If you buy toroidals from Toroidy or Plitron you can get SE transformers (think $400+), but to use non-gapped power transformers for OPTs you need to balance the current. You could make a SE amp with a dummy load on one half of the transformer, but your efficiency will be halved. In reality it would be less expensive to build a push pull amp with substantially more output power.
If you want to go for maximum power, then an EL34 operating as a pentode is what you want.
An amp with a triode/pentode switch will be severely compromised with at least one of the two positions (maybe both!). There are no mains transformers suitable for single ended tube applications; they will all saturate.
The $20 Edcor single ended transformers will be good enough to mess around with on a piece of plywood.
An amp with a triode/pentode switch will be severely compromised with at least one of the two positions (maybe both!). There are no mains transformers suitable for single ended tube applications; they will all saturate.
The $20 Edcor single ended transformers will be good enough to mess around with on a piece of plywood.
I did read about a technique where you run an opposing DC current in a secondary.
For the ease of numbers say you have a B+ of 100V and the tube is biased at 100ma. If the power transformer has two 10V secondaries, you can run 1A through one to counteract the DC from the primary, and the speaker to the other. Seems like a pain in the butt to get right, but a neat idea none the less.
For the ease of numbers say you have a B+ of 100V and the tube is biased at 100ma. If the power transformer has two 10V secondaries, you can run 1A through one to counteract the DC from the primary, and the speaker to the other. Seems like a pain in the butt to get right, but a neat idea none the less.
Update: I have calculated and wound and output transformer for one EL34. I have disassembled the mains tranny and ať an rebuilded the core, so its air gap in it. I have 525 turns on a primary and 25 turns on secondary side. 213 turns of primary, then a srcondary and another half of primary.
How did you come up with the number of turns?
I'm by no means a transformer designer, but I have a feeling that these may not be enough turns for the required inductance (and therefore bass).
How big is your airgap?
I'm by no means a transformer designer, but I have a feeling that these may not be enough turns for the required inductance (and therefore bass).
How big is your airgap?
Impedance ratio is voltage ratio squared. So, el34 has impedance is 3k, impedance of my speaker is 4 ohms, so 3000/4 = 750, then unsquare of 750 is 21 and this is the turns ratio which I need. So, for every 210 primary turns I also wind 10 turns of secondary. And this is all I must know, then Ive mhltiplied and multiplied. I chosen 525 turns because I didnt know, how much turns I can wind on a transformer bobbin. Finally, it was ok, the bobbin was fillet to about 80%. My air gap is about 0.3mm maybe little bit less.
This depends on the operating voltage and current. Practically any value from 3k to 5k is fine for triode connected EL34. Higher impedance gives a little less power, but essentially lower THD.
Yeah, I know, I have tesla datasheet. With 300V anode voltage the el34 will have impedance 3 kiloohm.
Pardon me, but sqrt 750 = 27.4!
Anyway, your chosen number of turns seems a bit low to me, too.
Best regards!
Sorry, I made a mistake: thank you for correction; I have on the primary about 160 turns less. But its still ok, now I have smaller ratio of the tranny, so output impedance is not 4 ohms, but it raised to about 6 ohms (i didnt calculated it). So if I use 4 ohm speaker, it will still be OK. Speakers dont have constantly 4 ohm impedance, but its little bit higher.
No. The internal impedance of the triode EL34 will be closer to 1000 Ohms.
There are some texts on audio transformer design that you could read through.
But internal resistance of the tube doesnt matter. The output transformer will be connected in anode, so I must know anode impedance and that is 3k. Or no? EL34 has internal resistance 1k, and 6P3SE has this value 65k, and these tubes are equivalent (its something between el34 and 6l6). If this isnt true, I couldnt connect 6p3se to amp designed for el34.
As audiowise suggested, please read some texts on output transformers... Of course, the internal resistance of the tube matters, besides, the 65k value you quoted is for the pentode, not the triode connection.
Thanks for inform. At this price level power Toroidals are not viable as OPTs, as a second class solution it should be cheap. An Hammond OPT EI 5kg 30W is around $150USD.
Check again... Toroidy's SE OPT's are not that expensive: TTG-EL84SE - Tube output UL transformer [5kOhm] EL84 / 6V6 SE - Shop Toroidy.pl , so about $80.
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