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Fender Studio Bass weird noise

poorbassist15

poorbassist15

Dec 29, 2009
1,372
148
Danville, VA
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#1
So I just got my Studio Bass back from the tech and I have to say I LOVE it. It occasionally has some crackling/bacon frying noises that I'm attributing to the fact it was probably drug on the bottom of the Mississippi for about 5 miles, a cleaning of the pots has seemed to remedy that problem. I have been told some of the tone caps are also not quite to spec but that the amp was tested and verified working with new power tubes.

The issue is upon shutdown of the amp I get like a pinging sound that's reminiscent of the noise a car's exhaust makes after shutdown as it cools. The tubes are Tung Sol 7581As, and they weren't cheap tubes(as I'm sure you guys know). I've not had the amp at true gig levels yet(because it's simply too damn loud for my house), I will test it on a gig next weekend. I've had a couple of tube amps and none of them ever made this noise so I'm chalking it up to me just not being super familiar with them. Can anyone tell me if this is normal?
 
#3
Those are nice tubes, I use them in an Ampeg V4B. Like Rod said, it sounds like it is related to the tube cooling. Mine don’t ping as you described but tubes doing this is not unusual. It can go away with time.
 
#4
No speaker noise that I can tell, just a pinging sound. The 7581As run hotter than any tube I've ever used, so much so that I can feel the heat coming off of them with the head out of the cabinet. I think a fan is in order when I get the head cabinet for it. I didn't know tubes could run that hot so that's possibly it.
 
#5
poorbassist15 said:
No speaker noise that I can tell, just a pinging sound. The 7581As run hotter than any tube I've ever used, so much so that I can feel the heat coming off of them with the head out of the cabinet. I think a fan is in order when I get the head cabinet for it. I didn't know tubes could run that hot so that's possibly it.
Click to expand...

The bias should be checked if it hasn't been. That can make them run hotter if the bias is set to have a higher cathode current. These tubes can run very hot, they are capable of more plate dissipation than a 6L6GC. People bias them hotter to get a little more power out of the amp.

In general, it can help to blow a small desk fan into the back of a hot running amp. I use one of these: https://www.amazon.com/Caframo-7-Inch-White-Chinook-Fan/dp/B0010UPOEQ.
 
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#6
I have a Studio Bass with 7581A's too. great amp!

sounds like you are just hearing the tubes pinging a bit as they cool which as others have already said, is pretty normal.
The tubes running super hot is not so normal in my experience. They are tubes and they do throw off some meaningful heat .. and the 7581A's dissipate 5w more per tube than the std 6L6GC's .. but they should not be burning the thing up. I would strongly advise you to follow Beans-on-toast's guidance and have the amp's bias checked specifically for the higher dissipation 7581A's.

as for the cost of the Tung Sol 7581A's, they are not that much more expensive than good 6L6GC's or STR's in my experience. Tung Sol's 7581A's run around $27/tube compared to Tung Sol 6L6STR's @ $22 each or Tung Sol 6L6GC's @ $24 each ..... so not a huge difference in price.

enjoy the Studio Bass .. it kicks some serious old-school booty and the eq section gives you tons of tone shaping options over the std Fender tone stack.
 
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#8
poorbassist15 said:
I believe that the tech biased it according to 7581A specs. It's not the transformers running hot, it's the tubes themselves. It makes me think that these tubes are no joke, and tonally, thus far I have to concur.
Click to expand...

More current through a tube translates into more heat. So you would expect more heat from the tubes. There is a range within which you can bias a tube, it isn’t one voltage written in stone. Some choose to run them more conservatively rather than the typical 70% maximum plate dissipation. This allows the tubes to last longer.

These options are worth discussing with your tech when the bias is being set. The best option is to bring in your bass and cabinet and have the tech set the bias voltage at 70%, play through the amp and note how it sounds. Then dial it back to 65% or 60% and compare. Then decide which you prefer at gigging levels.

In the case of my V4B for example, setting the 7581A’s at 60% maximum plate dissipation works well for me. There is a bit less grind, a few less watts. You don’t tend to run the amp flat out anyway.
 

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