Vidor Henley CN426 - UK Vintage Radio Repair and Restoration Discussion Forum

112stereo · 27th May 2017, 9:32 pm

Can anyone help please.
Trying to get this radio going for a friend's family who has had it from new and just found it when clearing out a relative's property.
Had to replace the mains cable which had gone open circuit due to cracking.
Now when turned on the speaker clicks and a slight noise if the centre terminal on the volume control is touched but nothing else.
The HT is running at 88 volts, but valve 3 (DAF 91 ) on the anode is 35 volts which is quite high, but the heaters are 4.5 volts per valve which is far too high.
Have checked the circuitry around the heater circuit and can't find anything wrong.
Can anyone help please.

Herald1360 · 27th May 2017, 9:56 pm

If the filaments show 4.5 V, they're open circuit! Check between pins1&7 of each pulled valve to be certain.

julie_m · 27th May 2017, 10:21 pm

Yes, that would be my thought -- at least one of the filaments could well be open-circuit. There are shunt resistors across the filaments, to dispose of the anode current which otherwise would flow through the filaments of the next valves downstream, and an extra resistance in series when operating from mains. All this could mask problems. Simplest thing is to carefully remove each valve in turn and measure with a digital meter set to 200Ω range across pins 1 and 7. Post your readings here; also please post the readings you get with nothing connected to the probes, and with the probes touching.

For testing purposes, it might be best to use a home-made battery pack using disposable batteries bought from a pound store; you can wire ten 9V smoke alarm batteries in series to make 90 volts, and five AA walkman batteries in series to make 7.5V.

112stereo · 29th May 2017, 1:12 pm

Thanks for responding.
Have checked all valve heaters and all give readings.
Having checked the bypass restors I can't find one for valve 3 ?
I removed all the valves and expected to read the bypass resistors in circuit , the only reading I get is a slight kick from c 22 ?
I am reading from c22 positive to earth which by my calculations should go via r18, r15, s9 open, r6, r11, and r2 to chassis......there is no reading other than the kick from c22.
Just as a test I put a resistor across valve 3 heaters and behold I have a reading of the correct value !
Nothing appears to have been touched internally so I can't work out, if my circuit is correct, how it ever worked, but clearly it did.
I have not tried to power it up again, do you think I should try it ?

Herald1360 · 29th May 2017, 1:44 pm

Only with batteries and be ABSOLUTELY sure that the 90V supply is NOT connected to the filament circuit!

112stereo · 29th May 2017, 1:54 pm

Just as a follow up, the valve heaters all read 20 ohm except DL94 which reads 30 ohm, read on an ago 8.
Perhaps o should try the battery test first, this might have to wait till Wednesday when I can get to the shops.

ukcol · 29th May 2017, 2:28 pm

If the OT or anyone else is interested, this set is a Vidor model and service data is on Paul's DVD and here.

Chris55000 · 29th May 2017, 4:48 pm

Hi!

The first thing to do with this type of set is to ensure the filament-circuit is OK. To safeguard the delicate valves you can use ordinary carbon-film resistors as dummy loads, three x 27 ohm for the DK92, DF91 & DAF91 and a 56 0hm for the DL92 (O/P valves have a centre-tapped 2.8V filament), insert the 56 ohm resistor between 1 and 7 of the DL92 socket, and one 27 ohm resistor in pins 1 and 7 of the other three, switch the set on and make sure the voltage drop across each resistor is no more than 1.4V maximum.

If you find any valve has a voltage-drop much too high or too low, this suggests problems with the filament shunt resistors dotted along the chain. I can only generalise on these as they vary from model to model, but the Service sheet will detail what the manufacturer originally fitted!

I've attached the Mullard Paper giving the theory behind operating battery valves from the mains here!

Chris Williams

Chris55000 · 29th May 2017, 9:13 pm

Hi!

Just a quickie point I forgot to clarify earlier!

If you use carbon-resistors as dummy Valve-Filaments I appreciate the voltage-distribution along the chain will not be the same as with actual valves fitted because the shunt-resistors will only bypass a portion of the chain current rather than the anode/G2 currents of each valve, but you should still be able to prove, using dummy resistors, that the chain, wiring and filament-dropping arrangements are intact!

If Pin 5 (fct & G3) of the DL94 output valve has it's own bypass shunt connected to chassis, then use 1 x 27R from 1 & 5 plus a second 27R from 5 to 7 to substitute for the DL94 by the way!

Chris Williams

Chris55000 · 29th May 2017, 9:25 pm

PS!

The DAF91 diode-detector/AF amplifier stage only takes minute anode and screen-grid currents, hence there being no shunt-resistor across the filament of this valve!

Chris Williams

peter_sol · 30th May 2017, 6:42 am

Hello if you want valves I can dig some out FOC and I am local
just PM me your address I will see what I have

112stereo · 30th May 2017, 7:53 am

Thank you all very much for all the info. It looks like a long job so I need some batteries to keep the thing safe till I can check it all out properly.
Thank you also Peter I might be taking you up on your offer of valves once I get the heater chain right.
My circuit certainly shows a bypass shunt resistor on each valve, it's just I can't find one for valve 3 in the actual radio !?
I am just wondering if there is a modification sheet for perhaps later models, but I can't find one.

