Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: markmalin on June 28, 2021, 02:10:12 pm
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Hello, all!
This is kind of a funny question, but someone was asking me about a way to have individual power tube sections for a dual channel amp. So you'd have 2 preamps each with their own power amp, but into a single speaker output and have it switchable. I'm not sure this can work because you have a specific impedance requirement on an OT for a given set of power tubes into a given impedance for the speaker. But the idea would be:
[preamp 1] -> Phase Inverter 1 -> [Class A/B power amp section 1] -----\
-------> [single speaker load]
[preamp 2] -> Phase Inverter 2 -> [Class A/B power amp section 2]------/
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In theory you could, as long you don't run both amps together but instead switch between them (and provide dummy load to the unused "channel". In practice, no.
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It appears that you intend for only 1 power amp at a time to be connected to the speaker. Assuming the power amps are tube amps, the disconnected amp should be switched to a dummy load, at the same time that the other amp is switched to the speaker. I think some years ago PRR proposed a circuit based on an automotive hi/lo beam floor switch. There are more sophisticated A/B amp switches for this purpose; or it could be a DIY project.
For impedance matching: if a power amp does not match the speaker's impedance rating, a matching transformer could be used. Weber sells them.
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sounds very inefficient partswise