I used a SPP board from Tubelab and modified it for 6HB6's. I added another board so I could parallel the 6HB6's but then it sat on my bench for nearly a year. I took 2 weeks off over Christmas and built a chassis and cover for it. This is the result.
I used toroidal transformers from Amplimo, at the time the Euro and the dollar weren't to far apart so I bought them for about what Edcor transformers would have cost and amazingly shipping was under $30. The 400mA power transformer fits nicely under the chassis.
I have only listened to it for about a half hour with my shop speakers but I'm pleased with the results.
I still have to clean up the aluminum and a few other details but it looks like the sketch I drew nearly a year ago. Its never going to be perfect like a cnc built chassis but I’m getting older and easier to please. The Japanese have a word for it, Wabi-sabi “beauty that is imperfect and transient.” I'm going to go with that.
I have bought a couple different boards from George at Tubelab, they are first rate.
I used toroidal transformers from Amplimo, at the time the Euro and the dollar weren't to far apart so I bought them for about what Edcor transformers would have cost and amazingly shipping was under $30. The 400mA power transformer fits nicely under the chassis.
I have only listened to it for about a half hour with my shop speakers but I'm pleased with the results.
I still have to clean up the aluminum and a few other details but it looks like the sketch I drew nearly a year ago. Its never going to be perfect like a cnc built chassis but I’m getting older and easier to please. The Japanese have a word for it, Wabi-sabi “beauty that is imperfect and transient.” I'm going to go with that.
I have bought a couple different boards from George at Tubelab, they are first rate.
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doubling the number of output tubes will only slightly boost the output power unless the load impedance is reduced. Twice the number of tubes AND half the load impedance will double the power output.
I did not try quad 6HB6's, but I made a SPP that ran 4 X JJ EL84's in PPP. I also pushed the plate voltage a bit, 430 volts plate, 300 volts on G2. Power? Yes, plenty. How about nearly 60 watts per channel with a 3300 ohm OPT.
The Amplimo 3A524UL has a primary impedance of 3.5k for an 8 ohm secondary.
http://www.amplimo.nl/images/downloads/ds%20vdv/3a524-ul.pdf
This seems to be a good combination of tube and transformer. The transformers have impressive specifications and reasonable cost. The tubes are still a great value at $3, even though many of us caught a previous sale. Am I correct no trace cuts are needed? Although several pins will have to be jumpered. And the screen resistors moved over from pin 9 to pin 8. The picture shows the cathode resistor values have been adjusted. Did you change any other values? I am looking forward to further posts, thank you.
http://www.amplimo.nl/images/downloads/ds%20vdv/3a524-ul.pdf
This seems to be a good combination of tube and transformer. The transformers have impressive specifications and reasonable cost. The tubes are still a great value at $3, even though many of us caught a previous sale. Am I correct no trace cuts are needed? Although several pins will have to be jumpered. And the screen resistors moved over from pin 9 to pin 8. The picture shows the cathode resistor values have been adjusted. Did you change any other values? I am looking forward to further posts, thank you.
You are right, the screen resistor to pin 9 on the board now needs to go to pin 8. I did this by cutting the trace to pin 9 and connecting it to pin 8. The cathode,pin 1, needs to be connected to pin 3 or 9. Pins 3 & 9 are connected internally.
I reduced the cathode resistor to 110 ohms and for now there are 2 110 ohm resistors paralleled for R1 giving me a 55 ohm 10W resistor equivalent. This about 300v B+.
I reduced the cathode resistor to 110 ohms and for now there are 2 110 ohm resistors paralleled for R1 giving me a 55 ohm 10W resistor equivalent. This about 300v B+.
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I made a mistake in my earlier post when I stated the cathode resistor was 110 ohms. I had tried a 110 ohm resistor but whats in the amp now is 150 ohm 6.5 watt resistor.
I did take some measurements and the plate dissipation per tube is approximately 11 watts and plate current is about 39mA.
photo 1 is a 1Khz sine. ch 1 is the input, ch 2 is the output.
photo 2 is a 1Khz square wave. ch 1 is the input, ch 2 is the output.
photo 3 is a 5 Khz square wave. ch 1 is the input ch 2 is the output.
photo 4 is a 500 Hz square wave. ch 1 is the input ch 2 is the output
photo 5 is a 1Khz sine. ch 1 is left, ch 2 is right.
I did take some measurements and the plate dissipation per tube is approximately 11 watts and plate current is about 39mA.
photo 1 is a 1Khz sine. ch 1 is the input, ch 2 is the output.
photo 2 is a 1Khz square wave. ch 1 is the input, ch 2 is the output.
photo 3 is a 5 Khz square wave. ch 1 is the input ch 2 is the output.
photo 4 is a 500 Hz square wave. ch 1 is the input ch 2 is the output
photo 5 is a 1Khz sine. ch 1 is left, ch 2 is right.
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