Vidor CN396A dismantling? - UK Vintage Radio Repair and Restoration Discussion Forum

boiss · 8th Oct 2023, 12:16 am

I have been given a Vidor CN396A to look at for someone but I can't get the chassis out of the case. I can't read the radio musem instructions. I have unscrewed the round nuts but the chassis doesn't move at the front. It goes a bit up and down (mm) but will not go to the right.
Does anyone have experience of dismantling these little radios?
Cheers
M

TonyDuell · 8th Oct 2023, 7:23 am

Yes, that model of radio gave me problems getting inside years ago.

The trick is to unscrew the 2 lefthand metal feet on the underside of the set. They go through the wooden case into tapped holes on the chassis.

boiss · 8th Oct 2023, 5:33 pm

I wondered about that, but one of the feet is missing anyway and it looked like there was a place for a pin to go in. I just thought that the feet were like sort of tacks. I'll give it a try tomorrow. One other thing I noticed is that there is a connector for a PP3 (9V) Or did the original 7.5V battery have the same sort of connector as the PP3? A standard PP3 (with series dropper resistor) would only last about 10 hours, with 50mA filaments.
Thanks Tony.

TonyDuell · 9th Oct 2023, 4:38 am

It's only the 2 feet on the left hand side (opposite side to the battery compartment) that you remove. The other 2 are fixed to the wood.

The original 7.5V battery had a 2 pin socket. The -ve pin is 1/8"(3.2mm) diameter, the +ve pin is 5/32" (4mm) diameter and the centres of the pins are .53" (13.5mm) apart . I just hope that somebody hasn't tried to run the vave filaments off a 9V battey, this could well have burnt out one of them.

Techman · 9th Oct 2023, 12:59 pm

I would advise checking things like valve filament continuity and wound components such as the output transformer primary (a well known problem on battery sets) before delving to deeply into this, as these type of faults may make the set not worth repairing financially.

David G4EBT · 9th Oct 2023, 2:11 pm

Well worth downloading the Service Data from the top right.

There are two options, Trader Sheet 981 and the ERT datasheet. Of the two, I prefer the ERT sheet, which has excellent diagrams and a clearer circuit, plus detailed information on how to remove the chassis, as well as all the other info on voltages and alignment. (One marginal benefit of Trader Sheets is that the explain the function of each component, which can be helpful to less experience restorers).

Well worth £1.99. https://www.service-data.com/section.php/8450/1/396a

If you did download the ERT sheet, it's in landscape format, so ensure you set the printer to landscape rather than portrait).

Good luck with the radio.

Sideband · 10th Oct 2023, 2:12 pm

If you do need any valves, I have a number of these (more than I will ever use). Just cost of postage. Not all new but have good tested pulls.

boiss · 11th Oct 2023, 12:11 am

Quote:

Originally Posted by TonyDuell

It's only the 2 feet on the left hand side (opposite side to the battery compartment) that you remove. The other 2 are fixed to the wood.

The original 7.5V battery had a 2 pin socket. The -ve pin is 1/8"(3.2mm) diameter, the +ve pin is 5/32" (4mm) diameter and the centres of the pins are .53" (13.5mm) apart . I just hope that somebody hasn't tried to run the vave filaments off a 9V battey, this could well have burnt out one of them.

Hi Tony,
I unscrewed the other foot and out it came.
The Lt connector is definitely a PP3 type. so I will have to check if there is a 33R or 39R half watt dropper resistor in series.
I brought the set up on the mains with a series of old fashioned light bulbs in series with the radio. After a few runs with the selector on 240 I connected it directly to the mains 230V. The volume was very low as the owner had said.
A slight wiggle on the O/P bottle gave an intermittent higher volume level.
Contact cleaning and then contact spray on all bases and Wow, Quite loud now! What are the 2 springs with red wires attached on the inner LHS. They appear to have a sort of connector which isn't used as they are soldered to the springs?
Not an easy set to work on, my little Romac is much easier. I'm glad it was just contacts.

boiss · 11th Oct 2023, 12:16 am

Quote:

Originally Posted by Sideband

If you do need any valves, I have a number of these (more than I will ever use). Just cost of postage. Not all new but have good tested pulls.

I'll keep you in mind.
YES with Rick were great, saw their last concert in Munich about 1972. Still got some of their stuff on MP3s.

boiss · 11th Oct 2023, 12:19 am

Quote:

Originally Posted by David G4EBT

Well worth downloading the Service Data from the top right.

There are two options, Trader Sheet 981 and the ERT datasheet. Of the two, I prefer the ERT sheet, which has excellent diagrams and a clearer circuit, plus detailed information on how to remove the chassis, as well as all the other info on voltages and alignment. (One marginal benefit of Trader Sheets is that the explain the function of each component, which can be helpful to less experience restorers).

Well worth £1.99. https://www.service-data.com/section.php/8450/1/396a

If you did download the ERT sheet, it's in landscape format, so ensure you set the printer to landscape rather than portrait).

Good luck with the radio.

