Alembic Guitars Club
Connecting => Miscellaneous => Topic started by: edwardofhuncote on April 17, 2021, 11:54:10 AM
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My Princeton Reverb Reissue is making a weird sound... I would describe it as a harmonic distortion, that seems to be most noticeable on a high A note, but also present in frequencies on either side of that. (think; 2nd string, 10th fret)
This obnoxious little ringy-thing is happening even a low volume. It's happening whether I'm pushing the gain stage or not, but more obvious when pushing towards overdrive. The whatever-it-is dissipates if I let the offending note sustain... it will eventually fizzle into a clean decay.
It's a fairly new amp; 2019. Groovetubes tubes, Celestion Cream 90w 8ohm speaker, both supposedly upgrades. Has not been abused. I got it from a keyboard player. It was "too much amp for his home studio". It just started this aggravating racket a couple weeks ago.
I've read as much as I can find online. Nobody seems to be describing what I hear. It isn't the backboards loose. I tried swapping preamp tubes one at a time. What does this seem like to you all- Power tubes? Rectifier? Sockets? Speaker? I love the amp when it's right. Can't suffer this foolishness though.
TIA. ~Ed of H (who Thanks to Alembic, has a whoop-ass set of rabbit ears)
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I’d try swapping the power tubes first. A good general rule of thumb is try the easiest stuff first.
Bill, tgo
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Power tubes (I have learned) are best acquired in matched sets.
I'll go ahead and ask the obvious (possibly stupid) question... with tubes, how much difference is there between this brand and that? In shopping for sets, I see this set voiced for Silverface, this set for Tweed, that set for Marsh... my only experience is replacing the preamp tubes in my Mesa WalkAbout. (the fine folks in Petaluma sent me a new Mesa-branded pair of 12AX7 tubes)
Anything wrong with a set of J/J's ? For instance-
https://reverb.com/item/27890603-jj-tube-set-fender-princeton-reverb
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Do you have an old tube lying around or another amp using the same tubes? I don’t believe you need to worry about matching tubes just to do some trouble shooting.
Bill, tgo
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Nah. I had a couple spare 12AX7 preamp tubes only because that's what the Mesa bass head takes. I don't have any 6V6 tubes, and never owned any other Fender tube amp. I wish there was someone around here that could listen to it and tell me definitively what it is I'm hearing. It's just odd to me how these certain frequencies seem to be setting it off.
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Can you connect it to another speaker to see if it is the speaker causing the noise?
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That's a good idea. I don't have another guitar cabinet though. I know someone who has a couple... for the purposes of a test, I could try an 8 ohm bass cab. I have a Bag End S10D that is coaxial... I'm not sure the sensitivity will allow for hearing it though. They actually advertised that thing as being perfect for amplifying a banjo. ::) Worth a shot.
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well as my boss at the amp shop where i cut my teeth fixing big tube amps many moons ago said after he watched me chase my tail for a coupla hours trying to track down a similar problem using scope, knowledge and finesse - "sometimes ya just gotta change all the tubes!"
i've found that to be sage advice through the years in a varity of tubular and non-tubular situations.
HTH
BD139
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I am not a fan of Groovetubes, new Tung Sol either. They seem to have a high failure rate and to my ear are not very musical. JJ's are new tubes I really like. Try both inputs, another cord, another instrument, etc too. However, tubes are the usual suspect.
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Thanks for checking in guys... I figured you might have a couple thoughts too David.
Well here's the update-
per Rob's suggestion I dug out my little Baggie 10, (it provided the 8 ohm load) I disconnected the onboard Celestion from the amp, and hooked up the Bag End and rung it out. The distortion is still there, same spot, just harder to discern using the little cube with a a bass driver in it rather than the much more articulate Cream speaker in my Princeton cab. It was lower, more warble-y, and less fizzle-y on the note's decay, but definitly still there. The closer you play to that high A note the more pronounced it becomes.
