Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on July 05, 2012, 01:21:18 pm
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Has anyone tried to use mixed tube set in an SE amp with two power tubes?
E.g. used pairs like EL34-6L6, EL34-6550, EL34-KT88 etc.
/Leevi
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Has anyone tried to use mixed tube set in an SE amp with two power tubes?
E.g. used pairs like EL34-6L6, EL34-6550, EL34-KT88 etc.
/Leevi
I haven't tried it. However, if the OT is rated for enough standing current for the two tubes, I don't see why you couldn't have 6V6/EL84, 6V6/6L6, 6V6/EL34, 6L6/EL34, etc.
You'll want to give each tube its own cathode resistor, if you cathode bias. That's just because different type may idle better with different cathode resistor values (especially true with EL34 vs 6L6, or EL84 vs 6V6).
One of the tube may have a non-optimum load, but that will just result in less than full possible output power.
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I welcome being shot down like snoopy by the red baron from you real amp builders
It's been my experience this isn't the site for that. I've found everyone here's cool and genuinely trying to help. No one here's trying to prove they got the biggest tube.
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I assembled a concept for an SE amp with dual out put transformers that could be adapted to what you might be asking.
Thanks drgonzonm for sharing the schematic that looks interesting. However the idea was to use one OT
and two different power tubes.
You'll want to give each tube its own cathode resistor, if you cathode bias. That's just because different type may idle better with different cathode resistor values (especially true with EL34 vs 6L6, or EL84 vs 6V6).
The basic idea is to use a common cathode resistor since it should be possible to place the tubes randomly to the sockets.
I don't see why you couldn't have 6V6/EL84, 6V6/6L6, 6V6/EL34, 6L6/EL34, etc.
I'm actually asking that. One motivation could be the expectation for new type of sound?
/Leevi
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I don't see why you couldn't have 6V6/EL84, 6V6/6L6, 6V6/EL34, 6L6/EL34, etc.
I'm actually asking that. One motivation could be the expectation for new type of sound?
/Leevi
Exactly. I'm saying I don't see any technical reason you shouldn't use dissimilar tubes into a single OT.
You'll want to give each tube its own cathode resistor, if you cathode bias. That's just because different type may idle better with different cathode resistor values (especially true with EL34 vs 6L6, or EL84 vs 6V6).
The basic idea is to use a common cathode resistor since it should be possible to place the tubes randomly to the sockets.
I'm thinking EL84 vs 6V6 would provide two unique sounds. However, the EL84 has much higher transconductance, and needs a smaller cathode resistor to bias properly. This is not so bad, because you need two different-type sockets anyway, so matching the cathode resistor to the socket works well.
Similar argument applies to EL34 and 6L6, though you could use a single resistor common to both sockets. If you determine that different-value resistors would provide optimum bias for each tube, you could select a single value that biases one tube a little cooler than optimum in order to use a single, shared cathode resistor.
Also, if it were my amp, I'd add a dedicated volume control preceding each tube, so that you could balance the amount that each tube contributes to the overall sound. Kind of like a post-phase inverter master volume, without the phase inverter.
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Exactly. I'm saying I don't see any technical reason you shouldn't use dissimilar tubes into a single OT.
Yes, sorry I didn't properly read your response.
Similar argument applies to EL34 and 6L6, though you could use a single resistor common to both sockets. If you determine that different-value resistors would provide optimum bias for each tube, you could select a single value that biases one tube a little cooler than optimum in order to use a single, shared cathode resistor.
I agree, using single resistors and by marking the sockets for the tube types could be the solution. Maybe there could
be third socket for noval tubes.
Also, if it were my amp, I'd add a dedicated volume control preceding each tube, so that you could balance the amount that each tube contributes to the overall sound. Kind of like a post-phase inverter master volume, without the phase inverter.
That is the idea.
/Leevi
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and if you want to switch between different types without adding even more sockets you can use a rotary switch for the cathode resistors:
(http://img515.imageshack.us/img515/715/dsc06130r.jpg)