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Post subject: Fender Bassman hiss
Posted: Sun Feb 12, 2012 6:16 am
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I've just taken delivery of a 6 month old, 2nd-hand '59 Bassman Ltd and I love the tones. However, the hiss when you go past 2 on the normal channel (and, to a lesser degree on the bright) is annoying and positively monumental at 5!! I don't need to have anything plugged into it. I never expected this on a relatively new amp. Any techheads available to comment?


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Post subject: Re: Fender Bassman hiss
Posted: Sun Feb 12, 2012 6:20 am
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A bad ( noisy ) 12AX7 tube ?

Remove the first one, view from the back , the one at right , if no more hiss , replace this one.

If hiss, try the second tube, no hiss replace the second tube......


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Post subject: Re: Fender Bassman hiss
Posted: Sun Feb 12, 2012 11:29 am
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+1

You might also want to try a 12AY7 in the V1 position as used in the original Bassman. I used this in my hand-wired 5F6A clone I just finished building and it sounds great.

http://www.kcanostubes.com/content/nos-jan-ge-12ay7

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Post subject: Re: Fender Bassman hiss
Posted: Mon Feb 13, 2012 6:02 am
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Ok, I'll try that later this morning.

And I did. Tapping the 1st valve with a screwdriver, with volume at 5, you can here the 'tap-tap' rather loud; the others don't make much nosie when you tap them. I swapped the 2nd valve into the 1st slot and put in another GT valve (from my Blues Junior) into 2nd slot. The hiss is much more liveable, thoguh still there when you crank it right. Guess I shoul just get another pair of 12AX7s?


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Post subject: Re: Fender Bassman hiss
Posted: Mon Feb 13, 2012 2:25 pm
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Jaykeyhunter wrote:
Ok, I'll try that later this morning.

And I did. Tapping the 1st valve with a screwdriver, with volume at 5, you can here the 'tap-tap' rather loud; the others don't make much nosie when you tap them. I swapped the 2nd valve into the 1st slot and put in another GT valve (from my Blues Junior) into 2nd slot. The hiss is much more liveable, thoguh still there when you crank it right. Guess I shoul just get another pair of 12AX7s?


This mean nothing. Tapping the tube is not good for finding hiss, Only for finding microphonic tube

You did not do the test the way I suggest.


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Post subject: Re: Fender Bassman hiss
Posted: Mon Feb 13, 2012 7:49 pm
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stratele52 wrote:
Jaykeyhunter wrote:
Ok, I'll try that later this morning.

And I did. Tapping the 1st valve with a screwdriver, with volume at 5, you can here the 'tap-tap' rather loud; the others don't make much nosie when you tap them. I swapped the 2nd valve into the 1st slot and put in another GT valve (from my Blues Junior) into 2nd slot. The hiss is much more liveable, thoguh still there when you crank it right. Guess I shoul just get another pair of 12AX7s?


This mean nothing. Tapping the tube is not good for finding hiss, Only for finding microphonic tube

You did not do the test the way I suggest.


+1

And for heaven's sake, don't tap the tubes with a screwdriver! :shock:

Tap them gently with the eraser end of a pencil or a wooden chop stick. :wink:

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Post subject: Re: Fender Bassman hiss
Posted: Tue Feb 14, 2012 2:21 am
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I use myself a screwdriver... I hold it by the bit and tap gently with the rubber handle.

When doing hand working , in amp or other thing, it is more important to use is head than his hand......


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Post subject: Re: Fender Bassman hiss
Posted: Tue Feb 14, 2012 4:34 pm
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stratele52 wrote:
I use myself a screwdriver... I hold it by the bit and tap gently with the rubber handle.

When doing hand working , in amp or other thing, it is more important to use is head than his hand......


