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Old 22nd May 2011, 04:43 PM   #1
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Default I have 4 Pl504's. Are they best used as SE or PP ?

I have 4 PL 504's . Are they better used as SE or in a PP scheme. What is a realistic output I can get from them in PP ?
Are they as good as EL84's or better ?
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Old 22nd May 2011, 05:05 PM   #2
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They are best used in TV sets as line output in the horizontal deflection amplifier or other switching applications. These tubes weren't build to match each other instead they should be able to withstand high voltage transients (off-switch spike from line transformer). This results in horrible differences not only in static parameters (bias), but particular in different gm. When G2-driven you don't have to worry about that BTW, since the G1 has far less distance to the cathode than the G2.
So far so good...

SE sounds horrible, I can't say anything to PP. Maybe you could try triode operation.

Your last sentence is..well..let me answer it this way:
In a lovely operating deflection amp (steep slope, high current delivery), a PL504 is better. In a lovely sounding audio amp (linear, few harmonic distortion), a EL84 is better. Simply because these tubes were made for a specific reason
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Old 22nd May 2011, 07:49 PM   #3
DF96 is offline DF96  England
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For conventional g1 drive they will be rather non-linear so PP would be best as you will get some cancellation of even-order distortion. G2 drive might linearise them enough that SE could work.
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Old 22nd May 2011, 08:38 PM   #4
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Another option I see is a circlotron.
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Old 22nd May 2011, 10:37 PM   #5
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Quote:
Originally Posted by the_manta View Post
They are best used in TV sets as line output in the horizontal deflection amplifier or other switching applications. These tubes weren't build to match each other instead they should be able to withstand high voltage transients (off-switch spike from line transformer). This results in horrible differences not only in static parameters (bias), but particular in different gm. When G2-driven you don't have to worry about that BTW, since the G1 has far less distance to the cathode than the G2.
So far so good...

SE sounds horrible, I can't say anything to PP. Maybe you could try triode operation.

Your last sentence is..well..let me answer it this way:
In a lovely operating deflection amp (steep slope, high current delivery), a PL504 is better. In a lovely sounding audio amp (linear, few harmonic distortion), a EL84 is better. Simply because these tubes were made for a specific reason
Nevertheless, TV horizontal line output tubes were used in some commercial amplifiers (BOGEN DB130 , SANSUI , ...) and many OTL amp's. Low maximal screen voltage and poor linearity are the main limiting factors. There are many better choices unless you're trying to build a lousy sounding P.A amp.
Used in S.E mode, PL504's will very likely sound terrible and I would not even consider this option for any good quality amp.
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Old 22nd May 2011, 10:49 PM   #6
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Some Cinema amplifiers used the forerunner of the PL504, the PL36.....

PL36 has a worse reputation than PL504 from what I gather....
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Old 22nd May 2011, 10:59 PM   #7
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Quote:
Originally Posted by Alastair E View Post
Some Cinema amplifiers used the forerunner of the PL504, the PL36.....

PL36 has a worse reputation than PL504 from what I gather....
I remember I had a SANSUI SM-80 receiver who used a pair of PL36/25E5 in its ouput stage in Ab1 PP for about 30W ouput power. Whatever I did (parts replacement,upgrades,etc...) it still sounded terrible and I finally gave up. PL504's are more powerful but certainly not better in audio applications. To be avoided.
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Old 23rd May 2011, 02:01 AM   #8
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Thanks for the replies. Looks like it isn't worth spending time and money on the 504. I have some EL84's too ! But since I have the 504's I thought I might as well try to do something with it. I'll try to see what it sounds like in triode mode if it doesn't take too much time.

I guess the PL509's ( which I do not have ) were better ?
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Old 23rd May 2011, 05:15 AM   #9
AJT is offline AJT  Philippines
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PL504 - EL504 15 watt ~ AUDIO DESIGN
Impedans of trafo for EL504 inSE
Transformadores
http://edonion.com/documents/EdonionSpeedy.pdf
Unity coupled circuit amplifier.

enjoy....
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Old 23rd May 2011, 06:45 AM   #10
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Thanks Tony. I will explore this further. Apparently it can sound decent. I will know for sure only if I try it ! Since all parts will be different from other designs the only way to say how good will be by building one.
OP trafo is the only (big!) issue for me though I seem to have a way out of that one.
Thanks.
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