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Old 23rd February 2004, 10:20 PM   #1
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Default El509 Plate current question

Hello,
How many plate current of EL509 when bias at -40V?

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Old 24th February 2004, 01:43 AM   #2
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Hi,

Quote:
How many plate current of EL509 when bias at -40V?
Depends...What's the anode load and voltage?

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Old 24th February 2004, 04:15 AM   #3
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You been playin with too many triodes... what about screen?

Tim
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Old 24th February 2004, 01:10 PM   #4
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Sorry.
Plate voltage is 170V and screen connect to anode through 100ohm resistor.(same as Bruce T8 OTL config)

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Old 25th February 2004, 12:54 AM   #5
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Under those conditions a real El509 should show about 40-45mA idle current.
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Old 25th February 2004, 01:18 AM   #6
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Hi,

Quote:
Under those conditions a real El509 should show about 40-45mA idle current.
The T8 OTL amps' output stage is run icecold so to speak:

From their website:

Quote:
The output stage is a low heat, class AB type. It is biased to run with as low an idle current as possible.
Maybe the exact figure is given in B.R.s' book ?

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Old 25th February 2004, 02:04 AM   #7
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Amazingly enough, I have the book. And I don't think it says what typical currents would be. There will be variation for sure, but I think 40mA is a good ballpark number. The T8s are AB, but mostly B.
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Old 25th February 2004, 02:07 AM   #8
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Default MINDBOGGLING...

Hi,

Wow...Are you reading my mind or what?

As it happens I was busy reading your replies to arthur on the Transcendent forum:

Quote:
However, in AB mode, where the operating point is very low(~40mA idle current per tube in the T8), during each power cycle, one set of tubes is completely cut off because their grids are going very negative driving the current to zero quickly and providing no current sinking for the load. Therefore, the only current into load comes from the conducting tubes and so the maximum load current is whatever the conducting tubes can provide (assuming they can also make the voltage necessary). In this case, a little over 4A for 4 real EL509s in parallel.
Talk about coincidence...

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Old 25th February 2004, 09:50 AM   #9
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My friend have a El509 tester (same config as Bruce amp).

I tested 40 tubes, most of them showing 80mA - 130mA at -40V bias, around 7 tubes showing 40mA - 79mA, few tubes showing >130mA.

Is it my El509 not real El509?

I selected the tubes showing 80mA - 130mA in my T8 amp.

Comment, please.

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Old 25th February 2004, 11:01 PM   #10
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these numbers are higher that the few el509s that i've played with, but given normal variation, they don't seem unreasonable.

I think your selection of tubes for the T8s is a good way to choose.
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