Hi That can work, but CTS makes the control and places like Mouser carry it. Using the capacitors introduces another set of non-linear components and each one will in some way alter the sound. Plus it is impossible to get the balance exact with two CCS. Part of the high quality sound is related to the excellent performance at very low signal levels. The better the balance is the better that will be. The sub one watt range is where all the fine details occur in most music with typical speakers. In sensitive systems (like my present ones) this is actually in the 100milli watt and lower range. Without the tubes being really well balanced they will exhibit some differences in response. I grant that it may be small, but when you are building a moderately costly amp, the effort and cost to not get one component is IMO not a great idea. There is an alternative way to balance the tubes. See the attached schematic. Applying a small positive voltage to the grids can do it as well. This works fine for tubes that bias at moderate levels. The issue is that each volt added to the grids adds one to the cathodes and in turn raises the voltage across and dissipation of the CCS. 5-7 volts are normally OK in the Poddwatts. With the bigger amps you need to be cautious not to exceed the limits of the CCS and 3-5 volts are max IMO. There is a side benefit to adding a small positive voltage to the grids in the Poddwatts. If the voltage is the same on each then it will raise the cathode voltage as well. Using about 5 volts it will make sure the cathode voltage never drops below that level on signal swings. This in turn provides more headroom for the CCS and will keep it out of a potentially non-linear range. You will also gain about 1/2 of a watt output power. All late model Poddwatt DMBs have this modification. They still use the 25 ohm control as it is reliable and works perfectly for this application.
Good listening
Bruce
Attachment:
Odd-Block-Series-1A Bias Mod 4 Jan2010b.jpg
Attachment:
Poddwatt DMB Main Circuit August 25, 2013.jpg
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