Greetings from the Great White Afterthought,

On a Garne 3-tube amp, I replaced the "normal" jack and the "brite"
jack. I didn't go near the treble, vol or bass pots, but when I
powered the thing up the treble knob supplied the volume and vice
versa. While I fiddled with the thing they changed back to "normal"
for a while then into "bizarro" mode once again and so on back and
forth. All the while there was no crackling or hum to suggest a loose
wire or bad contact or ground fault. I know nothing about tube theory
and only slightly more about transistors. Anybody got a clue what's
going on?

Thanks in advance,

Gil

(Gil) said:

Greetings from the Great White Afterthought,

On a Garne 3-tube amp, I replaced the "normal" jack and the "brite"
jack. I didn't go near the treble, vol or bass pots, but when I
powered the thing up the treble knob supplied the volume and vice
versa. While I fiddled with the thing they changed back to "normal"
for a while then into "bizarro" mode once again and so on back and
forth. All the while there was no crackling or hum to suggest a loose
wire or bad contact or ground fault. I know nothing about tube theory
and only slightly more about transistors. Anybody got a clue what's
going on?

I've been thinking hard and long about this.
Then I got my Aspen Pitman from the shelf, alas, the Game isn't there.

I found a possible explanation in a Ward Airline schematic.

In case of a simple treble- and volume pot arrangement, right at the
input of the amp, it would be possible for the treble pot to act as a
volume pot, but ONLY if the 'normal' jack has a breaker switch.
That switch makes contact btw. the 'bright' input (or circuit) and the
amp's input. When a jack is inserted, the connection is open and the
guitar signal is fed directly into the amp.
Maybe you reversed the 2 leads to this switch, or something is wrong
with it?
I'm assuming you used the same type of jack receptacle as a
substitute?

That's the only thing I could come up with, and it may well be wrong.

Maybe you should post this quesion in alt.guitar.amps, there are some
grey bearded gurus there who might recognize this problem.

--
Sander deWaal
Vacuum Audio Consultancy

I'm assuming you used the same type of jack receptacle as a
substitute?

Aeiii! That must be it. The original"normal" jack had this weird extra
metal strip in front of and about a mm away from the main(taller)
contact. I replaced it with a typical Radio Shack type(stereo) wired
up to take a mono plug. I'll have to dig the old one out of the trash
and see if I can trace its operation.

The one labeled "brite" was a simple, mono jack. It also got the Radio
Shack treatment.

But why the swapping back and forth?


That's the only thing I could come up with, and it may well be wrong.

Maybe you should post this quesion in alt.guitar.amps, there are some
grey bearded gurus there who might recognize this problem.

I did, thanks for the tip!

(Gil) said:

I'm assuming you used the same type of jack receptacle as a
substitute?

Aeiii! That must be it. The original"normal" jack had this weird extra
metal strip in front of and about a mm away from the main(taller)
contact. I replaced it with a typical Radio Shack type(stereo) wired
up to take a mono plug. I'll have to dig the old one out of the trash
and see if I can trace its operation.

There's a possibility that there is a ground connection made btw.
ground and this ring when the plug is inserted.
The ring probably connects the treble pot + cap to ground.
You can simulate this connection by using the ground ring as ground,
and the R channel ring as switched contact.
The L-channel tip remains the signal carrying contact.

The one labeled "brite" was a simple, mono jack. It also got the Radio
Shack treatment.

That one presumably is OK.

But why the swapping back and forth?

I can't explain that, other than that plugging into the 'normal' will
cause the effect, while plugging into the 'brite' input doesn't.

--
Sander deWaal
Vacuum Audio Consultancy