Comments for page: A New Look

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Posted by Bill March 11, 2012 - 08:19 pm
One more thing: I can get these resistors in metal film and carbon film (not carbon comp). I'm assuming the metal film might be better in this application?

Posted by Bill March 11, 2012 - 08:15 pm
I have been working on an original ST-35 with EFB for some time now and over heated a 2W 360K Kiwame resistor. All other resistors work fine so maybe that was a bum sample. Anyhow, this value of resistor is hard to source and I don't have room for (2) 180K's in series, but I can do something in parallel. I can get a 1M and and a 560K (1W both) for a value of 358.97K 2W. I guess that would be close enough to 360K?

Thanks, Bill

Posted by Dave March 01, 2012 - 01:28 pm
Hi Steven --

Because the ST-35 remains predominantly a class AB1 amplifier even when operating in triode mode, there will still be significant benefits from using the EFB(tm) modification when operated that way.

While there will not be nearly the power supply concerns for the "Enhanced" element of EFB to address, the basic conversion to fixed bias operation that EFB affords will still provide for increased power output and lower distortion in triode mode over that of a conventional cathode bias installation. This is due to the greater current flow that EFB allows the output stage to draw when needed to.

Without EFB, most of the increased current needs become increased bias applied to the output tubes as well when cathode bias is used. This reduces the available current the stage can draw as it tries to faithfully follow the input signal, resulting in the increased distortion and reduced power output as mentioned above. Using the EFB modification will eliminate these concerns, and provide for optimized performance in triode mode, just as it does in UL mode.

Also, you will still enjoy the increased tube life that EFB allows for with a lower quiescent current operating point as well.

Thanks for your interest in the EFB modification, and good luck with your amplifier!


Posted by Steven Wood March 01, 2012 - 12:31 pm
I am going to buy the Autoregenisis ST-35 EFB/Cap board as soon as it reaches the market. I am wondering if you can run the upgraded ST35 in Triode mode, speakers are very efficient. Thanks

Posted by Dave November 09, 2011 - 10:20 pm
Hi Hrudu -- The EFB(tm) mod is just as appropriate for the ST-35 as it is for the SCA-35. On the ST-35, R-42 is located near the bottom of the can cap, and connects between one of its main terminals, and one of its ground lug terminals. If the original R-42 component is still installed in your amplifier, it is a 95 ohm 5 watt resistor.

While the article itself shows installation in an SCA-35, there are numerous examples on both the and sites showing how folks have installed the modification in their ST-35 amplifiers as well. If you go to those sites and search under "EFB", you will find plenty of discussion and very good pics showing different ways the EFB mod has been installed in these amplifiers. You can use them and the discussion to help with your installation. If I can help anymore, don't hesitate to ask. Good luck with it!


Posted by Hrudu November 09, 2011 - 11:41 am
Can I do this mode on a ST-35?
Where is the R42?

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