I simply put the zeners in place of Rk. I strung together 6 zeners for 33.6V. At 120mA this was going to give a little more than 2/3W dissipation per device. This would be OK for my 1W devices, but I like to give zeners a little room, hence the second string in parallel.
The zener string's cathode goes to the triodes cathode and the anode goes to ground. The bypass cap is connected like a typical CRk. Without the cap, the amp is quite useable but it has a little background hash, and a few small pops and crackles from time to time.
I use a Wima MKP at present and it does well. I plan to play with maybe a larger value film and a small low esr bypass, but I've been too busy listening
There was some talk on another thread about wrapping the zener with a transistor. I don't have access to it at the minute and haven't tried it yet but will post if interested.
The zener string's cathode goes to the triodes cathode and the anode goes to ground. The bypass cap is connected like a typical CRk. Without the cap, the amp is quite useable but it has a little background hash, and a few small pops and crackles from time to time.
I use a Wima MKP at present and it does well. I plan to play with maybe a larger value film and a small low esr bypass, but I've been too busy listening
There was some talk on another thread about wrapping the zener with a transistor. I don't have access to it at the minute and haven't tried it yet but will post if interested.
SY said:
Picky, picky picky. But true. I should have made it clear that I wasn't referring to any specific example cited here. And with a single ended power stage I guess adequate current would hardly be the issue. But still, one of you creative folks will have a circuit where the phase does warrant a try.
Sheldon
Lots of LEDs have been tested for that; problem is, they're all different depending on manufacturer, process, material, and efficiency. I've posted a simple jig for testing LED impedance- I'd recommend setting up something like that and running the candidates you have on hand to pick the best one
Ryssen said:
Even with the highest gain triodes (CCS loaded 6C45PE @ ~4 Vdc on the cathode, 5 ma current) series LEDs never brought the noise floor above the 24-bit limit of my test kit, about 130 dB below 1 volt. I can't see how LEDs could inject enough noise into the cathode of a tube with a quarter the gain like a 76 to approach the limits of any contemporary audio storage system.
Here's an excerpt from Morgan Jones' 'Valve Amplifiers' third edition about LED forward drop at 10mA (! coincidence?) and typical Ra:
cheap red led = 1.7V @ 4.3ohms
cheap yellow yellow/green led = 2.0V @ 10ohms
true green led (525nm) = 3.6V @ 30ohms
blue led (426nm) = 3.7V @ 26ohms
ez81 and ez80 diodes are also featured but have much higher Ra (about 200 and 500ohms)
Simon
cheap red led = 1.7V @ 4.3ohms
cheap yellow yellow/green led = 2.0V @ 10ohms
true green led (525nm) = 3.6V @ 30ohms
blue led (426nm) = 3.7V @ 26ohms
ez81 and ez80 diodes are also featured but have much higher Ra (about 200 and 500ohms)
Simon
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