Moderator: longfxukxnhair
You're right.slowpokerhino wrote:I believe the seperate bias pots negates the need for matched tubes entirely. Could be wrong but I don't think I am.
Shit, I hate it when I'm wrong, slowpoke was wrong first.Sorry guys but you're wrong.
Like George Carlin says, everybody is a winner.slowpokerhino wrote:Yay, first!!
I thought about trying that to see how it sounds. I'm glad I asked because now I can make good use of some pairs that aren't so well matched.KevinOConnor wrote:If the bias control voltage range is wide enough, you can use alternative tubes AND mix tubes.
The asymmetric behaviour of unmatched tubes merely results in a fatter tone; you still get full output power and loudness.
:cussKevinOConnor wrote:Hi Guys
To those who thought they were wrong: you are actually right.
Steve's response was a bit heavy handed inasmuch as making a blanket "wrong-ness" statement.
The bias pots let you balance hum. They also allow a higher percentage of available tubes to be used in the amp, provided there is sufficient control voltage range designed in.
For an amp designed for EL-34, 6550, KT-88 or similar with a 1,600mA heater, it is easy to swap in low-heater-current tubes such as 6L6GC or anything related. If the bias control voltage range is wide enough, you can use alternative tubes AND mix tubes.
The reason matched tubes was ever important was because the first guitar amps were actually hi-fi circuits. Designers and techs followed hi-fi rules without being aware that that was what they were doing. Lethargy set in and we still battle with it today, and that is prabably why Steve's first response was that wrong thingy. Then he became aware that guitar amps are not hi-fi tone reproducers rather they are tube-safety-following tone creators.
Also, most companies do not want to deal with potential liabilities that may arise if they suggest to the equipment user that other tubes could be used, or that the user can bias them himself, or that mixing of tubes is possible, or that you can pull any tube from any position you want in a fixed-biased amp.
The asymmetric behaviour of unmatched tubes merely results in a fatter tone; you still get full output power and loudness.
My amps have always allowed the player to mix, match, pull tubes at his own choosing. It's not rocket science or even voodoo.
Have fun
Kevin O'Connor
Many of the technical concepts discussed here on tube matching are a bit subjective. The engineer in me would like to see actual numbers to indicate when mismatching would cause problems. I've never really tried to find such data myself as I only work on amps part-time, and only for myself.KevinOConnor wrote: There is a minimum symmetry or balance required to attain full output power, BUT... this is so far from needing anything matched that one needs ever consider matching to any great extent.
It's a very common "mod" for a Twin Reverb to pull 2 tubes and disconnect 1 speaker (pulling the tubes will cause the transformer to look for an 8 ohm load instead of 4). I've tried it, and while it does work, I prefer it "stock".MKB wrote: There is the old story of a guitarist (Paul Burlison with the Rock n Roll Trio) that reportedly pulled one output tube from his amp to get a distorted tone, and did some famous early recordings like that. That should have caused a large current mismatch in the output trasformer as well as perhaps some asymmetry/distortion in the output waveform.
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