Of course I have tried both inputs, every cable in the house, 2 Les Pauls, two Telecasters, and another nameless beast. Every one produced the same results. I think this eliminates the speaker, and the cabinet, or some random piece of hardware like a screw being loose, maybe ever negates user error. ::)
I believe it's time to buy some new light bulbs for my Fender and swap 'em out. Thanks for the insight on GT David. There's a whole 'nother world of keyboard jockeys out there saying this tube or that is great/sucks. I'd much prefer to take my advice from here.
*any thoughts on Tube Amp Doctor? Stew-Mac sells a variety of retube kits for Fender amps... I notice they like these.
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I had an old Peavey Deuce amp from the 70s, great amp but heavy, sold it a couple of years ago. I changed the tubes in it once, I just took one of the tubes down to a local electrical supply place and said I need six (or however many it was) of these, went back and installed them all and it worked great. So you never know :)
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It's a crying shame that they no longer have a tube tester (and tube sales) in every department store, hardware & pharmacy.
Peter
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It's a crying shame that they no longer have a tube tester (and tube sales) in every department store, hardware & pharmacy.
Peter
We used to have a 4- foot tall contraption at the Fret Mill for testing tubes... had all kinda' different sockets and chicken-head dials on it, I don't think anybody but Ken knew how the blame thing worked. It never occurred to me until you posted that, but I don't know what ever became of it. They may even still have that thing upstairs somewhere. I know it hasn't been on the sales floor for at least 20 years. I'll have to ask Aaron, he'd be the only one who would remember it.
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How about these guys: http://www.uptownaudio.com/about.htm (http://www.uptownaudio.com/about.htm)
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Perhaps this is what we need:
https://www.ebay.com/itm/B-K-Model-700-Dynamic-Mutual-Conductance-Tube-Tester-Nice-Working/313484205242?hash=item48fd1d5cba:g:IIMAAOSwvCdgbjrf
Is that not a fine looking piece of kit? Tempting. And I'm not even a tube guy. :o
Also, I don't know if these testers could ever tell you when a tube went microphonic - which may be what's happening to Ed's. Give a gentle tap on the glass and see what comes out of the speakers.
Jimmy J
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How about these guys: http://www.uptownaudio.com/about.htm (http://www.uptownaudio.com/about.htm)
Woah, look at that! Maybe 10 minutes from me and I never heard of them. Thanks Dave!
Also, I don't know if these testers could ever tell you when a tube went microphonic - which may be what's happening to Ed's. Give a gentle tap on the glass and see what comes out of the speakers.
Jimmy J
There's another good idea. The fine folks down in Corona put a little safety cage around the power tubes and rectifier though, I reckon to keep Wire Dunces like me from blistering their fingerprints off. I think I can bypass it to do that test though. Good call, Jimmy J!
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Found this V6V tube comparison that might be of interest...
https://www.thetubestore.com/6v6-tube-review
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I tried Jimmy J's suggestion, and sure enough by tapping on the power tubes with a small screwdriver (with the amp turned up just enough) I can indeed hear the sound coming through the speaker. It is more of a 'thump' on one, and more of a 'tink' on the other. Not really hearing much on the rectifier tube... very faint maybe.
So. There's that.
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So maybe switch the two and see if the sound moves with the tube? (Carefully; after they've cooled???) (not my area expertguessing)
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So maybe switch the two and see if the sound moves with the tube? (Carefully; after they've cooled???) (not my area expertguessing)
Another good idea. If nothing else, to see if the sound follows the individual tube or the circuit it plugs to. Yep, they make it so you have to take one of the backboards off of a Princeton now to swap the power tubes or rectifier. I'm guessing to help avoid burn injuries. The preamp tubes are still easily accessible, but they have metal spring-loaded sleeves around them. I really hate to be so ignorant about these things, but I'm learning more every day. :)
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Have you tried another guitar? Maybe, it's something on that end...
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Hey Stef, nice to see you!
