Hello to all,

I have a Boyuurange A-50 MKIII. I watched all of Stephe’s modification videos. I don’t understand schematics but can solder and have rudimentary knowledge about using a multimeter. So I decided I could follow the videos and do what he did even if I didn’t understand it. What a mistake! I did all mods, put tubes in, powered up amp, and blew it’s fuse. Ordered new fuses. After having worked on the mods on my kitchen table for 2+ weeks, my wife was out of patience so I moved to garage workbench. I put new fuse in, turned amp on, and tripped the ground fault interrupter (we didn’t have one in the room where I had blown the fuse). That gave me a clue to what was wrong. I opened the back cover and discovered I had pinched the orange insulation to the bare wire that runs from the AC receptacle to the on/off switch. The wire had grounded against the chassis. It was intact but scorched. I applied some liquid tape and turned the amp back on. The lights on the meters came on, the ground fault interrupter didn’t trip, but no sound came from the speakers. I took the tubes back out, turned it over, and checked the points for voltage that Stephe had checked in the videos. There was no voltage anywhere, so I decided I must have blown the power transformer even though I didn’t know how to actually check it. The Tube Amplifier Store got the factory in China to ship another transformer for about $159 including freight. I put it in but still had no voltage, so I decided the on/off switch had been damaged. I put a new one in and still have no voltage. I’m stumped. Any ideas?

Below is a step-by-step of what I did.

FRONT END REBUILD

ALL REFRENCES TO “SIDE” ARE FROM FRONT VIEW OF AMP WITH AMP UPSIDE DOWN

BOTH SIDES:

(1) Black wire that runs from Pin 2 to Pin 4: (Stephe repl w/white wire)

· Disconnect other end from Pin 4 and solder to Pin 6

(2) Grid Stopper

· 1K, 1W (101001JR500) Cut both leads short, cover resistor w/ H.S. & solder to yellow wire .—

Will connect to Pin 1 at step (9)

(3) 1M, 1W (101004JR500)

· PFTE tubing to wires & solder Pin 1 to Ground & cut lead short after

(4) 47K, 2W (204702JR400)

· Solder to Pin (5) and to B1 (under board with some lead sticking out)

(5) 680K, 1W (FMP100JT-52-600K)

· Solder to Pin (4) and to B1 (top board)

(6) 200K, 1W ((102003JR500)

· Solder to Pin (4) and to Ground

(7) Mundorf EVO, 22uF, 450Vdc silver/gold/oil (MUNDORF-76448)

· Solder to Pin (4) and to Ground

(8) (a) Solder 200R (ohm), 1W (CMF60200R00FKEB) Ground

(b) LED Resistor- Cut leads short & solder to Pin (3) with Blue side away from Pin

(c) Solder LED Resistor Blue side to 200R (ohm)

(9) Solder Resistor that’s on yellow wire (from step 2) to Pin 1 and connect Black wire solder to cap wire at Grnd

(10) Repl Brown Wires from plate to 300B Boards

o R. to Pin 5

o L. to Pin 5

LEFT SIDE ONLY

(11) Two (2) 100R, 1W (101000JR500)

o Looks like split off the wire like a Y & put H.S. tubing around them.

o Cut 1 lead short & connect lead to Pin 7

o Cut 1 lead not quite as short & put short, put PFTE tube & connect lead to Pin 8

o Put other ends of leads together in one H.S. & connect to ground

o Solder to Pins and ground

300B/5AR4 REBUILD

Did the mods Stephe described but for 300Bs used bipolar 100uF 100Vdc KAISEI Radial, Audio Note Electrolytic Caps (ANKECAP-81786) and Mundorf 22uF 450Vdc MCap EVO Oil MUNDORF-76424)