumb for S6's 6.3V. If someone advises me otherwise, I'll easy change. Yep, just monitoring the 6.3V is much safer that full HT. If it was my own set & I was going to use it regularly, then I might have added the HT. Had there been more room on the calibration panel, one could have fitted a multi-wafer yaxley switch, and read all the test points off one pair of terminals.
The Forum's Test Card project is massive, I see. Being an HSVT novice, I'm just not going to get involved. But perhaps there is another EF37A Card floating about ? Looking at the VD Manual, EF36, 37 & 37A's all have the same spec & working voltages, and connections. I wonder how many cards cover all three valves.
Thanks for the link for lacing cord.

Regards, David
David Simpson is offline  
Old 11th Mar 2016, 5:18 pm   #22
David Simpson
Nonode
 
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,838
Default Re: Mullard HSVT 7600/4

Problem solved at last. Whoopee !
Went back to basic fault finding, and decided to individually test every single resistor which had been changed in the recent past. Particularly R's 69 to 79.
(Folks, remember last year sometime, someone raised a thread about modern paint tones used for resistor banding), well, eventually got round to R74(300 ohm) & found - bright brown/black/brown - which turned out to be 100ohms ! Changed for high spec 300ohms, and got the EF37A's Va to 220V, and dot settled a couple of mm below the dotted line in the green zone.
I've done 10 press-ups for not finding it sooner, and will tell the previous repairer to do 20.
From what I can establish, whatever wee voltage is dropped across the resistor or resistors, chosen out of R69 to R79 by the card - that's the voltage passed on to R41 via loom wires c & d(see circuit diagram) for Test 6.
Its been an interesting delve into the HSVT, and many thanks guys - particularly Frank, for all advice & support. Hopefully, the mods I've put in place will enhance the use of this tester for years to come.
I've completed drawing up the T/F tag layout, but am experiencing scanning difficulties. Will post asap.
Accompanying picture shows healthy R41 voltage, along with decent dot position on crt.

Regards, David
Attached Thumbnails
Click image for larger version

Name:	EF37A Spot-on.jpg
Views:	113
Size:	110.3 KB
ID:	121419  
David Simpson is offline  
Old 11th Mar 2016, 8:35 pm   #23
DuncanLeece
Pentode
 
Join Date: Oct 2010
Location: Banff, Aberdeenshire, UK.
Posts: 103
Default Re: Mullard HSVT 7600/4

As the lucky owner of what is now a very comprehensively checked-over HSVT, please may I add to David's thanks for all those who have helped with advice, and of course, to my good mate David for his splendid work. I will bribe him with scones and coffee until he teaches me that cable lacing technique!

regards
Duncan
DuncanLeece is offline  
Old 11th Mar 2016, 9:52 pm   #24
Norman Raeburn
Heptode
 
Join Date: Feb 2008
Location: Leven, Fife, Scotland
Posts: 823
Default Re: Mullard HSVT 7600/4

Hi David, I did hope it wasn't something I had done! sorry for the trouble I caused. My arms are aching now after the twenty press ups. I knew you were the man to sort it out. All the best, Norman
Norman Raeburn is offline  
Old 11th Mar 2016, 10:47 pm   #25
David Simpson
Nonode
 
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,838
Default Re: Mullard HSVT 7600/4

Just a dodgy resistor, Norman. Something we both missed, I guess. At least the press-ups will keep us fit. Mind you, you did a great job changing heaps of capacitors & resistors. Just about all of them, I reckon. It would've taken me ages & ages.
Complete change now - a lovely old medical induction coil with all the chrome plated attachments. I guess about 80 years old. Then on to Duncan's battery eliminator. Isn't electronicing fun ?

Regards, David
David Simpson is offline  
Old 12th Mar 2016, 1:04 am   #26
frankmcvey
Rest in Peace
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 858
Default Re: Mullard HSVT 7600/4

Good result, David. I learned quite a bit as well!

Cheers,

Frank
frankmcvey is offline  
Old 17th Mar 2016, 4:07 pm   #27
David Simpson
Nonode
 
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,838
Default Re: Mullard HSVT 7600/4

Well Folks,
I've now finished with this lovely old machine, and will return it to Duncan on Saturday. I've attached a copy of my T/F connections.
Provoking thoughts :-
1. Yes, I understand that these were designed for simplistic 'Go/No Go' use by possibly semi-skilled operatives.

2.They are relatively cheaper than AVO VCM's.

3. But hey - they are fully functioning DC Valve Testers, which AVO's are definitely not.

4. If R41's wee voltage is an obvious indication of Spot movement on the crt, and therefore of Ia drawn on Test6, then just how linear is it ? Then can it be fed off to feed an external meter calibrated in mA ? Obviously, the meter & it's circuitry would need to be of jolly high O/P/V.

5.In my book, as well as the modifications I've installed, what other mods can be done ? Several, I submit.

6. If some keen valve collector on restricted means wants an all-round Tester/VCM, then maybe, suitably modified, an HSVT could meet the bill at half the price of a (silly AC functioning) AVO.

Regards, David
Attached Thumbnails
Click image for larger version

Name:	HSVT T.F Conn's.jpg
Views:	84
Size:	29.6 KB
ID:	121623  
David Simpson is offline  
Old 17th Mar 2016, 4:41 pm   #28
ukcol
Rest in Peace
 
ukcol's Avatar
 
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
Default Re: Mullard HSVT 7600/4

Is that a bit clearer David?
Attached Thumbnails
Click image for larger version

Name:	D_Simpson.jpg
Views:	97
Size:	95.8 KB
ID:	121626  
ukcol is offline  
Old 17th Mar 2016, 7:52 pm   #29
David Simpson
Nonode
 
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,838
Default Re: Mullard HSVT 7600/4

Many thanks, Colin. My cheapo Brother Scanner/Printer has been playing up recently.

Regards, David
David Simpson is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:15 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.