I have a fresh plan making a little different otl, for driving speakers having multiple 8ohm series connected speakers.
At first, it sounds like quite easy load for otl.
Ok, first of all I want 50watts/channel for 80 ohm impedance.
There should be option for half impedance, like 40 ohms.
4 x EL509 / channel should do this job easily?
powersupply/power transformer will be 2 x 110VAC. 400VA/ch, should be enough..
what do you think about this idea?
At first, it sounds like quite easy load for otl.
Ok, first of all I want 50watts/channel for 80 ohm impedance.
There should be option for half impedance, like 40 ohms.
4 x EL509 / channel should do this job easily?
powersupply/power transformer will be 2 x 110VAC. 400VA/ch, should be enough..
what do you think about this idea?
50w is quite a lot for an OTL !
Just do some math:
A EL509 as cathode follower has an R-out of 1/(0.018ma/V) = 55Ohms. As circlotron it's a bit lower and as futterman its half the cathode follower R-out. So even without further global feedback this isn't bad.
Power:
P=(I^2)*R, for P=50W and R=80Ohms, this yields: ~0.8A-rms and ~1.1A-peak and for 40Ohms: ~1.1A-rms and ~1.6A-peak.
EL509 max. Ik is 500mA. So you can calc. for yourself how much tubes you need for that much power you want.
I have never built an OTL amp, so I can't tell you about some good designs. But I have some names in my head. Just google for: "Rosenblit OTL", "Sandman OTL", "Pickie Makovski OTL", "Murray OTL"
Just do some math:
A EL509 as cathode follower has an R-out of 1/(0.018ma/V) = 55Ohms. As circlotron it's a bit lower and as futterman its half the cathode follower R-out. So even without further global feedback this isn't bad.
Power:
P=(I^2)*R, for P=50W and R=80Ohms, this yields: ~0.8A-rms and ~1.1A-peak and for 40Ohms: ~1.1A-rms and ~1.6A-peak.
EL509 max. Ik is 500mA. So you can calc. for yourself how much tubes you need for that much power you want.
I have never built an OTL amp, so I can't tell you about some good designs. But I have some names in my head. Just google for: "Rosenblit OTL", "Sandman OTL", "Pickie Makovski OTL", "Murray OTL"
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I just looked into Bruce Rosenblit's book and on page 74 he says: "The maximum current that a 509 can pass is just over one amp."
This disagrees with the datasheet value of 500mA and seems to be the solution why bruce gets 80W into 8Ohms with "only" 8 tubes.
According to this, 4 tubes per channel should be enough. But as I said, have neither used EL509 for audio nor built an OTL
This disagrees with the datasheet value of 500mA and seems to be the solution why bruce gets 80W into 8Ohms with "only" 8 tubes.
According to this, 4 tubes per channel should be enough. But as I said, have neither used EL509 for audio nor built an OTL
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I say go for it!
Here is some more info about OTL and calculations with EL509:
Ultra-Linear OTL Power Amplifiers
Here is some more info about OTL and calculations with EL509:
Ultra-Linear OTL Power Amplifiers
You should consider the schematic on post 25 on this thread:
http://www.diyaudio.com/forums/tubes-valves/161112-what-tubes-tube-amp-3.html
I think the circuit is very elegant in its approach and the output tubes does not cost that much.
http://www.diyaudio.com/forums/tubes-valves/161112-what-tubes-tube-amp-3.html
I think the circuit is very elegant in its approach and the output tubes does not cost that much.
Mechanical damping is either part of the drive unit or the cabinet. I'm not a speaker expert so others will know more than me. All speakers have some mixture of mechanical and electrical damping of the bass resonance, but in your case you will need most of it to be mechanical unless you want a bass peak.
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