Parafeed 2A3

by Martin
(United Kingdom)

In 2003 I constructed a parafeed 2A3 stereo amplifier. I too used the Sowter 8995 output transformers and Sowter 8982 plate chokes.

The amplifier has gone through several changes since the original build, it has gone from a three stage amplifier with direct coupling between the input and driver stage and capacitor coupling between the driver and output stage. And now to a two stage interstage transformer coupled amplifier.

In it's current form it uses 6N1P-EV drivers with both triodes of each valve in parallel, led cathode bias and no cathode bypass capacitor. The driver is biased at 15mA 200 volts with the current set by a cascode Ixys 10M45 ccs between the B+ supply and the primary of the interstage transformer.

The output stage uses the Sowter 8995 with 4uf russian PIO parafeed capacitors, but the parafeed capacitors are in the negative side of the output transformer leg and return direct to the cathode of the 2A3 rather than ground, this has enabled me to remove the cathode bypass capacitors on the 2A3's.

I would recommend you move the return side of the output transformer to the cathode of the 2A3 rather than ground.

Ken Wow... nice to hear from another Sowter 8995 user! Looks like we have almost the same taste. My favorites are using interstage (Lundahl), LED cathode bias, Russian PIO caps, current source as load or cathode bias and etc!

I heard of putting the parafeed cap on the negative side of the OPT but I'm a bit paranoid that there might be mishaps and the amp would fry my OPT as well as my speakers. How much improvements did you observe with this modification? We'd be interested to know!

By the way, could you share the pictures of your creations? :)


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