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Parafeed Baby O

189.216.142.91
Posted on March 31, 2019 at 20:09:08
xcortes
Audiophile

Posts: 1221
Joined: July 23, 2003



One down and already singing:

 

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RE: Parafeed Baby O, posted on April 1, 2019 at 17:20:47
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 Looking good!

 

, posted on April 1, 2019 at 18:33:44
mqracing
Manufacturer

Posts: 4323
Joined: June 29, 2000
 ...



Builder of MagneQuest & Peerless transformers since 1989

 

RE: Parafeed Baby O, posted on April 4, 2019 at 12:16:04
Sidewinder
Audiophile

Posts: 254
Joined: April 13, 2001
 Hi,
Nice looking build. Any pics of the top side? What changes did you make to convert the standard Baby-O to Parafeed?
Regards,
David

 

Pic of top and circuit notes, posted on April 5, 2019 at 07:24:14
xcortes
Audiophile

Posts: 1221
Joined: July 23, 2003



Paul Joppa helped me with the circuit adjustments so the credir goes to him.

Paul's goal was to retain the normalized load impedance so that the distortion character of the output tube remains the same with changes in the load impedance and power. At the same time he retained the plate dissipation fort the 2A3.

For the parafeed BabyO with 2A3, run the tube at 295v plate to cathode and 49.4mA current. Bias will be about 58 volts, so the cathode resistor should be 1173 ohms. Plate voltage is thus 353 volts; I did that with a 0.82 input cap instead of the original's 0.68uf and got the voltages spot on (with 115 vac supply).

Paul also suggested that the driver may have may marginal headroom, To improve that situation without changing the topology or tonal character, he recommended changing the 333-ohm cathode resistors (both sections) to 500 ohms.

I grounded the opt to the cathode of the 2A3.

I'm sure Gordon/Paul's circuit is worthy of Mike's Mexico Series masterpieces. I hope my build is too!

 

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