Gents,
I'm willing to build a new amp, using the following valves: 2xPL504, 3 (or is it 4?)EL84, 1xECC83, 1xECC88.
Now, regarding the PL504, here are the circuit values i have computed, due to very little info/use of this tube on the net:
Triode connection (very linear!)
B+=125V
Iidle=150mA
Grid bias= -20V
Rload=800 Ohm
With these values i estimate 1,29W of power output at around 4,5% 2nd order distortion.
My problem with these little current beasts is exactly that - one SE output tranny to handle 125mA of current at idle (it peaks around 200~230mA) and not be the size of a living room. PP would be also considered, but i still haven't learned on how to do it/caculate it :/
EL84... a SE amp would be nice too, but again, more expensive and harder to find. The "Compact 6W" is being considered at the moment.
So here comes a question: how do i choose the plate resistor for a parafeed amp? Either that or SSCCS loading - but i haven't found one that sources 200mA! I've read almost all posts regarding parafeed on this forum, searched all over the net, but couldn't find an answer! Choke loading is a bit out of the question because of it's size.
I have a 230/230V 300W tranny, so power dissipation isn't a problem . Of course, a simpler lower wattage isolation tranny is also found nicelly.
Any input would be greatly appreciatted
Thank you
I'm willing to build a new amp, using the following valves: 2xPL504, 3 (or is it 4?)EL84, 1xECC83, 1xECC88.
Now, regarding the PL504, here are the circuit values i have computed, due to very little info/use of this tube on the net:
Triode connection (very linear!)
B+=125V
Iidle=150mA
Grid bias= -20V
Rload=800 Ohm
With these values i estimate 1,29W of power output at around 4,5% 2nd order distortion.
My problem with these little current beasts is exactly that - one SE output tranny to handle 125mA of current at idle (it peaks around 200~230mA) and not be the size of a living room. PP would be also considered, but i still haven't learned on how to do it/caculate it :/
EL84... a SE amp would be nice too, but again, more expensive and harder to find. The "Compact 6W" is being considered at the moment.
So here comes a question: how do i choose the plate resistor for a parafeed amp? Either that or SSCCS loading - but i haven't found one that sources 200mA! I've read almost all posts regarding parafeed on this forum, searched all over the net, but couldn't find an answer! Choke loading is a bit out of the question because of it's size.
I have a 230/230V 300W tranny, so power dissipation isn't a problem . Of course, a simpler lower wattage isolation tranny is also found nicelly.
Any input would be greatly appreciatted
Thank you
Hi Simpleton,
Estimating Po up 1/100 Watt precision and H2 to 1/10% precision certainly requires extremely sharp eyes and precise rulers (among lots of other factors to consider) to measure out loadlines drawn on plate curves of extreme precision
If you have the triode strapped plate curves of E/PL504 at hand, I would be most interested to have a look at them (I am maintaining a small collection of such triode strapped pentode/tetode curves on my homepage).
Tom
Triode connection (very linear!)
B+=125V
Iidle=150mA
Grid bias= -20V
Rload=800 Ohm
With these values i estimate 1,29W of power output at around 4,5% 2nd order distortion.
Estimating Po up 1/100 Watt precision and H2 to 1/10% precision certainly requires extremely sharp eyes and precise rulers (among lots of other factors to consider) to measure out loadlines drawn on plate curves of extreme precision
If you have the triode strapped plate curves of E/PL504 at hand, I would be most interested to have a look at them (I am maintaining a small collection of such triode strapped pentode/tetode curves on my homepage).
Tom
Let's just say my printer is very good
Here is the datasheet with the curves:
http://www.mif.pg.gda.pl/homepages/frank/sheets/010/p/PL504.pdf
Dave, i've read that page before (maybe not with the maximum attention), but i still can't figure it out very good. I admit i'm a dunce...
I'll give it another read tomorrow, thanks.
Here is the datasheet with the curves:
http://www.mif.pg.gda.pl/homepages/frank/sheets/010/p/PL504.pdf
Dave, i've read that page before (maybe not with the maximum attention), but i still can't figure it out very good. I admit i'm a dunce...
I'll give it another read tomorrow, thanks.
Here is the datasheet with the curves:
http://www.mif.pg.gda.pl/homepages/frank/sheets/010/p/PL504.pdf
Excellent pointer, thank you very much!
Tom
Think of building it as a SEPP with another PL504 as the triode load. Otherwise as you say the SSCCS could be a little tricky. The DIYAUDIO CCS popularised by SY could be configured to do duty. Finding a transistor capable of delivering 200mA with 150V across it shouldn't be to difficult, though heatsinking it might be (25w of transistor heat ).
Shoog
Shoog
Simpleton said:i've read that page before (maybe not with the maximum attention), but i still can't figure it out very good. I admit i'm a dunce...:
The main thing i got from that is that if you use a CCS or an R as a load instead of a choke is that you need a lot more B+...
dave
If you used the PL504 as a SEPP you could configure the top PL504 as a Pentode. Because the Pentode will act more like a CCS this will simplify the tuning of the circuit. Also creating a good screen supply at such low voltages should be relatively simple. If doing this I wouldn't try it as a MU-follower, because the speaker load will effect linearity more than if taken from the anode of the triode. Because the output load is so small, excellent results can be achieved with using mains Power toroidals as output transformers. I have built a similar circuit and they sound good. This is definately the way I would go.
Shoog
Shoog
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