Home » Audio » Group Build » Carbon comp vs carbon as grid stoppers
Carbon comp vs carbon as grid stoppers [message #30888] Wed, 09 March 2005 00:09 Go to next message
colinhester is currently offline  colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
I still have a little noise in one channel, and I'm having a bitch of a time tracking it down. I used carbon film resistors as grid stoppers. I was looking back through some posts and it was recommend that carbon comps be used. Should I have used carbons comps in this application? If I used the wrong type of resistor, could this account for the noise?.....Colin

Re: Carbon comp vs carbon as grid stoppers [message #30889 is a reply to message #30888] Wed, 09 March 2005 04:34 Go to previous messageGo to next message
PakProtector is currently offline  PakProtector
Messages: 935
Registered: May 2009
Illuminati (2nd Degree)
I have built with both, and forty2wo( I think) built w/o. It is supposed to be an electrical shock absorber, putting in electrical springs( capacitance and inductance ) can't be good, but I don't think there is much risk here.

What kind of noise? is it like a dog barking or a car driving by? or is it completely random...what pitch/character?

Actually on noise, the CC has the higher likleyhood of producing noise IMO.

There are more than a few silly things to go wrong here. My local project just suffered a real head-scratcher. Used the 100k, stereo Alps from Radio-Shack. Got a ~6 dB difference in channels after a bit. Turns out the open construction of the device probably allowed in some conductive debris and it shorted itself from end to end, yet left the wiper still functioning. Input jack to ground measurement of Ohms showed ~100k for the god side and 1k for the other. It was not the first thing we looked at either....

I wish I could have spent the weekend with each one of you in turn as we Ironed out some bugs. I think I have learned more than you guys doing the building. I wish I were as good at remote diagnosis as my heros, Click and Clack.
regards,
Douglas


Re: Carbon comp vs carbon as grid stoppers [message #30891 is a reply to message #30889] Wed, 09 March 2005 08:08 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
You know I have that volume control and the resistance measurements were off by 100% from one side to the other. I have read the replies with help but it is 12 deg. here and too cold to work on fine stuff. I really don't mind troubleshooting, I believe you learn more that way than any other method.
I love the names that click and clack give the help;
Heywood Yabuzzoff
Their cheuffeur is Russian; Peikup Andropov
The butler; Mahatma koat.

Noise [message #30892 is a reply to message #30889] Wed, 09 March 2005 08:52 Go to previous messageGo to next message
colinhester is currently offline  colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
The noise is coming only from one channel. The best way to describe it is that it sounds like radio static. The volume of the static tracks with the volume knob itself. As the volume is turned up, the staic level increases. This happens until full volume, except here the static suddenly goes away.

Another thing, at half volume if I wiggle the wires the only thing that affects the noise level is the wire connecting the voulume pot and the grid resistor. This is why I suspected the grid resistor. But as I type this I'm thinking of a comment John S. made earlier: I may have a bad volume pot. I think I'll stop by RS and pick up a new one and see what happens......Colin

Re: Noise [message #30893 is a reply to message #30892] Wed, 09 March 2005 10:06 Go to previous messageGo to next message
GarMan is currently offline  GarMan
Messages: 960
Registered: May 2009
Illuminati (2nd Degree)
Colin,

Does the noise increase or descrease with you touch the pot? I've found that the body of the pot needs to be grounded in many cases.

gar.

Noise increases [message #30894 is a reply to message #30893] Wed, 09 March 2005 10:43 Go to previous messageGo to next message
colinhester is currently offline  colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
Do you ground the pot's body to the signal ground or chassis?

What's reaaaallllly buging me is that the "white" noise that tracks with the volume is coming from one channel only. I either have a bad volume pot, bad resistor, bad tube socket or bad tube. And since the noise disappears at full volume, it's starting to sound like a volume pot with a bad ground connection. Hopefully I just need to ground as you suggested and all will be fine....Colin

GarMan, Thanks for suggesting that the top chassis should be without ugly little screw heads poking out. It cost me a bit of time to rearrange the layout, but the end result was well worth it. I should have pictures up tonight.....

Re: Noise [message #30897 is a reply to message #30892] Wed, 09 March 2005 13:58 Go to previous messageGo to next message
Forty2wo is currently offline  Forty2wo
Messages: 163
Registered: May 2009
Master
As a professional service Engineer, I well know how dificult it can be to to track down the source of a problem. It can be a real bitch to find something you can hang your hat on. You have to trust your instincts.
So far you have found two separate indacations of a bad vol pot. In my mind, it's out of there. Maybe it's just a bad solder joint but for five bucks, it's not worth it. While your at it replace the grid resitors. you'll feel better...John


Re: Noise increases [message #30898 is a reply to message #30894] Wed, 09 March 2005 14:01 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18792
Registered: January 2001
Illuminati (33rd Degree)

Maybe swap the potentiometer sides to check and see if the problem follows.


Re: Noise increases [message #30910 is a reply to message #30894] Thu, 10 March 2005 13:41 Go to previous messageGo to next message
GarMan is currently offline  GarMan
Messages: 960
Registered: May 2009
Illuminati (2nd Degree)
I usually ground the pot body to signal ground if it's generating a hum.

Nice job on the clean top plate. I'm putting together a tube phono stage right now and I'm taking the most difficult route possible to keep my top plate clean. Couldn't avoid putting over a dozen screws through the top plate to attach various solder strips and vector boards. To keep the top plate clean, I countersunk flat head screws, lock-tite the bottom, Bondo'ed the holes on top, sand down, primed and paint. More difficult than it should have been, but if anyone wants bodywork done on their car, I have the skills now.

Gar.

Erector Set [message #30911 is a reply to message #30910] Thu, 10 March 2005 14:45 Go to previous message
colinhester is currently offline  colinhester
Messages: 1349
Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)

I was lucky enough to be able to put these L-bracket supports (PHP, 16 x 1/2 x 1/2, item number 20802) under the Tx's and choke for support. It was held in place by the screws that would normally be used, so no extra holes to drill. These brackets are available from Home Depot for around $2. The holes are spaced 1/2" OC alternating between large and small openings. If one were to make a 6" x 6" square out of these and set them off the top plate by using washers, one could have 96 mounting holes and only need 4 screws to secure it to the top plate. This is what I mounted the CCS and heater PS on.....Colin

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