Tube DIY Asylum: Re: Latest version of my 7788/7721 LCR 600Ohm RIAA Stage by BBeck Do It Yourself (DIY) paradise for tube and SET project builders.

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Posted by BBeck (A ) on October 3, 2005 at 13:10:57

In Reply to: Re: Latest version of my 7788/7721 LCR 600Ohm RIAA Stage posted by Thorsten on October 3, 2005 at 01:16:54:

How to measure? Easy. Disconnect any input transformer or cartridge. Measure the voltage across the 47K input resistor, divide by 47K and that's your input grid current. Also, measure plate current if possible (or plate voltage) and then alternately short and then leave alone that 47K resistor. If there is any significant change in plate current or voltage, then you have to suspect grid current.

If you are using a transformer, then there should be no problem, but those who connect your RIAA stage directly to a cartridge, whether MC or MM, should consider either a different design with more grid bias or an input transformer,IMO.

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