Sunn 300T Fender Bassman 300 Pro crackling noise help

[thedude77md]

I am hoping some of you good folk can offer some input here and in advance, thanks for even reading this.

I recently bought a used Sunn 300T locally (not through TB) from a private seller. It has been nothing but trouble from the moment I brought it home.

Initially, it was making a whistling sound through the drive channel and some hissing at high frequencies. It took two trips and a lot of trouble shooting but a reputable tech fixed it. Worked fine for a rehearsal and then it sat for a few days. The next time I plugged it in, it sounded great but started making a crackling sound, almost like a bad cable but REALLY loud, when I was digging in at all. Back to the tech, he swapped out the pre-amp tubes and it was fine. 20 minutes into firing it up, it started making the same noises again.

I am trying to save myself a little bit of bread in bench time here and am looking for possible problems. In a nutshell:

-At very low input levels (a passive bass with the bass' volume low) it sounds fantastic. I can dime the master volume on the amp and it sounds great still and gets fairly loud

-As soon as I crank the volume on the bass itself or on the the input gain knob for either channel, an overpowering crackling sound comes out of the speakers (I've tried it with several different cabinets and it's always the same problem). When the input level light on the amp doesn't light up at all, no crackle, when it goes to green (normal) sometimes it does, and if I really dig in and the light goes red into clip mode, the crackle is constant. Also, the lower the frequency, the higher the chance of it crackling. My buddy's SG playing power chords even made it do it.


I assume it wouldn't be the output transformer as I can dime the master volume and it doesn't affect the crackling?

From searching the threads here, I think it might be a cold solder joint, some sort of plate resistor, or a problem with the input jack. Any guesses as to what it might be?

I am no tech, obviously, and certainly wouldn't mess with it myself, but I am thinking that if it's the input jack, the crackle would be present regardless of the note's frequency or input level?

Any input is appreciated as I can't afford to shell out much more money into this puppy

[D.M.N.]

Good news is it's most likely nothing to do with the amp itself. It's not the pre-amp tubes. Bad news is it's probably one of your power tubes. Mine did the exact same thing a few weeks back. Horrible crackling sounds, like a bad cable. The bad tube was picking up vibrations, so when you turn the volume up to a point, and there was enough power to start rattling stuff, that's when the crackling started. I removed the back panel, and with the amp on, gently tapped on the tops of all the power tubes. When I tapped one and it made the horrible crackling sound, I turned the amp off and pulled the plug on that pair of tubes. TA-DA! No more crackling, and now you're operating at somewhere close to 200w, but nonetheless still operating without spending anything additional.

That's my advice. Hopefully it helps.

[thedude77md]

Originally Posted by D.M.N.

Good news is it's most likely nothing to do with the amp itself. It's not the pre-amp tubes. Bad news is it's probably one of your power tubes. Mine did the exact same thing a few weeks back. Horrible crackling sounds, like a bad cable. The bad tube was picking up vibrations, so when you turn the volume up to a point, and there was enough power to start rattling stuff, that's when the crackling started. I removed the back panel, and with the amp on, gently tapped on the tops of all the power tubes. When I tapped one and it made the horrible crackling sound, I turned the amp off and pulled the plug on that pair of tubes. TA-DA! No more crackling, and now you're operating at somewhere close to 200w, but nonetheless still operating without spending anything additional.

That's my advice. Hopefully it helps.

I might try that tomorrow. Already had one knock on the door from the neighbor's when I brought it home earlier.

My tech checked all the power tubes and said they were crappy but new (Ruby KT-88's) which I was aware of. He did say they all tested well and pulled all the cheap Chinese solder off them and put quality stuff on. I may see if I can borrow some tubes off someone as I can't shell out the loot for a whole new set at the moment due to all the repair costs. Otherwise I'd be going for it as I know a backup set is good to have (I stopped using tube amps a couple years ago b/c of issues like this and no longer have extras. They sound sooooooo darn good though that I decided to go back)

[D.M.N.]

Yeah, I'm surprised it has Ruby's in it. The previous owner must have switched them out, as they normally come with Groove Tube-branded Svetlana's (you can actually see the Svetlana logo underneath the GT logo on mine), which are pretty good. And yeah, even if you pull the fuse and are only running on 200w, it's still stupid loud.

[thedude77md]

Originally Posted by D.M.N.

Yeah, I'm surprised it has Ruby's in it. The previous owner must have switched them out, as they normally come with Groove Tube-branded Svetlana's (you can actually see the Svetlana logo underneath the GT logo on mine), which are pretty good. And yeah, even if you pull the fuse and are only running on 200w, it's still stupid loud.

He told me he just had a tech put them in and claimed it was completely gone over and given a clean bill of health. My tech found some questionable repairs inside of it so that obviously wasn't the case.

I had one before badged as a Fender 300 Pro and loved it, regretted selling it since. Even with one pair of tubes running it was louder than heck.

[D.M.N.]

Yeah, that's what I'm using, the Fender 300 pro. I can't recall where I read it right now, but I vaguely remember hearing that the first run or so of the Sunn 300Ts had some heat issues or something like that. It could just be hear-say and what not. Either way, the Sunn/Fender 300T/pro is one of the best amps on the market right now IMHO. Hopefully you get things sorted out.

[xjeremiahx]

Originally Posted by D.M.N.

Yeah, that's what I'm using, the Fender 300 pro. I can't recall where I read it right now, but I vaguely remember hearing that the first run or so of the Sunn 300Ts had some heat issues or something like that. It could just be hear-say and what not. Either way, the Sunn/Fender 300T/pro is one of the best amps on the market right now IMHO. Hopefully you get things sorted out.

