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Old 29th December 2011, 07:40 PM   #1
bamph is offline bamph  United States
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Default Volume Pot for RH84

Hi,

Just finishing up my RH84 build and wanted to see if anyone had used a 100K pot for a volume control.

The schematic shows a 1 Meg resistor on the input. If I put a 100K pot across that, the resistance will drop. Is that something to be concerned with?

BTW, this project started life as a Dumont console. I reused the transformers and output tubes. You can see the before and after photos.

Thanks,
Ben
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Old 29th December 2011, 09:39 PM   #2
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100k is perfect.
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Old 29th December 2011, 10:57 PM   #3
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Sweet build .........
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Old 29th December 2011, 11:42 PM   #4
GloBug is offline GloBug  Canada
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Ya, how do you like it?
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Old 30th December 2011, 04:07 AM   #5
bamph is offline bamph  United States
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Still not finished -- Hopefully tomorrow. I just hope there aren't any problems and it sounds great.

Soldered up the 100k pot. Thanks for the confirmation Bas.
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Old 1st January 2012, 05:01 AM   #6
bamph is offline bamph  United States
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Default Finished

Finished the amp last night. It sounds great. Plenty of power and a nice clean sound. Spent the day listening.

There was one hiccup. When I first powered it up, all the votages looked normal. When I added the 12AT7 and turned it on, there was some nice blue sparks in the tube and and a curl of smoke. I found the grid and cathode resistors fried. I also noticed that there was a wire from the output transformer that looked like it might be touching the input end of the grid resistor for one channel. In the original circuit, there was an extra winding on the primary side of the output transformer that was used as a filter choke in the power supply. That wire probably had about 300V on it. It was clipped, but I guess that there was enough metal to make contact with the resistor lead. After I cleaned it up and replaced the resistors, it worked perfectly. Oh, I had to replace the 12AT7 too. Guitar Center to the rescue.

I'm very pleased. The amp sounds great and looks good too.

Ben
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Old 1st January 2012, 12:05 PM   #7
GloBug is offline GloBug  Canada
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Right on, it is a nice project, glad everything worked out for you.
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