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Post subject: Re: Fender Bassman... does this look good?
Posted: Sat Sep 20, 2014 6:46 pm
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stratele52 wrote:
You can do another test ; remove the two 6L6 tubes and power amp ON with a good fuse .

If fuse don't blow you need two new 6L6's .

If you go to see a tech, be sure it is a qualified one if you don't want to loose your money and worse have your amp damaged.


Stratele = very good way to test for shorted tubes.

To continue with this test... if the fuse blows without the 6L6GC's --- you prolly have a bad power supply. Check the caps and resistors under the doghouse. It looks like the two big caps (ones on the right of your photo) are leaking. Just replace all of the caps. I'd even replace the blue Sprague on the left. Then, you'll know exactly when all caps were redone.

Also, check the resistors under the doghouse for out-of-spec (greater than 20% off). And the wiring, for shorts and poor soldering.

If the fuse still blows... pull one secondary wire off the power transformer (and tape it). Install a new fuse. Still blows? Bad power tranny.

Good luck!


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Post subject: Re: Fender Bassman... does this look good?
Posted: Sat Sep 20, 2014 6:58 pm
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BMW2002Ti wrote:
stratele52 wrote:
You can do another test ; remove the two 6L6 tubes and power amp ON with a good fuse .

If fuse don't blow you need two new 6L6's .

If you go to see a tech, be sure it is a qualified one if you don't want to loose your money and worse have your amp damaged.


Stratele = very good way to test for shorted tubes.

To continue with this test... if the fuse blows without the 6L6GC's --- you prolly have a bad power supply. Check the caps and resistors under the doghouse. It looks like the two big caps (ones on the right of your photo) are leaking. Just replace all of the caps. I'd even replace the blue Sprague on the left. Then, you'll know exactly when all caps were redone.

Also, check the resistors under the doghouse for out-of-spec (greater than 20% off). And the wiring, for shorts and poor soldering.

If the fuse still blows... pull one secondary wire off the power transformer (and tape it). Install a new fuse. Still blows? Bad power tranny.

Good luck!


I put a new fuse in and pulled the 2 tubes. The amp stayed on! Now I need to find some tubes. I did't; realize how expensive tubes were until I just started looking.

Thanks for all the help.

On a side note, the person I bought this from said the the amp worked great and there were no issues. I bought it online so I guess the tubes could have been damaged in shipping? Does that sound reasonable?


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Post subject: Re: Fender Bassman... does this look good?
Posted: Sat Sep 20, 2014 9:17 pm
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Before you buy new 6L6GC's, be sure that the bias power supply is ok. It should be putting out around (-) 45 to 50 VDC at read point.

What year model Bassman do you own? Need to get correct schematic, online.


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Post subject: Re: Fender Bassman... does this look good?
Posted: Sun Sep 21, 2014 1:18 am
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BMW2002Ti wrote:
Before you buy new 6L6GC's, be sure that the bias power supply is ok. It should be putting out around (-) 45 to 50 VDC at read point.

What year model Bassman do you own? Need to get correct schematic, online.



First post ; 67-68 :lol:

Lespaulist .

One or both of your tube look short OR circuit around these tubes is defective.
Ask the seller a refund , some money to buy new tubes.

Follow BMW advise.

New tubes need a bias check and adjust if needed by a qualified tech .
Wrong bias = poor sound or short tubes life .
Also a cleaning and tighten socket pins.


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Post subject: Re: Fender Bassman... does this look good?
Posted: Sun Sep 21, 2014 7:00 am
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" First post ; 67-68 " :lol:

I knew that! When in doubt, read the entire thread. :oops:

Your circuit, most prolly: AB165

http://bmamps.com/Schematics/fender/bas ... _schem.pdf

The bias voltage should read (-) 45 VDC at the wiper (middle tang) of the balance pot. Pot turned to midpoint. Check the voltage at pin 5 of the 6L6GC sockets (tubes out). Should be around negative VDC.


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Post subject: Re: Fender Bassman... does this look good?
Posted: Sun Sep 21, 2014 11:41 am
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The label on the inside of the amp does say it is a AB165.

I think I am in over my head as far as the re-bias. I am going to take it to a tech and see what they say. Between the cost of the tubes and this work I'm not sure if it worth keeping.

Thanks for all of the help and insight.

I have a set of groove tubes below in the amp now:
Image


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Post subject: Re: Fender Bassman... does this look good?
Posted: Sun Sep 21, 2014 3:34 pm
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lespaulist wrote:
Between the cost of the tubes and this work I'm not sure if it worth keeping.

Seriously? Fix it and you have a cool vintage amp, well worth the investment $, £, €.

_________________
If you hear voice within you say.."you cannot play"...then by all means play guitar and that voice will be forever Silenced Vincent Van Gogh

I know I can't play, I don't care


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Post subject: Re: Fender Bassman... does this look good?
Posted: Sun Sep 21, 2014 3:49 pm
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Flinly wrote:
lespaulist wrote:
Between the cost of the tubes and this work I'm not sure if it worth keeping.

Seriously? Fix it and you have a cool vintage amp, well worth the investment $, £, €.


+10000


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Post subject: Re: Fender Bassman... does this look good?
Posted: Tue Sep 23, 2014 11:39 am
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The amp is definitely worth keeping and having the needed maintenance done by a worthy tech. Looks like someone did some skimpy maintenance already. If you have it completely done now, it will in return provide you with years of tonal pleasure. While your new amp tech is getting the amp ready, you could go to your local library and order in "The Guitar Amp Handbook" by Dave Hunter. It would be good info for you in the future.

UN


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