I planed to build up a tube amplifier with all WE tubes long times ago and bought WE300B, WE417, WE437, WE274A/B for over 10 years,
but I never made up my mind which 300B architecture to go.
At end of 2021, TU-8600 with LL2785B cured my decidophobia.I bought one TU-8600R and ordered a pair of LL2785Bs from Taiwan dealer THL.
I could not wait to enjoy music played by the vintage 300B, so I tried the transformer LL1623 on hands before LL2785B arrive.
LL1623 sounded excellent with thicker mid range compared to the LL2875B which was a bit more air and more clear sound stage.
I liked both of them and was glad that I could swap based on my moods ! ^_^.
Although TU-8600+Lundahl's transformers were excellent, but my target was an amplifier with all WE tubes.
TU-8600's case is small and outputs of AC power transformer can't support WE274A/B tube rectifier and DC coupling,
so WE417/437- interstage transformer - 300B was the choice.
For the interstage transformer, I used LL2756 and wired it to 1:2 ratio to get 2x voltage gain and accommodate the high bias current of WE437.
I re-wired the input tube sockets for WE417, made a conversion sockets for WE437 and made cathode resistors replaceable for adjusting bias current so that I can try both tubes.
Due to WE437's cathode current can be as high as 40mA, add a buffer transistor with heatsink after the high voltage regulator LR8 for suppling voltage to WE417/WE437 is necessary.
Fortunately, all the 5 transformers can be put into the case by turning the power transformer 90 degree vertically and output transformers and interstage transformers 90 degree horizontally.
I also CNC a black matte acrylic front panel for TU8600 to match my TU8800. (note: TU8800's case was also painted to black to match TU8600)
About the sound, I was happy with my 1959 WE300B and 1982 WE437A, but shocked by the engraved base WE300B and 1952 WE437A brought by my friend for AB test.
Have fun.
but I never made up my mind which 300B architecture to go.
At end of 2021, TU-8600 with LL2785B cured my decidophobia.I bought one TU-8600R and ordered a pair of LL2785Bs from Taiwan dealer THL.
I could not wait to enjoy music played by the vintage 300B, so I tried the transformer LL1623 on hands before LL2785B arrive.
LL1623 sounded excellent with thicker mid range compared to the LL2875B which was a bit more air and more clear sound stage.
I liked both of them and was glad that I could swap based on my moods ! ^_^.
Although TU-8600+Lundahl's transformers were excellent, but my target was an amplifier with all WE tubes.
TU-8600's case is small and outputs of AC power transformer can't support WE274A/B tube rectifier and DC coupling,
so WE417/437- interstage transformer - 300B was the choice.
For the interstage transformer, I used LL2756 and wired it to 1:2 ratio to get 2x voltage gain and accommodate the high bias current of WE437.
I re-wired the input tube sockets for WE417, made a conversion sockets for WE437 and made cathode resistors replaceable for adjusting bias current so that I can try both tubes.
Due to WE437's cathode current can be as high as 40mA, add a buffer transistor with heatsink after the high voltage regulator LR8 for suppling voltage to WE417/WE437 is necessary.
Fortunately, all the 5 transformers can be put into the case by turning the power transformer 90 degree vertically and output transformers and interstage transformers 90 degree horizontally.
I also CNC a black matte acrylic front panel for TU8600 to match my TU8800. (note: TU8800's case was also painted to black to match TU8600)
About the sound, I was happy with my 1959 WE300B and 1982 WE437A, but shocked by the engraved base WE300B and 1952 WE437A brought by my friend for AB test.
Have fun.
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