Sky chief USA radio

[Goldieoldie]

Hi
I have a sky chief USA radio with no model number.
One of the valves is missing .Looking at old posts on this forum I think it is the output valve .Possibly either 12A6 or 50L6 by looking at info on the net but would like confirmation on what it should be
The valves that are there are 12j7,12sk7,36z5 and a 49a ballast .
Does anyone have any info on this radio please ?
Cheers
Pete

[Goldieoldie]

Pics

[Goldieoldie]

More pics

[paulsherwin]

It looks like yet another American set made for the British market in the 40s. A 50L6 or 35L6 seems plausible, depending on the heater arrangements.

[Goldieoldie]

Yes Paul, forgot to say it is MW and LW.

[vinrads]

I would go for the 12 volt heater 12 +12+ 12+ 36+49 =121 volts Mick.

[Goldieoldie]

The 12a6 and 50l6 are both 12 v .15 a heaters.
Would either work or perhaps another easily obtainable valve work ?

[vinrads]

Hi the 50l6 is a 50 volt heater ! I would go for the 12a6 for the easiest , or a 35l6 with a resistor across the ballast ,check the pin out connections , a circuit of the output valve connections would be helpful , Mick.

[Goldieoldie]

Sorry you are right !
The 50l6 is 50 v
Could it be it was chosen for the radio to work on uk mains ?
The radio has LW as well as MW so presumed it was made for the uk

[HamishBoxer]

One of our members may have a copy of info, G6OneDave.

[vinrads]

It may have a line cord mains lead that is one with a resistance wire inside ,it will be no good if it has been shortened, best to forget the mains lead and go for a capacitive dropper , I see there are several 12a6.s on Ebay at reasonable prices, Mick.

[Goldieoldie]

Yes the mains cord is 558 ohms in one leg.

[Goldieoldie]

Could be asbestos ?
I’m cutting it off outside with a mask !

[G6Tanuki]

Yes, the old-fashioned 'line cords' often contained asbestos.

Replacing with a capacitive dropper [or running the entire radio from a 240-120V autotransformer/isolating transformer] is the way to go.

[PJL]

This set most likely has (or had) a line cord dropper that will contain asbestos fibres. If it still has one then it is best to remove it (preferably outside) and place it in a bag and bin it. The power supply will then need a rework and either to put it back to 120V AC operation and use a stepdown transformer or use a capacitor/rectifier/resistor dropper to lose the additonal voltage. I would suggest a 35L6 or perhaps a 50L6 was most likely the original. I personally favour the 120V AC operation as these sets are often not too good at insulating the user from chassis potential.

[vinrads]

Ah ! so a 50 l6 may well do ,you would need 159 volts , with the lead that is on you would get 156 near enough . or better still use a capacitor / transformer , Mick.

[Goldieoldie]

The existing valve heaters add up like this
12 plus 12 plus 35 ( rectifier ) 49 ( ballast ) equals 108
So if the missing valve is also 12 that would make 120 which would be right for USA
That would suggest the 12a6 would be correct rather than the 50l6 with its 50 v heater ?

[vinrads]

Yes it would be if the line cord was dropping 119 volts but it is only dropping 84 volts ,that means you could use the mains lead if you fit a 50ls . Mick.

[PJL]

Judging by other seta that use the 49A it appears to be a 300mA ballast tube and your is a 150mA chain. I have seen this done before where the 'conversion' to 240V changed the valves to 150mA to lower the line cord dissipation.

[Goldieoldie]

I think I’m going to go with a 12a6 with its 12 v heater and get rid of the dropper mains lead.
This would make it a 120 v set which I will use with a step down tx.
This would also keep in keeping with it being a USA radio .