Volume Pot for RH84

bamph · 29th December 2011, 07:40 PM

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

Bas Horneman · 29th December 2011, 09:39 PM

100k is perfect.

Soonerorlater · 29th December 2011, 10:57 PM

Sweet build .........

GloBug · 29th December 2011, 11:42 PM

Ya, how do you like it?

bamph · 30th December 2011, 04:07 AM

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.

bamph · 1st January 2012, 05:01 AM

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

GloBug · 1st January 2012, 12:05 PM

Right on, it is a nice project, glad everything worked out for you.

29th December 2011, 09:39 PM	#2
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	100k is perfect. __________________ Boatanchor amps forum My "adventures" in audio

29th December 2011, 10:57 PM	#3
Soonerorlater diyAudio Member Join Date: Jul 2008 Location: Belfast	Sweet build ......... __________________ When white moths were on the wing, And moth-like stars were flickering out,

1st January 2012, 05:01 AM	#6
bamph diyAudio Member Join Date: Nov 2009 Location: Oklahoma City	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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29th December 2011, 11:42 PM	#4
GloBug Banned Join Date: Jun 2011	Ya, how do you like it?

30th December 2011, 04:07 AM	#5
bamph diyAudio Member Join Date: Nov 2009 Location: Oklahoma City	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.

1st January 2012, 12:05 PM	#7
GloBug Banned Join Date: Jun 2011	Right on, it is a nice project, glad everything worked out for you.

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