A problem : Where to start ? - UK Vintage Radio Repair and Restoration Discussion Forum

georgesgiralt · 13th Apr 2010, 8:01 am

Hi !
I ran this Bajazzo valve portable on mains when the sound faded and disappeared totally.
So I turned it to batteries thinking that one selenium rectifier was dying.
The set ran fine for a couple of minutes and the same phenomena happened again. As the converter I use for the 90V has a "on" led I saw that without sound, the led was off. (the converter is automagically turned on by the conduction of the final valve).
So I though it could be either the heaters cell being too low or the DL94.
A new Nicad later the set returned to life for ... 30 seconds. So I got a new DL94 and the behaviour was the same.
As this set does not run hot, has the same behaviour on mains and on batteries, I wonder what's wrong ?
so I need some leads to follow, here.
Thanks in advance !

jjl · 13th Apr 2010, 8:08 am

Bonjour Georges

Sounds like the output valve(s) are cut off when the fault occurs due to changing circuit conditions, cathode resistors gone high or something similar. This would explain your convertor switching off as the output valve(s) will draw no current when cut off. I'd measure all voltages around the output valves before and after the fault arises and report back.

John

georgesgiralt · 13th Apr 2010, 6:15 pm

Hello John !
So I took the chassis out of the box. Plugged the mains and started the set. It ran perfect.
So I waited, and measured the voltages and compared them to the trader's sheet. A bit high (the transformer has only a 220V tapping and my mains is at 230 minimum).
After having heard the radio for more than one hour, the set is still perfect. So I thought that it is position related. I turned the chassis upside down to make it the same as in place. Another hour and still perfect. Grrr .... Intermittent are annoying.
Thanks for your help. I'll make more test when the set fail again. If it fails.

Steve_P · 13th Apr 2010, 6:43 pm

Do any suspect joints and check switches etc.

Cheers,

Steve P.

georgesgiralt · 13th Apr 2010, 6:47 pm

Alas, Steve, I've done that for more than a couple of hours (waiting for it to fail). None come obvious. Using my grip test lead, I played with all the caps I changed when I got the set month ago and none come loose.
For now the set is fine. I'll let it run for a couple more hours and see where I am.
Thanks for your advice.

jjl · 13th Apr 2010, 9:19 pm

Georges

Thinking about this a bit more, it could be a valveholder problem; one or more of the output valve socket contacts may not be making good contact with the valve pins.

This is a very common problem in battery valve sets.

It's worth trying carefully to close up the forked contacts with a sharp tool. I've broken a few contacts in battery valve sets attempting this though. If you break a contact you can often replace it with a spare one from another socket of the same type.

John

georgesgiralt · 13th Apr 2010, 10:24 pm

John, I do hope this is not the cause.
The wiring is so packed it would be a hell of a job just to get to the contacts. So prying them will be really difficult. As would be changing one socket.
The wiring is so packed that I burnt some resistors while changing the caps and one cap changing the resistor... I've used all my small irons, JBC and Antex 15 W and even these touch something while going deep into the wiring.
The set still runs fine.
Wait and see ....

georgesgiralt · 14th Apr 2010, 8:22 pm

So my set ran all day (from 6 AM to now) without any flaw. On mains.
Yesterday it ran on batteries. Perfect also. I needed a couple of NiMh cells charge to sustain the extended play, tough.
So I think you can close this thread now. I'll open a new one if need arose.

13th Apr 2010, 8:01 am	#1
georgesgiralt Hexode Join Date: Jul 2008 Location: Toulouse, France Posts: 406	A problem : Where to start ? Hi ! I ran this Bajazzo valve portable on mains when the sound faded and disappeared totally. So I turned it to batteries thinking that one selenium rectifier was dying. The set ran fine for a couple of minutes and the same phenomena happened again. As the converter I use for the 90V has a "on" led I saw that without sound, the led was off. (the converter is automagically turned on by the conduction of the final valve). So I though it could be either the heaters cell being too low or the DL94. A new Nicad later the set returned to life for ... 30 seconds. So I got a new DL94 and the behaviour was the same. As this set does not run hot, has the same behaviour on mains and on batteries, I wonder what's wrong ? so I need some leads to follow, here. Thanks in advance !

13th Apr 2010, 8:08 am	#2
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: A problem : Where to start ? Bonjour Georges Sounds like the output valve(s) are cut off when the fault occurs due to changing circuit conditions, cathode resistors gone high or something similar. This would explain your convertor switching off as the output valve(s) will draw no current when cut off. I'd measure all voltages around the output valves before and after the fault arises and report back. John

13th Apr 2010, 6:15 pm	#3
georgesgiralt Hexode Join Date: Jul 2008 Location: Toulouse, France Posts: 406	Re: A problem : Where to start ? Hello John ! So I took the chassis out of the box. Plugged the mains and started the set. It ran perfect. So I waited, and measured the voltages and compared them to the trader's sheet. A bit high (the transformer has only a 220V tapping and my mains is at 230 minimum). After having heard the radio for more than one hour, the set is still perfect. So I thought that it is position related. I turned the chassis upside down to make it the same as in place. Another hour and still perfect. Grrr .... Intermittent are annoying. Thanks for your help. I'll make more test when the set fail again. If it fails.

13th Apr 2010, 6:43 pm	#4
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: A problem : Where to start ? Do any suspect joints and check switches etc. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

13th Apr 2010, 6:47 pm	#5
georgesgiralt Hexode Join Date: Jul 2008 Location: Toulouse, France Posts: 406	Re: A problem : Where to start ? Alas, Steve, I've done that for more than a couple of hours (waiting for it to fail). None come obvious. Using my grip test lead, I played with all the caps I changed when I got the set month ago and none come loose. For now the set is fine. I'll let it run for a couple more hours and see where I am. Thanks for your advice.

13th Apr 2010, 9:19 pm	#6
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: A problem : Where to start ? Georges Thinking about this a bit more, it could be a valveholder problem; one or more of the output valve socket contacts may not be making good contact with the valve pins. This is a very common problem in battery valve sets. It's worth trying carefully to close up the forked contacts with a sharp tool. I've broken a few contacts in battery valve sets attempting this though. If you break a contact you can often replace it with a spare one from another socket of the same type. John

13th Apr 2010, 10:24 pm	#7
georgesgiralt Hexode Join Date: Jul 2008 Location: Toulouse, France Posts: 406	Re: A problem : Where to start ? John, I do hope this is not the cause. The wiring is so packed it would be a hell of a job just to get to the contacts. So prying them will be really difficult. As would be changing one socket. The wiring is so packed that I burnt some resistors while changing the caps and one cap changing the resistor... I've used all my small irons, JBC and Antex 15 W and even these touch something while going deep into the wiring. The set still runs fine. Wait and see ....

14th Apr 2010, 8:22 pm	#8
georgesgiralt Hexode Join Date: Jul 2008 Location: Toulouse, France Posts: 406	Re: A problem : Where to start ? So my set ran all day (from 6 AM to now) without any flaw. On mains. Yesterday it ran on batteries. Perfect also. I needed a couple of NiMh cells charge to sustain the extended play, tough. So I think you can close this thread now. I'll open a new one if need arose.