| Author |
Message |
mitch
Guest
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 Posted:
Mon Dec 27, 2004 5:14 am Post subject:
Stromberg Carlson Stereo 8 - Balance setting |
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I have an old integrated amp and I'd like to set the balance of the
output stage(s). I think that I have to measure the voltage across a
particular resistor, and rotate the pot until it reaches zero. Is
anyone familiar with how to correctly set it?
Does anyone know if the schematic available on-line? They stuck a copy
to the inside surface of the chassis base plate, which is kind of
inconvenient.
thanks
Mitc h
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shiva
Guest
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| Posted:
Mon Dec 27, 2004 11:25 pm Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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"mitch" <mbillianNoSpam@verizon.net> wrote in message
news:UtIzd.18083$rL3.984@trnddc03...
| Quote: | I have an old integrated amp and I'd like to set the balance of the
output stage(s). I think that I have to measure the voltage across a
particular resistor, and rotate the pot until it reaches zero. Is
anyone familiar with how to correctly set it?
Does anyone know if the schematic available on-line? They stuck a copy
to the inside surface of the chassis base plate, which is kind of
inconvenient.
|
No, but if you unscrew the bottom plate & put it on a scanner or a Xerox
machine, you'll have the schematics. It's actually lucky to get gear with
schematics in it, 'coz you never run into "but wait, R1706 is *not* 220k!" -
it's always the right revision. Anyhow, don't you usually have the cover
off anyway, when you're working on the thing?
-dim
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mitch
Guest
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| Posted:
Tue Dec 28, 2004 5:42 am Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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shiva wrote:
| Quote: | "mitch" <mbillianNoSpam@verizon.net> wrote in message
news:UtIzd.18083$rL3.984@trnddc03...
I have an old integrated amp and I'd like to set the balance of the
output stage(s). I think that I have to measure the voltage across a
particular resistor, and rotate the pot until it reaches zero. Is
anyone familiar with how to correctly set it?
Does anyone know if the schematic available on-line? They stuck a copy
to the inside surface of the chassis base plate, which is kind of
inconvenient.
No, but if you unscrew the bottom plate & put it on a scanner or a Xerox
machine, you'll have the schematics. It's actually lucky to get gear with
schematics in it, 'coz you never run into "but wait, R1706 is *not* 220k!" -
it's always the right revision. Anyhow, don't you usually have the cover
off anyway, when you're working on the thing?
-dim
thanks
Mitc h
Yea, I guess you're right. |
thanks
Mitch |
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Ian Iveson
Guest
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| Posted:
Wed Dec 29, 2004 6:02 am Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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"mitch" <mbillianNoSpam@verizon.net> wrote
| Quote: | I have an old integrated amp and I'd like to set the balance of the
output stage(s). I think that I have to measure the voltage
across a particular resistor, and rotate the pot until it reaches
zero. Is anyone familiar with how to correctly set it?
No, but if there are two output valves in PP, and there are |
resistors of same value between cathodes and ground, then set the DC
balance pot such that there is 0V between cathodes. That ensures
equal current through each output valve.
cheers, Ian |
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Wbittle
Guest
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| Posted:
Fri Dec 31, 2004 1:19 am Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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Hi,
There are two balance adjustments you can make to a push pull power
amp circuit. One is the more common DC balance. If you have separate
cathode resistors for each tube, just set the balance pots so the
voltage drop across each resistor is the same. If there are no
resistors, what you do is connect an AC volt meter across the speaker
terminals and adjust the balance pot till you get the lowest AC volt
reading. This will be where the tubes balance and where you get the
least hum.
The other balance commonly found is called AC balance. Here your
goal is to have each half of the phase inverter producing the same
voltage. So, you run a sine or square wave into the amplifier's input,
then turn up the level and just measure each half of the phase
splitter's output. Actually the best place to measure this is at the
control grids of the output tubes. Adjust the phase inverter balance pot
till both voltages are the same. The last adjustment is bias. Again, if
the amp has a cathode resistor, you can measure the voltage and
calculate the current using ohm's law. I find this more accurate then
shunting a miliamp meter across a low value resistor. If you don't have
cathode resistors, you can install a set of 10 ohm resistors between the
cathode and ground. This is assuming the amp is fixed bias.
Bill Bittle
Archangele sound: Offering service for all makes of tube hifi and
guitar amplifiers. |
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mitch
Guest
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| Posted:
Fri Dec 31, 2004 4:59 am Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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Wbittle wrote:
| Quote: | Hi,
There are two balance adjustments you can make to a push pull power
amp circuit. One is the more common DC balance. If you have separate
cathode resistors for each tube, just set the balance pots so the
voltage drop across each resistor is the same. If there are no
resistors, what you do is connect an AC volt meter across the speaker
terminals and adjust the balance pot till you get the lowest AC volt
reading. This will be where the tubes balance and where you get the
least hum.
