If a 12DW7 is essentially half a 12AU7 plus half 12AX7 could one not use half of each times two in a stereo to drive el34's ? I heard the JJ-Tesla ones are not too great, so if one wanted too use current production would this be the way to go? the 12DW7 to 12AX7 conversion does not seem very efficient to me. I mean they are DUAL triodes right?
Below is an extract from the DIYTUBE ST-35 manual;
Overview of the Schematic and Design
The design closely resembles the Dynaco Stereo 35. The use of one 12DW7 per channel has
been replaced by 1/2 a 12AX7A and 1/2 a 12AU7. The 12AX7A is a voltage amplifier that directly
drives the 12AU7, a cathodyne phase splitter.
Hope it helps,
Eric
Overview of the Schematic and Design
The design closely resembles the Dynaco Stereo 35. The use of one 12DW7 per channel has
been replaced by 1/2 a 12AX7A and 1/2 a 12AU7. The 12AX7A is a voltage amplifier that directly
drives the 12AU7, a cathodyne phase splitter.
Hope it helps,
Eric
A separate 12AX7 and 12AU7 is a much better way to go if you can do it. A near as I can determine there is currently only one manufacturer, possibly two, of 12DW7/7247 equivalents. Separate tubes gives you a much wider selection. Using a separate 12AU7 allows the use of other "pin for pin" compatible tubes, with better linearity, such as the 12BH7.
actually I was thinking of the Dynaco 35. Having heard no great shakes on the JJ-Tesla new version that is exactly where my mind was going. But I was thinking of 12AY7's for the pre-amp or I got me couple of hundred 6111 sub miniatures yanked out of old PRIC's along with sockets to swap out. I've got the quad can and was going to get 1% resistors, NOS wire pots and really debate the PS and OT.
Sharing a valve envelope between channels will cause a small amount of HF crosstalk due to interelectrode capacitance. Probably nothing to worry about. There was a thread on here a few months ago in which someone measured it.
Anybody know where that is? Might be my first build along. I'm just finishing a cigar box amp with two bridged nte-1288 chips and my take on a heavy-watter.
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