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All American Five radio receivers

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Re: All American Five radio receivers

#31

Post by Aloha »

gumboza wrote: post #29
Aloha wrote: post #25

Earlier quoted context omitted.

240 was too high, and most of the non-110v sets use a transformer. In reality, the case is meant to isolate the set, so the thing is only relevant when performing service work, and honestly, I just measure voltage between chassis and earth and make sure there is zero volts of potential.

That’s ok until you accidentally find you have an earth fault.

Well, in most cases I'm sitting on a chair isolated from earth, several feet in the air (wearing rubber soled shoes), so long as my test equipment shows 0v of potential to the chassis, its pretty safe. It could be that the earth bond has failed, but provided I have both pieces of gear sharing an earth, its all good.

Re: All American Five radio receivers

#32

Post by gumboza »

Aloha wrote: post #31
gumboza wrote: post #29

Earlier quoted context omitted.

That’s ok until you accidentally find you have an earth fault.

Well, in most cases I'm sitting on a chair isolated from earth, several feet in the air (wearing rubber soled shoes), so long as my test equipment shows 0v of potential to the chassis, its pretty safe. It could be that the earth bond has failed, but provided I have both pieces of gear sharing an earth, its all good.

Famous last words.

Leave that scope probe ground clipped on something and every earth is floating live on your bench.

Source: ex EE.

Re: All American Five radio receivers

#33

Post by aidenn0 »

buescher wrote: post #23

The hot chassis design is mind-blowingly dangerous by contemporary standards. These things weren't designed to modern creepage distances either. I would worry about creepage to controls on these things. THe article mentions screws potentially being hot as well as other shock hazards finger-accessible through vent hols so no joke be careful to unplug a radio before moving it or otherwise handling it in a way beyond tu…

Even wiring the chassis to the neutral line with a polarized plug would be a bit archaic today, though it greatly improves things (assuming the power-switch isn't on the same line as the chassis, which on many of these radios it is !!)

Re: All American Five radio receivers

#34

Post by neilv »

Even when the local department store was selling home computers based on microprocessors, they still devoted a chunk of retail floor space to a self-service vacuum tube tester.

https://www.ebay.com/itm/195497221166 https://www.ebay.com/itm/324762243586 https://www.ebay.com/itm/403979880899

I wonder when these finally disppeared from stores, and what the market is like for vacuum tubes for antique TVs and radios?

Re: All American Five radio receivers

#35

Post by aidenn0 »

floren wrote: post #3
gumboza wrote: post #2

Definitely read the potential hazards section. Dangerous as hell these things.

Dangerous to poke around inside when plugged in, but quite safe unplugged (unlike say an old TV).

My dad used to repair TVs; I asked him what the easiest way to discharge a tube was and he said "grab the anode lead and the chassis" then after I gave him a look he said "well you didn't ask for the easiest safe way to discharge one"

Re: All American Five radio receivers

#36

Post by kpgraham »

I repair tube guitar amplifiers from time to time, and I cringe when I see the 50L6 power tube and the 35Z4 rectifier. These tubes light up like lightbulbs, and run so hot that the amplifier case is often charred near them. The chassis shows staining from the heat, and the plastic tube socket can even melt. These amps always hum because the same reasoning that goes for the cheap on the circuit design also uses cheap and low value capacitors. I hate these circuits. Several times I've gutted the chassis, screwed a power transformer in place and wired the amp as a tweed champ, Gibson Skylark or Premier 50, so I have a chassis with the right number of tube sockets and pots, and I get a brand-new vintage amp for the cost of a used transformer. I have a Gretsch amp that had two 50L6 tubes, that made a beautiful 1957 Fender Pro amp and sounds wonderful.

Re: All American Five radio receivers

#37

Post by gumboza »

jhallenworld wrote: post #22
gumboza wrote: post #2

Definitely read the potential hazards section. Dangerous as hell these things.

Yeah, they are dangerous, but their safety can be improved: add polarized cord (probably have to move the power switch to the hot side for this) and replace the chassis ground capacitor. Table top FM radios and TVs also tend to be hot chassis.. (that mains transformer is just too expensive). Even today you can find capacitor dropper powered devices which are hot. AA5s are nice in that you can almost always get them t…

Polarised cord only works if your house sockets are wired correctly which is not necessarily the case and your earth bond might not be as good as you think it is. Always assume that the lowest competence is applied when it comes to safety evaluation.

At this point I wouldn’t run one of these things at all. If you drop dead you have no idea if some relative is going to plug it in and kill themselves with it. They were designed to a cost target when safety wasn’t a business concern. Steal the tubes and variable caps out and dispose of the rest. At best, stick it in a museum, preferably of dangerous things that should never be plugged in.

There’s plenty of tube kit out there you can buy which isn’t even remotely this dangerous.

Re: All American Five radio receivers

#38

Post by gumboza »

Aloha wrote: post #24
gumboza wrote: post #2

Definitely read the potential hazards section. Dangerous as hell these things.

They're perfectly safe to work on, just measure voltage between chassis and earth and make sure there is zero volts of potential - or be fancy and use an isolation transformer.

You can still kill yourself with an isolation transformer fairly easily if you don’t know what you’re doing. See my other comments about earth assumptions.

Re: All American Five radio receivers

#40

Post by Aloha »

gumboza wrote: post #32
Aloha wrote: post #31

Earlier quoted context omitted.

Well, in most cases I'm sitting on a chair isolated from earth, several feet in the air (wearing rubber soled shoes), so long as my test equipment shows 0v of potential to the chassis, its pretty safe. It could be that the earth bond has failed, but provided I have both pieces of gear sharing an earth, its all good.

Famous last words. Leave that scope probe ground clipped on something and every earth is floating live on your bench. Source: ex EE.

And at 110v, thats a risk I'm willing to take.

I wanna note, I worked as an FSE for a telecom, I've been 'bit' more than once by 130v, and by 160v B+ in shit, the sparks from crossed neutral are fine.

Anyone who is deeply concerned can buy an isolation transformer.

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