The other balance commonly found is called AC balance. Here your
goal is to have each half of the phase inverter producing the same
voltage. So, you run a sine or square wave into the amplifier's input,
then turn up the level and just measure each half of the phase
splitter's output. Actually the best place to measure this is at the
control grids of the output tubes. Adjust the phase inverter balance
pot till both voltages are the same. The last adjustment is bias.
Again, if the amp has a cathode resistor, you can measure the voltage
and calculate the current using ohm's law. I find this more accurate
then shunting a miliamp meter across a low value resistor. If you
don't have cathode resistors, you can install a set of 10 ohm
resistors between the cathode and ground. This is assuming the amp is
fixed bias.
Bill Bittle
Archangele sound: Offering service for all makes of tube hifi and
guitar amplifiers.
Thanks for your help. How do I know what the current through the |
cathode should be? Is that something I can get from a spec sheet for
the tube? It uses 7355's.
Mitch |
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Wbittle
Guest
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| Posted:
Sun Jan 02, 2005 5:36 am Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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| Quote: | Thanks for your help. How do I know what the current through the
cathode should be? Is that something I can get from a spec sheet for
the tube? It uses 7355's.
Mitch
Hi Mitch, |
If your plate voltage is 400 volts, you should bias these tubes at
25 ma per tube or 50 ma per pair. You can go as high as 60 ma per pair
(30 ma per tube). But, it is best to find out what the amplifier's
manufacturer recomends. Failing that, the specs I mentioned should work.
This tube is usually used in amps producing 25 - 35 watts per channel.
Hope this helps.
Bill Bittle |
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scottp
Guest
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| Posted:
Tue Jan 04, 2005 10:51 pm Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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Mitch,
Just search for the specs online using google.
Lots of folks have the tube specs online now
adays.
Scott
mitch wrote:
| Quote: | Wbittle wrote:
Hi,
There are two balance adjustments you can make to a push pull power
amp circuit. One is the more common DC balance. If you have separate
cathode resistors for each tube, just set the balance pots so the
voltage drop across each resistor is the same. If there are no
resistors, what you do is connect an AC volt meter across the speaker
terminals and adjust the balance pot till you get the lowest AC volt
reading. This will be where the tubes balance and where you get the
least hum.
The other balance commonly found is called AC balance. Here your
goal is to have each half of the phase inverter producing the same
voltage. So, you run a sine or square wave into the amplifier's
input, then turn up the level and just measure each half of the phase
splitter's output. Actually the best place to measure this is at the
control grids of the output tubes. Adjust the phase inverter balance
pot till both voltages are the same. The last adjustment is bias.
Again, if the amp has a cathode resistor, you can measure the voltage
and calculate the current using ohm's law. I find this more accurate
then shunting a miliamp meter across a low value resistor. If you
don't have cathode resistors, you can install a set of 10 ohm
resistors between the cathode and ground. This is assuming the amp is
fixed bias.
Bill Bittle
Archangele sound: Offering service for all makes of tube hifi and
guitar amplifiers.
Thanks for your help. How do I know what the current through the
cathode should be? Is that something I can get from a spec sheet for
the tube? It uses 7355's.
Mitch |
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mitch
Guest
|
| Posted:
Tue Jan 11, 2005 5:54 am Post subject:
Re: Stromberg Carlson Stereo 8 - Balance setting |
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|
scottp wrote:
| Quote: | Mitch,
Just search for the specs online using google.
Lots of folks have the tube specs online now
adays.
Scott
mitch wrote:
Wbittle wrote:
Hi,
There are two balance adjustments you can make to a push pull power
amp circuit. One is the more common DC balance. If you have separate
cathode resistors for each tube, just set the balance pots so the
voltage drop across each resistor is the same. If there are no
resistors, what you do is connect an AC volt meter across the
speaker terminals and adjust the balance pot till you get the lowest
AC volt reading. This will be where the tubes balance and where you
get the least hum.
The other balance commonly found is called AC balance. Here your
goal is to have each half of the phase inverter producing the same
voltage. So, you run a sine or square wave into the amplifier's
input, then turn up the level and just measure each half of the
phase splitter's output. Actually the best place to measure this is
at the control grids of the output tubes. Adjust the phase inverter
balance pot till both voltages are the same. The last adjustment is
bias. Again, if the amp has a cathode resistor, you can measure the
voltage and calculate the current using ohm's law. I find this more
accurate then shunting a miliamp meter across a low value resistor.
If you don't have cathode resistors, you can install a set of 10 ohm
resistors between the cathode and ground. This is assuming the amp
is fixed bias.
Bill Bittle
Archangele sound: Offering service for all makes of tube hifi and
guitar amplifiers.
Thanks for your help. How do I know what the current through the
cathode should be? Is that something I can get from a spec sheet for
the tube? It uses 7355's.
Mitch
Thanks for the help. |
Mitch |
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