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I have a fine sounding persnickety Counterpoint SA-5.1 pre amp in the second system. It just blew the AC input fuse. I put in a 3 amp fuse as I could not immediately source a 2 amp fuse. Poof! Blue flame, open fuse. I got creative and disconnected the umbilical from the power supply to the pre amp itself. I'm not sure if this is valid as the power supply may require a load for the PS to come up. Poof! The new fuse blew. Same blue puff in the tube.
Before I order another tube, is this how they normally fail?
Follow Ups:
I replaced the 6CA4 tube and the proper 2 amp fuse. Running strong 2 hours later. Sounding fab, and ready for the wifey to watch The Bachelor tonight.
It was a 30 dollar gamble, and I was right in taking it.
I might have mentioned that I had the preamp completely overhauled 10 years ago.
Excellent!
Glad it turned out to be that simple. That's sweet old pre. I had one of Mike Elliott's later designs for 15 years.
When I bought my SA5 back in the mid 80's I remember being told to never run it without the umbilical connected. Mind you this is the SA5, not the SA5.1 you have.
I dug out and took a peek in my manual and it said to wait at least 10 minutes after powering down before disconnecting the umbilical so it could drain. Otherwise the fuse would blow.
Reasonable to think the fuse would certainly blow if not connected and powered up. But again, this is the SA5, and even it had some revisions. Can't seem to find an SA5.1 manual on the net. Weird.
I'm not a technician but have managed to maintain my preamp all these years initially with pro service, but thereafter for decades with lots of help from forums, a DVM, DIY part replacements, and likely dumb luck LOL. The 5.0 and 5.1 are more similar than different so keep posting and I'll certainly see if I can assist in any way.
Good luck with the replacement tube (and fuses!)
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
That preamp has to be what, 40 years old by now? If the caps are original equipment, then extremely high likelihood the power supply is culprit, and a new 6CA4/EZ81 won't help.
Mike Elliott of Counterpoint has gone off into retirement sunset, but just about any competent tech could do the job unless you're up to it yourself.
I am fairly certain the PS caps were changed about 6 years ago. I am going to swap the tube and cross my fingers. Ordered one yesterday. It is worth 25 bucks.
Ozzie,
Don't waste the tube-
There is some part of the power supply that has a short-
A visual inspection could identify it possibly -
A resistor would be discolored, and may also have burned the PCB below it-
An electrolytic cap may have a bulge on the top, or one end (depending upon axial or radial), or possibly a stain/spray around the base/unit from a rupture...
I realize that the $25 may not be much, but if you have done nothing since the last test, I'll wager $100 that it will blow!
Happy Listening
I'd agree with 6bq5, it's broken. With the umbilical cable, it would be separate and the issue is the power supply.
I had a 45 tube and went poof and also smelled like smoke. The culprit was a resistor that was taken out when the old globe shorted out. As 6bq5 mentioned, a PS caps could be a issue or it be a resistor. It's old enough that I'd have someone go through it and replace the electrolytic caps and check resistors and replace anything else that's out of spec.
-Rod
Ozzie,
You describe: " It just blew the AC input fuse. I put in a 3 amp fuse as I could not immediately source a 2 amp fuse. Poof! Blue flame, open fuse."
2X input fuse blew, I would look at P/S Caps to make sure that there is no short to Ground-
However you then say: "I got creative and disconnected the umbilical from the power supply to the pre amp itself. I'm not sure if this is valid as the power supply may require a load for the PS to come up. Poof! The new fuse blew. Same blue puff in the tube." - Did the 6CA4 have a blue spark earlier?
Per the data sheet on the 6CA4 it is fairly robust, and having a reverse voltage could definitely cause the blue flash-
The issue is that there is a short somewhere-
Yes, the tube could be bad (how many hours on it?, how is the getter flash?, still opaque?
I am not sure that the rectifier is the issue- I am more concerned that there is a bad input cap / filter cap that is dooming the system.
You should be able to power the Power supply w/o the PreAmp connected - and you might think about bringing it up on a variac to check voltages -
But based on what you have said so far - my money is on a bad Electrolytic cap.
Yes, there could be a basd resistor or other component, but...
Tube data at Linky
Happy Listening
Exactly, replacement fuse also blew at higher rated value, (3A pops at ~6A).
Keep that up and power transformer may decide it's fuse too.
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