27th May 2017, 9:32 pm	#1
112stereo Pentode Join Date: Jan 2014 Location: St Albans, Hertfordshire, UK. Posts: 215	Vidor Henley CN426 Can anyone help please. Trying to get this radio going for a friend's family who has had it from new and just found it when clearing out a relative's property. Had to replace the mains cable which had gone open circuit due to cracking. Now when turned on the speaker clicks and a slight noise if the centre terminal on the volume control is touched but nothing else. The HT is running at 88 volts, but valve 3 (DAF 91 ) on the anode is 35 volts which is quite high, but the heaters are 4.5 volts per valve which is far too high. Have checked the circuitry around the heater circuit and can't find anything wrong. Can anyone help please.

27th May 2017, 9:56 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Henley CN 426 If the filaments show 4.5 V, they're open circuit! Check between pins1&7 of each pulled valve to be certain. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

27th May 2017, 10:21 pm	#3
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Henley CN 426 Yes, that would be my thought -- at least one of the filaments could well be open-circuit. There are shunt resistors across the filaments, to dispose of the anode current which otherwise would flow through the filaments of the next valves downstream, and an extra resistance in series when operating from mains. All this could mask problems. Simplest thing is to carefully remove each valve in turn and measure with a digital meter set to 200Ω range across pins 1 and 7. Post your readings here; also please post the readings you get with nothing connected to the probes, and with the probes touching. For testing purposes, it might be best to use a home-made battery pack using disposable batteries bought from a pound store; you can wire ten 9V smoke alarm batteries in series to make 90 volts, and five AA walkman batteries in series to make 7.5V. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

29th May 2017, 1:12 pm	#4
112stereo Pentode Join Date: Jan 2014 Location: St Albans, Hertfordshire, UK. Posts: 215	Re: Henley CN 426 Thanks for responding. Have checked all valve heaters and all give readings. Having checked the bypass restors I can't find one for valve 3 ? I removed all the valves and expected to read the bypass resistors in circuit , the only reading I get is a slight kick from c 22 ? I am reading from c22 positive to earth which by my calculations should go via r18, r15, s9 open, r6, r11, and r2 to chassis......there is no reading other than the kick from c22. Just as a test I put a resistor across valve 3 heaters and behold I have a reading of the correct value ! Nothing appears to have been touched internally so I can't work out, if my circuit is correct, how it ever worked, but clearly it did. I have not tried to power it up again, do you think I should try it ?

29th May 2017, 1:44 pm	#5
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Henley CN 426 Only with batteries and be ABSOLUTELY sure that the 90V supply is NOT connected to the filament circuit! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

29th May 2017, 1:54 pm	#6
112stereo Pentode Join Date: Jan 2014 Location: St Albans, Hertfordshire, UK. Posts: 215	Re: Henley CN 426 Just as a follow up, the valve heaters all read 20 ohm except DL94 which reads 30 ohm, read on an ago 8. Perhaps o should try the battery test first, this might have to wait till Wednesday when I can get to the shops.

29th May 2017, 2:28 pm	#7
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Henley CN 426 If the OT or anyone else is interested, this set is a Vidor model and service data is on Paul's DVD and here.

29th May 2017, 9:13 pm	#9
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: Vidor Henley CN426 Hi! Just a quickie point I forgot to clarify earlier! If you use carbon-resistors as dummy Valve-Filaments I appreciate the voltage-distribution along the chain will not be the same as with actual valves fitted because the shunt-resistors will only bypass a portion of the chain current rather than the anode/G2 currents of each valve, but you should still be able to prove, using dummy resistors, that the chain, wiring and filament-dropping arrangements are intact! If Pin 5 (fct & G3) of the DL94 output valve has it's own bypass shunt connected to chassis, then use 1 x 27R from 1 & 5 plus a second 27R from 5 to 7 to substitute for the DL94 by the way! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 29th May 2017 at 9:21 pm.

29th May 2017, 9:25 pm	#10
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,864	Re: Vidor Henley CN426 PS! The DAF91 diode-detector/AF amplifier stage only takes minute anode and screen-grid currents, hence there being no shunt-resistor across the filament of this valve! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

30th May 2017, 6:42 am	#11
peter_sol Octode Join Date: Aug 2003 Location: Welwyn Garden City, Herts. UK. Posts: 1,906	Re: Vidor Henley CN426 Hello if you want valves I can dig some out FOC and I am local just PM me your address I will see what I have Last edited by peter_sol; 30th May 2017 at 6:49 am.

30th May 2017, 7:53 am	#12
112stereo Pentode Join Date: Jan 2014 Location: St Albans, Hertfordshire, UK. Posts: 215	Re: Vidor Henley CN426 Thank you all very much for all the info. It looks like a long job so I need some batteries to keep the thing safe till I can check it all out properly. Thank you also Peter I might be taking you up on your offer of valves once I get the heater chain right. My circuit certainly shows a bypass shunt resistor on each valve, it's just I can't find one for valve 3 in the actual radio !? I am just wondering if there is a modification sheet for perhaps later models, but I can't find one.