AXEL

Does it matter where the volumes (preamp & master) are set when baising this amp? I read on another website that the volumes should all be set at zero. Anyone??

bluebear

I have been waiting to see if someone with technical knowledge would respond to your post... I am not a tech but I recently biased my DSL 50. Like you I read that the knobs should be set to zero (not sure how important that is but this is the way I did it). I set all my knobs to zero and then biased to 42mv using the video on eurotubes as a guide:

euro-m

The above procedure seemed to work well for me.

Dennis

timstoel

The volume controls do not matter. Bias is the "idle current" that your output tubes are consuming with no signal passing. The volume controls have no impact on this voltage.

There is no "right" bias for any amp. The factory may suggest one, but there isn't one bias that is right and all other points are wrong. You can actually adjust the bias to run the tubes higher or lower depending on the sound you are looking for, what brand/type your tubes are, and how long you want your tubes to last. If you adjust your tubes to consume more current, you get more volume, but more heat, shorter tube life, and you run the risk of imploding your tubes. Some recently manufactured tubes are less resistant to this than tubes manufactured in the 50s 60s and 70s. This is why a lot of the new old stock tubes from back then are more valuable. Many older amps use huge plate voltages that some modern tubes don't handle as well as others.

Improper bias can cause crossover distortion, which is where the output tubes are not amplifying the entire waveform, instead they are ignoring the lowest voltage parts of the AC signal, around the zero crossings. Because each set of tubes is different, you should bias your amp every time you install new tubes, and check it periodically throughout the life of the tubes. It is not necessary, but it is really best to have an oscilloscope to set the bias.

Tim

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bluebear

Thank you Tim for a great post and information!

AXEL

Since I first started this thread I have since gotten some advice from an amp tech who said it's a good practice to keep the volumes at 0 when biasing. But he referenced as long as no noise was coming thru the speakers it shouldn't make that much of a difference. I assume that is what Tim was referring to when he said "no signal passing". I was also advised much the same as Tim has said about experiementing with different bias settings. Lower bias would generate a fatter, warmer tone, higher bias is more gain. My 50 watt DSL is spec'ed at 45mv per side or 90mv total. I have found that I like the bais set at 29mv per side. This setting sounds the best to my ears. I'm using Ruby EL34's and have a Tung-sol in V1. I also play thru a Avatar vintage Bluesbreaker 2 x 12 loaded with V30's. So far I'm still very happy with this setting. I have a gig this weekend and will have a chance to hear the amp in a more open setting to see how it really perfoms.