Line Cord Dropper. To cut off or leave?

[kalee20]

Valve heaters are designed to be connected to a 'stiff' voltage source, such as the mains, and yes, many series-connected sets do add up to around 115V. So they were directly connected.

Having said that, a dropper, as you say, will give a level of surge limiting. So replacing with an auto transformer will negate this. It's unlikely that any switch-on surge would fuse a valve heater - but if that ever happens, you'd kick yourself for throwing out your trusty line cord!

[raditechman]

Just to more or less round off this thread. As I had already ordered the capacitor and bits, and they arrived earlier than I expected -the next morning- I fitted the capacitor etc. and the radio works OK. I am also going to order one of the "Wall Wart" autotransformers from Amazon as suggested by Jeffrey, as they are available there at a low price, and I may try that method later.
As for the valves blowing from switch on surge, to prevent this a thermistor could be used.
I have also rewired the single pole mains switch in the radio to switch the "live" side of the mains. It originally switched the neutral.
A 470K resistor has been fitted across the "dropper capacitor" to discharge it when the set is turned off and prevent shocks from touching the mains plug pins.
The old line cord has been placed in a large glass jar with a screw on lid for safe keeping, whilst still being able to look at.

John

[ppppenguin]

A small point when ordering low cost voltage converters. Some of these are electronic devices, akin to triac dimmers, totally unsuited to our purposes. If there is a weight given and it's over 500g then there's real copper and iron present. I think the little 45W transformers weigh around 1kg. If no weight is given then be wary.

[peetleetech]

Not to harp on the matter, John, the HT is possibly a problem, more for the capacitors, though. No, I meant for the filaments. Would the filaments benefit from slowing the build up of voltage? There is actually a device for this sort of thing. I first encountered it when building a Lindsay Hood amplifier, it's called a "brimistor".
Peter. (peetleetech is such a long word)

[Herald1360]

Originally Posted by raditechman

As for the valves blowing from switch on surge, to prevent this a thermistor could be used.

Originally Posted by peetleetech
There is actually a device for this sort of thing. I first encountered it when building a Lindsay Hood amplifier, it's called a "brimistor".



A Brimistor is simply a trademark name for a thermistor (cf Hoover, Biro etc etc)

[murphyv310]

One snag with a thermistor is that even when hot it stays hot and drops voltage so when the heater chain adds up to 115v and is supplied with 115v a thermistor is less than ideal as the the valves will then be under run with the loss through a "hot" thermistor.

[fidobsa]

One idea if the set is always used in the same room is to have a transformer hidden somewhere connected to an American 110 volt socket mounted near the set. You could then leave the set totally original, even down to the original type of mains plug.

[Derek vivian]

Hi I have several line dropper sets and have always ditched the cord and used cap droppers instead they work fine