Fender Princeton Reverb '65 RI

[edwardofhuncote]

How about these guys:  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!

[rv_bass]

Found this V6V tube comparison that might be of interest...

https://www.thetubestore.com/6v6-tube-review

[edwardofhuncote]

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.

[David Houck]

So maybe switch the two and see if the sound moves with the tube?  (Carefully; after they've cooled???)  (not my area expertguessing)

[edwardofhuncote]

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.   

[StefanieJones]

Have you tried another guitar? Maybe, it's something on that end...

[edwardofhuncote]

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. 

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.

[BeenDown139]

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...

[cozmik_cowboy]

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

[edwardofhuncote]

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.

[lbpesq]

I bet it's the power tubes.

Bill,tgo

[gtrguy]

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

[edwardofhuncote]

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!

[cozmik_cowboy]

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

[keith_h]

- snip -

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.