Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fossilshark on September 11, 2023, 09:16:04 pm
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Ok so i'll admit, I have always had a really hard time wrapping my head around exactly how to bias a pair of bottles, the last 2 full amps I built were 50w EL34 jobbies and I just run them around -51v arbitrarily and they have withstood my near daily abuse over the past few years and still sound pretty good.
That being said this next amp isn't for me, it will be 100w and furthermore I would like to be able to pop in either 6L6s or EL34s with just a quick rebias. This is the bias supply I came up with stolen from Sluckeys Pheonix All American Dual Lite schematic :icon_biggrin: and I was wondering how I would go about calculating the value of the drop resistor (R43) so that my range can go from about 58v to 45v for 6L6 and EL34 respectively (I did calculate those values using the MU and the 460v applied to the output transformer ct).
I was also wondering:
-Shouldn't there only be 1 set of 100r resistors either before or after the bridge rectifier on the heater?
-When I build the power amp section, I have gathered it would be wise to throw in some 1% 1R resistors on the cathodes of each valve, what wattage should those be?
I feel like I keep posting the same questions over and over and I apologize for that. This particular topic is just something I really struggle with for some reason.
Any advice is greatly appreciated!
P.S.
Just in case anyone is wondering more about the last 2 preamps I built, I am doing the final tone tweaks on the Wendigo and my friend is play testing the Top Boost 420 to see what tweaks that requires. I am working on getting some demos for each "professionally" recorded and then I will post final schematics/layouts/demos to the forum.
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Cathodes resistor ; 1/2 watts is good, more powerfull is just more expensive ans bigger.
1/2 watt = 0.500 watts and most amp cathode current did not go over 0.050 watts
Heater supply ; in DC you don't need artificial center tap with 2 X 100 ohms resistors
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...I was wondering how I would go about calculating the value of the drop resistor (R43) so that my range can go from about 58v to 45v for 6L6 and EL34 respectively
On sluckey's website he has a good explanation of how to calculate the drop resistor. It's in a document called "My amp scrapbook", down on the 8th or 9th page.
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I was wondering how I would go about calculating the value of the drop resistor (R43) so that my range can go from about 58v to 45v for 6L6 and EL34 respectively
I would leave R43 alone and adjust the 220K to give the proper bias voltage range. This circuit already has a wide range of bias voltage adjustment.