I turn my laptop on its side!

boiss · 19th Oct 2023, 5:18 pm

Quote:

Originally Posted by boiss

Quote:

Originally Posted by TonyDuell

It's only the 2 feet on the left hand side (opposite side to the battery compartment) that you remove. The other 2 are fixed to the wood.

The original 7.5V battery had a 2 pin socket. The -ve pin is 1/8"(3.2mm) diameter, the +ve pin is 5/32" (4mm) diameter and the centres of the pins are .53" (13.5mm) apart . I just hope that somebody hasn't tried to run the vave filaments off a 9V battey, this could well have burnt out one of them.

Hi Tony,
I unscrewed the other foot and out it came.
The Lt connector is definitely a PP3 type. so I will have to check if there is a 33R or 39R half watt dropper resistor in series.
I brought the set up on the mains with a series of old fashioned light bulbs in series with the radio. After a few runs with the selector on 240 I connected it directly to the mains 230V. The volume was very low as the owner had said.
A slight wiggle on the O/P bottle gave an intermittent higher volume level.
Contact cleaning and then contact spray on all bases and Wow, Quite loud now! What are the 2 springs with red wires attached on the inner LHS. They appear to have a sort of connector which isn't used as they are soldered to the springs?
Not an easy set to work on, my little Romac is much easier. I'm glad it was just contacts.

Wrong !!!!
it is intermittent, Spoke to the owner and he said yes that is right!
Sometimes it's loud and sometimes it isn't.

boiss · 20th Nov 2023, 1:55 pm

Took the chassis out of the case, found C21 variably leaky, changed it for a modern cap inside the green sleeving. seems ok now. However I noticed that the anode and screen volts on the DAF91 were rather low, better than with the old cap but now removing the cap causes no change. The Anode is about 27 volts and the screen is about the same. Screen decoupling cap is Ok as is 1M resistor. Changed the DAF91 with one from the spare set, It was about 2V higher but less volume which explains the higher V.
Is 27V on the anode normal for these sets? HT is 88V.
Cheers
M

Station X · 20th Nov 2023, 2:46 pm

Service sheet says Anode 11V and Screen 14V. Could be using a low sensitivity analogue meter.

boiss · 21st Nov 2023, 9:32 am

I'm using a DVM, I will try an analogue meter 20K/V.
Those readings are very low, Valve datasheets point to 45V?
With a 270K anode load, doesn't take much current change for a big swing.
Thanks for the info.
M

ms660 · 21st Nov 2023, 11:23 am

I think the g2 current for the DAF91 that's quoted in the Trader sheet is in serious error.

Divide by 10 possibly.

Lawrence.

Station X · 21st Nov 2023, 12:31 pm

The BRT service sheet has the same error in showing a g2 current of 0.5mA for mains operation. The figure quoted for battery operation is 0.06mA which seems more likely.

boiss · 22nd Nov 2023, 1:18 am

G2 R, 1M with 61.3V across it, gives 0.061 ma., so the 27Va and 26,7 Vg2 are about right. looks like the 2 old 0.01uF caps drop the Va by 4V. New caps make no difference. Haven't checked the 65pf jobbie yet but I have loads of volume now.
I thought the resistor values would be wildly out but they are not bad, within 20%.
Thanks!

boiss · 24th Nov 2023, 6:53 pm

My analogue meter is 2K/V, not much cop in these ccts. I do have an old AVO8 MkIII (20K/V which I might try before putting the chassis back in the case.
The LT connector is PP3 but there is no added resistor (27R or 30r) in the circuit for use on 9V. Need to ask the owner. He also gave me a battery converter which fits in a B126 battery cardboard outer along with a battery holder for 6 AA cells. However with new Alkaline cells the OP volts off load are only 72V. The owner says it was was a kit from a company in Kent, It is built on 3 pieces of PCB soldered together but not very rigidly. the cct board and the 2 ends one has a 3 pin Din socket for the O/P. the I/P is a PP3 connector for the AA cell battery pack. It uses a toroid and 4 transistors, 2x 3904, 3819 and BS170.
Does anyone know anything about this converter and have a circuit diagram for it. I think it was in PW, but I have trawled through many copies of PW for a few hours without finding anything.

8th Oct 2023, 12:16 am	#1
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Vidor CN396A dismantling? I have been given a Vidor CN396A to look at for someone but I can't get the chassis out of the case. I can't read the radio musem instructions. I have unscrewed the round nuts but the chassis doesn't move at the front. It goes a bit up and down (mm) but will not go to the right. Does anyone have experience of dismantling these little radios? Cheers M

8th Oct 2023, 7:23 am	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,055	Re: Vidor CN396A dismantling? Yes, that model of radio gave me problems getting inside years ago. The trick is to unscrew the 2 lefthand metal feet on the underside of the set. They go through the wooden case into tapped holes on the chassis.

8th Oct 2023, 5:33 pm	#3
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Re: Vidor CN396A dismantling? I wondered about that, but one of the feet is missing anyway and it looked like there was a place for a pin to go in. I just thought that the feet were like sort of tacks. I'll give it a try tomorrow. One other thing I noticed is that there is a connector for a PP3 (9V) Or did the original 7.5V battery have the same sort of connector as the PP3? A standard PP3 (with series dropper resistor) would only last about 10 hours, with 50mA filaments. Thanks Tony.

