So i was doing some back of the paper calculations and needed a little help. See the pdf. I was thinking of just doing a transformer coupled 12AT7 headphone amp. I was having a bit of trouble with the Turns ratio on the transformer.
Also any comments would be helpful. I know that I have this tube running as hot as possible but I was going to adjust but I was having problems with the transformer ratio.
Also any comments would be helpful. I know that I have this tube running as hot as possible but I was going to adjust but I was having problems with the transformer ratio.
Has anyone made such an amplifier with any success? I was thinking I could get about .42 watts out of it minus transformer losses. Do you think a standard input will be able to drive it just fine? Using the load line a 2 v peak to peak would produce the .42 watts. what about a transformer with a 21.9 TR for that low a wattage?
12AT7 is a terrible choice here. You want the primary impedance of the transformer to be several times higher than the rp of the tube, so if the tube's rp is 11K, the transformer should be ~50K. A 50K OPT is not really possible.
If you want to transformer couple a dual triode, try something like a ECC99, 6H30, 6N6p, 5687, or possible ECC88 instead.
If you want to transformer couple a dual triode, try something like a ECC99, 6H30, 6N6p, 5687, or possible ECC88 instead.
Hello,
I have done several versions of what you are discussing, SET headphone amplifier. The two I liked the best were the 6BX7 and triode connected 6BQ6GTB. The transformer is an impedance matching device the turn ratio will depend on the rp of the tube and headphones. I tried an ElectraPrint 8000 ohm to 300 ohm 3 watt transformer (40ma) and an Edcor 5000 to 300 3 watt transformer.
If you are interested I will look up the Edcor transformer model number. After paying the one custom fee they were about $20 a piece. The B+ voltage does not need to be too high to drive the limited voltage swing required to produce a half a watt output. For a power transformer I used a Triad N 51X isolation transformer.
DT
All just for fun!
I have done several versions of what you are discussing, SET headphone amplifier. The two I liked the best were the 6BX7 and triode connected 6BQ6GTB. The transformer is an impedance matching device the turn ratio will depend on the rp of the tube and headphones. I tried an ElectraPrint 8000 ohm to 300 ohm 3 watt transformer (40ma) and an Edcor 5000 to 300 3 watt transformer.
If you are interested I will look up the Edcor transformer model number. After paying the one custom fee they were about $20 a piece. The B+ voltage does not need to be too high to drive the limited voltage swing required to produce a half a watt output. For a power transformer I used a Triad N 51X isolation transformer.
DT
All just for fun!
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Well I contacted edcor to see if they had a transformer to match what i was looking for. Also if they have the design on the shelf then they get rid of the custom fee (which is about $40) I will see about the 6BX7 and 6BQ6TB. I guess to reduce the primary impedance of the transformer i could also parallel a couple of the 12at7 triodes. Surly they have a transformer with the proper turns ratio. As long as the Tr is correct then it should produce the proper primary impedance.
Would you mind looking up the Edcor part number? Did you perhaps try the 12AT7, the only reason is i ask is I have about a dozen on hand. Thanks for the comments.
Also, why dsavitsk do you say that the primary impedance should be in the 50K range? Did i miss a rule of thumb or something?
Would you mind looking up the Edcor part number? Did you perhaps try the 12AT7, the only reason is i ask is I have about a dozen on hand. Thanks for the comments.
Also, why dsavitsk do you say that the primary impedance should be in the 50K range? Did i miss a rule of thumb or something?
That one. Same reason the plate resistor is 10x rp, or you use a CCS. The higher the load the better. If it is too low, you will get a lot of distortion. But, as I said, it is not really possible to wind a (good) transformer with a 50K primary Z.
Tubes are cheap. The fact that you have some 12AT7's should not limit you to them. You are going to spend hundreds of dollars to save $6 and end up with an amp that performs poorly.
Hello,
Selection of the turn ratio in a SET output transformer is an interesting topic. The discussion for headphones is somewhat different than for the typical speaker application. There are lots of variables and tradeoffs to consider; frequency bandwidth, power output, distortion, output impedance and dampening ratio to name a few. “The higher the better” has some limitations.
The sky is not the limit. Start raising the turn ratio, a couple of things happen. The load line goes flatter and flatter which means that the voltage swings in the primary increase and the current swings diminish. Also a higher turn ratio increases the internal capacitance of the transformer. The combination of the reduced current and increased capacitance results in reduced frequency bandwidth and increased distortion in what remains of the high frequencies.
I do not disagree with the common wisdom of starting at the output and working the design back from there. This method points to picking a triode with an low Plate resistance.
DT
All just for fun!
Selection of the turn ratio in a SET output transformer is an interesting topic. The discussion for headphones is somewhat different than for the typical speaker application. There are lots of variables and tradeoffs to consider; frequency bandwidth, power output, distortion, output impedance and dampening ratio to name a few. “The higher the better” has some limitations.
The sky is not the limit. Start raising the turn ratio, a couple of things happen. The load line goes flatter and flatter which means that the voltage swings in the primary increase and the current swings diminish. Also a higher turn ratio increases the internal capacitance of the transformer. The combination of the reduced current and increased capacitance results in reduced frequency bandwidth and increased distortion in what remains of the high frequencies.
I do not disagree with the common wisdom of starting at the output and working the design back from there. This method points to picking a triode with an low Plate resistance.
DT
All just for fun!
How about using this output transformer with the 5687 tube. EDCOR Electronics Corporation. XSM10K/150 ; the ratio is 8.2 so with a 50 ohm load that gives a 3.3 Kohm primary Looks like I would have to use two tubes in parallel and that transformer to get down to that level of impedance.
I have also seen this design http://www.recordcrate.net/diy/5687/pat5687.gif which is transformer less. Dont know what you guys thoughts are. Also the 5687s are pretty cheap.
I will probably end up using this power transformer on either route. EDCOR Electronics Corporation. XPWR024-120
I have also seen this design http://www.recordcrate.net/diy/5687/pat5687.gif which is transformer less. Dont know what you guys thoughts are. Also the 5687s are pretty cheap.
I will probably end up using this power transformer on either route. EDCOR Electronics Corporation. XPWR024-120
Hello J_Hart_14,
That Edcor XSM10K/150 transformer will need a Parafeed style DC blocking capacitor to let it work. It will work well. SET transformers see the entire plate current of the triode. That transformer is not constructed for B+ to be connected to the primary, only AC.
You might try using that transformer connected to the output of Pat’s Ultimate Preamp.
You may want to run the 5687’s as cathode followers that will reduce the output impedance a lot.
I used a similar Edcor 15K : 600 in series with a 5uf capacitor to connect 300 ohm headphones.
DT
All just for fun!
That Edcor XSM10K/150 transformer will need a Parafeed style DC blocking capacitor to let it work. It will work well. SET transformers see the entire plate current of the triode. That transformer is not constructed for B+ to be connected to the primary, only AC.
You might try using that transformer connected to the output of Pat’s Ultimate Preamp.
You may want to run the 5687’s as cathode followers that will reduce the output impedance a lot.
I used a similar Edcor 15K : 600 in series with a 5uf capacitor to connect 300 ohm headphones.
DT
All just for fun!
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