1950 Gretsch Electromatic Artist

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:santa: Just thought I would share a very cool little amp schematic. All of the resistor values are from the color bands so the schematic should be exactly as intended. Actual measurements were "close". The 20uF+20uF+20uF @450v cap is still holding up. The coupling caps have working voltage 600v and test voltage of 1800v...:eek:. I picked this thing up very cheap. It had a pretty bad hum. I had to replace the small cap on the primary of the power transformer and the cathode bypass on the first stage.

Sounds very nice with single coils, sounds insane with humbuckers.

If you had this amp in 1950 you were the coolest kid in town. If only the volume would have gone to 10 in 1950...;):p
 

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Are you sure that the tone and volume controls come before the 6SJ7 and not after?

Yes quite sure. If you look at the picture of the under side where I replaced the cathode bypass cap (black electrolytic) you can see the bottom of the RCA jack that the top panel plugs into. The brown wire from that goes right to pin 4 of the 6SJ7. You can also see the unplugged RCA cable that comes from the top panel hanging down in the picture.
 
What you replaced is known as a "death cap". It should be removed. Maybe there are two of them, from earth to Live + Neutral.

There is only one "death cap ". Looks like it's on the wrong side of the fuse too...:eek:

It would appear every old amp had one....interesting. I will remove it and see what happens.

An interesting thing I noticed in this amp is that they just grounded one side of the 6.3v filament circuit. There is no center tap and no artificial center tap. It is a pretty quiet amp despite that.
 
I've been looking at old amp schematics and it is the same type circuit as in the highly sought after valco Supro Thunderbolt. Of course the Gretsch was made by Valco too.

Death Cap gone. No difference in hum.
 

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Yes I have seen that ''death '' cap in some other older designs up to '73, and like you say ''live and neutral'' was typically interchangeable with non-polarized plugs, no earth ground plug and ''polarity switch''. Back in the day you pretty much had a 50/50 chance of getting zapped touching a mic and an electric guitar at the same time. For me it was usually about 80% chance..and getting hit with 120VAC on the lips if you happened to complete the circuit on the mic..is mighty dangerous . Is that why they call it a death cap?? Yeah I remove em and put 3 prong polarized plugs. It's essential safety wise.
 
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