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Old 7th March 2015, 02:37 AM   #1
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Default Simple Se build, Which tube?

Hi all,

I have a pair of 10 watt 5k outputs on my shelf and am looking to build an SE amp to utilise them.

Tubes I have in my stash,

Westinghouse 807
Pl500 sweep tube
El33 mini watts
Mini watt el84 ( parallel Se?)

I want to use the tube that will give the most power, I want the 807, but it's screen voltage is only 300 max vs its 750v plate voltage.
Would a triode connected 807 output more at 600V with a 5-6k load in triode mode than it would at 300v pentode mode?

Or am I better to go for the pl500?

Thanks in advance for your help

Mike
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Old 7th March 2015, 06:24 AM   #2
Svein_B is offline Svein_B  Norway
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A couple of 5W resistors and an electrolytic cap will make a suitable voltage divider for the 807 screen voltage (eg. 10K / 33K , 470uF)

SB
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Old 7th March 2015, 07:47 AM   #3
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Look at this tread (post 8).
Question about 6P31S

That circuit can be directly used with PL500.
Does your OPTs have UL-taps ?
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Old 7th March 2015, 10:17 AM   #4
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Thanks for the replies,

Yes they do have screen taps...
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Old 7th March 2015, 11:55 AM   #5
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Then I recommend you to also try ul-circuit, not only triode.
I have got very good results with ul-connected 6P31S (=EL500) SE-amp.
Higher power, same linearity and almost as low output impedance as with triode.
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Old 7th March 2015, 09:58 PM   #6
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Artosalso, I like your circuit, thank you for sharing it with me, it says that you measured distortion at 3W. Is this the maximum output possible from a pl500?



Quote:
Originally Posted by artosalo View Post
Look at this tread (post 8).
Question about 6P31S

That circuit can be directly used with PL500.
Does your OPTs have UL-taps ?
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Old 8th March 2015, 07:21 AM   #7
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With PL500 some 4 W to 5 W is maximum depending if the circuit is triode connected or UL.
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Old 8th March 2015, 09:01 PM   #8
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Thanks a lot.
Will try the 807 first as this has a plate dissipation of 24w, which should deliver the 10w I'm after in Se mode.

Will try the pl500 if I have issues

Thanks again!

Quote:
Originally Posted by artosalo View Post
With PL500 some 4 W to 5 W is maximum depending if the circuit is triode connected or UL.
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Old 8th March 2015, 09:54 PM   #9
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Quote:
Originally Posted by preludefan View Post
Artosalso, I like your circuit, thank you for sharing it with me, it says that you measured distortion at 3W. Is this the maximum output possible from a pl500?
I am a "signal capacitor" hater!
There are so many capacitors in the signal path for my liking. I have counted four! not counting PSU caps (some consider those to be in signal path too).
The first 1uF can be replaced with a few kilo-ohm resistor.
Use the best 220nF you can afford, I like paper in oils.
For the larger electrolytic ones, use quality caps, at least nichicon fine gold or better.
Also for the pot, 100K 220K and 680R use low noise resistors, to get minimum hiss.
Good luck.
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Old 9th March 2015, 06:24 AM   #10
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807 will produce some 8...10 W when pentode connected, but THD will be about 10 %.
As a triode or UL the output power will be essentially smaller, but THD still relatively high.

The input capacitor can be excluded if the signal source is producing no DC to output.

Power supply and filtering capacitors are naturally in the signal path.
How the signal (AC) current could flow otherwise ?
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