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In Reply to: RE: Cary CAD 300 SEI dropping out posted by badteacher on August 20, 2016 at 11:03:55
If it's both channels it's something in the power supply or some thing that can control BOTH channels, like a faulty switch.But my money is on something in the power supply. Does it have a rectifier tube? Do a visual check on the board and capacitors. Look for any physical changes.
Post your findings.
Charles
addendum I noticed it has a driver tube. Try changing that one. And also check it's components for changes.
Edits: 08/20/16Follow Ups:
Thanks for the suggestions. I swapped out both 6SN7 driver tubes. As for a rectifier tube, I don't think so. From the Cary manual: "The power supply is a full wave center tap configuration running high voltage, high current fast switching diode rectifiers. The rectified 450 VDC is fed to a PI-L filter network."
As an electronic newbie, I am a bit nervous about opening it up. Based on the case, it looks like after removing the tubes, I have to flip it upside down to remove the bottom plate in order to inspect the innards? Is it okay to turn the transformers upside down?
when this happens and they measure good it could be something in the B+ power supply. Most likely the rectifier tube. Do you have a spare to try? If not, then you have to buy one to try to make sure.
Have you also tried calling Cary? Sometimes companies will honor warranties that are expired if it's not too far out from the expiration date. Won't hurt to try.
They are good folks to work with. Helped with with a tough trouble shoot and didn't milk me on the service issues.
I recently had a very positive experience with Cary service. Great service at a reasonable price.
Looked at the pictures. No rectifier tube so it looks like a component in the power supply is fading. I recommend he has it checked FAST before it blows and takes a bunch of stuff out with it.
The amp has solid state rectifiers, so something is going bad. I recommend not turning it on again until a technician or Cary looks at it.
Thanks for the advice on keeping it powered down. I am disconnecting the power cord. I sent an email to Cary and will follow up with a phone call on Monday to them.
John
John,
If you would like a local opinion, contact Pat Hickman @ Classic Tube Audio. He is in Camus, has a top notch lab and worth the trip if only just to see his setup.
Graham,
I shot Pat an email and he got back to me in a matter of minutes. I am going up to Camas on Friday.
John
Good call John, I think you will be glad you did.
Edits: 08/25/16
Graham,
Thanks for the lead in Camas. I think I will contact them and see what they have to say. I would prefer not to ship it across the country. I could also have them check out all of my tubes while they are at it.
Happy Listening,
John
I would be very interested what the cause was.
Cary's prompt response to my email inquiry:
"Most likely what is happening is your filament supply is failing. You'll have to measure and monitor the voltage for the 300B tubes over time to see if it falls off to zero. If it does then it is most likely the rectifier bridge that is failing and will have to be replaced. Let me know what you would like to do."
I will be taking it to Classic Tube Audio in Camas Washington this Friday; will post a followup once the repair is complete.
John
My moneys on failing solder joint in the PS
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