Mc275ce

[Tubesin]

Like to share some experience in servicing the McIntosh MC275CE for red plate kt88 and found that the buffer tube 12AZ7/12AT7 quality is very critical in setting the bias to the powr tubes, unbalanced and poor buffer tube in this place will cause the power tube to fail. Also failed the 18k cathode resistor...
I found that this amp use a 2.2M resistor plus a parallel 0.1mf to couple from the V2 to V3, but, don't understand why they do that, as usually a coupling cap of 0.1mu is enough.....! Will someone have the answer?

[jane]

Originally posted by Tubesin
I found that this amp use a 2.2M resistor plus a parallel 0.1mf to couple from the V2 to V3, but, don't understand why they do that, as usually a coupling cap of 0.1mu is enough.....! Will someone have the answer?

Lower phase shift: The phase shift will be limited to less than 60 deg.
It will also bias V3: Vg{V3}=Va{V2}*220/(2200+220)=~23Vdc.

Jan E Veiset