|
Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
|
Thread Tools |
20th Mar 2023, 3:59 pm | #1 |
Triode
Join Date: Nov 2018
Location: Risca, South Wales
Posts: 48
|
Mullard HSVT - "Reset" button woes
Hi all,
I have a Mullard HSVT (MK1) (to be fair i have one working and a couple that need "further attention" - which i will eventually get to as they are "on the list" to be fixed). However on this one whenever to run the "HT" test card, it trips the Reset cct. If I press the reset button on the top to reset it whilst the handle is still down, all is good and I can carry on with that test no problems. Raise the handle, Lower again and the same as above happens. This morning i found it also happened when trying to test an EL84. Continuity test is no issues - but when i try a "Heather Cathode INS" test, it trips. Pres reset and i get the usual nice heaters firing up, and a dot firmly in the green. I had a couple of questions if i may ask those that know far more than me... 1. What is the Reset button there for? 2. What would trigger it? 3. Anyone any thoughts as to what to look for to resolve? Many thanks Paul |
20th Mar 2023, 8:03 pm | #2 |
Nonode
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,301
|
Re: Mullard HSVT - "Reset" button woes
Be aware that pulling the handle down momentarily disconnects the mains from the MHSVT. As you complete the pull it reconnects.
The trip measures the current in the transformer and trips if it get too large. Check the action of the arm and consequent actions, it involves an inhibit flag that prevents the mains being applied if there is no card inserted. Looks like there is a momentary short as the arm is pulled down. Peter |
21st Mar 2023, 9:21 am | #3 |
Triode
Join Date: Nov 2018
Location: Risca, South Wales
Posts: 48
|
Re: Mullard HSVT - "Reset" button woes
Hi Peter,
Many thanks - that makes sense... I wasnt sure what triggered the "reset" - but an excess of current draw would explain it... Will investigate further around the arm, switch and inhibit flag (on another unit i have repaired the inhibit flag, so completely understand the process). Quick final question - Would i be right in saying that the "reset" circuit doesnt seem to appear on the Cct diagram? If it does, could someone point me to it please? Thanks Paul |
21st Mar 2023, 10:24 am | #4 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,099
|
Re: Mullard HSVT - "Reset" button woes
Look at the later models. The mk-1 diagram seems not to show it.
I think it feeds the common point of the HT winding through the relay. |
21st Mar 2023, 10:51 am | #5 |
Triode
Join Date: Nov 2018
Location: Risca, South Wales
Posts: 48
|
Re: Mullard HSVT - "Reset" button woes
Ahh yes... Marked as RLA, and if triggered it breaks the PRI feed into the Transformer.. Not present on the Mk1 cct diagram, however present on the MK3/4.
From what i understand (reading about), was retrofitted to a bunch of Mk1's, which would explain why it's not on the Mk1 cct diagram. |
22nd Mar 2023, 1:01 pm | #6 | |
Nonode
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,301
|
Re: Mullard HSVT - "Reset" button woes
Quote:
However a lot of MK1s have a Reset as it was supplied as a retro fit option. Peter |
|