Yep... every guitar. I reach for Les Pauls or Teles, just depending on the day, but I tend to rotate guitars by the week because of humidity (or lack thereof) in cold, dry seasons. But this was so irritating, that I instinctively tried every other combination I could think of with cables, guitars, even had somebody else play it. I even carried the amp outside one afternoon and serenaded my neighbors for a while at varying volumes, so I could tell if it was the cab rattling something in the room or not. ;D
If I get outta' here in time today, I'm hoping to check out Uptown Audio that Moderator Dave spotted, right near my home. Could be they have someone who knows exactly what I got going on here.
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Ahhh... tube testers. or as my TV repair shop mentor (back in the 70's when you could actually still repair a TV) called them - automated tube salesmen.
Bear in mind that a tube is a mechanical device much more so than it's an electronic device. All the way from the socket pins to the heater and all the strangely shaped bits in between. Almost any kind of vibration is gonna make something rub against something else or make intermittent contact and generate some kind electrical noise - it's only a matter of degree. That's what the insidious part of this is - ya move the tubes around and maybe the noise moves with it. or maybe it doesn't. Or maybe you've got a cold solder joint (i've also had to hit all the solder joints in an amp to get it to stop misbehaving) that's masquerading as a microphonic tube. Those point-to-point wired chassis were notorious for that. A tube socket mounted on a PCB puts a lot of mechanical stress on the soldered joints that are likely the only thing supporting it, leading to hairline cracks that work most of the time except when they don't. Or maybe you've got tube socket with some schmutz or corrosion in it. Ya move the tube, the schmutz falls off or moves with it. It's really not too hard to wind up chasing your tail on this kind of problem.
so the point is - ya gotta be methodical and eliminate the suspects one at a time and focus on what's left. Changing all the tubes out might be drastic and expensive. Maybe it's a last resort after nothing else works. It helps if you have a known good set laying around that you can swap in and out. But once you've eliminated the tubes, then you can confidently go after the other suspects if that didn't solve the problem.
i miss the old days fixing tube amps. every now and then we'd get some smoke and lightning to make the day interesting...
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A year or 3 ago, my Silvertone Twin Twelve 1484 was acting up; reverb would sound like you'd kicked the cab out of nowhere.
My neighbor came over & we looked inside while he called his friend who had recapped it for me. We swapped a tube into the socket in question, and it worked. "OK, I need a tube; let's put this one back in until I can get one."
Just on an impulse, I tried it again, and presto - repaired reverb!
Peter
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Don'tcha' jus' love stuff that fixes itself?! :-\
In this little adventure, I learned that the odd preamp tube (12AT7) is for the reverb, and maybe the vibrato too. In my reasoning, which may very well be flawed, I just switched off both effects, even unplugged the reverb tank... made no difference insomuch as the trouble still is present, but I will say the offending noise is easier to hear with the reverb on.
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I bet it's the power tubes.
Bill,tgo
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I like JJ's from Eurotubes.
I get a lot of use from my vintage tube tester monolith monster machine. I have learned several things from it too; A few tubes that test OK are microphonic or flawed, Often tubes that don't test as high as others actually can sound better (especially preamp tubes for guitar amps), British tubes often flare up a lot when first turned on but that is normal. Also, if you ever find one for sale, make sure it has the tube chart!
https://www.eurotubes.com/store/pc/home.asp
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Ordered a set of tubes. We shall see in a few days.
David, that device is almost exactly what I remember we had at the Fret Mill years ago. That's it!
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The ones I recall had a sharper angle to the face, which was red - but yeah, same basic thing.
I forgot to mention that the tubes in my amp are the original Silvertone-branded ones.
And I've said this before, but it bears repeating: these things are having a resurgence these days (and not with high school kids who can't wait to trade up, like when they were current). One company even makes a pedal to duplicate its sound. So, if anybody has an urge to be hip & with-it, and has a Rivera-designed Super Champ, or a Super Reverb - silverface is fine - that they want to trade even-up, the link to my email is under my avatar...........
