| Author |
Message |
EC
Guest
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 Posted:
Thu Jan 20, 2005 9:10 pm Post subject:
Re: 25L6 for hi-fi? |
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| Quote: | I generally don't like the idea of line-op stuff,cause it's kind of
dangerous.(if something is mis-wired,amp,outlet,housewiring)
The speaker outputs are isolated with the OPT's,but the inputs and
chassis aren't.
If the amp gets plugged in the outlet with the plug reversed,it could
end up with 120vac between it,and the chassis of the CD player (or
whatever) below it.(RCA cables have been known to go up in smoke,the
shield gets shorted across the mains!...Tim?..don't feel bad,I did it
once too!) Not a happy feeling if/when you become the current
path,instead of the interconnect cable...
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There is a decent sized power transformer on top of the chassis.
There's 12AX7's and assorted other 6V tubes for the AM/FM section,
so I think there's a good chance there's 25V taps on the PT. I
also don't like the idea of line driven series-heaters for the
25L6GT's.
I'm assuming the OT's are underneath. I also should have taken
note of the rectifier.
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robert casey
Guest
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| Posted:
Fri Jan 21, 2005 1:45 am Post subject:
Re: 25L6 for hi-fi? |
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| Quote: | There's 12AX7's and assorted other 6V tubes for the AM/FM section,
so I think there's a good chance there's 25V taps on the PT. I
also don't like the idea of line driven series-heaters for the
25L6GT's.
A 25V transformer from Rat Shack (one of the few |
usable things they still sell) can run the heaters.
Connect the centertap to a DC source of around 30V,
this reduces hum getting into the cathodes some.
This also avoids having one of the 25L6's heater
having about 100V AC on it. Less of this whopping big
hum source nearby grid circuits to hum the audio. |
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John Byrns
Guest
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| Posted:
Fri Jan 21, 2005 2:33 am Post subject:
Re: 25L6 for hi-fi? |
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In article <zLUHd.2057$cZ1.387@newsread2.news.atl.earthlink.net>, robert
casey <wa2ise@ix.netcom.com> wrote:
| Quote: | There's 12AX7's and assorted other 6V tubes for the AM/FM section,
so I think there's a good chance there's 25V taps on the PT. I
also don't like the idea of line driven series-heaters for the
25L6GT's.
A 25V transformer from Rat Shack (one of the few
usable things they still sell) can run the heaters.
Connect the centertap to a DC source of around 30V,
this reduces hum getting into the cathodes some.
This also avoids having one of the 25L6's heater
having about 100V AC on it. Less of this whopping big
hum source nearby grid circuits to hum the audio.
|
Hum from the heater wiring, even at 100V AC, is not a problem for the
25L6s, unless maybe the wiring is very poorly done indeed. Hum can be a
problem with the heater wiring for the driver tubes, but careful layout
and wiring minimizes this. Another possible approach would be to power
the heaters of the low level stages with DC from the cathode circuit of
the 25L6s.
Regards,
John Byrns
Surf my web pages at, http://users.rcn.com/jbyrns/ |
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ptaylor
Guest
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| Posted:
Fri Jan 21, 2005 3:47 pm Post subject:
Re: 25L6 for hi-fi? |
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John Byrns wrote:
| Quote: | In article <zLUHd.2057$cZ1.387@newsread2.news.atl.earthlink.net>, robert
casey <wa2ise@ix.netcom.com> wrote:
There's 12AX7's and assorted other 6V tubes for the AM/FM section,
so I think there's a good chance there's 25V taps on the PT. I
also don't like the idea of line driven series-heaters for the
25L6GT's.
A 25V transformer from Rat Shack (one of the few
usable things they still sell) can run the heaters.
Connect the centertap to a DC source of around 30V,
this reduces hum getting into the cathodes some.
This also avoids having one of the 25L6's heater
having about 100V AC on it. Less of this whopping big
hum source nearby grid circuits to hum the audio.
Hum from the heater wiring, even at 100V AC, is not a problem for the
25L6s, unless maybe the wiring is very poorly done indeed. Hum can be a
problem with the heater wiring for the driver tubes, but careful layout
and wiring minimizes this. Another possible approach would be to power
the heaters of the low level stages with DC from the cathode circuit of
the 25L6s.
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A friend has a Bell 6060 that I worked on,which uses the cathode current
of the 4x EL34's to heat the small signal tubes (12AX7's).
Schematic at: http://www.users.qwest.net/~ptaylor/Audio/Bell6060B1.gif
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