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Old 26th December 2013, 12:58 AM   #1
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Question PL84 schematic question.

Hey all.

I found this simple schematic online but not sure what is connected to the speaker. Is that a 24k or 2.4k transformer?

Thanks!
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Old 26th December 2013, 01:14 AM   #2
6L6 is offline 6L6  United States
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2.4K makes more sense than 24K...

About 8K is 'right'.
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Old 26th December 2013, 02:13 AM   #3
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2.4k for PL84 is more reasonable. Tube is quite tolerant but 24k is definitely too high.
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Old 26th December 2013, 07:29 AM   #4
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PL84 is NOT an EL84 with 300mA heater.
2.4K is absolutely right.
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Old 26th December 2013, 08:56 AM   #5
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PL84 is an EL86 with a different heater. I've never understood why that is so.
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Old 26th December 2013, 11:35 AM   #6
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Quote:
Originally Posted by barretter View Post
PL84 is an EL86 with a different heater. I've never understood why that is so.
Well, let's try to explain:

In 1953, when the EL84/6BQ5 was developed, not all households in Europe had AC mains power - there still were many DC systems around. So there was some need for AC/DC radios, and thus for a parallel type to the EL84, suitable for lower plate voltages. This type has been called UL84. About 1956 Philips had the idea to bring radios with OTL power stages. Power tubes for AC/DC radios seemed to be suitable for this purpose. But unfortunately the use of the UL84 required a separate 45 V heater winding on the mains transformer. To avoid this, the EL86 has been derived from the UL84 by replacing the heater, as has also been the PL84 for television services in 1955.

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Old 26th December 2013, 02:09 PM   #7
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Quote:
Originally Posted by Kay Pirinha View Post
Well, let's try to explain:

In 1953, when the EL84/6BQ5 was developed, not all households in Europe had AC mains power - there still were many DC systems around. So there was some need for AC/DC radios, and thus for a parallel type to the EL84, suitable for lower plate voltages. This type has been called UL84. About 1956 Philips had the idea to bring radios with OTL power stages. Power tubes for AC/DC radios seemed to be suitable for this purpose. But unfortunately the use of the UL84 required a separate 45 V heater winding on the mains transformer. To avoid this, the EL86 has been derived from the UL84 by replacing the heater, as has also been the PL84 for television services in 1955.

Best regards!
Which begs the question : why did Philips violate its own naming conventions for the UL84? The same is true of the E182CC : I once had the financially punishing experience of inserting one of these into a socket wired for an ECC82 and suffering the loss of a fair amount of money! Season's greetings.
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Old 26th December 2013, 03:15 PM   #8
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PL84/EL86 are ideal for low voltage PP. This is my version. Still only in LTSPICE. Maybe one of my next projects. OT is 2880:8, power 25W, THD at full power 0.73%.
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Old 27th December 2013, 01:13 AM   #9
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I have been experimenting with some UL84/45B5 tubes. They are series heater versions of the EL86/6CW5 type and do work well with 2.5 to 3K ohm OPT's in SE and 2.7 to 3.3K OPT's in P-P amps. Yes 25 watts is easy in P-P.
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Old 27th December 2013, 10:36 AM   #10
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Quote:
Originally Posted by barretter View Post
Which begs the question : why did Philips violate its own naming conventions for the UL84?
From the beginning, i.e. from pre WWII times on, it has been quite usual to name AC/DC power output valves for series heater chains similarly to their parallel heated, but rather different companions. See CL4 vs. AL4, UL12 vs. EL12, UL41 vs. EL41 etc. All of them, besides their maximum plate dissipation, totally different valves, not only regarding their heaters!

Quote:
Originally Posted by tubelab.com View Post
I have been experimenting with some UL84/45B5 tubes. They are series heater versions of the EL86/6CW5 type and do work well with 2.5 to 3K ohm OPT's in SE and 2.7 to 3.3K OPT's in P-P amps. Yes 25 watts is easy in P-P.
Quite right! See this 6CW5 datasheet, page 2!

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