| Author |
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Fox
Guest
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 Posted:
Wed Dec 22, 2004 1:38 pm Post subject:
fixed bias EL84 |
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Hi
Can anyone suggest a ruff fixed bias voltage for a pair of EL84 in push pull
ultralinear connection, HT 300V, I'm thinking between -20/-24V but I aint
sure.
cheers
Fox
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Ned Carlson
Guest
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| Posted:
Wed Dec 22, 2004 2:17 pm Post subject:
Re: fixed bias EL84 |
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On Wed, 22 Dec 2004 08:38:04 +0000, Fox wrote:
| Quote: | Hi
Can anyone suggest a ruff fixed bias voltage for a pair of EL84 in push
pull ultralinear connection, HT 300V, I'm thinking between -20/-24V but I
aint sure.
cheers
Fox
|
That sounds like too much, but that's besides the point.
You should be biasing for cathode current, given the
voltage, something like 30-40 ma per tube. I'd go for as
little as possible that doesn't affect the sound quality.
--
Ned Carlson Triode Electronics Chicago,IL USA
www.triodeelectronics.com |
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JamesG
Guest
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| Posted:
Wed Dec 22, 2004 10:32 pm Post subject:
Re: fixed bias EL84 |
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I am running some EL-84s under those same conditions (ultralinear at 300V
regulated plate voltage). I am running them between 35-40mA per tube
(Cathode current measured across a 1 ohm sensor resistor) depending on
whether I am running them at fixed bias or cathode bias (I built the amp so
it is selectable). I don't remember the voltage offhand, but -20-24 V sounds
high.
"Ned Carlson" <postmaster@triodeel.com> wrote in message
news:pan.2004.12.22.09.14.28.248583@triodeel.com...
| Quote: | On Wed, 22 Dec 2004 08:38:04 +0000, Fox wrote:
Hi
Can anyone suggest a ruff fixed bias voltage for a pair of EL84 in push
pull ultralinear connection, HT 300V, I'm thinking between -20/-24V but I
aint sure.
cheers
Fox
That sounds like too much, but that's besides the point.
You should be biasing for cathode current, given the
voltage, something like 30-40 ma per tube. I'd go for as
little as possible that doesn't affect the sound quality.
--
Ned Carlson Triode Electronics Chicago,IL USA
www.triodeelectronics.com
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Sander deWaal
Guest
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| Posted:
Wed Dec 22, 2004 10:39 pm Post subject:
Re: fixed bias EL84 |
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"JamesG" <georglab@uabcvsr2.cvsr.uab.edu> said:
| Quote: | I am running some EL-84s under those same conditions (ultralinear at 300V
regulated plate voltage). I am running them between 35-40mA per tube
(Cathode current measured across a 1 ohm sensor resistor) depending on
whether I am running them at fixed bias or cathode bias (I built the amp so
it is selectable). I don't remember the voltage offhand, but -20-24 V sounds
high.
|
It would be more like 12...14 volts for AB operation @ 300V.
--
Sander de Waal
" SOA of a KT88? Sufficient. " |
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Fox
Guest
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| Posted:
Thu Dec 23, 2004 1:52 am Post subject:
Re: fixed bias EL84 |
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Ok thnx I just needed a ball park figure to choose a voltage reg from, then
adjust from there.
cheers
Fox
"
| Quote: | I am running some EL-84s under those same conditions (ultralinear at 300V
regulated plate voltage). I am running them between 35-40mA per tube
(Cathode current measured across a 1 ohm sensor resistor) depending on
whether I am running them at fixed bias or cathode bias (I built the amp
so
it is selectable). I don't remember the voltage offhand, but -20-24 V
sounds
high.
It would be more like 12...14 volts for AB operation @ 300V.
--
Sander de Waal
" SOA of a KT88? Sufficient. " |
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Wbittle
Guest
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| Posted:
Sun Dec 26, 2004 3:49 am Post subject:
Re: fixed bias EL84 |
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Hi,
That is going to be a bit high. If your fixed bias circuit is such
that it is adjustable, start at -15 volts and see how it reads with
respect to current. If your B+ is 300 volts, you would not want to go
over 40 ma per tube or you will start to exceed the tube's maximum plate
dissipation in watts. I'd suggest setting your mid point for your bias
supply at -15 volts with a +- adjustment of 5 volts either way. Install
a set of 10 ohm resistors between the cathode of each tube and ground.
Look for no more then .4 volts across each resistor. Adjust your bias
voltage to get this reading. At 300 volts, I'm betting your proper bias
will be close to -15 volts.
Bill B.
Fox wrote:
| Quote: | Hi
Can anyone suggest a ruff fixed bias voltage for a pair of EL84 in push pull
ultralinear connection, HT 300V, I'm thinking between -20/-24V but I aint
sure.
cheers
Fox
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