Mullard High Speed Valve Tester : help! - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

PJL · 3rd Jul 2020, 7:54 pm

I am surprised you get no +ve volts at all on C3+ and too high -ve on C4-. Apologies on getting you to double check but:
C3 & C4 are the large 4uF electrolytics and they are definitely wired in the correct way?
C3 & C4 have been replaced with electrolytics with a high enough working voltage?
You can measure 590V between the +ve and -ve terminals of C4?
C3- should be connected to C4+ and this is the junction you are measuring from?
C14 has been replaced?

Probably best not to turn it on too long with that high voltage on C4!!!

zillerfish · 3rd Jul 2020, 8:21 pm

No thats absolutely fine to question my findings.

the electrolytics are 4.7uF as opposed to 4uF, with a working voltage of 450v.Is that adequate?

I wondered if the new caps might have been damaged by the high voltages, so disconnected one end of each and checked them ... still showing 4.7uF

Pretty sure they are correctly installed regards polarity but will check tomorrow (my workshop is at my daughters house) and provide the additional info required, and carry out the further voltage measurements.

Your help thus far has been great, thank you.

Ed

zillerfish · 4th Jul 2020, 11:27 am

I checked the capacitors and voltages and was able to confirm they were installed correctly and voltages were as previously described.

C14 had been replaced. ( I first started looking at this 2 years ago and life had in the meantime got in the way )

PJLs obvious disbelief at the voltages got me to thinking had I done something wrong 2 years ago. His learned advice to look at C14 led me to discover that I had reconnected R42 to C11 not C14 that sits alongside !! Now I am usually very careful in my work (being relatively new to the Â‘gameÂ’) makes me think that a previous repair attempt had wired it up wrong too as the same failure to adjust the Y spot position was the reason I started the repair in the first place. Did I just repeat a previous error ? Who knows but happy to take the blame as I now have a fully adjusted and working MHSVT

Great thanks to PJL whose help has been invaluable, and to all others who have assisted and increased my knowledge of the circuitry.

What a great resource this is !

PJL · 4th Jul 2020, 4:35 pm

Good to hear it is fixed and congratulations on finding the error.

stevehertz · 4th Jul 2020, 5:22 pm

Out of interest I had two Mullard HSVTs that had faulty TRFs before I got a good one. And that one has been with me for 40 years.

3rd Jul 2020, 7:54 pm	#21
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! I am surprised you get no +ve volts at all on C3+ and too high -ve on C4-. Apologies on getting you to double check but: C3 & C4 are the large 4uF electrolytics and they are definitely wired in the correct way? C3 & C4 have been replaced with electrolytics with a high enough working voltage? You can measure 590V between the +ve and -ve terminals of C4? C3- should be connected to C4+ and this is the junction you are measuring from? C14 has been replaced? Probably best not to turn it on too long with that high voltage on C4!!!

3rd Jul 2020, 8:21 pm	#22
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! No thats absolutely fine to question my findings. the electrolytics are 4.7uF as opposed to 4uF, with a working voltage of 450v.Is that adequate? I wondered if the new caps might have been damaged by the high voltages, so disconnected one end of each and checked them ... still showing 4.7uF Pretty sure they are correctly installed regards polarity but will check tomorrow (my workshop is at my daughters house) and provide the additional info required, and carry out the further voltage measurements. Your help thus far has been great, thank you. Ed

4th Jul 2020, 11:27 am	#23
zillerfish Triode Join Date: Feb 2015 Location: Faversham, Kent, UK. Posts: 31	Re: Mullard High Speed Valve Tester : help! I checked the capacitors and voltages and was able to confirm they were installed correctly and voltages were as previously described. C14 had been replaced. ( I first started looking at this 2 years ago and life had in the meantime got in the way ) PJLs obvious disbelief at the voltages got me to thinking had I done something wrong 2 years ago. His learned advice to look at C14 led me to discover that I had reconnected R42 to C11 not C14 that sits alongside !! Now I am usually very careful in my work (being relatively new to the Â‘gameÂ’) makes me think that a previous repair attempt had wired it up wrong too as the same failure to adjust the Y spot position was the reason I started the repair in the first place. Did I just repeat a previous error ? Who knows but happy to take the blame as I now have a fully adjusted and working MHSVT Great thanks to PJL whose help has been invaluable, and to all others who have assisted and increased my knowledge of the circuitry. What a great resource this is !

4th Jul 2020, 4:35 pm	#24
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Mullard High Speed Valve Tester : help! Good to hear it is fixed and congratulations on finding the error.

4th Jul 2020, 5:22 pm	#25
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,831	Re: Mullard High Speed Valve Tester : help! Out of interest I had two Mullard HSVTs that had faulty TRFs before I got a good one. And that one has been with me for 40 years. __________________ A digital radio is the latest thing, but a vintage wireless is forever..