Yes they are, in an Einsteinian universe. The problem is, memphis, that they're never going to exist in isolation like this, and it depends exactly how you connect up the input and output whether you get equivalent results, and then it'll be results at AC, not DC.
To design the one on the right, one should take a course in electronics design, as the question is beyond the scope of a simple answer on a public forum.
w
To design the one on the right, one should take a course in electronics design, as the question is beyond the scope of a simple answer on a public forum.
w
I am thinking a VAC amplifier.
I'm very familiar with basic tube audio circuits, a journeyman of tube guitar amp designs. But that type of voltage amplifier (+ and - voltage) is not something that I've ever seen in that application.
But I stumbled across a design for a "tube op-amp" that used something similar with + and - voltages at the anode and cathode instead of using ground below Rk. (BTW, I'm not really interested in the op-amp application.)
But if I can make it work in a MI tube pre-amp, feeding a MOSFET power section, it would make designing the PS that much easier.
peace,
memphissound <><
I'm very familiar with basic tube audio circuits, a journeyman of tube guitar amp designs. But that type of voltage amplifier (+ and - voltage) is not something that I've ever seen in that application.
But I stumbled across a design for a "tube op-amp" that used something similar with + and - voltages at the anode and cathode instead of using ground below Rk. (BTW, I'm not really interested in the op-amp application.)
But if I can make it work in a MI tube pre-amp, feeding a MOSFET power section, it would make designing the PS that much easier.
peace,
memphissound <><
As long as the inputs and outputs are not DC coupled to anything else in the circuit (which should be obvious) I don't see a reason why these two shouldn't be equivalent in any universe.
The other connection to watch out for is the heater, which would be elevated if it were still referenced to ground. Some tubes have a rather stringent limit on the voltage difference allowed between heater and cathode.
The other connection to watch out for is the heater, which would be elevated if it were still referenced to ground. Some tubes have a rather stringent limit on the voltage difference allowed between heater and cathode.
Heater to Cathode voltage...
Let's see for a 12AX7 it's listed as 180V -- so that should be fine.
Any special tips for a coupling capacitor? Or would the ubiquitous .022uf - 400V work?
peace,
memphissound <><
Let's see for a 12AX7 it's listed as 180V -- so that should be fine.
Any special tips for a coupling capacitor? Or would the ubiquitous .022uf - 400V work?
peace,
memphissound <><
The coupling capacitor combined with any resistance in the grid circuit forms a first order highpass filter, so its value will have an impact on the lower bandwidth limit of the stage.
You may want to read the PDF document at this web site, for example:
http://www.freewebs.com/valvewizard1/gainstage.html
Best,
Kenneth
You may want to read the PDF document at this web site, for example:
http://www.freewebs.com/valvewizard1/gainstage.html
Best,
Kenneth
Indeed as kavermei says, you still have an RC circuit and must pay attention to the critical frequency, but this is no different in the two cases. If you are working from an existing design, the same capacitor will work equally as well (or poorly) in the two circuits.
The juggling of the rails on a circuit like this is used to create circuits that allow DC coupling. Taking care of the grid bias is a part of the art, as well as watching any heater issues wspecially with any dual section tube.
dave
dave
Regarding Wakibaki's original point, you do need to be careful to ensure the input isn't DC coupled at all. One easy way to do this is to use a transformer, but if you are using a typical grid resistor, this needs to be connected to the negative voltage rail (not ground) and capacitively coupled to the input. Make sure, however, that you don't inadvertently attach the input ground reference to the negative rail. That would be bad...
Regarding wakibaki's original point, the inputs require to be DC coupled to somewhere. This is what determines the Operating Point, and the quiescent or DC conditions. The circuits can only be considered functionally identical at AC if they share a common operating point, although this is not the only necessary condition.
This is why I said 'in an Einsteinian universe'. The answer should probably have been 'No, not in an Einsteinian universe', since this is, after all, an Einsteinian universe. Or is it? I mean, probably? That makes it quantum mechanical. No, these circuits are not identical. Except on the days of the week that Schrödinger lets his cat out.
Really? You want me to teach you electronics design by correspondence on a public forum? You must think I'm a glutton for punishment.
w
This is why I said 'in an Einsteinian universe'. The answer should probably have been 'No, not in an Einsteinian universe', since this is, after all, an Einsteinian universe. Or is it? I mean, probably? That makes it quantum mechanical. No, these circuits are not identical. Except on the days of the week that Schrödinger lets his cat out.
Really? You want me to teach you electronics design by correspondence on a public forum? You must think I'm a glutton for punishment.
w
Didn't know this was Pandora's Box...
Since this is not hi-fi the x-former is prohibitively expensive.
The 0.022uf cap is typical for guitar/bass amp applications.
Once I get the whole circuit down I'll come back for clean-up.
Thanks to everyone... and Schrödinger cat too.
peace,
memphissound <><
Since this is not hi-fi the x-former is prohibitively expensive.
The 0.022uf cap is typical for guitar/bass amp applications.
Once I get the whole circuit down I'll come back for clean-up.
Thanks to everyone... and Schrödinger cat too.
peace,
memphissound <><
They are equivalent, just be sure like the other posters said that the quiescent/operating conditions are the same (not hard, just treat the -125v like ground in the first example with reference to grid/cathode voltages). There are other issues, however. You now have to filter two supplies at 125v instead of one supply at 250v. The caps are cheaper, however.
You can even DC couple, as long as the quiescent/operating conditions (AKA bias) of the following stages are maintained.
You aren't trying to run a preamp off a euro mains/US dryer or oven socket are you? Any transformer power supply capable of circuit B can probably be wired to make circuit A.
/I am not sure wakibaki passes the turing test!
You can even DC couple, as long as the quiescent/operating conditions (AKA bias) of the following stages are maintained.
You aren't trying to run a preamp off a euro mains/US dryer or oven socket are you? Any transformer power supply capable of circuit B can probably be wired to make circuit A.
/I am not sure wakibaki passes the turing test!
- Status
- Not open for further replies.