> 47 globe tubes and want to built a Se amp with these tubes. Now I am looking for the triode data.
Back when they were writing datasheets for the '47, you could buy a perfectly good power triode and socket for less than the cost of a '47 and its odd/new 5-pin socket, so they didn't bother to measure the triode curves. Maybe someone has measured a '47 in triode; good luck finding that data.
We can do some guess-work from the pentode curves. We know the triode curves intersect the pentode curves where plate voltage equals the G2 voltage. In the published curves, G2 is held at 250V, so we know the triode grid current and plate current at that voltage.
There are two simple approximations for triode plate curves. We can assume they all point to the origin, or we can assume the zero-bias curve is slightly curved to intersect the origin and the others are parallel. For most real triodes, the truth is in between these two simplifications.
We should also plot the limiting ratings. Both plate and G2 are 250V max. There is no plate dissipation rating, but the "typical" condition is usually about as much as the tube can stand, and it is 7 or 8 watts plate dissipation.
In attachment: Published pentode curves black, my approximated triode curves in red, 7.5W and 250V in yellow.
The blue line is a possible load-line. Using straight-line approximate triode curves, the power is about 3/4 watt and the THD is high. Using bent triode curves, THD is lower, but power before clipping will not be a lot higher. Maybe a Watt at 10% 2nd harmonic.
As pentode: 2.7 Watts; as triode, estimated 0.5 to 1.0 watts. Is this reasonable? A quarter the power by going triode? Look at 6L6: 5 or 10 watts pentode, 1.4 watts triode. 6L6GC can do a lot better than 1.4 watts triode because it is allowed a high plate+G2 voltage. But we should not run more than 250V-275V on irreplaceable globe '47s.
Back when they were writing datasheets for the '47, you could buy a perfectly good power triode and socket for less than the cost of a '47 and its odd/new 5-pin socket, so they didn't bother to measure the triode curves. Maybe someone has measured a '47 in triode; good luck finding that data.
We can do some guess-work from the pentode curves. We know the triode curves intersect the pentode curves where plate voltage equals the G2 voltage. In the published curves, G2 is held at 250V, so we know the triode grid current and plate current at that voltage.
There are two simple approximations for triode plate curves. We can assume they all point to the origin, or we can assume the zero-bias curve is slightly curved to intersect the origin and the others are parallel. For most real triodes, the truth is in between these two simplifications.
We should also plot the limiting ratings. Both plate and G2 are 250V max. There is no plate dissipation rating, but the "typical" condition is usually about as much as the tube can stand, and it is 7 or 8 watts plate dissipation.
In attachment: Published pentode curves black, my approximated triode curves in red, 7.5W and 250V in yellow.
The blue line is a possible load-line. Using straight-line approximate triode curves, the power is about 3/4 watt and the THD is high. Using bent triode curves, THD is lower, but power before clipping will not be a lot higher. Maybe a Watt at 10% 2nd harmonic.
As pentode: 2.7 Watts; as triode, estimated 0.5 to 1.0 watts. Is this reasonable? A quarter the power by going triode? Look at 6L6: 5 or 10 watts pentode, 1.4 watts triode. 6L6GC can do a lot better than 1.4 watts triode because it is allowed a high plate+G2 voltage. But we should not run more than 250V-275V on irreplaceable globe '47s.
Attachments
47 triode data
I found this link with triode data of the 47 Penthode
http://homepage2.nifty.com/Kame/47syu.htm
I found this link with triode data of the 47 Penthode
http://homepage2.nifty.com/Kame/47syu.htm
I have a single ended amplifier with 6SJ7 & 45 tube. I decided to replace the 45 with 47 tube because I am fancy with the beautiful look of the 47.
Based on the 47's data sheet, I took the reference of Vg @ 16V and 500 ohm cathode resistor for self bias. I use the LL2766 50mA output transformer configured for 6K to 8 ohm.
After the replacement work is done, I tuned the 6SJ7 bias to lower the THD at 0.5Wrms.
There's an issue when the output power gets to 1 watt, the lower peak got clipped. I found the clipping is caused by the driving voltage to the 47 tube grid is clipped when it goes above cathode bias voltage. That is : the 47 tube grid is driven to positive region.
I put it in system for audition. It sounds nice but not smooth as other amplifiers that I have. I can't find any data for the plate resistance of the 47 tube in triode mode. I then try to find way to measure it. I found a way to make the measurement. The Ra of 47 is measured at 3.9K. Then, I changed the tapping of the LL2766 OPT for 12K to 8 ohm and fine tune the THD to minimal. It seems this new configuration better match the 47 tube. Now the 47 amp sounds a lot better and right to my ears.
Even though the output power is so small, it sounds big and strong that impressed me.
Johnny
facebook : vanccouverdiyaudio
Based on the 47's data sheet, I took the reference of Vg @ 16V and 500 ohm cathode resistor for self bias. I use the LL2766 50mA output transformer configured for 6K to 8 ohm.
After the replacement work is done, I tuned the 6SJ7 bias to lower the THD at 0.5Wrms.
There's an issue when the output power gets to 1 watt, the lower peak got clipped. I found the clipping is caused by the driving voltage to the 47 tube grid is clipped when it goes above cathode bias voltage. That is : the 47 tube grid is driven to positive region.
I put it in system for audition. It sounds nice but not smooth as other amplifiers that I have. I can't find any data for the plate resistance of the 47 tube in triode mode. I then try to find way to measure it. I found a way to make the measurement. The Ra of 47 is measured at 3.9K. Then, I changed the tapping of the LL2766 OPT for 12K to 8 ohm and fine tune the THD to minimal. It seems this new configuration better match the 47 tube. Now the 47 amp sounds a lot better and right to my ears.
Even though the output power is so small, it sounds big and strong that impressed me.
Johnny
facebook : vanccouverdiyaudio
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