OTL Asylum

RE: 6C19 PP schematic?

150.148.0.27

In Reply to: RE: 6C19 PP schematic? posted by Peter H-son on April 21, 2008 at 10:32:53

The big problem for designing a low power OTL, is that you want a low output impedance. The major determinants of output impedance are the net plate resistance of all the tubes paralleled and mu. Kevin Covi has posted a formula for the output Z of a circlotron, for example: Zo = Rp/2+mu. So if you wanted an OTL using one pair of 6C19, the predicted output Z would be 200/2+3 = 40 ohms. Obviously this is too high to drive any real world speaker, even a very efficient one. The only cure is to use NFB. With a modified Futterman-type circuit, you get a slightly lower Zo, but there you definitely also need NFB. It's actually therefore easier to make a high power OTL that could get by without NFB. Check out the Atma S30 and the Transcendent website.

Follow Ups:

RE: 6C19 PP schematic? - acres verde 14:46:32 04/22/08 (1)
- Thanks for the parentheses, - Lew 08:57:12 04/23/08 (0)

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