View Single Post
Old 13th Feb 2018, 10:15 pm   #7
tri-comp
Heptode
 
Join Date: Oct 2008
Location: Aalborg, Denmark
Posts: 903
Default Re: Marantz 2230 tuner amp

You could have received fake transistors. Possibly common with semiconductors sold on the Bay from China and other places. I've been there with 2N3055. Since you actually paid more than next to nothing, you should at least expect to receive the genuine article. My 2N3055's were CHEAP so I had it comming.
If you didn't maybe the problem is caused by instability or selfoscillation in the output amplifier. Substituting with BU208A will drastically lover the frequency response of the output transistors. The BU208A has a transition frequency (fT) of just 4-5MHz which is LOW as output transistors go. The 2SC897 manages a fT of 15MHz which may just be enough to set off the deadly oscillation. The current gain (hFE) of a BU208A is also very low compaired, below 5 which is about 5 times lower than that of the 2SC897 adding to the instability problem.
You should do a re-cap (replace all electrolytic capacitors) on both output amplifier boards before mounting any new output transistors imho, and while you're at it do the same to the low voltage regulator board P800.
Then there's the problem of a Marantz 2230 not using 2SC897 as output transistors at all. My servicemanual for a 2230 states 2SD217 as output transistors. How can that be ?
tri-comp is offline