issue with '66 bassman

[charriman]

Hey guys, I have a '66 bassman that was recapped, 3 prong cord installed and new powertubes about 5 years ago. It seems to be making some noises.
The first noise is when it's been powered on a while. It's like popping and crackling. Even with the volume turned down. The second is like i'm running a fuzz box as the note dies out. Really faint in the background. Here are some links to a couple of mp3s i made of the amp for reference. Any ideas what may be causing both?

http://mysite.verizon.net/vzez97g5/bassmannoise.mp3
http://mysite.verizon.net/vzez97g5/bassmannoise2.mp3
Thanks in advance
Chad

[brad347]

Have you tried swapping tubes?

[gldtp99]

Bad tube(s) and/or dirty tube sockets are always the first place to look in a situation like this.............gldtp99

[slider313]

Bad 100K plate load resistors will give you plenty of snap,crackle and pop.

[charriman]

Have you tried swapping tubes?

I was trying to avoid that since all of the pres are original. The 6L6's are Svetlanas.

[charriman]

bad 100k plate load resistors will give you plenty of snap,crackle and pop.
:beer

[AL30]

I was trying to avoid that since all of the pres are original. The 6L6's are Svetlanas.

You've got 40 year old tubes in there. Even great tubes go down. Hoepefully it's not one of 'em but... take a known good preamp tube and swap 'em out one at a time. You might wanna try another set of power tubes also. Worse case scenario is you end with a back-up set of tubes which you're going to need sometime anyway.

If that's not it check the insides for loose connections, bad solder joints, plate loads etc.

A friend had this same problem with his Twin Reverb. Two of the 470 ohm resistors on the power tube sockets were cracked in half. One was noticeable at first glance the other just fell in two pieces when it was unsoldered. Something to think about.

AL

[skipm45]

Two of the 470 ohm resistors on the power tube sockets were cracked in half. One was noticeable at first glance the other just fell in two pieces when it was unsoldered.

+1
Screen resistors are a fairly common failure in older amps. The original wattage on these is only 1W
If that's the case replace, with 2W or even 5W resistors


Skip

www.skipzcircuits.com (http://www.skipzcircuits.com)

[tlpruitt]

Have you tried swapping tubes?
I was trying to avoid that since all of the pres are original. The 6L6's are Svetlanas.

Can't say I am on board with your logic there, charriman. It's okay to swap tubes when you are troubleshooting a problem. If it turns out the tube is not the problem then you can put the "original" back in.

My guess is you have a 100k plate load resistor and/or a preamp tube problem.

-Tim