Anyone know what's wrong with my amp?

  • Thread starter Thread starter fat_fleet
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fat_fleet

fat_fleet

Swollen Member
Crackling noises have been getting worse the last couple weeks. It makes me very sad.
It's definitely the amp head- I tried multiple amps/cabs/cords/guitars with the same results-

Noises are not present unless a cord is plugged in. Once a guitar is connected, lowering the master gain on the guitar eliminates the crackling completely, but if I then unplug the guitar it comes right back.

It's a '68 Fender Bassman. Here's a clip, thanks in advance if you can help-

:-(
 
That would be awesome if that's all it was, but if so would lowering the gain on the guitar make it stop like it does?
And unplugging the instrument cable from the amp?
 
I'd still try swapping out the preamp tubes just to eliminate the most obvious possible cause.
 
Ok. Couple quick quesses.

1. For new tubes (JJs, Groove Tubes etc) Russian is considered better than Chinese right?

2. Is there anything to the NOS glass myth? And if so, where would I notice the difference more? With the power tubes or pre-amp tubes? Thanks.
 
fat_fleet said:
1. For new tubes (JJs, Groove Tubes etc) Russian is considered better than Chinese right?
Click to expand...
Yes

fat_fleet said:
2. Is there anything to the NOS glass myth?
Click to expand...

Yes some NOS tubes are far better than modern tubes.

fat_fleet said:
And if so, where would I notice the difference more? With the power tubes or pre-amp tubes?
Click to expand...

It depends on the amp but IMO preamp tubes make more of a difference. If you don't want to spend a crap load of money for NOS tubes then get some new Tung Sol 12Ax7.
 
That's an old amp. Have you ever had it looked at by a real amp tech? It could be well worth it. He can check/replace your filter caps and all the other stuff that ancient tube amps need done. As for swapping tubes, give it a try. Preamp tubes are cheap. If you mess with power tubes, learn how to check and set your bias.
 
Well, I swapped out the power tubes, phase inverter, one preamp tube (v3), and cleaned all the sockets and I think I killed the crackling, though when I get a chance to really put it through it's paces later I'll know for sure.

ocnor said:
It depends on the amp but IMO preamp tubes make more of a difference. If you don't want to spend a crap load of money for NOS tubes then get some new Tung Sol 12Ax7.
Click to expand...

I'm still trying to decide what I'm going to put in the preamp section. Why new Tung Sols? Are they better than JJs/Grooove Tubes?

Greg_L said:
That's an old amp. Have you ever had it looked at by a real amp tech? It could be well worth it. He can check/replace your filter caps and all the other stuff that ancient tube amps need done. As for swapping tubes, give it a try. Preamp tubes are cheap. If you mess with power tubes, learn how to check and set your bias.
Click to expand...

Nah... I just bought it a year and a half ago it had allegedly been serviced recently. The guy still had receipts for recent Mercury Mag transformers and I guess I assumed that all the routine stuff (tubes, filter caps) were up to date. Now I'm not so sure.
The AB165 Bassmans don't have proper bias circuitry. Instead they have a "hum balance" pot.
 
fat_fleet said:
I'm still trying to decide what I'm going to put in the preamp section. Why new Tung Sols? Are they better than JJs/Grooove Tubes?
Click to expand...

Groove Tubes are just rebranded tubes from other manufacturers which cost more because they slap a sticker on them. JJs are decent utility tubes that are good to keep around as spares because they are fairly rugged and sound ok in most positions. I like Tung Sol because they have a good amount of gain,are pretty quiet,and have an open/less compressed sound than JJs.
 
JJ's can also sound kind of dark for whatever reason. I'm not a tube guru, but I've played around with a handful of them, and JJ's are my least favorite.
 
Crackling on my amp is always the first sign I need new tubes...I've learned to replace them before it gets worse and loses volume.
 
Google search is turning up 'bad plate load resistors' but that's a little beyond my expertise.
 
could be any number of things. Bad caps can cause odd sounds like that too. The tech (if he's any good) is gonna be the best way to go.
 
fat_fleet said:
2. Is there anything to the NOS glass myth? And if so, where would I notice the difference more? With the power tubes or pre-amp tubes? Thanks.
Click to expand...

IMHO Yes there is something to the myth about NOS glass. Here's my take on it. For the tube types I have any experience with, the best NOS tubes sound better than new production tubes. The better new production tubes are as good or better than much of the remaining NOS stuff. It's very easy to buy NOS tubes that aren't up to snuff, sometimes from very reputable dealers (who will at least take them back). After alot of experimentation I've settled on new production Tung-Sol 12AX7s, JJ EL84s, Tung-Sol 6V6s, & Winged C 6L6s. I haven't tried enough different versions of other types to make a recommendation.

Groove Tubes are very inconsistent. the best ones sound great but you can't count on the next one to sound the same.

Tone is subjective. My choices may not be the best ones for you.
 
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