Fender Twin Amp - Gain channel sucks, clean channel has limited Bass

[TerryCline]

Hi all - ran across this forum searching for info about my Fender Twin Amp. Great stuff in here, thanks to all who contribute.

Not sure of the year of this Twin, but it is very new, in decent physical shape, but with two annoying issues. Saw a similar thread from early June about the tubes in a Twin Amp, and it seemed a promising start.

1) Clean channel is very nice, but the Bass pot has very little effect from 1 - 10. (in comparison, the gain channel's bass pot has what I would consider a normal response - very obvious). Back to the Clean channel - the pot DOES have SOME slight effect; it is not plain old dead. Any ideas why and how it might be repairable, or is this normal behavior for this amp? It makes no difference whether I am on 1/4 or 100 watt mode.

2) Gain Channel - the gain is, well, blappy! kind of farty, not at all musical. Harsh. Brittle. At only 1 or 2, the sound is far from warm and full. One top of the obvious upper frequency gain, it has an obvious, mysterious low end distortion/grunge even when only playing the higher notes. At very high gain (8 - 10), it starts to get a little better/useful, but I am not after that much gain and overdrive most of the time.

What I really want is for the Gain channel to simply be a bit crunchier than the clean channel. That way I can go from Clean, to crunchy to full distortion (with my pedal). I can't get "crunchy" mode to be useful.

Could a bad tube or tubes be part of the problem? Or based on my unscientific description, is this a job for someone who can really poke around inside? (which ain't me!). And if so, would anybody know a good guy out here in California (Central coast? SF? LA?)?

Can I provide any other info that would help? Happy to dig in and do my due diligence.

Much thanks,
tc

[Chuck H]

It would help to know the actual model of the amp. I say this only because "Twin" could be a generic model description for a lot of Fender amps. Is it a Twin, a The Twin, a Twin Reverb, etc.

Since it has a distortion channel I'm guessing it's a red knob model and probably much older than it looks. The odd low end distortion you describe could be ghosting by your description. If the amp is as old as I think it is it could well have tube and filter capacitor issues. Let's work on determining the age and then decide if it needs to be taken to a tech for service.

And, FWIW, if it's the amp I think it is then even in good working condition the gain channel doesn't sound very good. But I think there are some mods developed for that amp to improve it. It might be a good idea to find out about this and take the mod info to your tech if you do take the amp in for service.

Chuck

[TerryCline]

Thanks Chuck;

The model is the "Twin-Amp", definintely not a Twin Reverb, no red knobs. It has a black face, two channels, reverb, tremolo and a Presence knob (though, I can't hear that it changes much!). The clean channel has a Bright switch.

The channels are switchable with the footswitch (which works fine). The footswitch has four options - channel, Effects loop, Reverb, Tremolo. I have not used the effects loop to date, but I also don't note any issues with it - the send and return can affect volume, doesn't seem to introduce noise, so it appears to be working.

It has the original two Fender 12" speakers, of which I assume are 8 ohm, wired in parallel.

I am not sure how to determine approximate age - a cursory look with a flashlight while the chassis is in the cabinet reveals no date stamps anywhere. Would there be some indication on the inside of the chassis? The serial number is CR-276064. The tube chart says Corona, CA on it if that is any help.

Ready to take this guy apart if that gets us closer to a resolution!

Terry

[Chuck H]

Ok. That's the current model and probably not in need of filters. I can't say for sure of course. Tubes are probably also fine. But with the same disclaimer.

In light of this your problem sounds obscure. You should have plenty of bass and swing on the knob in the clean channel. I would suspect the pot but you also have some other tonal issues with the drive channel that you mentioned. I don't do repairs and I'm not familiar with any common problems with those amps.

You might want to go to a dealership in your area. Since that amp is the current model you can hear what it's supposed to sound like. Take your own guitar for an apples to apples comparison. This will also have the side benefit of making the staff think you may be amp shopping so they're more likely to let you crank it up

The next thing I would try is a preamp tube swap. Get a known good 12ax7 tube and plug it into the first preamp socket. If there is no change, take the one you just pulled and swap it for the second preamp tube...etc. If that doesn't fix it, and your comparison revealed that your amp is not working right, you may want to take it in for service.

Does the amp make any funny noises or have any other unusual issues like scratchy pots?

Chuck

[TerryCline]

Thanks again, Chuck.

Seems the path is pretty straightforward - swap and test the 12ax7 to see if any of those are the problem, but really, probably get it into a service tech who is familiar with amps and hopefully Fenders.

No other noise/squeaks/buzzes at all. As I say, the amp is actually pretty nice and performs quite well, other than the Bass and Gain Channel problems. In fact, just finished a rather successful 3 hour outdoor gig at a local community summer concert thing. Amp rocked!

tc

[Kage]

I used to have an older version of that amp, can't say as I ever really liked the gain channel. The way that you describe the sound of the gain channel makes me wonder if someone before you got it replaced one of the 12AX7's with an AT7 to try to knock down the gain. I tried that once and it sounded like poo. Maybe check the diagram on the inside and make sure that there's an AX7 in each of the sockets that supposed to have one, especially in V1 2 and 3. If so, then try swapping in a known good tube through 1 2 and 3 and see how it changes the sound.