An old wives tale or ...?

Don

Active Member
I have heard a ton of people speak how one should never plug in and turn on an older tube powered (and even some soild state) radio components. I think we've all heard the horror stories. I have done this many times and never had a unit blow up scarring me for life, melt down ...ruining the unit, turn bright red catching my bench on fire or emitting a green haze of deadly elecronic haze. :p:

What's the deal? Have any of you personally seen any old radios explode by simply plugging them in after a long hiatus?

The reason I ask is because at an estate sale today I plug in an old emerson tabletop radio and am sitting there waiting to see if will power up. Immediately a husband and wife team come right over and tell me all these reasons why I shouldn't plug an old radio in. :uzi: To listen to them one would think we were all in imminent danger just being within a 100' radius of this now ready to detonate, plugged in radio-explosive. :uzi:
 
You know Don, while it's true that plugging in older equipment has a higher degree of problems or failures. I like you have never had this happen to me. I even own a variac but I still just plug things in to see if it flys. Older gear can be more prone to smoke but I don't think it worth setting up barracades when plugging it in. Shoot, let it smoke I say. That way I have a trail to the problem part. :dunno:
 
Well like many old wives tales there is enough true to it but mostly it gets over blown by those that don't have the backround in electronics.

In the era of older tube gear it was not unusual, after a long time, for some of the capacitors (especialy the old paper type) to dry out and possibly be shorted out. If the main power supply filter capacitors are shorted then there could be a very high inrush of current on powering up, which could cause quite a show. Higher end tube equipment usually are fused for safety but cheaper equipment often have no such safety components and a short circuit just finds something to burn open.

So a lot depends of the specific equipment your dealing with. If you stumble on a very hi end Mac tube amp one might want to do a good visual inspection and possibly test all the tubes and then power up slowly with a Variac. But for a cheap 5 tube am radio I would just inspect the power cord first and if it looks ok go for it.
 
Originally posted by Lefty
Well like many old wives tales there is enough true to it but mostly it gets over blown by those that don't have the backround in electronics.

In the era of older tube gear it was not unusual, after a long time, for some of the capacitors (especialy the old paper type) to dry out and possibly be shorted out. If the main power supply filter capacitors are shorted then there could be a very high inrush of current on powering up, which could cause quite a show. Higher end tube equipment usually are fused for safety but cheaper equipment often have no such safety components and a short circuit just finds something to burn open.

So a lot depends of the specific equipment your dealing with. If you stumble on a very hi end Mac tube amp one might want to do a good visual inspection and possibly test all the tubes and then power up slowly with a Variac. But for a cheap 5 tube am radio I would just inspect the power cord first and if it looks ok go for it.

If, possibly, could, usually, mostly, depends, might ...exactly the words that keep an old wives tale alive. :D

Has anyone ever seen one of these things blow up from simply plugging it in and turning it on?
 
It's rare but it does happen. Usually caused by a leaky cap or bad filament that can't handle the sudden rush of current. Like everyone is saying, it is best to run it up slow and watch for increasing current draw that warns you to shut it down. Although I have seen amps that had a high initial draw that spiked and then settled down. It's two parts electronics and one part experience.
 
But has anyone seen it happen.

UFOs are rare too and they supposedly happen :D

I just don't believe it. It was probably an ad campaign by variac way back when they were first made. :dunno:
 
I've Seen...

A tranny melt in an old Philco Radio Console. I was in a local vintage store and the fellow brought the unit out to the showroom (for lack of better words) and put a 100 dollar price tag on it. He then plugged it in and turned it on. No light show just a poof of smoke and crackle and thats all folks. I looked under the hood and the tranny was melted, scorched completely toast. I went back the next day and the price was reduced to 50 bucks.
 
I've let the smoke escape from many components by doing that. But it all depends if you're talking about a TV or a radio. Rob and I will both tell you that it's pretty much gospel in vintage TV restoration to use a variac, but on radios it's not such a big deal.....as long as you check tubes for shorts and do a quick test of the electrolytic capacitors (I got a capacitor tester for $30 through Antique Radio Supply). Of course, that won't save you if the transformer's got a leak and possibly an internal short that slow bringup on voltage would fix.

Care to comment on this one, Rob?
 
The sites administrator has just answered one of my posts! :smsex:

I feel so important! :D :cool:


Just kidding karma ...it just looks very official "administrator" under your name. :eek:
 
Originally posted by Kamakiri
I've let the smoke escape from many components by doing that. But it all depends if you're talking about a TV or a radio. Rob and I will both tell you that it's pretty much gospel in vintage TV restoration to use a variac, but on radios it's not such a big deal.....as long as you check tubes for shorts and do a quick test of the electrolytic capacitors (I got a capacitor tester for $30 through Antique Radio Supply). Of course, that won't save you if the transformer's got a leak and possibly an internal short that slow bringup on voltage would fix.

Care to comment on this one, Rob?

Sure Kama,

First I'd like to dispell a myth further propagated by Lefty in an otherwise technically sound treatise (sorry Lefty), that old paper capacitors don't dry out. If they did there'd be less problems with them. Fact is over the years thay tend to absorb and trap moisture inside. How much depends on factors like how the gear has been stored. A damp basement would be one of the worst places this way. This moisture causes them to go leaky and when the power is applied they can catastrophically fail with applied voltage. The insulation breaks down in a cascade as current starts to flow, heating develops, more current flows and finally catastrophic failure. Depending on the current limiting capability of the associated circuitry this can be rather uneventful, or create a smoke show.

BTW, you all do know that electronic components all contain injected smoke from the factory and when you let that smoke out they no longer function. :)

I had a 1947 Fada TV-30, 10" tabletop TV that after a soft start with the variac showed a raster for about 30 seconds followed by a fade to black and a boiling sound under the chassis in the horizontal/high voltage section. One of the large wax paper capacitors was rolling over and dying. You can often tell which ones are ready to go by visual inspection because they are covered with miriad little bubbles or have started puking their wax, indicating leakage current and heat.

The new generation of polypropelene and evaporated metal film capacitors are fantastic and should never fail once installed. They are even self healing. If they are grossly overvoltaged the thin aluminum merely evaporates where the dielectric puncture occurs leaving the cap unshorted to continue working. The old oil filled aluminum foil and kraft paper capacitors were somewhat self healing, but not nearly so good as these new dry poly caps.

BTW, those inserted tab construction kraft paper and foil Vitamin-Q oil filled caps that many audiophiles have been told are the best are a 60 year old design and aren't nearly as good for coupling caps as the new poly caps with extended foil and negligible inductance. The poly's are also way, way...did I say way(?) smaller and cheaper.

Rob
 
Not a wifes tale!

I have an old Leak tube set Amp preamp amd tuner. I am recaping before I power it up. Sometimes the caps go bad with age and the results while not spectacular won't be good. You can damage the tubes as a result. :puke: So I will power up after I recap.
 
Back
Top Bottom