Dumb question about amp

Some of the old amps didnt have ground prongs unfortunately. However two things: some 2 prong cords are connected to devices that are double insulated, especially in tools ( probably not amps) but if you feel unsafe? Get an inline GFCI adapter and plug your cord into it, then it into the outlet. If there is ANY ground potential, it will trigger at less than 5mA and you're good to go
 
Clockworkmike said:
Some of the old amps didnt have ground prongs unfortunately. However two things: some 2 prong cords are double insulated, especially in tools ( probably not amps) but if you feel unsafe? Get an inline GFCI adapter and plug your cord into it, then it into the outlet. If there is ANY ground potential, it will trigger at less than 5mA and you're good to go
Click to expand...
sparky knows his stuff :)
 
Catmandue said:
I have a two prung electrical plug, with no ground on an old Harmony Model H303A. This ancient ( made 1960 to 1964 ) is way cool and takes pedals nicely. My dumb question is, am I safe if I'm plugged into a power strip which plugs in with a ground and two prung?
https://imgur.com/mNPHQGr
Click to expand...

I'm glad you asked that because some of these amps are particularly dangerous....

The answer is that the 3 prong grounded cord MUST be added.
Simply because it could shock the poop out of you.

1608070014611.png
 
I had my old Ampeg Gemini II converted to a grounded plug after a two inch arc jumped from my microphone to my teeth at a gig. It almost knocked me to the floor. Even though I thought the polarity seemed good, it wasn‘t. It wasn‘t an experience I wanted to relive.
 
Thatbastarddon said:
I’ve converted a couple to 3 prong...no problem. My last was a 68 Kustom K200-A....much happier since.
:cheers:
Click to expand...
This particular amp can be changed.
Some amps cannot be converted because of the power supply.
The chassis on some old style amps was actually hot and not grounded.
Some of the amps Harmony made (probably made by Valco amps) did not have an isolation transformer....
so these type amps cannot really be played safely.
But an isolation transformer could be added if it's really that important / just not practical to do it.

Recently we put a harmony amp out to pasture because it had no isolation...
it was just too dangerous to play.
That was the way it was built.
The particular rectifier tube changed 115 volt AC into B+ voltage directly...without a transformer.
And the power wire is connected directly to the chassis....
This is the way that tube equipment was built before grounded chassis were used.
 
This is the Harmony H 400, which has no isolation transformer.
You cannot ground this amp because the chassis is hot.
But watch out for this amp, it's called "the widow-maker..." It's too dangerous to play.
But this is how some tube amps used to be made back in the day.
So as you can see, one of the AC 115 volt power wires is connected to the chassis....
1608094254205.png
 
I'm late to this thread (as usual), but luckily AMS has answered it properly.
If anyone has an old "two prong power cord" type amp, get it to a decent tech for possible conversion to 3 prong. More often than not they can be converted & it's a small job that shouldn't cost much (what price do you put on staying alive).
If you have the knowledge & ability to convert it yourself, after fitting the cord & plug, use an ohm metre to check that there is less than 2 ohms resistance between the earth prong on the plug & the amp chassis. Cheers
 
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