kenneth,
if you want to change the M3 to direct coupled, you need to get rid of the c34, r47 and the 470uf by pass cap of the second tube. then you need to work out the new value of r42. in order to do that, you need to know the plate voltage of the of first tube and the bias of the second tube. of course you need to rework the power supply for the second tube in order to suppor the higher voltage.
if you want to change the M3 to direct coupled, you need to get rid of the c34, r47 and the 470uf by pass cap of the second tube. then you need to work out the new value of r42. in order to do that, you need to know the plate voltage of the of first tube and the bias of the second tube. of course you need to rework the power supply for the second tube in order to suppor the higher voltage.
I think it is no need to change to direct couple, making one more higher B+ just make things complicated, or even only using the existing PSU but adjusted to higher enough for the 2nd stage and using resistor and cap to produce required B+ for the first stage. But using existing PSU still cause problem too!
I guess the increase should be at least 90V or above if using the existing PSU, the mains transformer only 300V something for the secondary windings. It implies that you have to buy a new one or using rectification method to double the desired pre - regulated DCV, but this is not a good idea because of the performance of the regulation. Either one will also lead to a result to add one more set of filter cap for the increased tolerance !!!
If you aim to avoid the coloration caused by the using of Cap in the first stage, then what about the transformer connected at the output ? I don't believe the transformer would not cause any coloration. It presents a major and very crucial part in M3, except you want to get rid of it too and this is another story !!!!
Further more, if not satisfied with the result after the modification, think about your energy to restate M3.
My point is, tube is not as stable as semiconductor, as time goes by, the tube become premature that is faster than semi-conductor and even faster than you can imagine, then the operating point will shift and lead to a shift of the second stage, vice vera.
Like Ongaku, IMO is not a good amp for Diyer, no matter of its price is comparable to your fortune, the large amount of direct couple found in the schematic, it is not a good idea and lower the interest and flexibility to modify to fit for the user taste. I don't believe there's any tube amp. in the world would fit the user's taste after certain period of listening and they will try to place some different kind of tube with completely different spec. to fit for their taste or to upgrade but just need to change small amount of components, say one to two resistors for the correct bias.
That's what I guess. Correct me if I am wrong.
I guess the increase should be at least 90V or above if using the existing PSU, the mains transformer only 300V something for the secondary windings. It implies that you have to buy a new one or using rectification method to double the desired pre - regulated DCV, but this is not a good idea because of the performance of the regulation. Either one will also lead to a result to add one more set of filter cap for the increased tolerance !!!
If you aim to avoid the coloration caused by the using of Cap in the first stage, then what about the transformer connected at the output ? I don't believe the transformer would not cause any coloration. It presents a major and very crucial part in M3, except you want to get rid of it too and this is another story !!!!
Further more, if not satisfied with the result after the modification, think about your energy to restate M3.
My point is, tube is not as stable as semiconductor, as time goes by, the tube become premature that is faster than semi-conductor and even faster than you can imagine, then the operating point will shift and lead to a shift of the second stage, vice vera.
Like Ongaku, IMO is not a good amp for Diyer, no matter of its price is comparable to your fortune, the large amount of direct couple found in the schematic, it is not a good idea and lower the interest and flexibility to modify to fit for the user taste. I don't believe there's any tube amp. in the world would fit the user's taste after certain period of listening and they will try to place some different kind of tube with completely different spec. to fit for their taste or to upgrade but just need to change small amount of components, say one to two resistors for the correct bias.
That's what I guess. Correct me if I am wrong.
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