Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: alange5 on August 18, 2016, 01:59:50 pm
-
I just purchased a non-working Guild Maverick bass amp. The original two-prong cord was cut, so I'm installing a 3-prong.
On this amp, the power switch is also the polarity switch (3-position on+/off/on-), and there's also a standby switch.
I've replaced many power cords, but never with this setup, and I want to make sure I do it right. Here's the schematic:
http://www.prowessamplifiers.com/schematics/misc/Guild_Maverick_Bass-7591s_SS_rectifier_7247_driver.html (http://www.prowessamplifiers.com/schematics/misc/Guild_Maverick_Bass-7591s_SS_rectifier_7247_driver.html)
How would I go about this?
-
.
-
The original two-prong cord was cut, so I'm installing a 3-prong.
I'll assume you can see the cut ends of the original power cord inside the chassis. Connect the black wire of your new power cord to one of the cut ends of the original. Connect the white wire of your new cord to the other cut end of the original power cord inside the chassis. Connect the green wire of your new power cord directly to chassis. Using a PT bolt is handy. (It would look better if you actually remove the original cord and connect the new cord directly to the components the old cord is attached to.)
-
Alright, sounds simple enough. I wasn't sure if I had to move around the fuse and transformer leads. And I'm assuming I can just snip out the death cap?
-
alright! this thing sounds awesome. Runs nice and quiet, super loud, and I found a couple of Telefunken 12AX7's hiding in there. Sweet!
-
The "problem" with my fix (I think Sluckey's the same) is that the switch has two "ON" positions, center off. Like before, but now the two ONs do the same thing. (If it makes a difference, your ground is bad.) And to turn OFF you have to get the lever centered. (After some gigs, I can't center myself, nevermind a switch.)
I figure that's all OK.
If you really "need" the OFF position at an extreme, you can snip the "X" in the center of the on-off-on switch. (If it is snippable and not hard links.) Now the switch works off-off-ON.
-
Here is a way to have a polarity switch. The center position is off, that is, no capacitor connected to line (hot) or neutral. This is the same as an amp without a polarity circuit. In the other positions the cap is connected from ground to hot or neutral. This serves to reduce high frequency line noise. There is another cap across line and neutral.
Here is a Y2 safety cap, Kemet PHE850EA4470MA03R17 that can be used in both positions.
Here is a schematic: