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...😱. 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...😉😛
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Pretty cool, but given the age of the amp I would at least replace the triple section electrolytic and the coupling caps to the output tubes.
I did also put a three prong plug on it.
@kevinkr
Ya I'm going to look into fitting 3 x 20uF caps into the original can that is there. Everything is riveted on to the chassis. Unless someone knows where to get a 3 x 20uF @~450v cap in a can.
@kevinkr
Ya I'm going to look into fitting 3 x 20uF caps into the original can that is there. Everything is riveted on to the chassis. Unless someone knows where to get a 3 x 20uF @~450v cap in a can.
A quick look around and this is close as CE gets:
https://www.tubesandmore.com/products/C-EC1020X3-450
There's also a 4 x 20uf @475v by CE.
jeff
https://www.tubesandmore.com/products/C-EC1020X3-450
There's also a 4 x 20uf @475v by CE.
jeff
Vinylkid beat me to it, but that was exactly what I was going to recommend. 😀
There is this: https://www.tubesandmore.com/products/C-EC20X3-525
The higher voltage rating cannot hurt. (3 x 20uF/525V)
There is this: https://www.tubesandmore.com/products/C-EC20X3-525
The higher voltage rating cannot hurt. (3 x 20uF/525V)
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...😱
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 am guessing the secret of the great tone is also in this weirdo paraphase / common cathode splitter. Cool and few parts!
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.
Death Cap gone. No difference in hum.
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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