Tube Amp Problems

G

gooley

New member
I bought my first tube amp, a Fender Deluxe Reverb RI, a little while ago, and I'm having a couple problems with it.

First, whenever a turn up the volume past a certain point (around 4-5 for humbuckers, 5-6 for single coils) and turn my guitar's volume on full or play hard so a lot of signal is going through, I get a really nasty, out of place distortion from the amp. At really low volumes it sounds fine, but when the amp is cranked the noise is awful. It doesn't sound like natural distortion at all. Could this be caused by bad tubes? If so, preamp or power tubes? Could it just be a single tube that's giving me trouble or would I need to replace all of them?

Second, if I turn the reverb on my amp anywhere above 1 and a half, it becomes obnoxiously loud. I've seen videos of people playing with the reverb around 6 or 7, so I know there must be some sort of issue there. Anyone heard of this issue before?

Thanks in advance.
 
when you have the amp set at high gain and high reverb you will have to regulate your volume and tone pots on your guitar that is why they are there.

too much reverb will make the amp sound like shit anyway and a little gain on the amp will go a long way with the volume pot on your guitar wide open :D
 
Probably a microphonic preamp tube.

Turn the amp on and lightly tap the pre tubes with a pencil eraser. The one(s) that make ungodly noise are microphonic.
 
Roguetitan said:
when you have the amp set at high gain and high reverb you will have to regulate your volume and tone pots on your guitar that is why they are there.

too much reverb will make the amp sound like shit anyway and a little gain on the amp will go a long way with the volume pot on your guitar wide open :D
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Not trying to start a fight, here, but I am afraid Roq is a bit off base, here. I have owned similar amps (RI Hot Rod Deluxe, vintage Deluxe-, Pro- and Twin- Reverbs), and I have cranked the 'verb to 12 and never heard excess reverb nor volume at lower values. Nor would I expect excessive distortion at volume settings of 4 to 6. I can't be sure, of course, as I haven't heard your amp, but neither of those things sound anything close to normal.

The pencil tap test is a good one for microphonic pre-amp tubes, but they could be going south other ways- tubes are not covered by the 5-year warranty, so your best bet would be to take them to a shop that has a tube testing machine and check them out. Those machines have gotten a bit rare, but shops that specialize in tube amps (either guitar or hi-fi) usually have one, and will usually let you test your own tubes, for free- they just sorta expect you to buy any replacements from them, which is only fair. If you have never tested tubes, they shop personnel can usually help you with the testing.

If you bought from one of the big-box gear retailers, within the last 30 days, bring it back for either an exchange or refund. Warranty tube exclusion be damned- you should not be having those problems that soon.
 
Roguetitan said:
when you have the amp set at high gain and high reverb you will have to regulate your volume and tone pots on your guitar that is why they are there.

too much reverb will make the amp sound like shit anyway and a little gain on the amp will go a long way with the volume pot on your guitar wide open :D
Click to expand...

I think you misunderstood me. When I say I have the volume at 4 or 5, I don't mean 4 or 5 o'clock. I mean 4 or 5 out of 10. I'm not diming the amp. Nor do I consider a reverb setting of 2 out of 10 to be "high reverb."
 
gooley said:
I think you misunderstood me. When I say I have the volume at 4 or 5, I don't mean 4 or 5 o'clock. I mean 4 or 5 out of 10. I'm not diming the amp. Nor do I consider a reverb setting of 2 out of 10 to be "high reverb."
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aparently I did misunderstand:o

if that is the case you may have bad tubes.
 
stevieb said:
The pencil tap test is a good one for microphonic pre-amp tubes, but they could be going south other ways- tubes are not covered by the 5-year warranty, so your best bet would be to take them to a shop that has a tube testing machine and check them out. Those machines have gotten a bit rare, but shops that specialize in tube amps (either guitar or hi-fi) usually have one, and will usually let you test your own tubes, for free- they just sorta expect you to buy any replacements from them, which is only fair. If you have never tested tubes, they shop personnel can usually help you with the testing.
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I recently had one of the preamp tubes replaced because it was making a high-pitched whine while I was playing. The guy who replaced it put some industrial brand tube in though, unfortunately (Pro/Comm). I'm wondering if I should just replace all the preamp tubes.

