I thought I would show off my newly finished SE-OTL amplifier project;
Anyway, the amp uses beautiful 13E1 output tubes - just one per channel for around 1.5W per channel, which is plenty for my 15ohm Lowther horns. The 13E1s are beam tetrodes, run in triode mode. Input/driver tubes are 6H30Pi
Chassis is a custom-machined Modushop Slimline. The front panel is olive wood (repurposed from a kitchen chopping board)
It's sounding very good with my Valve DAC as the source.
I'm feeling pretty chuffed! 🙂
Anyway, the amp uses beautiful 13E1 output tubes - just one per channel for around 1.5W per channel, which is plenty for my 15ohm Lowther horns. The 13E1s are beam tetrodes, run in triode mode. Input/driver tubes are 6H30Pi
Chassis is a custom-machined Modushop Slimline. The front panel is olive wood (repurposed from a kitchen chopping board)
It's sounding very good with my Valve DAC as the source.
I'm feeling pretty chuffed! 🙂
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I'd like to hear that driving my midrange horns. They are 115db efficient so 1.5 wpc I'd more than enough.
That is a very nice looking amp!
An OTL amp with only a single output tube.
Is that a Cathode Follower output?
What did you use for the current source for the 13E1?
Solid state, or a Choke?
Can you post a schematic, please?
Thanks!
An OTL amp with only a single output tube.
Is that a Cathode Follower output?
What did you use for the current source for the 13E1?
Solid state, or a Choke?
Can you post a schematic, please?
Thanks!
A 13E1 has two parallel cathode-grid structures, so in that sense there are two output valves after all 😉
13E1 @ The Valve Museum
13E1 @ The Valve Museum
MarcelvdG,
13E1
There is only 1 Plate connection pin.
There is only 1 Cathode connection pin (they are internally connected in parallel).
That means there is only one output terminal . . . either the plate, or the cathode.
Where is the current source, in the plate circuit, or in the cathode circuit?
13E1
There is only 1 Plate connection pin.
There is only 1 Cathode connection pin (they are internally connected in parallel).
That means there is only one output terminal . . . either the plate, or the cathode.
Where is the current source, in the plate circuit, or in the cathode circuit?
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MarcelvdG,
There is one output, not two, unless you are building a Power Concertina.
A Power OTL using 2 coupling caps, one from the plate, and one from the cathode?
Perhaps.
Or, use a current source in the plate, and a coupling cap.
Or, use a current source in the cathode, and a coupling cap.
2 other ways to make a single tube OTL.
There are 2 separate control grids.
If they are driven with separate signals, that Makes a good Power Mixer.
Not an OTL.
There is one output, not two, unless you are building a Power Concertina.
A Power OTL using 2 coupling caps, one from the plate, and one from the cathode?
Perhaps.
Or, use a current source in the plate, and a coupling cap.
Or, use a current source in the cathode, and a coupling cap.
2 other ways to make a single tube OTL.
There are 2 separate control grids.
If they are driven with separate signals, that Makes a good Power Mixer.
Not an OTL.
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Indeed Marcel, just like the other tube popular in this scenario, the 6C33C, but also like that tube you can only use it as a 'single' tube.
Here's the schematic I based the project on;
My build varies in several areas, primarily in my use of a Mosfet-based Constant Current Sink on the 13E1 cathodes and different power supplies - a CLCLC psu for each 13E1 and a '21st Century Maida' regulator for the 6H30Pi stages.
I'm running the 13E1s at around 70W dissipation - 150V B+ with the current sink set to 475mA.
The small knob on the front panel isn't a volume control but a selector switch to experiment with different feedback settings.
There are some build images here;
13E1 SE-OTL - Album on Imgur
My build varies in several areas, primarily in my use of a Mosfet-based Constant Current Sink on the 13E1 cathodes and different power supplies - a CLCLC psu for each 13E1 and a '21st Century Maida' regulator for the 6H30Pi stages.
I'm running the 13E1s at around 70W dissipation - 150V B+ with the current sink set to 475mA.
The small knob on the front panel isn't a volume control but a selector switch to experiment with different feedback settings.
There are some build images here;
13E1 SE-OTL - Album on Imgur
I don't think you can, because like the cathode and anode, the control grids are internally connected. The two internal beam tetrodes are really completely in parallel.
Attachments
MarcelvdG,
The best example of a Power Mixer is a shortwave AM transmitter output tube, that uses Screen Modulation.
60% or 65% AM modulation still gets the message through.
Amazing . . . the ingenuity of those Amateur Radio designers . . .
