I managed to win some cheap 6C41Cs on ebay and I want to build a simple Class-A PP with them.
I came up with the attatched schematic. It's my first ever design for a tube amp but I have yet to come up with exact component values.
The input transformer is a 1:10 step-up and is to be driven from a low impedance source. The output transformer will probably be a mains toroid. No DC will flow through it because of the coupling caps (not scared of electrolytics).
As you can see it's very simple and I THINK it will also be a very hum and hiss free design as well, since the current sources on the anode offer no reasonable path for AC, and any noise that gets through will be cancelled by the other half.
It's a PP design, will it be as efficient as normal class-a PP designs? Will it work with suitable component values?
Lastly, I hope to get around 25W from this design, is this feasable?
I came up with the attatched schematic. It's my first ever design for a tube amp but I have yet to come up with exact component values.
The input transformer is a 1:10 step-up and is to be driven from a low impedance source. The output transformer will probably be a mains toroid. No DC will flow through it because of the coupling caps (not scared of electrolytics).
As you can see it's very simple and I THINK it will also be a very hum and hiss free design as well, since the current sources on the anode offer no reasonable path for AC, and any noise that gets through will be cancelled by the other half.
It's a PP design, will it be as efficient as normal class-a PP designs? Will it work with suitable component values?
Lastly, I hope to get around 25W from this design, is this feasable?
Attachments
Forget about the caps and think through the circuit
...Right, any DC will cancle in the Transformer because in is wound in anti-phase seen from the center tap. Only the out of phase AC voltage will add/summarize. So omit the CCS and put the B+ to the center tap.
25W ? Hmmm a bit optimistic
Tell us your exact Transformer data and the operating point, voltages etc. Then it can be calculated
Futhermore I don't think that your 10:1 input tarnsformer will suffice. 6S41 needs much driving voltage AND and low impendance source because of its miller capacity. Remeber, a 10:1 transformer will tarnsform the resistance by a factor of 100 !
If I were you, I would build a tube stage.
regards, Manta
...Right, any DC will cancle in the Transformer because in is wound in anti-phase seen from the center tap. Only the out of phase AC voltage will add/summarize. So omit the CCS and put the B+ to the center tap.
25W ? Hmmm a bit optimistic
Tell us your exact Transformer data and the operating point, voltages etc. Then it can be calculated
Futhermore I don't think that your 10:1 input tarnsformer will suffice. 6S41 needs much driving voltage AND and low impendance source because of its miller capacity. Remeber, a 10:1 transformer will tarnsform the resistance by a factor of 100 !
If I were you, I would build a tube stage.
regards, Manta
I agree with the sentiment about needing a tube input stage, a 1:10 step-up can't possibly drive the grids enough
As for the CCS, that is to bias the output tube without any DC going through the toroid
As for what transformer I'm going to use, I don't know I want to use a mains transformer because people have reported good results from them if there isn't any DC offset (I'm avoiding this problem entirely by havign the DC through a CCS)
As for the CCS, that is to bias the output tube without any DC going through the toroid
As for what transformer I'm going to use, I don't know
I want to use a mains transformer because people have reported good results from them if there isn't any DC offset (I'm avoiding this problem entirely by havign the DC through a CCS)
Those CCSs won't work. You have the emitter and collector transposed. The collector goes to the anode of the valve. You will be lucky to get 6W. One of the advantages of an output transformer is that it allows you to swing to twice the HT voltage. You have just lost that advantage using CCS loads.
Yeah, a cathode follower output stage is possible. But you will definitly need a good driver stage. Moreover this would be an amp which will require 200 to 250V for the 6S41 and 500 to 700V for the driver Except you will use a choke loaded driver.
I would buy a good output transformer and make an old fashioned amp. Of course a mains tarnsformer is cheaper but has a much smaller primary inductance which gives a lack in the bass.
Except you will use a choke loaded driver.I would buy a good output transformer and make an old fashioned amp. Of course a mains tarnsformer is cheaper but has a much smaller primary inductance which gives a lack in the bass.
Where ever you put'em CCS innevitably asks for doubling PSU voltage, one half being vasted in heat in the CCSs.
Moving the load in the cathode does not change its value to extract the same power but you loose the voltage gain in the tubes and thus need vy huge voltage drive.
Of course, this kills Miller effect ! But designing the driver becomes a real challenge.
Yves.
Moving the load in the cathode does not change its value to extract the same power but you loose the voltage gain in the tubes and thus need vy huge voltage drive.
Of course, this kills Miller effect ! But designing the driver becomes a real challenge.
Yves.
Phase splitting input transformers will only work satisfactorily at 1:1 or 2:1 (ie step down). Even then a good 20mA driver infront is obligatory. Not a big deal but worth doing.
Put CCS in the tails of the output tubes. Simple LM317's based ones work very well. They will need bypassing of course. This setup can be changed to a differential output stage quite simply - though the bypass caps need to be doubled in size.
Inductance in Toroidal mains transformers is less of an issue than many people seem to believe. The ones I use are good down to 10hz.
Basically you are building a very similar circuit to the one I am listening to now. If you are interested I can email you a copy as a reference.
Shoog
Put CCS in the tails of the output tubes. Simple LM317's based ones work very well. They will need bypassing of course. This setup can be changed to a differential output stage quite simply - though the bypass caps need to be doubled in size.
Inductance in Toroidal mains transformers is less of an issue than many people seem to believe. The ones I use are good down to 10hz.
Basically you are building a very similar circuit to the one I am listening to now. If you are interested I can email you a copy as a reference.
Shoog
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.