July 2015 9
for use with a guitar is
only around $350 (close
to the costs of tubes and
The only inputs I
see for the PB-350 are
terminal strips labeled
“Relay or Dummy
Plug” and “Installation
descriptions say there is
an RCA input and speaker
tap outputs which may be
4/8/16 ohms or 70. 7 volts
as used by PA systems. Look for a parts placement diagram
and schematic inside the housing which was typically
included in most vintage equipment. The schematic can
confirm the type and number of tubes that are used and
the input/output information. The parts placement diagram
will show you the exact placement of the tubes.
I have included a sketch in Figure 1 of the best tube
placement I can determine. Some units have the tube
identity printed on the chassis beside the tube location;
if so, ignore my parts placement. Sorry, I could not find a
You could always buy a new guitar amp and use the
PB-350 as a conversation piece if all else fails, or unless you
REALLY love working with vintage electronics.
Maybe some of our “vintage” readers can help with
schematics, parts placement diagrams, etc.
QGFI breakers and outlet plugs function pretty simply. They compare current in with current out, and either open the circuit to protect the user or they continue to function. That’s pretty
much all I can find concerning GFI.
I have run into this situation now a couple of times,
and cannot find an answer. Recently, I was changing plugs
in a vintage 1978 home. It was wired in 12 gauge with a
ground wire, and the box was populated with many circuits
— all breakered at 15 amps. I changed a plug in a bathroom
with a GFI typical box store item. The load side was in the
proper connections which protected the second plug in
this bathroom. Checking with a wiggy, all was well.
A day later, I get a call the plugs will not power a radio
(a new off-the-shelf clock radio). I make another visit. Sure
enough, the radio will work in a standard duplex receptacle
but not the GFI. My assumption was I missed something.
The wiggy worked. I tested with a carpet vac, a hair dryer,
and a curling iron. They all worked, but not the radio. I
have spent a while looking for an answer and nothing pops
up. Pretty much every Google gives only how they work.
My assumption is because the neutral has this GFI circuit
blocking the direct flow back to the panel, some devices
on two wire power supplies don’t see the neutral and
crap out. I have seen this with two wire power supplies on
computers. The power supply will not run. I have seen this
twice in the last year and nothing is written as to what the
cause and effect is that I have found. Can you shed some
light on this issue?
— Tim Edwards
AYou are correct. The Ground Fault Interrupter (GFI) — also called a Ground Fault Circuit Interrupter; GFCI — is a very high speed switch (shuts down in 1/40th of a second) that is
triggered by a current imbalance between the “hot” and
“neutral” conductors of an electrical circuit. The imbalance
is most often caused by current from the “hot” wire being
diverted somewhere (such as a human body during
electrocution), so a different amount of current
flows in the “neutral” wire. GFCIs can be either
mounted in place of a traditional receptacle or be
placed inline with a power or an extension cord.
GFCIs should be used anytime there is a possibility
of a human making contact with the electrical
device and a ground (usually water in some form).
The National Electric Code (NEC) requires
GFCIs to be used to protect humans in bathrooms,
kitchens, and swimming pools, so you are doing
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