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Old 25th Sep 2021, 12:27 am   #1
AdrianH
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Default A question on my CN430 Vidor Lady Anne

The radio works, but has a niggle that I can not fathom. I can not turn the sound fully off! There is always some sound (On channel).
The volume pot is OK, even if I ground the wiper I still have some audio, all be it low level. If I ground the grid of V3 by shorting the 10 Meg grid leak resistor it shuts up. I have tried another couple of valves in place of V3 with no difference I have been looking at the circuit of the Vidor and that of my Ferguson Flair and the main difference I can see around the DAF96 is the anode and screen resistor values.
The Anode and Screen values are 1 and 2.7 Meg on the Vidor and 2.2 & 6.8 Meg on the Flair.

The 2.7 Meg is a bit low at 2.2Meg and I actually have a lower anode voltage (18V) than the screen (25V) on the Vidor, this measured with a DMM.

The stronger the signal the louder the min volume, the flair no where near as bad. So would appreciate thoughts, I wonder if I am looking in the wrong area. The radio has been recapped before I bought it, and everything looks to be correct.

Adrian
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Old 25th Sep 2021, 12:35 am   #2
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Default Re: A question on my CN430 Vidor Lady Anne

You have leakage somewhere!. I would suggest its coming through the power supply, but I am only guessing without the whole circuit.

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Old 25th Sep 2021, 6:22 am   #3
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Default Re: A question on my CN430 Vidor Lady Anne

It sounds like the bottom end of the volume control is O/C or very high resistance. J.
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Old 25th Sep 2021, 7:58 am   #4
Mr 1936
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Default Re: A question on my CN430 Vidor Lady Anne

Hi

What does the volume pot measure on an ohmmeter, out of circuit if necessary ?

Is the residual audio of the same tonal quality, or is it more muffled ?

What happens if you shunt the grid to ground with a large value non-electrolytic capacitor (say 1 uF), i.e. shunt the AC but don't alter the DC biasing conditions ?

I'm just wondering if there is some residual audio on the AGC line, maybe its decoupler is defective or the wrong value ?
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Old 25th Sep 2021, 8:33 am   #5
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Default Re: A question on my CN430 Vidor Lady Anne

I think this may be a deliberate design because I think I remember my one did the same.
I wonder if it was so that you couldn't accidentally leave it turned down and turned on.

Mike
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Old 25th Sep 2021, 10:16 am   #6
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Default Re: A question on my CN430 Vidor Lady Anne

Going through the replies in order. Thanks for responding.

I am running the set from batteries at present, although the circuit does run the heaters from the HT supply when on mains and I have been wondering regarding the extra heater by-pass resistors.

The potentiometer is OK grounding the wiper does not silence the radio.

The volume pot measures around 520K ohm, The audio is very slightly muffled when down at the bottom of it's travel, getting to have more treble when turned up. I will shunt the grid resistor as you suggest and post back. OK about the detector/agc line, all done from a single diode within the same valve.

Mike interesting comment, wonder if anyone else sees the same.

Adrian

A free download of the circuit here: -
https://elektrotanya.com/vidor_cn430.../download.html
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Old 25th Sep 2021, 10:27 am   #7
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Default Re: A question on my CN430 Vidor Lady Anne

Could this just be fallout from the non grounded end of V3 filament being closer to the diode anode than the grounded end? In which case it's probably a design feature as suggested rather than a fault as such.
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Old 25th Sep 2021, 11:18 am   #8
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Default Re: A question on my CN430 Vidor Lady Anne

Hi Chris, I did wonder about the diode location, but think that the circuit is just badly drawn, when looking at the circuit for the Ferguson Flair which is better drawn and also a data sheet on the valve and looks as though it is correct right heater pin to ground?

I grounded the grid leak resistor with both a 0.1uF and with a 10uF non-pol cap to deck and both muted the audio, still a very low level there but massively better.

Move the caps to the other side of the af coupling cap 100pF and it makes no difference. Have also tried another cap across the agc line with no difference.

Perhaps it is some function of the radio, but poor?

Adrian
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Old 25th Sep 2021, 1:01 pm   #9
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Default Re: A question on my CN430 Vidor Lady Anne

Quote:
Originally Posted by crackle View Post
I think this may be a deliberate design because I think I remember my one did the same.
I wonder if it was so that you couldn't accidentally leave it turned down and turned on.

Mike
This is exactly right they are all like it. it is to stop the volume being turned down and the set left on . Some sets are louder than others at minimum volume. There is no fault.
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Old 25th Sep 2021, 1:06 pm   #10
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Default Re: A question on my CN430 Vidor Lady Anne

Hi!

The symbol shown for the DAF91/DAF92/DAF96 valves is the only one that can reasonably be drawn in practice, altho' it is perfectly possible to split it into two "half" valve symbols, (drawn separately), one for the diode and one for the pentode, with (+) and (–) signs appended to the filament pins, but I don't recall any service sheet where this has been done!

Admittedly it's difficult to draw in an "electrically correct" manner as both the suppressor grid (g3) and the diode anode a(d) are connected to, or mounted at, the –ve end of the filament!

I draw the one shown in the OP's circuit extract, it's as good as any and is the one Mullard use!

Chris Williams
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Old 25th Sep 2021, 1:18 pm   #11
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Default Re: A question on my CN430 Vidor Lady Anne

If the radios were designed to have a minimum volume then why not just lift the volume control above chassis with a small value resistor? What is causing the minimum audio?

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This is from the data sheet, but you would probably need a full A4 to get the circuit on a trader sheet with this much detail in it, so I can understand why the diagrams are like they are.

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Old 25th Sep 2021, 1:47 pm   #12
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Default Re: A question on my CN430 Vidor Lady Anne

To try to show why I asked the question in the first place: -
https://youtu.be/D7BhJsaYLz0

The circuits are very similar except for the heater supply feeds and I could not find the issue.

Adrian
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Old 25th Sep 2021, 1:55 pm   #13
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Default Re: A question on my CN430 Vidor Lady Anne

Philips decided to draw it on the +ve side in this data:

https://frank.pocnet.net/sheets/030/d/DAF96.pdf

EDIT: Post crossed.

Lawrence.
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Old 25th Sep 2021, 2:16 pm   #14
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Default Re: A question on my CN430 Vidor Lady Anne

Just checked mine..... It does the same.
looks like it's just part of the design.
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Old 25th Sep 2021, 3:09 pm   #15
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Default Re: A question on my CN430 Vidor Lady Anne

In that case as two are saying it is the case, I will stop looking for an issue, the radio was one I purchased from a forum member and i bought a made up battery pack for it some months ago so it means I tend to listen to it more.

Thanks all for the assistance.

Adrian
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Old 22nd Oct 2021, 8:02 pm   #16
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Default Re: A question on my CN430 Vidor Lady Anne

Closing a finished thread. Mods please close.

Adrian
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