# Traynor YCS-100 H re-bias



## surlybastard (Feb 20, 2011)

I've got a Traynor Custom Special 100 H (not the H2) with KT77's currently dying a slow death. I want to switch them to EL34's, but I've never had to re-tube and re-bias an amp myself before. I've figured out where all the test points, ground and bias pot are, I just wanted to check in and see if anyone else has changed the bias on one of these and if they have any advice or direction for a newbie?

The manual says to set the bias to 25mV, that strikes me as being very cool. Any opinions? 

Thanks!


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## bcmatt (Aug 25, 2007)

It depends what your plate voltage is. That will be the factor to tell you whether 25 mV is hot or cold.


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## surlybastard (Feb 20, 2011)

I'm checking on this, but I believe the plate voltage of the 100 is 500v.


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## bcmatt (Aug 25, 2007)

Did you measure the plate voltage yourself from pin #3?
So, if the Plate Dissipation Figure for an EL34 is 25 Watts --> 25 Watts / 500 Volts = 0.050Amps or 50mA
With the 1R resister usually rigged up for test points, you would be able to read the current as mV with your DMM.
So, you're idling at 50%. People often recommend somewhere between 50-70% with different amps having more specific recommendations. If Traynor anticipates your plate voltage is 500V, I guess they are recommending 50%.
So, if:
50% of 50mA = 25mA (mV at Test Points)
60% of 50mA = 30mA
70% of 50mA = 35mA
I would say, just play it and see how it sounds. Your tubes will last longer running a bit cooler like this. Then, maybe just adjust to your tonal taste, while avoiding going over 35mA. I usually just shoot for 60%.


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