Interesting, because I posted a thread after I got my 300t, talking about how hot it was getting. Sucker sounds GREAT, but she gets hot, that's for sure.

Hope the amp ends up working out fine man, you know how sweet these things are, hate to see you go through all the trouble, but she's worth it.

Sounds like a power tube to me...$0.02

[D.M.N.]

Well, mine gets pretty hot too, enough so that I feel I could probably strap bacon to the rear screen and grill it up for a tasty snack in between sets. But apparently the really early ones were meting tubes they were getting so hot. I mean, REALLY hot.

[coreyfyfe]

Originally Posted by D.M.N.

Yeah, I'm surprised it has Ruby's in it. The previous owner must have switched them out, as they normally come with Groove Tube-branded Svetlana's (you can actually see the Svetlana logo underneath the GT logo on mine), which are pretty good. And yeah, even if you pull the fuse and are only running on 200w, it's still stupid loud.

They're probably the same tube. Ruby, like groove tubes, just buys and matches other brands of tubes. I actually got Ruby labeled (stickers on the base, not rebranded) Winged C 6550s when I bought my SVT. That was a surprise.

I had a similar issue with a dying power tube before, so that could be it. Try tapping lightly with a pencil until you find the one. Just remember when you pull that pair, it changes the expected impedance on your output transformer, so it probably isn't a good idea to be running 2/3 of your tubes on the same load.

[thedude77md]

Originally Posted by coreyfyfe

They're probably the same tube. Ruby, like groove tubes, just buys and matches other brands of tubes. I actually got Ruby labeled (stickers on the base, not rebranded) Winged C 6550s when I bought my SVT. That was a surprise.

I had a similar issue with a dying power tube before, so that could be it. Try tapping lightly with a pencil until you find the one. Just remember when you pull that pair, it changes the expected impedance on your output transformer, so it probably isn't a good idea to be running 2/3 of your tubes on the same load.

That is one great thing about this amp- it's set up so that if a tube goes, that pair shuts down and the other four keep going at the same impedance. There is a separate fuse for each pair. The design is great. Too bad mine is all jacked up!

[bellis1]

My Sunn did the same exact thing. Sold it right away. (not to you of course)

[thedude77md]

Originally Posted by bellis1

My Sunn did the same exact thing. Sold it right away. (not to you of course)

Any freak chance it was to a guy in Baltimore?

[jastacey]

I have a Bassman 300 Pro, and the tubes that came stock in it were Grove Tubes Branded Sovteks 6550's ... they are an O.K. tube, and if money is an issue that would be the one to buy, the Winged "C" is another choice, but more money ... I also have heard that the Valve Art KT-88 are good and thier KT-100 are good ...most Ruby tubes that I've used in the past have been not very reliable in amps that have plate voltages over 600 volts ... P.S. you might want to get several of the fuses that control the power tubes, as they are an odd size/shape ...just in case !!!!!

[nicfargo]

Yeah, I have the Fender 300 pro...best amp I've ever owned by far. What you have going on is a bad power tube but for some reason it hasn't caused your fuse to go out yet...which is odd. Once you find the tube, pull the fuse, that will let your amp run on 4 tubes at 200w. For that amp, a matched set is best, but honestly you can do a matched pair and be just fine...that should make it a little easier to afford when a tube goes out. You only have to replace a pair rather then all 6.

[thedude77md]

Thanks for the input, guys.

One of the fuses did blow initially but apparently the problem was with the tube socket which my tech fixed and the tube still tested OK.

My tech is taking 'er in again next week and I think I may just take the plunge on tubes if I can work some OT this weekend. Regardless, I will share this with him.

[bellis1]

Sorry it took so long, but @ Thedude77md: Nah, it was in Atlanta, and it was a Sunn 1200s. But had the same problem.

[BassmanPaul]

Originally Posted by D.M.N.

When I tapped one and it made the horrible crackling sound, I turned the amp off and pulled the plug on that pair of tubes. TA-DA! No more crackling, and now you're operating at somewhere close to 200w, but nonetheless still operating without spending anything additional.

That's my advice. Hopefully it helps.

You do realize that you are no longer matched to your load properly. There is no such thing, in an amp with more that two tubes, as a pair unless the amp has an adjustable bias for each pair.

Paul

[eyeballkid]

ya know BassmanPaul,
youre right on that, but what is weird is that ALOT of amps advertise this!
like when i got my 300t I remember some write up that pointed out the features of the amp being that if a tube goes itll blow a pair and you can keep running on 4 tubes at a lower wattage....but they NEVER point out that it changes your Ohm load and can damage it..

Orange does the same thing...
its weird.. youd think theyd say in bold letters "if ya blow a tube STOP PLAYING so you dont damage your amp!'

[thedude77md]

Originally Posted by eyeballkid

ya know BassmanPaul,
youre right on that, but what is weird is that ALOT of amps advertise this!
like when i got my 300t I remember some write up that pointed out the features of the amp being that if a tube goes itll blow a pair and you can keep running on 4 tubes at a lower wattage....but they NEVER point out that it changes your Ohm load and can damage it..

Orange does the same thing...
its weird.. youd think theyd say in bold letters "if ya blow a tube STOP PLAYING so you dont damage your amp!'

Good point. That kinda bugs me that it is promoted as such but it isn't mentioned in any of the marketing material.

[BassmanPaul]

You see a lot of guitar amps, and some bass amps, that have switches to disconnect pairs of output tubes. It's not so important at the frequencies guitars work at and the way that tubes react can add some "Mojo". I'd not recommend doing this except to get through a night.

Paul