hi there!
I was just thinking, with transistor circuits if you connect multiple transistors in parallel, it allowed more current through to the output load while the voltage generally stays the same.
so put very simply, if I had enough tubes in parallel, (to increase the output current) could the output transformer be eliminated? or does it still need Impedance matching? the number of tubes may be impractical, but it was just a thought I had.
cheers
I was just thinking, with transistor circuits if you connect multiple transistors in parallel, it allowed more current through to the output load while the voltage generally stays the same.
so put very simply, if I had enough tubes in parallel, (to increase the output current) could the output transformer be eliminated? or does it still need Impedance matching? the number of tubes may be impractical, but it was just a thought I had.
cheers
Do a search on "OTL", which stands for Output Transformerless.
These Amps do work as you suggest, by paralleling output tubes to get the impedance down to the point where an output transformer is not needed.
A few calssic designs, even a couple of threads here dedicated to OTL design.
Cheers,
Ian
These Amps do work as you suggest, by paralleling output tubes to get the impedance down to the point where an output transformer is not needed.
A few calssic designs, even a couple of threads here dedicated to OTL design.
Cheers,
Ian
Hi,
I put 6 amplifiers in parrallel yust for the power I needed.
The output line is a so called constant voltage line (100 V) with now more current. Sometimes there where 50 or more speaker cabinets connected over a distance of 4 a 5 Km.
See my website ( Amplifiers with valves )
Some schematic diagrams and photo's are there.
I put 6 amplifiers in parrallel yust for the power I needed.
The output line is a so called constant voltage line (100 V) with now more current. Sometimes there where 50 or more speaker cabinets connected over a distance of 4 a 5 Km.
See my website ( Amplifiers with valves )
Some schematic diagrams and photo's are there.
My first and last OTL had something like 64 sections of 6528s in parallel. You could peel wallpaper with the heat.
My one foray into OTL land resulted in a circlotron based design using six 6C33 per monoblock, scorcher, speaker destroyer, and heart breakingly good sounding during the short few hours when things sort of worked. Never achieved the target output power due to the stupidest driver design I have ever devised. Unreliable, and untrusted, and while I was doing this I was also tinkering with my first 45 SE design which ultimately sent me in another direction and to another world.
Yes, you can do that. However, there aren't very many tube types where this is practical. You have power triodes:
6AS7 (power dual -- series pass device originally)
6C33C (high gm, series pass device)
That's about it for power triodes.
You could also use the TV HD pents with screen drive to get the massive current peaks that 8R speeks will require. Back in "the day" OTLs used special speeks with unusually high voice coil resistances (up to 1K0) or you could series connect a lot of 8R drivers to get that load resistance up.
In any case, your two main topologies are the SEPP (seen with SS designs, as complimentary NPN/PNP or N-Channel/P-Channel devices are available) or the Circlotron bridged amp topology.
Since there are no "P-Channel" VTs, the SEPP will require some phase balancing tricks like the Futterman designs, or some other means of balancing the two phases.
I've built four OTLs so far; two using a pair of 6C33Cs in a Futteman style totem-pole configuration. One using four EL609s, in a circlotron. And the most recent is a Futterman-style using four 6082s, which are equivalent to 6AS7s. I've never had anything but a coupke of minor failures of tubes, with no dramatic effects. My speakers are 4 ohm (nominal) impedance, and all the OTLs drive them nicely. They are really all simple and trouble-free. I don't really see the point of messing with output transformers, when it is so easy to make tube amplifiers without them.
Chris
The most novel OTL's I have seen are those designed for directly driving electrostats. They usually use HV shunt regulator triodes and run at quite high voltages.
I dabbled with the OTL thing, but for regular PP topologies I find a good output transformer to be superior. If I want/need an amplifier without an output transformer, I use silicon.
I dabbled with the OTL thing, but for regular PP topologies I find a good output transformer to be superior. If I want/need an amplifier without an output transformer, I use silicon.
same here, to me a tube without the OPT is no tube amplifier...- Status
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