Viewing 9 posts - 1 through 9 (of 9 total)
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  • #2720
    Dan Walker
    CVRS Member

    I have a marconi model 117 which I have recapped and everything works except the tuning eye.. I have tried several tubes in the radio and they are all bright,,,but the eye does not close at all.. I put a new 1 meg resistor in the socket and still the same thing.. Any ideas??

    #2721
    rfenergy
    Forum Participant

    Check that you are getting AVC voltage to the tube.That is what drives it.The AVC will vary with signal strength.
    Jim

    #2723
    Rogers flipdial
    Forum Participant

    Yes – I don’t have the schematic handy right now – but in the AVC string there are some high resistance 1/4 watt resistors – 1 Meg and 2.2 Meg etc. – if you have an inexpensive modern VOM it likely won’t read higher than 2 Meg – I’ve been finding problems with a lot resistors lately – twenty years ago I wouldn’t have suspected too many problems with resistors – but the increased age is taking its toll on them now – even if they measure good when you first check them – after a few cycles of heating and cooling they tend to go bad – For the sake of 5 cent components – you might as well replace them at the same time you recap – that way you won’t have to fix the same radio more than once.

    #2726
    Dan Walker
    CVRS Member

    Well I got it to work.. On the Marconi there is a sort of small battery in side the chassis and i jusr put a clip across the terminal to connect the circuit and everything works fine now.. I will just remember it for the future.

    #2727
    John Bartley
    Forum Participant

    Dan Walker wrote:

    Well I got it to work.. On the Marconi there is a sort of small battery in side the chassis and i jusr put a clip across the terminal to connect the circuit and everything works fine now.. I will just remember it for the future.

    Dan,

    Those are biasing batteries. If yours is so dead that you have to short across it to make the radio work, then you should think about replacing it with either a watch battery or a resistor/cap combo. The set will perform better once the proper tube bias is in place.

    cheers

    John

    #2728
    Dan Walker
    CVRS Member

    Thanks for the information John… I don’t know what you mean by a resistor/cap combo…I could try a watch battery of 1.5 volts,if that is what you mean?
    So far it seems to work very well with a clip across it. If it works now do you think I should try anythiing else??
    Dan

    #2729
    Rogers flipdial
    Forum Participant

    Dan – did you leave the battery in – or did you remove it ? – if its still there you might be able to rejuvenate it – check the forums for details on how to do it. if you do a google search on bias cells you’ll find all kinds of info – keep your eyes open for a Canadian version of the Mallory-Yaxley encyclopedia – they are great books – there’s info in them on bias cells – I’ve seen them in different versions – some of the newer ones contain a lot of information – I haven’t checked – but maybe someone has scanned them and made them available online as well. Here’s a good article that directly relates to your post https://www.antiquewireless.org/otb/biascell.htm
    Maybe someone reading this could provide us with some "hard" facts about what placing a "clip" across the bias cell socket is doing to the circuit in terms of distortion and current draw – it would depend on the circuit – but it would be good to know.

    #2732
    cvrs
    Forum Participant

    Gerry did a good post on bias cells a while back, it’s here:
    viewtopic.php?f=6&t=143&p=435&hilit=bias+cells#p435

    if the link fails search for "bias cells" – that was the title.

    #2734
    Dan Walker
    CVRS Member

    I put a watch battery in place of the strip I soldered in and it seems to work fine,It works the same with a battery or with a strip but I did leave the battery in.

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