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RE: Interstages and grid load resistors???

Posted by TomWh (A) on December 8, 2014 at 06:56:36

In Reply to: RE: Interstages and grid load resistors??? posted by Michael Samra on December 7, 2014 at 22:31:22:

Hi Michael

I did not use the correct terms most likely. The above schematic uses single stage riaa where I use a split riaa like a Morgan Jones etc... I think you hit on a key here with the AC flowing in a certain direction. The large 220k resistor in the above schematic is in series and I think it is a part of the riaa network. The resistors I am talking about are shunt resistors which you see in most amp designs when you are not using interstage transformers. They are normally very large 1m and up. It was my understanding they where used to load the stage(This is where I might be wrong) The example above would be the standard 47k cart load to ground.

The 47k load is there to impedance match a standard mm cart. In the above schematic G1 on the second tube you state goes thru the 220k series resistor and also shunts to ground thru the secondary winding on the 1st interstage??? So does G1 on second tube see load combination of 220k and the secondary winding? (which is acting like a grid choke) This is where I
am confused. For example my 1st tube is plate loaded with the 1660 interstage then it goes thru a 100k series resistor a 2k series resistor and then a 600pf cap to ground. Which is 75 correction of the riaa. The grid circuit is connected between 100k and 2k resistor to the grid of the 2nd tube with that 1m shunt resistor to ground.

So I was under the assumption that this 1m resistor was there to load the grid of the second tube. I also read that if you use interstage transformers the secondary winding acts as a grid choke and that is why you normally do not see these big shunt resistors when using them.

I am all ears here I am a little confused on the ac path.

Thanks Tom

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