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Old 13th February 2016, 05:53 PM   #1
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Default 300B's inserted wrong. OMG!

Hello!

I am new here. I would appreciate some help or suggestions.

Last October I moved from Columbus, Ohio to Dallas, Texas--1019 miles. My stereo sat in a storage building in Columbus from July through October and then in a storage building until mid December down here in Dallas. After the movers finally put it in the house down here in Dallas, I just looked at it until yesterday, when I finally decided to get it set up.

My amplifier is old (+20 years) and I built it. It is called Audio Note Kit One and it came from England. It had performed faithfully all these years, until today. It took me a very long time yesterday to wire things up. (I hadn't touched the wiring or thought much about it for 20 years!)

So, I insert the Jolida 300B's and the other tubes and turn on the power. I get loud AC hum. I turn it off. I disconnect the speaker cables (four horns). I turn it back on. Suddenly acrid smoke arises from the Kit One. It appears to be coming from one of the transformers but it may have been coming up through the vents in the chassis. I turn it off as fast as I can. I remove the power tubes and realize I have inserted them with the labels facing the front of the amp. But the labels are 90 deg off from the pins. I had the large and small pins misaligned--instead of two large pins in front there were one large and one small pin in front. The Amp requires the small pins to be at the rear of the socket. (With my old tubes, the labels faced the front and I never gave it a thought.)

I put the 300B's and other tubes back in correctly and turned it on. The rectifier tube and the three small tubes light normally, but not the 300B's. They DO get warm but they don't light up. I tried an older set of power tubes. Same thing.

This old Kit One does not have a fuse built in or this probably wouldn't have happened.

I am not particularly adept at electronics. Pretty much monkey-sees monkey-does. I have a voltmeter but no voltage schematic.

After you stop laughing, I would appreciate any helpful suggestions. : )

Much thanks,

Lowtech75
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Old 13th February 2016, 06:30 PM   #2
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If you powered it up and off almost straight away, I would say the transformers were probably OK. To check this, remove the 300B's and power it up. If all OK, insert the 300B's in the correct way around, it can happen to the most experienced of us so don't worry, if all is OK, there may be damage to the HT supply feed resistor.
Fingers crossed for you and if it is the latter, take a look, it will be obvious.
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Old 13th February 2016, 09:18 PM   #3
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Much Thanks! Yes! There is a large resistor (23W 1.5K) that was swollen and discolored. Also a small (3K3) resistor actually charred. Also a fractured 10K Ohm on the driver board. I will start by replacing those and see if that does it. Appreciate your rapid response! Cheers!

Lowtech75





Quote:
Originally Posted by JonSnell Electronic View Post
If you powered it up and off almost straight away, I would say the transformers were probably OK. To check this, remove the 300B's and power it up. If all OK, insert the 300B's in the correct way around, it can happen to the most experienced of us so don't worry, if all is OK, there may be damage to the HT supply feed resistor.
Fingers crossed for you and if it is the latter, take a look, it will be obvious.
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