Princeton, dead tube?

[zebpedersen]

Just picked up a silverface Princeton from the 'bay - beautiful clean sound, really really nice and who isn't a sucker for tremolo. I was playing it for about 40 minutes or so and the sound went very distorted, thin and quiet. I took a look round the back and there was a feint electrical 'burning' smell and one of the tubes looked different to the other.

I've ordered a replacement pair of 6V6s anyway, but in the meantime could someone perhaps shed some light on the problem? Touch wood I've never had tube (or any other major) issues with my Boogies so I'm not massively well schooled in detecting them, but I think I'm right in this case. Confirmation, anyone?

Cheers

 

[212Mavguy]

It's hard to say without taking a look at the guts of the amp with a set of trained eyes and a voltmeter... Sometimes when a power tube dies it takes out a screen resistor or other chassis component(s) out with it. If you put in those new tubes that might not help. Sounds like a visit to a professional amp tech might do your Princeton some good. Peace.

 

[zebpedersen]

The tubes hopefully arrive later on today - I had the (bright-ish) idea of swapping the power tubes in their sockets and the same thing happens to the same tube when it's in the different socket, so I'm pretty sure it's the tube.

I had a further look at the tubes installed, the 12AX7s in the preamp look absolutely ancient so I've swapped those for the spares in the clips round the back of my Mark IV and II for good measure. The rectifier tube, a 5U4, is a Sylvania one - pretty sure they're only available as really expensive NOS Philips tubes these days (though I haven't checked) so I'm guessing that that one is pretty old as well.

I'll post how it goes with the new 6V6GTs which will hopefully be a bit later on today.

 

[RR]

Take 212Mavguy's word, you are likely will blow your new tube(s). Something inside fail causing the tube to blow out.

An amp technician will find the problem right away. These things happens with tube amps. Smelling smoke is a sign a capacitor went out. Could be screen or grid resistor, especially Princeton is quite old.

Does your SilverFace Princeton have an aluminum trim (1/8") around the grill's perimeter? That's a '68 or '69 Princeton. These are some of Fender SilverFace amps that didn't change much from its BlackFace brothers.

 

[zebpedersen]

Rough cost d'yreckon?

 

[RR]

depending on the amp tech.

Most charge a bench price meaning $50 to $75 whether its a 5 minute job or an hour job. You might think that's a lot but that's the way it goes almost like someone diagnose your computer. They diagnose your dinosaur computer say $65, and that's about already half the price of your computer.

I know one tech charged me $65 for bench price at first. Second time I went there, he remembered me and only charge me for parts this time around so sometimes depends on the amp tech.

I'm just guessing but what happened to your Princeton, a good tech should diagnose the problem easily. The circuit is a clean layout, point-to-point wiring.

There's a few tech members on this board like MonsterTone. He might give you what's expected from an amp tech.

Boy, I hope your Princeton problem is not intermittent. Intermittent problems are hard to determine. My very first guitar amp was a Princeton. (I'm an old fogey relative to the demograph of this forum). I sold it but eventually got it back.

 

[zebpedersen]

Re-tubed the power section with two JJ 6V6GTS (with the newer Mesa & EHX 12AX7's in the pre), problem solved. Now I've got those two old tubes out for a better look I can see just how old and haggard they are! Princeton back on form, now I can start playing with this awesome bit of kit! Cheers guys

 

[Guitar GeeK]

Turn the thing into a Princeton Boogie. That'll fix it.