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In Reply to: RE: choke input bias supply posted by hennfarm on March 02, 2015 at 14:11:14
My rationale is why go through the trouble to execute a quiet b+ and then land noise on the power tubes grid?
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IMHO the most important feature would be for the negative bias supply to have its own winding. I would like to see a full wave rectifier. I would like to see generous size capacitors. Mostly I want a supply that comes up fast and dies slow. I want low impedance.
I don't think choke input is best suited/needed towards those goals.
would it not make sense to use a similar topology as the main so that it tracks the same or has a similar sound. If not with such low current why not use the best supply you can build on what is a critiical supply.
This was sjs idea when building like choke input tube rectied supply for there bias on there 300b amp. google it it is a nice amp. No corners cut.
excuse typo this macbook i bought my daughter has only one mousepad click then i can find in the dark,,,
"would it not make sense to use a similar topology as the main so that it tracks the same or has a similar sound."This is taking the "sound of the power supply" to ridiculous levels. There is also some misunderstanding in this thread as to the importance of the bias supply as it relates to sonics. The bias supply must be highly reliable but that's another issue and equally easy to achieve.
Yes, the bias supply is tied to the output tube grid. But look at a typical circuit. There is often on the order of 300K of series resistance between the grid and the last bias filter capacitor. The current is miniscule. Filtering this current to virtually pure DC is not that difficult to do. Especially with today's caps and rectifiers.
Just because a CRC B+ supply is inferior and a corner cutting technique does not mean the same is true for a bias supply. A CRC is an excellent filter at these current levels.
Please don't take this the wrong way but this is a good example as to why it's important to learn the electronics behind these amps.
Learn how the circuit works. Throwing money at it does not always reap rewards.
Edits: 03/03/15
Well I have been reading up my ARRL handbook today. Since my new amp will be using hv. I wanted to seek inspiration from the old ham guys. As they really new their tubes I think. I happened to find the paragraph on bias supply's and it has many pages on bias supply's showing at least a dozen different examples.
All are choke input supply's
most are then shunt regulated via a gas tube or electronically regulated with gas shunt references and series 6080s 811 or even a 211. With one tube shuntregulated as well.
type 80 is the most common rectifier used.
Not one cap R to find
I am thinking they take regulation of there bias supplies seriously.
Yes these are radio amps.
But after reading this I am going with regulated bias supply's
RF power tubes have different bias coupling requirements due to the application. RF is much more critical in terms of layout and the coupling of bias voltage to the grid is often more complex. RF will also leak back out into the power line quite easily through power supplies if not taken care of. Audio amps don't have those issues.What I and the other posters are saying here applies only to audio amps.
I too an a fan of regulated bias supplies as well as regulated driver power sources. I have tried regulated finals and don't like the sound.
So if you want to build a good regulated bias supply, it certainly won't hurt anything.
Keep on reading that ARRL book. It's a wealth of good timeless information. I have a few myself.
Edits: 03/04/15
"if you want to build a good regulated bias supply, it certainly won't hurt anything"
If you do that, a regulated B+ supply is also required. Otherwise, the bias won't track the B+ when line voltage changes. The rule of thumb for this is that either both or neither of the supplies should be regulated. That way, they're stable relative to each other.
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Buy Chinese. Bury freedom.
Just regulate the AC going into the amp. That's what I do with my 833C amps since I couldn't find a regulator for 2.3kV that would fit in the amps. All bias supplies are regulated, but B+ is not...and it's rock stable. PS Audio P5 does the trick nicely. Not a cheap solution, but definitely effective. Keeping it at 117V or lower also helps keep the big Hammond HV transformer quiet, too!
Edits: 03/07/15
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