Do New Amps "Burn In?"

[DougGuy]

I completed a 5g9 tweed tremolux last year, and it sounded pretty dang good, a little weak on the trem intensity but it sounds TOO good to back off the bias just for the trem circuit.  Anyway, I accidentally left it on, near full volume, for 24hrs.  When I discovered this, I shut it off and I got my hand up under there and touched the PT.  It was hot of course, too hot to hold on to over a second or two.

Well I thought since it isn't making any noise now after being on this long, it might be okay so I shut it down.  Now, playing the amp it actually sounds better than it did!  It seems like it has more punch more sag, it's getting a real cool breakup that's got some reedy sounding resonance and a kinda chewy character to it like using alnico 2 magnets in the pickup.  Lead tones are clean and cutting with lots of bloom, it's hard to put into words but the sound the amp makes now is a WHOLE lot more dynamic than it was before.

It's definitely not the speaker loosening up, it's a 1960s Altec 417 that has certainly got the miles on it.

Does this sound typical of a new build? 

[PRR]

I'm sure that ears break in.

I don't doubt that in instruments amps, "fingers break in", the player learns what the amp "likes".

In radio stations we left tube audio gear on all day and some of it all night. I know a Fisher 500, a fairly hot chassis, ran 5,000 hours a year and no repairs in 3 years.

You don't leave your own amps on all day-and-night because that's a half-buck on the electric bill.

[shooter]

I've read (unsubstantiated) that tube's do have a "break in" period.  I've witnessed it on builds (SE)  The tube seems to drift around current wise for about 10hrs then find the happy place.

[WiderGates]

I'm sure that ears break in.

I don't doubt that in instruments amps, "fingers break in", the player learns what the amp "likes".

       

[pdf64]

… it sounds TOO good to back off the bias just for the trem circuit.  Anyway, I accidentally left it on, near full volume, for 24hrs.  …

What’s the bias now, ie has the idle anode or cathode current increased?

The amp reacts to signal, not control settings per se.
If the vol control was at max, there would just be a bit of hiss / hum surely, a fraction of a watt sound power output?
In the absence of signal, the amp’s power output / dissipation isn’t affected by the front panel control settings.

[DougGuy]

… it sounds TOO good to back off the bias just for the trem circuit.  Anyway, I accidentally left it on, near full volume, for 24hrs.  …

What’s the bias now, ie has the idle anode or cathode current increased?

The amp reacts to signal, not control settings per se.
If the vol control was at max, there would just be a bit of hiss / hum surely, a fraction of a watt sound power output?
In the absence of signal, the amp’s power output / dissipation isn’t affected by the front panel control settings.

It had a cable with a shorting jack plugged into the bright input.

[sluckey]

It had a cable with a shorting jack plugged into the bright input.

Why? If the input jacks are wired properly, they will all be shorted to chassis when nothing is plugged in.

[DougGuy]

It had a cable with a shorting jack plugged into the bright input.

Why? If the input jacks are wired properly, they will all be shorted to chassis when nothing is plugged in.

It stays plugged in but you are right about the jacks shorting.

[sluckey]

It stays plugged in but you are right about the jacks shorting.

OK, but why???

[tubeswell]

Amps don't 'break in', but like everything else in the universe, they will 'wear out' after a while - and different parts of the amp wear out at different rates. Jacks wear out, tube sockets wear out, pots can get worn out, tubes wear out eventually, speakers wear out, electrolytic capacitors wear out, and even some types of resistors wear out faster than others. Even some eyelet boards wear out (but it takes years). Some cabs, tweed and tolex get a real beating. Transformers and chassis will eventually turn to rust in a few hundred years. YMMV

[bmccowan]

And that "wearing out" could be reasonably viewed as burning-in. As parts go off new spec subtle sound changes certainly take place. Some for better, some for worse. (where have I heard that before?) I once bought an early Gibson GA-5 amp. When I played it, I thought it was the best small amp I had ever heard. Two minutes later the speaker blew. I think that near end of life Jensen speaker had mellowed to great a tone. It is still sitting on my shelf waiting to be reconed.