Peter
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Also, I don't know if these testers could ever tell you when a tube went microphonic - which may be what's happening to Ed's. Give a gentle tap on the glass and see what comes out of the speakers.
Jimmy J
Jimmy is on the mark. A tube can test good and still be microphonic. The only easy way to tell that I'm a ware of is to tap the tube gently with a pencil eraser and if you hear a ringing sound the tube is microphonic. If it is a thump the tube should be ok. For testing, swapping tubes would be the most effective method. To test the preamp if you have 12AX7 and 7025 tubes they are interchangeable though the 12AX7 might or might not be as quiet as a 7025. I don't know what other tubes the amp uses so cannot say if there are also other tubes you could swap for diagnostics. Sometimes changing the tube position in the amp can help. By that I mean if the preamp stage has for example two 12AX7's swapping them can sometimes decrease the effect of a microphonic tube.
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I tried Jimmy J's suggestion, and sure enough by tapping on the power tubes with a small screwdriver (with the amp turned up just enough) I can indeed hear the sound coming through the speaker. It is more of a 'thump' on one, and more of a 'tink' on the other. Not really hearing much on the rectifier tube... very faint maybe.
So. There's that.
Just saw this. The tink or ringing generally indicates microphonic, the thump that it's ok.
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Chopsticks are a great tool for amp work
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I tried Jimmy J's suggestion, and sure enough by tapping on the power tubes with a small screwdriver (with the amp turned up just enough) I can indeed hear the sound coming through the speaker. It is more of a 'thump' on one, and more of a 'tink' on the other. Not really hearing much on the rectifier tube... very faint maybe.
So. There's that.
Just saw this. The tink or ringing generally indicates microphonic, the thump that it's ok.
Fascinating. Thanks Keith. I would have assumed the opposite was true. Don't know if this matters, but when viewed from the back, the power tube on the right went 'thunk-thunk', the one one the left went 'tink-tink' when tapped. I wiped out and went to bed before I could disassemble the back and switch them around.
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Just to update and close out the thread;
The new tubes arrived in the mailbox today, and cured my Princeton. So now I know what to listen for in microphonic power tubes. Since they came as part of a matched set, I replaced all 7 tubes. Been playing for the past hour, putting the amp through paces. Good golly that thing sounds great. Hopefully that's the end of it.
As an added bonus, Thanks to Moderater Dave, I met some really nice folks right here in town who work on amps, if I need service in the future. They have some pretty cool stuff at http://www.uptownaudio.com
Thanks everyone for the helpful advice. :)
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Part of the educational experience gained here... I picked up a really good deal on a fairly new '68 Princeton Reverb RI that had exactly the same issue, plus a cabinet rattle. It's similar to my '65, but a totally different voiced combo-amp. The '65 is a15w and 12" speaker, while the '68 is a 12w, 10" speaker, but same general configuration. This one had the same weird harmonic distortion on certain notes. I seriously think Fender might've got a wonky batch of GrooveTubes 6V6's.
Longer story shortened; guy was tired of fiddling with it, and even more frustrated than I had been with mine. (less patience, which is hard to imagine... ::) ) Anyway, Jimmy J's screwdriver tap-test confirmed one of the power tubes was suspect, and new matched pair of J/J's cured that weird harmonic warbl-ey racket. It also had a rattle in the cab itself on the lowest A notes. I snugged all the screws, put some small loops of gaffers tape behind the backboard, and that seems to have cured it. I have read where the front baffle boards in these (particularly the '68 RI's) are prone to rattle. Mine seems to be fixed though.
I like things about each of these Fender Reissues but I really don't need both the '65 & '68... two nearly identical combo amps... I may eventually have to decide which one to keep. I have this fuzzy feeling there is an F-2B in my not-too-distant future. I can envision a trade happening.
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Nice job…I’d keep the 12” speaker :)