The best example of a Power Mixer is a shortwave AM transmitter output tube, that uses Screen Modulation.
60% or 65% AM modulation still gets the message through.
Amazing . . . the ingenuity of those Amateur Radio designers . . .
I remember once when I measuring that 13E1 tube. It turned very very hot in normal operation points. and I burn fingers badly... Didnt wait enough for tube to coll down...
.
13E1 have good internal constructon, huge power and it is reliable tube.
But 13E1 have pretty low internal impedance, so the output transformer chould be not an issue? I think to build myself one long time ago just because I have bunch of theese tubes. But somehow I never did... And I sold a half to the one member of this forum. years ago...
.
happy listeninig, good job - nice looking device 🙂
.
13E1 have good internal constructon, huge power and it is reliable tube.
But 13E1 have pretty low internal impedance, so the output transformer chould be not an issue? I think to build myself one long time ago just because I have bunch of theese tubes. But somehow I never did... And I sold a half to the one member of this forum. years ago...
.
happy listeninig, good job - nice looking device 🙂
Thank you 🙂
There are no output transformers or are you suggesting you would use them?
Yes, just the filaments generate a lot of heat (26V @ 1.3A) so I'm very cautious about touching the glass. Not as bad as a 6C33C though!
Hi Nautiboy,
At 150 volts plate supply and 475 mA cathode current, what is the voltage across the tl783? how many watts are dissipated by the CCS? I am also in the process of designing a similar OTL but with the 6C33 parallel tubes...I haven't made up my mind....two 6C33 bottles and filaments in series, 24vac @3A, not so much current...
At 150 volts plate supply and 475 mA cathode current, what is the voltage across the tl783? how many watts are dissipated by the CCS? I am also in the process of designing a similar OTL but with the 6C33 parallel tubes...I haven't made up my mind....two 6C33 bottles and filaments in series, 24vac @3A, not so much current...
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I would go with classic OT because it is easy to build. Not much henrys in primary. Not so many turns will give less capacitance. And You can use tin wire for minimal DC resistance of wires. So the damping factor will rise. Good bandwidth also.
There is no need for higher permeability cores just medioum or lower. Because high anode currents.
I think that this tube in triode mode have 120 to 130 ohms of internal resistance.
I will post some triofe datas and spice model - i think i still have it?
cheers 🙂
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Hi Tony.
As I mentioned in post #10, I don't use TL783s, instead I have Mosfet based current sinks - they're actually from K&K Audio, about halfway down this page;
Other kits – K & K Audio
I'll have a look at the documentation later and advise how much power is being dissipated in the current sink.
If you're two parallel 6C33C tubes with a cathode curent sink you might consider one CCS per 6C33C. I also have a Transcendent 300B SE-OTL and using John Broskie's alternative output arrangement with a CCS (TL783) per 300B made a good improvement, see the attached schematic below.
I'm working on another similar SE-OTL amp that will use 6C33Cs, one per channel, and a 6SN7 Broskie Aikido Cascade input/driver stage. I should get it finished and playing next weekend.
As I mentioned in post #10, I don't use TL783s, instead I have Mosfet based current sinks - they're actually from K&K Audio, about halfway down this page;
Other kits – K & K Audio
I'll have a look at the documentation later and advise how much power is being dissipated in the current sink.
If you're two parallel 6C33C tubes with a cathode curent sink you might consider one CCS per 6C33C. I also have a Transcendent 300B SE-OTL and using John Broskie's alternative output arrangement with a CCS (TL783) per 300B made a good improvement, see the attached schematic below.
I'm working on another similar SE-OTL amp that will use 6C33Cs, one per channel, and a 6SN7 Broskie Aikido Cascade input/driver stage. I should get it finished and playing next weekend.
Attachments
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thanks Nautiboy,
the circuit idea is also what i have in mind, but i am concerned about the dissipation in the CCS mosfet, so if i idle my OTL at 300vdc b+, the output node should then be sitting at 1/2 the b+ or 150 volts, and if the tubes dissipated 80 watts at the plates, then i will be dissipating 80 watts also at the CCS....
i am eager to know how you set up yours, an as-built will be nice and what where the problems encountered....
the circuit idea is also what i have in mind, but i am concerned about the dissipation in the CCS mosfet, so if i idle my OTL at 300vdc b+, the output node should then be sitting at 1/2 the b+ or 150 volts, and if the tubes dissipated 80 watts at the plates, then i will be dissipating 80 watts also at the CCS....
i am eager to know how you set up yours, an as-built will be nice and what where the problems encountered....