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It is currently 23 Sep 2020, 01:31

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PostPosted: 15 Jun 2020, 18:17 

Joined: 15 Jun 2020, 17:13
Posts: 1
Bought a 185 on ebay but it has been partially modified to be a line level ready amp. The preamp section was removed along with the 7025 tube/socket. How do I go about connecting the RCA's to the input tubes. Shouldn't there be some sort of buffer circuit from the rca to ground? I assume it can't be directly wired to the grid of the 12ax7 tubes. Also what is the hum pot's purpose. It looks like they started to take that out as well. Thanks for any help.

PostPosted: 15 Jun 2020, 20:40 
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Joined: 04 Jun 2008, 20:59
Posts: 4235
Location: Arizona, USA
Hi, As a line level power amp you will need a way to control the volume. I believe I would put a 100K volume control at the input and it should be fine. The output (center tap) of the control can probably go directly to the tube grid. The "Hot" end of the pot going to the RCA and the other end to the signal ground. The hum pot is not usually seen on consumer gear but is quite common on pro (like guitar) gear. It goes between the two sides of the heater circuit. The center tap then goes to the ground. Adjusting it tends to minimize the hum in the amp. There are other variations but that is the most common.

Good listening

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