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Vintage threads from the first ten years

Hum trouble with 6G15 Reverb kit

8/1/2004 12:28 AM
Howard	Hum trouble with 6G15 Reverb kit Hi, I'm not sure this is the place to ask this but I'm trying to get this annoying 60Hz hum out of my friends DIY 6G15. He's thrown his hands up and I'm trying to figure out what's going on. It was a kit from somebody, but I'm not sure who. It differs from the vintage unit in a couple of ways. 1. No center tap for the filament secondary, (but there is one for HV secondary). I'm using a 2 wire filament circuit and I did the virtual CT thing by using 2-100 ohm resistors (actually 200 ohm since that's all I could find) from ground to each side of the filament circuit. 2. Full wave bridge using a pair of 1n007's. 3. Modern 3 prong plug with fuse and switch on hot leg. Ground lug is firmly screwed in to chassis and green ground wire is soldered to lug. 4. Neutral, HV CT, one of the black PT primaries and a wire to the coppor plate is soldered to another lug that's screwed to the chassis. 5. Everything else is grounded to the copper plate. 6. I'm running coax to pin 8 of the 12at7 (First stage of wet channel) with coupling cap to dry circuit connected directly to the same lug. I have not checked caps yet, nor have I pulled the board to check the underside. But I guess that's next unless someone can suggest something better. The only thing that I can say about the hum is that 1. It's there even when the reverb is powered down (and plugged into wall). 2. Goes away immediatly when the plug is pulled. 3. It gets better with an isolation transformer 4. It gets worse when the mix control is more dry. Full reverb it gets quieter, but is still there. Other controls have no effecton hum. It sounds great in every other way. How can I get rid of this #%$^%^$ hum? Thanks for reading this far. Howard Chandler

8/1/2004 12:28 AM

Howard

Hum trouble with 6G15 Reverb kit

Hi,

I'm not sure this is the place to ask this but I'm trying to get this annoying 60Hz hum out of my friends DIY 6G15. He's thrown his hands up and I'm trying to figure out what's going on. It was a kit from somebody, but I'm not sure who. It differs from the vintage unit in a couple of ways.

1. No center tap for the filament secondary, (but there is one for HV secondary). I'm using a 2 wire filament circuit and I did the virtual CT thing by using 2-100 ohm resistors (actually 200 ohm since that's all I could find) from ground to each side of the filament circuit.

2. Full wave bridge using a pair of 1n007's.
3. Modern 3 prong plug with fuse and switch on hot leg. Ground lug is firmly screwed in to chassis and green ground wire is soldered to lug.

4. Neutral, HV CT, one of the black PT primaries and a wire to the coppor plate is soldered to another lug that's screwed to the chassis.

5. Everything else is grounded to the copper plate.

6. I'm running coax to pin 8 of the 12at7 (First stage of wet channel) with coupling cap to dry circuit connected directly to the same lug.

I have not checked caps yet, nor have I pulled the board to check the underside. But I guess that's next unless someone can suggest something better.

The only thing that I can say about the hum is that

1. It's there even when the reverb is powered down (and plugged into wall).
2. Goes away immediatly when the plug is pulled.
3. It gets better with an isolation transformer
4. It gets worse when the mix control is more dry. Full reverb it gets quieter, but is still there. Other controls have no effecton hum.

It sounds great in every other way. How can I get rid of this #%$^%^$ hum?

Thanks for reading this far.

Howard Chandler

Replies:

Wild Bill This problem has been around a whil... -- 8/1/2004 1:33 AM
rooster Between the green wire from your po... -- 8/1/2004 3:56 PM
MBSetzer DANGER! Will Robinson! -- 8/1/2004 6:52 PM