Re: really dumb question re direct line powering and safety

On Sat, 26 Jul 2008 20:36:13 GMT, Doggone <Running@xxxxxxxxxxx> wrote:

morris.slutsky@xxxxxxxxx wrote in news:f23f2228-6b08-4eb1-99d8-d7e111d33c11
@x35g2000hsb.googlegroups.com:

Hi guys,

I've been looking at schematics of various old radios and stuff - it
seems that a lot of old vacuum tube equipment just directly rectified
the power line to get the B+ supply, with no clunky and expensive
transformer. I understand that guitar amps are not and have never
been done this way, because the player (unless using a wireless)
actually has to be electrically connected to the chassis and it's just
way, way too dangerous.

There were many and yes, they were and are still very dangerous.

What I wonder is this - is there any reason not to build a hot-chassis
amp and simply isolate the audio inputs with smaller, cheaper
transformers? Say, just have a FET buffer running an audio
transformer, powered by a small cheap DC supply? Maybe buy a dual
secondary 6.3V transformer and use one for the filaments and the other
to operate the input buffer supply, something like that? Yeah you're
actually buying MORE transformers this way, but they're cheaper and
smaller even so.

What do you guys think?

Many amps especially the cheap beginner amp we used to get from
Sears Roebuck (Simpsons Sears here in Canuckland) were line powered.
I remember that time I was playing my Silvertone through a Pine
Electronics amp. This thing is a 3 tube afair, 35W4 rectifier, 12AX7
preamp and a 50L6 output tube. No power transformer. I had 2 or 3 of
them curly cords (very popular at that time) wired end to end so I
could practicaly go anywhere in the house and still hear that earth
shaking 2.5 Watts of pure tube power. I went into the kitchen to get
a glass of water. With my left hand holding the guitar neck, I reached
for the water tap with my right hand. Well, Lord Thunderimg Jesus, that
had to be the most unpleasant experience I'd ever had and may have well
cut my life short at the tender age of 14. Come to think of it, after 32
years in electronic, working on radar systems and power units that make
your hair stand on end just being near them, I have never experienced a
shock as severe as that one.

Here we are some 36 years later. Still have that "killer" amp. But
now it has an isolation transformer. They're really not expensive (far
cheaper than a funeral). Now my son uses it as a practice amp
and I want him to outlive me.
Got "creative" did ya?...lol ...funny but not funny either...
.

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