9th Oct 2023, 4:38 am	#4
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,055	Re: Vidor CN396A dismantling? It's only the 2 feet on the left hand side (opposite side to the battery compartment) that you remove. The other 2 are fixed to the wood. The original 7.5V battery had a 2 pin socket. The -ve pin is 1/8"(3.2mm) diameter, the +ve pin is 5/32" (4mm) diameter and the centres of the pins are .53" (13.5mm) apart . I just hope that somebody hasn't tried to run the vave filaments off a 9V battey, this could well have burnt out one of them.

9th Oct 2023, 12:59 pm	#5
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 4,829	Re: Vidor CN396A dismantling? I would advise checking things like valve filament continuity and wound components such as the output transformer primary (a well known problem on battery sets) before delving to deeply into this, as these type of faults may make the set not worth repairing financially.

9th Oct 2023, 2:11 pm	#6
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,568	Re: Vidor CN396A dismantling? Well worth downloading the Service Data from the top right. There are two options, Trader Sheet 981 and the ERT datasheet. Of the two, I prefer the ERT sheet, which has excellent diagrams and a clearer circuit, plus detailed information on how to remove the chassis, as well as all the other info on voltages and alignment. (One marginal benefit of Trader Sheets is that the explain the function of each component, which can be helpful to less experience restorers). Well worth £1.99. https://www.service-data.com/section.php/8450/1/396a If you did download the ERT sheet, it's in landscape format, so ensure you set the printer to landscape rather than portrait). Good luck with the radio. __________________ David. BVWS Member. G-QRP Club member 1339.

10th Oct 2023, 2:12 pm	#7
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,435	Re: Vidor CN396A dismantling? If you do need any valves, I have a number of these (more than I will ever use). Just cost of postage. Not all new but have good tested pulls. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

20th Nov 2023, 1:55 pm	#12
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Re: Vidor CN396A dismantling? Took the chassis out of the case, found C21 variably leaky, changed it for a modern cap inside the green sleeving. seems ok now. However I noticed that the anode and screen volts on the DAF91 were rather low, better than with the old cap but now removing the cap causes no change. The Anode is about 27 volts and the screen is about the same. Screen decoupling cap is Ok as is 1M resistor. Changed the DAF91 with one from the spare set, It was about 2V higher but less volume which explains the higher V. Is 27V on the anode normal for these sets? HT is 88V. Cheers M

20th Nov 2023, 2:46 pm	#13
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 20,624	Re: Vidor CN396A dismantling? Service sheet says Anode 11V and Screen 14V. Could be using a low sensitivity analogue meter. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

21st Nov 2023, 9:32 am	#14
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Re: Vidor CN396A dismantling? I'm using a DVM, I will try an analogue meter 20K/V. Those readings are very low, Valve datasheets point to 45V? With a 270K anode load, doesn't take much current change for a big swing. Thanks for the info. M

21st Nov 2023, 11:23 am	#15
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,444	Re: Vidor CN396A dismantling? I think the g2 current for the DAF91 that's quoted in the Trader sheet is in serious error. Divide by 10 possibly. Lawrence.

21st Nov 2023, 12:31 pm	#16
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 20,624	Re: Vidor CN396A dismantling? The BRT service sheet has the same error in showing a g2 current of 0.5mA for mains operation. The figure quoted for battery operation is 0.06mA which seems more likely. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

22nd Nov 2023, 1:18 am	#17
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Re: Vidor CN396A dismantling? G2 R, 1M with 61.3V across it, gives 0.061 ma., so the 27Va and 26,7 Vg2 are about right. looks like the 2 old 0.01uF caps drop the Va by 4V. New caps make no difference. Haven't checked the 65pf jobbie yet but I have loads of volume now. I thought the resistor values would be wildly out but they are not bad, within 20%. Thanks!

24th Nov 2023, 6:53 pm	#18
boiss Pentode Join Date: Jun 2006 Location: Malaga, Spain. Posts: 231	Re: Vidor CN396A dismantling? My analogue meter is 2K/V, not much cop in these ccts. I do have an old AVO8 MkIII (20K/V which I might try before putting the chassis back in the case. The LT connector is PP3 but there is no added resistor (27R or 30r) in the circuit for use on 9V. Need to ask the owner. He also gave me a battery converter which fits in a B126 battery cardboard outer along with a battery holder for 6 AA cells. However with new Alkaline cells the OP volts off load are only 72V. The owner says it was was a kit from a company in Kent, It is built on 3 pieces of PCB soldered together but not very rigidly. the cct board and the 2 ends one has a 3 pin Din socket for the O/P. the I/P is a PP3 connector for the AA cell battery pack. It uses a toroid and 4 transistors, 2x 3904, 3819 and BS170. Does anyone know anything about this converter and have a circuit diagram for it. I think it was in PW, but I have trawled through many copies of PW for a few hours without finding anything.