Hi Rob,
Sorry to see you are having some trouble with the new tubes, especially since your report on the sound was really compelling and positive.
The 275 is a cathode bias amp, meaning there is no manual bias adjustment for each tube. Grid bias is developed by the voltage drop across a resistor in the cathode circuit.
Tubes can be matched at different operating points - an operating point is a specific combination of plate current, plate voltage, and grid voltage.
It is likely that your tube supplier uses a tester that checks and matches the tubes at a different operating point than they see in your 275.
At this point it would be worth sending the quad back and maybe even your good tubes to see if he can achieve a closer match to them.
I can send you a set of oem or “winged c” kt-88’s to use in the interim if you’d like.
There is an overall bias adjustment for all the tubes, the service manual has the adjustment procedure.
Sorry to geek out on you - just hoping for a great outcome.
Tom
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Main System:
Amati Futura Mains
Amati Homage VOX Center,
Proac Response 1sc Rears,
Three MC2301's for L,C,R
MC 602 for the rears
C 1100, MX 151, MCD 1100, MR 80
Nottingham Dais with Wave Mechanic
Sumiko Palo Santos Presentation
SurfacePro 3, RPi 4, ROON, WW Starlight Platinum USB, Schiit Yggdrasil, Benchmark DAC3 HGC
MX 151, OppO BDP-95, JVC RS-500 DILA projector, 106" diagonal Stewart Luxus Screenwall Deluxe with Studiotek 130 G3 material.
Lake House:
Ohm F, MC 275V, C2300, MR 77, Rega P3
OnDeck:
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