Hi All, I have inherited a cyrus 3 amp, i believe its an early revision with PT77 finals. It sounded truly awful when i tested it! It defo. not been used for many years. I had a quick look inside & found numerous capacitors way out of spec. some were bulging others were dead! change a few just wating for new insulators to arrive in the post.
My query is, can anyone tell me what the idle current/voltage should be set at? the amp has not been opened by anyone and is, (sorry was until i did) as it left the factory (hopefully)
I have noticed they used silicone? type thermal pads & paste to case side is this normal?
Also is there any recommedations for the 2 reservoir caps, I cant find any 7000uf 50v rated types anywhere?
Thanks
My query is, can anyone tell me what the idle current/voltage should be set at? the amp has not been opened by anyone and is, (sorry was until i did) as it left the factory (hopefully)
I have noticed they used silicone? type thermal pads & paste to case side is this normal?
Also is there any recommedations for the 2 reservoir caps, I cant find any 7000uf 50v rated types anywhere?
Thanks
That would be because that's not a standard value. See whether you can find a small enough 6800 or 8200 µF part with the right number of pins, pin spacing etc.
Usually those caps are the ones to be least concerned about anyway. They rarely go bad in regular domestic use unless either marginally sized in voltage handling (Rotel's '70s receivers had a bit of a problem with that, for example) or of dubious quality to begin with. For ~40 V rails, other manufacturers have used custom 56 V caps in the past, but 50 V is by no means unreasonable. The next standard value up would be 63 V.
First check all the 0.22R emitter resistors for proper value.
Set the bias to 8mV across the 0.22R emitter resistor test points when warm.
Cyrus 3 - Manual - Stereo Integrated Amplifier - HiFi Engine
Set the bias to 8mV across the 0.22R emitter resistor test points when warm.
Cyrus 3 - Manual - Stereo Integrated Amplifier - HiFi Engine
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Hi sgrossklass, many thanks for your reply.
I had a feeling they would be specials that cyrus had custom made. 1 has blulged on top, so probably best to replace both rather than have an odd one
I might give cyrus a call & see if they keep them as a spare part. not a big fan fan of increasing values dramatically & like to keep things as close to how it was designed, if that fails i'm sure i can find some 6800uf that will fit.
I had a feeling they would be specials that cyrus had custom made. 1 has blulged on top, so probably best to replace both rather than have an odd one
I might give cyrus a call & see if they keep them as a spare part. not a big fan fan of increasing values dramatically & like to keep things as close to how it was designed, if that fails i'm sure i can find some 6800uf that will fit.
Hi rayma, Many thanks for the reply & link to service manual, I didn't think Cyrus service manuals were available!
I would buy newly manufactured caps. Don't get NOS, get fresh inventory from Mouser, Farnell, etc.
Remember the tolerance is at least 20%, so 8200uF is well within spec. Higher voltage is a big plus.
In the 80s and before, electrolytics often started out well above specified value, where now it's more common to find them coming in at less than the specified value (within the tolerance).
I would go 8200, or even 10000 to replace an older 7000u cap.
You'll also find the physical size / performance ratio has improved over time.
Within reason, larger caps here will not harm the performance or longevity of the amplifier. Indeed they may improve slightly the peak power handling of the amplifier.
I would go 8200, or even 10000 to replace an older 7000u cap.
You'll also find the physical size / performance ratio has improved over time.
Within reason, larger caps here will not harm the performance or longevity of the amplifier. Indeed they may improve slightly the peak power handling of the amplifier.
Hi Rayma, I have read through the manual, It seems there are several revisions of the Cyrus 3, the section on bias current says to set to 2mV (HA7A3145 revision) on the test points, does the measurement differ if you read the current across the 2 outside legs of the 0.22R resistor, the test point according to the manual is CRN/CLP & + side of speaker socket😕