Ummm, I assumed the OP used the metal end. :lol:

I still think something wooden and light is better. Don't need to hit the tube that hard to get it ringing. :D

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Post subject: Re: Fender Bassman hiss
Posted: Tue Feb 14, 2012 5:06 pm
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stratele52 wrote:
I use myself a screwdriver... I hold it by the bit and tap gently with the rubber handle.
.


Yes I hold it by metal end ( bit ? ). Small screw driver do the job very well . Wood conduct electricity .Tube's glass has no voltage but I read some people use wooden chopstic everywhere in the amp. I won't do that.


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Post subject: Re: Fender Bassman hiss
Posted: Tue Feb 14, 2012 5:15 pm
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stratele52 wrote:
Yes I hold it by metal end ( bit ? ). Small screw driver do the job very well . Wood conduct electricity .Tube's glass has no voltage but I read some people use wooden chopstic everywhere in the amp. I won't do that.


Ummm, a wooden chopstick does not conduct electricity. Measure one with an ohm meter if you don't believe me.

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Post subject: Re: Fender Bassman hiss
Posted: Wed Feb 15, 2012 2:35 am
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bluesky636 wrote:
stratele52 wrote:
Yes I hold it by metal end ( bit ? ). Small screw driver do the job very well . Wood conduct electricity .Tube's glass has no voltage but I read some people use wooden chopstic everywhere in the amp. I won't do that.


Ummm, a wooden chopstick does not conduct electricity. Measure one with an ohm meter if you don't believe me.


Yes I believe you.
Ohmeter is not the tool for that ; too low current and voltage. Probably an electrician Meger will do .


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Post subject: Re: Fender Bassman hiss
Posted: Wed Feb 15, 2012 3:06 am
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bluesky636 wrote:
Ummm, a wooden chopstick does not conduct electricity. Measure one with an ohm meter if you don't believe me.


Having seen someone get one hell of a jolt when poking inside a TV with a bit of wooden dowelling, I'd not be trusting a chopstick around the internals of a tube amp. You'd be surprised how good a conductor wood can be when coupled with high voltage and slightly moist fingers.

But for tapping tubes to check for microphonics? No problem there.


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Post subject: Re: Fender Bassman hiss
Posted: Wed Feb 15, 2012 10:48 am
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Vulpinity wrote:
bluesky636 wrote:
Ummm, a wooden chopstick does not conduct electricity. Measure one with an ohm meter if you don't believe me.


Having seen someone get one hell of a jolt when poking inside a TV with a bit of wooden dowelling, I'd not be trusting a chopstick around the internals of a tube amp. You'd be surprised how good a conductor wood can be when coupled with high voltage and slightly moist fingers.


Considering that the flyback transformer of a CRT based TV can output 50,000 volts, anything would become conductive. :shock: :lol:

If what you say is true, then it makes me wonder about the intentions of all those on this forum that advised me to tap all the solder joints with a chop stick in my hand-wired 5F6A clone when I was troubleshooting a crackling noise. :lol: I did just as suggested including tapping the B+ supply (about 450 VDC) and lived to tell about it. :D

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Post subject: Re: Fender Bassman hiss
Posted: Thu Feb 16, 2012 3:26 am
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Heaven's sake, guys, go easy on me! And if a tube can't take a gentle tap with the business end of a 'driver, then it isn't going to last a 300 mile journey and a bunch of package-handlers at the courier depots like this one did!

Anyways,ordered new valves and replaced valve 2 and, as stated, the hiss is nowhere near as bad as before, though if you crank it up to 8+ it's pretty bad.

So, replacing one valve - I followed the procedure you suggested, stratele52 - has reduced the hiss but not eliminated it.


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Post subject: Re: Fender Bassman hiss
Posted: Thu Feb 16, 2012 4:10 am
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Jaykeyhunter ,

Wich tube you remove for the hiss deasapear ?

If no hiss with this tube remove this mean ;

1- tube is noisy , It look this not the case if you put a new one

Or

2- Problem is in the circuit feeding this tube .


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