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B+~325VDC homebrew amp questions.

2/10/2000 1:41 PM
Ted	B+~325VDC homebrew amp questions. Hi, I am ready to start building 2x6L6 amp. I have a PS delivering around 360VDC unloaded and I am guessing it might drop to around 325V when loaded. I am thinking of a BF preamp (single channel though) and cathode bias with shared 270 Ohm cathode resistor. I have an additional secondary winding that I can use for fixed bias volage and may add a fixed/cathode switch. Also considering the dual-ganged 1M pot post PI MV. I have a lot of questions however: 1. Given the lower B+, will I be needing to adjust the preamp 100k plate resistors to lower values to target similar plate voltages to schematic or should I leave them at 100k (and resulting lower plate voltages)? Any pother design consequences as a result of overall lower B+? I am thinking that this will deliver perhaps 20-25W total given Cathode bias at this B+. (Class A - I wonder?) 2. Will a single channel BF design with 12AT7 Fender PI drive this output section well? (I saw someone post that that their single channel BF preamp was distorting (because it didnt have the other channel there which usually lowers the overall gain a little). 3. Is there a schematic around somewhere that shows a dual fixed bias control (one for each tube)? I would like to have independent controls on the fixed bias. 4. Preferences on the post PI MV vs. a Marshall type preamp stack with pre PI MV? I have no experience with Marshall amps but think it might be neat to consider that preamp as well. I am sure I will have lots more questions as I get down to work but thanks for any comments! Ted.

2/10/2000 1:41 PM

Ted

B+~325VDC homebrew amp questions.

Hi, I am ready to start building 2x6L6 amp. I have a PS delivering around 360VDC unloaded and I am guessing it might drop to around 325V when loaded.

I am thinking of a BF preamp (single channel though) and cathode bias with shared 270 Ohm cathode resistor. I have an additional secondary winding that I can use for fixed bias volage and may add a fixed/cathode switch. Also considering the dual-ganged 1M pot post PI MV.

I have a lot of questions however:

1. Given the lower B+, will I be needing to adjust the preamp 100k plate resistors to lower values to target similar plate voltages to schematic or should I leave them at 100k (and resulting lower plate voltages)? Any pother design consequences as a result of overall lower B+?
I am thinking that this will deliver perhaps 20-25W total given Cathode bias at this B+. (Class A - I wonder?)

2. Will a single channel BF design with 12AT7 Fender PI drive this output section well? (I saw someone post that that their single channel BF preamp was distorting (because it didnt have the other channel there which usually lowers the overall gain a little).

3. Is there a schematic around somewhere that shows a dual fixed bias control (one for each tube)? I would like to have independent controls on the fixed bias.

4. Preferences on the post PI MV vs. a Marshall type preamp stack with pre PI MV? I have no experience with Marshall amps but think it might be neat to consider that preamp as well.

I am sure I will have lots more questions as I get down to work but thanks for any comments!

Ted.

Replies:

Bruce q{I have a lot of questions however... -- 2/11/2000 4:17 AM