Hello!
I have a Bottlehead Stereomour configured for 45 tubes.
In stock form, it's running the 45 tubes at 300volts (360-60) and dissipating at 11.25watts (1.6K cathode resistor). I think this is pushing the tubes to its limit.
The power supply is 160 volts going thru a voltage doubler (pseudo-dual). Rectified DC is about 410 volts. Then it goes to a 1.2K/10W dropping resistor. I changed these resistors to 2k and it drops the voltage to 280 volts (p-k).
Is it okay to drop the voltage further to about 250-260 by increasing the the resistor value? Is there any disadvantage to using high-value resistor?
Right now, I've dropped the voltage to 270 by using a variac but I can only go down to the lowest voltage acceptable for the filaments (-5%) .
Thank you in advance.
I have a Bottlehead Stereomour configured for 45 tubes.
In stock form, it's running the 45 tubes at 300volts (360-60) and dissipating at 11.25watts (1.6K cathode resistor). I think this is pushing the tubes to its limit.
The power supply is 160 volts going thru a voltage doubler (pseudo-dual). Rectified DC is about 410 volts. Then it goes to a 1.2K/10W dropping resistor. I changed these resistors to 2k and it drops the voltage to 280 volts (p-k).
Is it okay to drop the voltage further to about 250-260 by increasing the the resistor value? Is there any disadvantage to using high-value resistor?
Right now, I've dropped the voltage to 270 by using a variac but I can only go down to the lowest voltage acceptable for the filaments (-5%) .
Thank you in advance.
you're welcome, that's the idea...best to use a wire-wound pot and then adjust it under loaded conditions, then once you get the desired operating point, you can get the nearest standard value resistor....
you can chop the 2k resistor into 3 680ohm series resistors so that you have a CRCRCRC filter, that way you can get the ripple voltage really low....
you can chop the 2k resistor into 3 680ohm series resistors so that you have a CRCRCRC filter, that way you can get the ripple voltage really low....
i understand, the rule of thumb is to use just the right amount(minimal) of coupling capacitance to give you a roll-off just below 20hz...
At low frequencies decoupling caps/smoothers have less effect, so any series resistance in the supply is seen as extra anode load by the valves. This could
a) boost subsonic gain in a simple voltage amplifier
b) reduce subsonic gain in a transformer-based stage
c) introduce inter-stage feedback which may be positive or negative, and frequency-dependent
The point where decouplers stop working may or may not overlap with the point where couplers stop working. Modern practice uses much bigger caps in both places than 50 years ago, so it is possible that what would have been a near-subsonic issue now becomes a syllabic-rate/envelope issue as it all happens lower in frequency. In olden days PSU's used big chokes and coupling caps were 10nF; now we use big PSU caps and coupling caps could be 0.47uF.
If it gets as bad as actual instability then it is called motorboating, but it could muddy-up LF stuff even if it is not oscillating.
a) boost subsonic gain in a simple voltage amplifier
b) reduce subsonic gain in a transformer-based stage
c) introduce inter-stage feedback which may be positive or negative, and frequency-dependent
The point where decouplers stop working may or may not overlap with the point where couplers stop working. Modern practice uses much bigger caps in both places than 50 years ago, so it is possible that what would have been a near-subsonic issue now becomes a syllabic-rate/envelope issue as it all happens lower in frequency. In olden days PSU's used big chokes and coupling caps were 10nF; now we use big PSU caps and coupling caps could be 0.47uF.
If it gets as bad as actual instability then it is called motorboating, but it could muddy-up LF stuff even if it is not oscillating.
Thank you DF!
The coupling caps are 0.1uf.
How much is too much resistance? I think I need around 2.7K to get to the correct voltage. I think I read somewhere that too much resistance can also make voltage stability worse.
Is there other way to shed around 100 volts?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.