Princeton Reverb - likely reasons for "farting out"?

[Bluefinger]

Hi,

I have a problem with my BF Princeton Reverb clone. As far as I remember it was working propperly a while ago but my harp player borrowed it for a year or so and now that I have it back it farts out badly. To put this in somewhat better terms, here is what it does:

Even on rather moderate volume settings (around 3 or 4) it has developed a very unpleasant distortion that sounds like a blown speaker but the speaker is ok. I have replaced it with a known good one and it still does it.... it has a weak and very "broken" tone especially in the low frequencies. There is no singing quality to it anymore ... the lower the frequency and the bassier the guitar the worse it gets. The bass frequencies feel pretty weak and the more I bring up the bass controll the more it farts and grinds without developing any real low end. It'S hard to describe tone but I hope you get what I mean.

Before I go any buy all kinds of new tubes, filter caps and such ... what would be the first things you would look into?

THANKS!!!

[nickb]

Farting out huh? Could it be gassy tubes?

Sorry, I couldn't help myself...

[Justin Thomas]

First thing? Tubes. Second, visibly loose connections, especially on an amp that's been "loaned out" for a year. Loose speaker mounting? Personally, I think the problem is before the Bass control, since that control has an effect on the distortionon, if it's not a mechanical problem. What do you have for test equipment? Anything else I can think of would probably require "poking around."

Justin

[mozz]

I'm voting filter caps.

[pdf64]

Is it a clone as in not having a bias adjustment trimmer?
Was the idle plate current and dissipation checked at some time prior to be lent out?
What is it now?

[Bluefinger]

Not much here except for a voltmeter Since the the speaker was swapped and nothing changed we can rule out the speaker mounting. All othert mechanical aspects are looking fine as far as i can tell. I can swap the preamp tubes with another amp to see if that changes anything. I don't have a new pair of 6V6 at the moment but it might be a good idea to have some spares anyway.

[Bluefinger]

I'll check ... didn't check it before I gave it away since it was working fine.

[pdf64]

Does that mean that you didn't check the plate current ever, or just immediately before the amp was lent out?

[Chuck H]

All of the above. The tubes are older and may require replacement. The bias could be out of adjustment with the aged tubes. The filter caps may not be doing everything they can anymore.

It's my experience that loaned equipment gets 'rode hard and put away wet'. Typical musicians treat loaned gear not so much as if it were yours, more like "it's not mine." I don't loan gear anymore.

The cumulative effects of wear and no maintenance could be part or all of the problem.

[Dave H]

I don't loan gear anymore.

I don't either as I've discovered that most musicians don't understand that if it's a loan then they do have to actually return it

[Bluefinger]

I didn't check it right before I loaned it but it was definitely within specs when it was new (two or three years earlier)

[Chuck H]

Well four year old filters should be fine in any case. It could just be old tubes and/or the bias needs adjusting. You might be surprised at how bad old tubes that are biased too hot can hamper performance. Especially in the LF.

[mikepukmel]

I don't either as I've discovered that most musicians don't understand that if it's a loan then they do have to actually return it

Return it, AND in as good a condition as it was loaned.

[The Dude]

Well four year old filters should be fine in any case......

Unless "Genuine Fender" Illinois caps were used for the clone.

[mikepukmel]

Unless "Genuine Fender" Illinois caps were used for the clone.

Oh man, Im way new to this amp building stuff and I can't tell you how many electronics blog posts complain about a bad Illinois cap. Sad.