I just bought an old portable record player with a vacuum tube amp and speaker built in. Everything works, but something's wrong with the sound. The bass sounds good and the hi tones aren't bad, but somewhere in the midrange it just sounds BAD--scratchy or "blown" or something. It does this at all volumes.
Could it be a tube? There are three (2 50c5's and a 12ax7) and one of the 50c5's has a black mark on the glass. I'm not sure if this is a sign of anything or not. Any thoughts on what I should try? How to troubleshoot this?
The black mark on your tube isn't a problem. The other tubes will also have this mark but may be in a different place.
If you have a meter measure voltage on pin #2 in relation to pin #1 on your 50C5's. Pin #2 should be around - 5 volts. If it's zero or positive you will have distortion.
Norm
:I'm pretty out of my league here--only some electronics knowledge and this is my first time working with tubes--but if anyone could spare some knowledge I'd truly appreciate it.
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:I just bought an old portable record player with a vacuum tube amp and speaker built in. Everything works, but something's wrong with the sound. The bass sounds good and the hi tones aren't bad, but somewhere in the midrange it just sounds BAD--scratchy or "blown" or something. It does this at all volumes.
:
:Could it be a tube? There are three (2 50c5's and a 12ax7) and one of the 50c5's has a black mark on the glass. I'm not sure if this is a sign of anything or not. Any thoughts on what I should try? How to troubleshoot this?
Most likely a leaky coupling cap between 12AX7 and 50C5 if you don't have negative grid voltage. Grid resistor could also be very high or open.
Norm
:I would think it is more than just a tube. It would more likely need the capacitor replaced.