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In Reply to: RE: my first 300B SET posted by sober1 on August 12, 2014 at 21:44:47
Mod till your hearts content. Nothing is ever done. You may find the bias to be lower than ~70 mil; don't worry, 60 mil you may like better (I did). Early American 2A3s sound close to genuine WE 300Bs; don't write them off. I hope you have a good stash of 6SN7s.
Follow Ups:
Many 300B DIY designs have operating points that result in around 5.5-6W with lower distortion. The kit is around 8-9W with 10% THD at full power. I think.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
Edits: 08/13/14
this amp is set for 425vdc plate and -74 cathode with 2.5K OPT.
it's my understanding that she has virtual no real run time on her so I'm going to kick back for a bit and enjoy some Jazz and Blues for awhile (Taj Mahal at present). No critical listening as of yet.
"the only thing necessary for evil to succeed is for good men to do nothing"
Running the 300B conservatively also prolongs tube life; however may require different OPTs.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
oh by no means would I ever "write off" 2A3s! I rank them as second only to the 45 as my favorite outputs tube. It's just I've never owned a 300B and this one was originally designed as a 300B so I returned it to that configuration to get the flavor of the original design.
I see the WE 300B tube data from the '50s called for 60 milliamperes bias @ -74 VDC and 350 plate volts for 8 watts output.
I couldn't find anywhere where the old producers (WE, RCA, Raytheon and the likes) even mention putting a greater strain on the tubes with greater plate voltage and higher current demands. I'm talking > +400 V plate and > 80 mA bias! I'm toying with setting mine at 350/60 when I change out some of the PS caps as I prefer to drive my outputs at less than full throttle to extend tube life and therefore money.
"the only thing necessary for evil to succeed is for good men to do nothing"
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