Fusistor Replacement - RCA 14PD8054

[mbear2k]

Sounds good - thanks for the info. The rating for the set is 1.1 amp, 125 watts at 117 volts. But I will do the electrolytics, then do a current test and see where I am with modern AC voltage. I'm guessing either a 2 to 2.5 amp fuse?

[DaveWM]

I have a predicta that has on of those, next time I pull it I may end up making my own out of a thermistor/fuse/resistor. The resistor will be sized to drop the B+ to what ever it should be after the thermistor warms up. The fuse will be a fast blow since the theremistor will reduce the inrush, that way the fuse can be set to just above the max B+ current for max protection.

[Findm-Keepm]

Look anything like this? http://www.talonix.com/images/WMF5.6.jpg
or is is rectangular/box shaped, like Belimiter Fuse Resistors?

The Belimiters were all merged into two RCA part numbers - one 5.6 ohm, and the other 7.5 ohm. Your RCA part number is one that was merged. I don't have my RCA guide here with the part numbers, but can get them if you need them.

Only replace a fuse resistor with another fuse resistor, or similarly sized (ohms/Current Rating) inrush limiter.

Cheers,

[mbear2k]

Brian - it does look like the one in the picture, except maybe a little bigger and is/was white.

If you have a source for replacement, please let me know. I would prefer to go that route.

Thanks!
Mark

[Findm-Keepm]

A Google search (actually a Google Image Search) for "5.6 Ohm Vintage Fuse Resistor" turned up the image - and a couple of sources.

Moyers in Pennsylvania might also have it in the original RCA...

Cheers,

[VintagePC]

Originally Posted by mbear2k

Sounds good - thanks for the info. The rating for the set is 1.1 amp, 125 watts at 117 volts. But I will do the electrolytics, then do a current test and see where I am with modern AC voltage. I'm guessing either a 2 to 2.5 amp fuse?

That sounds like it should be good - If you can get a peak current reading at turn-on, you can use that to better determine the safety margin you need - If it's too much larger you might want to up the wattage and resistance of the resistor a little bit - It's generally agreed that the the softer this old gear warms up, the better; many people have made modifications so that their tube filaments don't get a power-on current spike, like DaveWM is suggesting.

You'd probably want to be a bit more careful with a SS rectifier, but with a tube, the HV won't appear until it's good and warm along with the others, so a slightly slower start has no ill effects.

I probably wouldn't worry too much about which of those to get - short conditions usually cause current draw in excess of that 0.5A difference, so you'd be protected either way... but if you already have them on hand, then I'd go with the 2 and replace it with a 2.5 if it blows under normal operation.