re: need help on Counterpoint SA5.1 preamp - diyAudio
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Old 7th April 2005, 06:15 PM   #1
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Default re: need help on Counterpoint SA5.1 preamp

Hi there,

I am looking for the resistors' value which tied to the filement pins of 6GC5 tube inside the Counterpoint SA5.1 preamp. The existing two resistors were burnt so I can't figure out the value. Any info is greatly appreciated!


Adam
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Old 9th April 2005, 05:56 PM   #2
anatech is offline anatech  Canada
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Hi Adam,
I show those as 10K resistors to reference the filiments to approx. 245VDC (output voltage). The 6GC5 runs off it's own heater winding.

-Chris
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Old 11th April 2005, 05:28 PM   #3
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Dear Chris,

Thanks for the info, and looks like my SA5.1 might have some other problem to burn the 2 x 10K resistors. I will replace them and check, thanks again!

Regards,

Adam
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Old 11th April 2005, 11:45 PM   #4
anatech is offline anatech  Canada
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Hi Adam,
The only thing that can burn those is a connection to ground. There should be no connection to ground at all with those resistors open. THe filiment should float on it's own winding. Check for mods, resistive ground or a winding short to the core (bad news).
-Chris
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Old 10th May 2005, 08:31 PM   #5
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Hi Chris,

Thanks for the info, and I have tried to ohm the resistance between that two resistors to ground, and they are open. I have replaced them with two 10Kohm resistors, and found out that the timer (555) now won't engage. I only got around 2V dc from the retifier (half wave) out of the filement supply, to the 555 timer. The voltage on the 6GC5's filement does go to 235Vdc. Please provide your comments, or if you know where I can obtain the schematic for this model, thanks!

BTW, could you measure the resistance of the 10KOhm resistors? it is actually 10 times smaller than the color band.

Adam
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Old 10th May 2005, 11:44 PM   #6
anatech is offline anatech  Canada
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Hi Adam,
If you measure across a 10K resistor you should measure around 5K. The resistors are connected at one end by the transformer and the other by the filiment of the tube. The resistors will appear as in parallel. You may ahave a connection to ground that shorts at a higher voltage but is okay at low voltage.

The 555 timer will not switch at 2 VDC, you need the full 6.whatever V to operate it. Look for bad solder joints or an partially open resistor in the heater circuit. Also check the caps. Often they go open due to the load they are under.

The filiment of the 6CG5 is expected to be around the regulated output voltage. That is so the max heater - cathode voltage is not exceeded, causing an arc. There is a resistor to bias the heater up.

I'm not looking at a schematic, just going from memory on these.

-Chris
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