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dsergeant · 23rd Jan 2020, 5:55 pm

This first edition of the Cyrus One amp has one amp shorted. In fact just Q43 and the MJE243 driver Q33 in the upper half of the amp are shorted but best replace them all. R95 the 0.22R sense resistor is badly burned but measures correct. I have the service manual.

The original PT7/BUV28 transistors seem largely unavailable at sensible price. One thread here suggested a MJE3055T but that at 60V max Vce looks a bit marginal to run off the amps +/-30V rails. What is the recommended replacement nowadays?

Thanks
Dave

23rd Jan 2020, 5:55 pm	#1
dsergeant Octode Join Date: Mar 2006 Location: Bracknell, Berkshire,UK. Posts: 1,172	Cyrus One This first edition of the Cyrus One amp has one amp shorted. In fact just Q43 and the MJE243 driver Q33 in the upper half of the amp are shorted but best replace them all. R95 the 0.22R sense resistor is badly burned but measures correct. I have the service manual. The original PT7/BUV28 transistors seem largely unavailable at sensible price. One thread here suggested a MJE3055T but that at 60V max Vce looks a bit marginal to run off the amps +/-30V rails. What is the recommended replacement nowadays? Thanks Dave