February 7, 2012 at 12:40 am #2720
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??February 7, 2012 at 1:02 am #2721rfenergyForum Participant
Check that you are getting AVC voltage to the tube.That is what drives it.The AVC will vary with signal strength.
JimFebruary 7, 2012 at 2:38 am #2723Rogers flipdialForum 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.February 12, 2012 at 9:45 pm #2726
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.February 13, 2012 at 11:38 am #2727John BartleyForum 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.
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.
JohnFebruary 14, 2012 at 7:06 pm #2728
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??
DanFebruary 16, 2012 at 3:31 am #2729Rogers flipdialForum 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.February 16, 2012 at 8:33 pm #2732cvrsForum Participant
Gerry did a good post on bias cells a while back, it’s here:
if the link fails search for "bias cells" – that was the title.February 17, 2012 at 10:10 pm #2734
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.
- You must be logged in to reply to this topic.