Re: Comments on a B+ problem?
Posted: July 15th, 2016, 6:32 pm
Well, I'd say there is no need for a 650 ohm resistor. It is kind of a blunt weapon approach.
Shoot for 10% high B+ and you'll survive. A 300 ohm choke will get you there and add filtering instead of being only a small space heater for your capacitors, which don't need it. A 650 ohm resistor is like 10W dissipation @ 120mA and will be a smokin hot device.
Actually, resim that PSU with the 30 ohm 1H choke between the rectifier and the first filter cap and stick in a 250 ohm 10H choke where the 1H lies. A choke (or resistor) in that input slot will reduce charging impulses at 120hz, and a choke will add a bit of LP and ripple filtering. The series resistance makes the job of the rectifier easier.
A 1H choke is below the "critical inductance" so the power supply will charge up close to the peak value of the AC, i.e. it will still act as a capacitor input filter.
GZ34 is a real good rectifier, especially old production tubes, and I'd strive to keep it in there, personally. For one thing, it is indirectly heated/slow turn-on and, secondly, they sound really good. 5R4s in my experience tend to sound thinner than GZ34 and this may not be what you want/need....but experiment, by all means. Assume every case is different, experiment, and learn.
All bets are off with Russian GZ34s, unless they have gotten a lot better in recent years.
Shoot for 10% high B+ and you'll survive. A 300 ohm choke will get you there and add filtering instead of being only a small space heater for your capacitors, which don't need it. A 650 ohm resistor is like 10W dissipation @ 120mA and will be a smokin hot device.
Actually, resim that PSU with the 30 ohm 1H choke between the rectifier and the first filter cap and stick in a 250 ohm 10H choke where the 1H lies. A choke (or resistor) in that input slot will reduce charging impulses at 120hz, and a choke will add a bit of LP and ripple filtering. The series resistance makes the job of the rectifier easier.
A 1H choke is below the "critical inductance" so the power supply will charge up close to the peak value of the AC, i.e. it will still act as a capacitor input filter.
GZ34 is a real good rectifier, especially old production tubes, and I'd strive to keep it in there, personally. For one thing, it is indirectly heated/slow turn-on and, secondly, they sound really good. 5R4s in my experience tend to sound thinner than GZ34 and this may not be what you want/need....but experiment, by all means. Assume every case is different, experiment, and learn.
All bets are off with Russian GZ34s, unless they have gotten a lot better in recent years.