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Old 27th October 2019, 01:41 PM   #21
justmikey is offline justmikey  United States
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Quote:
Originally Posted by kstolleis View Post
Raytheon 5842 - sound great with Golden Lion 300B

Power Transformer:

Edcor XPWR178, 660V 200mA center tapped, 6.3V 6A center tapped, 5V 3Acenter tapped

I followed middle of the road on Georges BOM component values and ended up with about 380V B+. Using 5000K outputs and will say it sounds great. Not sure how long it will live. Output transformer does get plenty warm over about two hours (almost too hot to touch...). Running about 64mA per.
I have a similar PT. Did you use the BOM value of 47 uF for the first cap C4? What did you use for D6 and R36. In BOM Note 7 George recommends changing D6 from 150v to 200v at B+ over 350v. He notes that R36 "puts too much heat into the board" when dissipating the higher power level at an elevated B+. BUT - I am building my board upside down (with tubes out the top, components below on other side of the PCB) and I can easily fit a 10 or 12 watt Mills resistor with the leads slightly long and lots of air space around the resistor.
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Old 28th October 2019, 02:12 AM   #22
Tubelab_com is offline Tubelab_com  United States
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If you have room for a big resistor, and there is some means for air to escape from the top of the chassis, then a big resistor with a stock Zener diode is fine.

I have found that having too many hot parts under the board in a small chassis with no vent holes will slow cook the board. This can cause harmless discoloration after several years, but heat constantly traveling up the resistor wires can cause solder joints to become brittle in a PCB based amp, or a point to point wired amp.

A little air flow is your friend.
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Old 28th October 2019, 09:38 AM   #23
justmikey is offline justmikey  United States
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Thanks for the quick response. I will be sure to provide plenty of air flow. I typically provide vent holes on the top of my chassis just above warm items such cathode bias resistors etc and use perforated sheet metal bottom plates.
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Old 29th October 2019, 12:59 AM   #24
itsikhefez is offline itsikhefez  United States
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
My plans are to have B+ in the 380V-395V range with 80mA bias.
The project is still under way but I ended up ordering the 200V zener for D6 and Mills MRA-10 10W resistors. The zener is on top but the big resistors are on the underside of the board (as you're planning)

PT is Edcor XPWR178 also and will start with C4 = 47uF to try and reach that B+ range.

My chassis will have an open bottom so hoping that provides sufficient ventilation.
I may add 1-2 holes on top right above the resistors as you mention.
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