5842 grid leak

regal · 22nd October 2010, 04:21 AM

As I understand it the 6c45pi and SM5842 need a small grid leak, best around 50k. For a small spud amp would it be OK to just use the input volume pot as the gridleak if it is about 6" away from the tube? Or does the gridleak need to be near the tube as possible like the grid stoppers to counter the HF oscillations these tubes are known for.

Sch3mat1c · 22nd October 2010, 04:34 AM

The grid leak does not carry RF. It can be placed anywhere, minding general wiring rules.

Tim

DF96 · 22nd October 2010, 12:30 PM

Don't just use the pot as a grid leak, as one of the normal failure modes is for the wiper to lose contact with the track. Add a resistor from wiper to ground too, about 10-20 times the pot resistance. Then you still have some bias when the pot fails.

A valve which requires a small grid leak is clearly expected to have significant grid current so it will need a low impedance source, in order to avoid distortion. I would use a 10K pot, with 100K from wiper to ground.

regal · 22nd October 2010, 01:05 PM

Quote:

Originally Posted by DF96

A valve which requires a small grid leak is clearly expected to have significant grid current so it will need a low impedance source, in order to avoid distortion. I would use a 10K pot, with 100K from wiper to ground.

Yea that was plan B, luckily I have a strong SS DAC.

Thanks.

22nd October 2010, 04:21 AM	#1
regal diyAudio Member Join Date: Jan 2004 Location: MD	5842 grid leak As I understand it the 6c45pi and SM5842 need a small grid leak, best around 50k. For a small spud amp would it be OK to just use the input volume pot as the gridleak if it is about 6" away from the tube? Or does the gridleak need to be near the tube as possible like the grid stoppers to counter the HF oscillations these tubes are known for.

22nd October 2010, 04:34 AM	#2
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	The grid leak does not carry RF. It can be placed anywhere, minding general wiring rules. Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

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22nd October 2010, 12:30 PM	#3
DF96 diyAudio Member Join Date: May 2007	Don't just use the pot as a grid leak, as one of the normal failure modes is for the wiper to lose contact with the track. Add a resistor from wiper to ground too, about 10-20 times the pot resistance. Then you still have some bias when the pot fails. A valve which requires a small grid leak is clearly expected to have significant grid current so it will need a low impedance source, in order to avoid distortion. I would use a 10K pot, with 100K from wiper to ground.

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