Could a bad preamp tube be causing the problem with the reverb, too?

stevieb said:
If you bought from one of the big-box gear retailers, within the last 30 days, bring it back for either an exchange or refund. Warranty tube exclusion be damned- you should not be having those problems that soon.
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I got the amp used, so that option is out the window.
 
It's late, and I don't wanna strain my brain, but as I recall, the vintage Deluxe Reverb does use a tube as part of the reverb circuit, so the RI probably does, too. So the reverb problem could be caused by a tube.

As for replacing all the tubes, DON'T GO OFF HALF-COCKED. (For me, that would mean about 6 inches...;)) TEST those puppies before you replace ANY of them.
 
I just spent a couple minutes poking around with a pencil eraser, and here's what I've come up with:

Tapping on one tube is very audible through the speaker of the amp. One more is only slightly audible. Another is microphonic, but makes a warbly sound when tapped and is only audible when the reverb knob is turned up, which tells me it is the tube responsible for the reverb problems.

So all in all, three tubes are noticeably malfunctioning.

There's no good guitar techs around where I am, but I do know a decent A/V guy I can take it to to check it out.
 
One of us should have already mentioned that ALL pre-amp tubes are microphonic, to a point. It's when they get excessively so, that you should replace them. Sounds like the second tube may be within tolerances. Try moving it to one of the other spaces and check for a difference in sounds.

Your A/V guy may not necessarly be the guy you want- many very knowledgable techs have little or no experience with tube stuff.
 
stevieb said:
Try moving it to one of the other spaces and check for a difference in sounds.
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This should be a great way to diagnose your preamp tube problems. If the symptoms change when you switch around the preamp tubes, then you've found your culprit.

You might want to mark the tubes somehow to make sure you get them back in their rightful places after your tests. Sometimes the different preamp tubes are selected for very specific properties depending on which preamp function they'll be performing.

The guy you took the amp to should have known better than to put any old tube in the preamp. An industrial tube? WTF? After you get the amp serviced to fix whatever your current problem is, definitely spend the money on a set of preamp tubes for that amp. They're not all that expensive, and there are tons of different nice preamp tubes on the market. The folks here are full of suggestions when it comes to online tube retailers so come back when you're back in working order.
 
http://thetubestore.com/

I've had good use with the matched Tung Sol's.

Stay away from the Chinese "Mullard" re-issue from Groove Tube. They are very expensive crap. I had 3 that were microphonic right out of the box. AFAIC Aspen Pittman is a con artist.
 
As far as I can tell, the problem is coming from two of the four 12AX7 tubes in the preamp, one of which was the "industrial grade" tube he put in. The tube that was initially in the socket for the reverb circuit will occaisionally microphonically feed back when tapped. Swapping the tubes around did not solve the reverb issue, however. The other two 12AX7s seem fine, and the 12AT7s are solid.


The tubes that came stock in the preamp section appear to be relabeled Sovteks (There's a white Sovtek stamp on them that was stamped over with a "Fender / Groove Tubes" label). Should I just replace the two 12AX7s that are bad, all four 12AX7s, or the entire preamp section? From what I've read, the Sovtek 12AX7s aren't the greatest.

Does anyone recommend EHX tubes?
 
Sovtek tubes munch donkey parts. Get some Tung Sol reissue 12ax7 they are killer. They are much smoother than the EHX tubes.
 
Upon reading up a little more on the Fender DRRI, I'm a little confused about which tubes drive the reverb circuit. The 12AX7 I had mentioned before only made noise when tapped while the reverb circuit was engaged, however I have read that it is one of the 12AT7 tubes that drives the circuit. I'll try swapping those around and see what happens..
 
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