Setting Bias on Fender Hot Rod Deville
Moderators: pompeiisneaks, Colossal
Setting Bias on Fender Hot Rod Deville
Schematic calls for 60mV at TP 30. Only able to get 54mV with pot wide open. Any suggestions? All settings are set to prescribed levels on schematic.
Re: Setting Bias on Fender Hot Rod Deville
Reduce the value of R77 (100K) in the bias circuit a smidge.
You want to have a little less negative voltage (getting closer to ground potential) on the power tube control grids. Reducing that value gets you closer to ground potential.
You are pretty close to where you want to be so try a 10K to 20K reduction to start.
Good luck!
Dave O.
You want to have a little less negative voltage (getting closer to ground potential) on the power tube control grids. Reducing that value gets you closer to ground potential.
You are pretty close to where you want to be so try a 10K to 20K reduction to start.
Good luck!
Dave O.
Bias setting on Fender Hot Rod Deville
Great tip. The clean channel doesn't sound as clean as I remember so good place to start.
Thanks
Thanks
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Stevem
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Re: Setting Bias on Fender Hot Rod Deville
Are you going for 60mv with the original factory tubes?
Even if you got the called for 60 MV that does not mean that each tube is pull a matched 30mv each.
You should install one tube at a time you will find out how balanced / matched the tubes are.
Also note that the power transformer in these amps are really on the small side for what they say is a 40 watt amp, and they run hot and fail often,in fact these amps never output more than 33 watts rms even though they are rated at 40 even with the best testing set of new output tubes I own!
In regards to having only 30 MV each tube that will have them biased on the cold side and cold biased output tubes will make for nasty sounding crossover distortion when you push the output stage.
With the plate voltage these amps have each tube should be pulling 36 MV or more and the PT is gonna live a short life at that current if you play it near cranked 2 nights a week!
If you got the bucks and you like the sound of the stock speaker and have the wallet brimming than changing out the PT will make you smile!
Also note that the first preamp tube in any amp sets up the amps whole tonal nature.
Having a tube in that spot that gets you the closest to what you are looking for is worth spending the money on a new N.O.S tube.
Hi test N.O.S tubes in N.J can help you pick a brand that will help that amp sound better!
Even if you got the called for 60 MV that does not mean that each tube is pull a matched 30mv each.
You should install one tube at a time you will find out how balanced / matched the tubes are.
Also note that the power transformer in these amps are really on the small side for what they say is a 40 watt amp, and they run hot and fail often,in fact these amps never output more than 33 watts rms even though they are rated at 40 even with the best testing set of new output tubes I own!
In regards to having only 30 MV each tube that will have them biased on the cold side and cold biased output tubes will make for nasty sounding crossover distortion when you push the output stage.
With the plate voltage these amps have each tube should be pulling 36 MV or more and the PT is gonna live a short life at that current if you play it near cranked 2 nights a week!
If you got the bucks and you like the sound of the stock speaker and have the wallet brimming than changing out the PT will make you smile!
Also note that the first preamp tube in any amp sets up the amps whole tonal nature.
Having a tube in that spot that gets you the closest to what you are looking for is worth spending the money on a new N.O.S tube.
Hi test N.O.S tubes in N.J can help you pick a brand that will help that amp sound better!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!