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Guinevere Running [message #30803]

Thu, 03 March 2005 20:44

Forty2wo
Messages: 163
Registered: May 2009

Master

I finaly have a chance to listen. So far so good but I am going to have to get a better choke. I am using what was on hand and have some 120hz buzz. Did the Hammond 193 work out OK for you guys?

Don't tell Colin but my filaments are running a bit high...John

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Re: Guinevere Running [message #30804 is a reply to message #30803]

Thu, 03 March 2005 21:52

Wayne Parham
Messages: 18786
Registered: January 2001

Illuminati (33rd Degree)

Congratulations! I hope you get that hum cranked down and I'm anxious to see pics!

But I'm jealous because I haven't had time to build mine yet.

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Too late [message #30806 is a reply to message #30803]

Thu, 03 March 2005 22:01

colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas

Illuminati (3rd Degree)

I still have yet to track down my left channel hum. It does sound higher than 60Hz, so it might be 120Hz. How is your background noise? At full volume, with no input signal, running through a 100wpc ss amp into 92 dB/W/m open baffle speakers, I'm getting some noise. It's not too bad, but it is there. I need to switch preamps and see if it is the amp itself. Now that I know it works, I'm going to go back and cut some long leads and dress up the wire path and solder joints. I hope this helps.

I do have a problem that I cannot track down. I have continuity between signal ground and the top chassis. I have no idea why or even if this is a problem, but the two should be isolated. I cannot see anything that would make contact between the two. The RCA jacks are the obvious place to start, but the threads were heavily wrapprd in teflon tape before inserting. I did install a safety star ground, which is connected to the top plate, to electrical earth for the Txs and choke cases. This is the only possible place it could come from, but the cases should be isolated from the inner windings. Is this something to be concerned about?......Colin

PS. I still have not dropped the heater's voltage, so I won't tell if you don't.

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Re: Too late [message #30807 is a reply to message #30806]

Thu, 03 March 2005 23:50

Wayne Parham
Messages: 18786
Registered: January 2001

Illuminati (33rd Degree)

When you use a full-wave rectifier, the power supply ripple is always double the line frequency. If there is noise coupled into a signal line, it could be amplified to produce 60Hz hum. But if it's power supply ripple, and it probably is, then it's 120Hz.

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Re: Too late [message #30828 is a reply to message #30806]

Fri, 04 March 2005 15:01

Forty2wo
Messages: 163
Registered: May 2009

Master

I did order a new choke, until I install it I can't say how quiet it it is. I did a quick check of my signial ground and I have no leakage to the chassie. If you don't find anything at the RCA jacks check your vol pot...John

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Re: Too late [message #30829 is a reply to message #30828]

Fri, 04 March 2005 15:20

colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas

Illuminati (3rd Degree)

I mounted the RS volume pot (271-1732) without insulating washers or any effort to isolate from the chassis. I just assumed the wiper housing was isolated from the leads. Is this not the case? What volume pot did you use and how did you isolate it? I cannot really tell from your pictures, which BTW I have rally enjoyed looking at. Very clean layout, kinda makes mine look like a rat's nest.....Colin

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You da' man - volume pot it is [message #30830 is a reply to message #30828]

Fri, 04 March 2005 15:30

colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas

Illuminati (3rd Degree)

Pulled the volume pot up and now no continuity between ground and chassis. Bad thing is, I did my star-ground off the voulme pot and this is going to be a pain to insulate. How did you isolate yours?......Thanks a bunch, Colin

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Re: Too late [message #30834 is a reply to message #30829]

Fri, 04 March 2005 21:02

Forty2wo
Messages: 163
Registered: May 2009

Master

I think I am using the same pot RS 100k, I don't know the number.
I have seen pots that were shorted but take a look with a glass and a strong light to see if there is not one strand of wire that made it's escape when it was soldered...John

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