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I'm thinking of ordering a Triad C-14X choke to use in a GSG build. They're in stock at Mouser. I figure I can save on shipping by not having to source the choke from some other online vendor.

The C-14X is rated at 200mA, 6H, 150 ohms. The current handling is more than adequate. The inductance is higher than the suggested C354 in the GSG manual. I understand I may want to use 50 ohm parts at R11/R13, R12/R14 instead of the 51/47 ohm parts specified in the manual.

The 150 ohms DC resistance should mean it will lose about 11 more volts than a C354 choke. Will this be a big deal? Shannon mentioned something about the designed B+ of the GSG falling in a sweet spot, and I suspect everything was carefully tuned around that point.

If that doesn't complicate things enough, I've opted to go with the Edcor XPWR005 power transformer instead of a PA774. It's rated for 180mA at 660VCT with a 120 volt primary, but there's no telling where the actual working voltages will fall. I guess I should be prepared to tinker a little once I have all the pieces together...

Here's my stab at this, but YMMV:

Use your Triad choke and jumper R17A and don't populate R17B. Only populate C8 or C9. Probably no need for all that capacitance with the 6H choke. Your voltage range should be OK. The resistors at R17A and R17B were primarily meant to protect the old 6B4s.

Leave the 51/47 ohm resistors alone. They act like a hum balance pot, and those values work the best in the design.

Does the Edcor have dual 6.3V taps like the PA774?

separks wrote:The resistors at R17A and R17B were primarily meant to protect the old 6B4s.

Speaking of old 6B4G, I see references to 1100 ohms of cathode resistance in some of the early GSG designs. When was it changed to 900?

PostPosted: Tue May 01, 2007 5:20 am Post subject: Reply with quote
Hi Steve,

$49 plus $3.85 Priority Shipping will get you one ASAP. :)

I've had a stack of boards sitting here for maybe a month and a half. Tom and I were doing tiny last minute tweaks - and I think the BOM is finished. Basically, the Sovtek 6B4Gs are a bit of a hot rodded 6B4G, so they prefer a hefty bias current. So I changed the cathode resistor networks from 1100 ohms to 900 ohms. The old stock 6B4Gs work about the same at this bias (and most importantly stay within legal limits for this old dog), while the Sovtek's linearity increases by 50%. Some basically the parts list/BOM gets changed at R15abc & R16abc with 71-CW2B-2.7K. I'll probably add a front cover to the manual and post one one eBay this weekend.

Interestingly, if you look at the various Simple 2A3 schematics, you can see the bias resistors lowered over the years. Probably due to the Sovteks, methinks.

Thank goodness for search tools! I wouldn't have remembered that bit.