[DougGuy]

Just cause it's a clone don't mean it ain't a Fender! 

I couldn't help but think about the old days gigging in the bars at night, working in electronic repair shop in the day, we bought, sold, horse traded, and repaired used gear and we had these suspicions you know, like putting a good Fender sitting next to one with issues it will get jealous and start working, and of course if it started sounding too good, we'd look at each other with that "uh-ohhh" look, and it would never fail that amp would blow up.

So my 5g9 tremolux followed suit just like a real Fender..  After I stupidly left it on 24hrs, it sounded really good the next 2-3 days, and last night it has a brown out, slow dying away of volume just like turning the switch off while still playing, then it came back on.  It did this a couple times altogether, looking in the back the rectifier was dark.  Finally it quit coming on at all.  Only the filaments light up. 

Haven't looked inside but I'm under first impression that the PT gave up because it got HOT when I left the amp on all that time, I could touch it but could not hold my hand on it at all.

[Willabe]

It stays plugged in but you are right about the jacks shorting.

OK, but why???

Yes, why?

[DougGuy]

It stays plugged in but you are right about the jacks shorting.

OK, but why???

Yes, why?

The cable stays plugged in.  The guitar cable.

[DougGuy]

I put a meter on the red lead coming from the PT at pin 6 on the v6 socket and it reads a steady 340vac when the rectifier goes off so probably safe to rule out the PT.

The rectifier keeps going dark and cutting off, if I wiggle it, it comes back on for a few minutes then off again.  Socket is a new Belton, the 5U4 is a GE from 1956.  I will replace it with a new production JJ and see if the issue goes away.

[Ed_Chambley]

Speakers tend to change more character than any other thing in an amp. As they break in there character tends to have earlier break up unless you have something like jbl's. Tends to be the biggest change and sure tubes to float around for a little time but I don't know if you can hear much difference from when they're unsettled and settled

[DougGuy]

Speakers tend to change more character than any other thing in an amp. As they break in there character tends to have earlier break up unless you have something like jbl's. Tends to be the biggest change and sure tubes to float around for a little time but I don't know if you can hear much difference from when they're unsettled and settled

This is very true about speakers.  I use alnico JBLs in about evreything here, from the Vibro Champ to the Marshalls, this tweed Tremolux has a vintage Altec 417 from the 60s it's quite loosened up.  This speaker has a noticeable "whump" to it that you can feel in the floor around the amp, sitting on the amp while playing you can really feel it.  Lots of excursion.  USPS bringing a new JJ 5U4GB today, the old GE won't stay lit off more than a few seconds.  I never had one do this, matter of fact I can't ever remember having a bad rectifier tube, let alone one that is intermittent.

Update, new JJ 5U4GB came, it works but not as strong as the old 1956 GE tube.  I should have reflowed the solder on the pins before but I did today and now it works again like it always did.  Must have cracked a solder joint when I left it on 24hrs.  The amp SOUNDS much better with old glass!  The 12AY7 I had was a 1956 GE tube, I replaced both that one and the rectifier with new production JJ tubes and it just lost the edge, was not as loud, didn't have as much gain. I couldn't dial it in to sound like it did before, so I repaired the rectifier and put the old glass back in v1 and v6, now it's kicking butt again.

[sluckey]

Update, new JJ 5U4GB came, it works but not as strong as the old 1956 GE tube.

How can you tell?

[DougGuy]

Update, new JJ 5U4GB came, it works but not as strong as the old 1956 GE tube.

How can you tell?

Just ears.  I didn't even put a meter on it before I fixed the old one and put it back in.  I know this isn't very scientific but if it don't pass the ear test then ya gotta drop back and punt.

[jojokeo]

Shorting jacks on a guitar cable = no loud popping when changing guitars on the fly. (something lost in translation causing confusion?)


I've read many amp builders from Dr Z and others that like to leave their new builds on overnight and call it a "burn in".


Many tube suppliers "burn in" their power tubes to help with the "settling" then match them. And you pay more for this (as Sluckey says, for the electric bill. And quoting Caddy Shack, Carl Spackler, "How 'bout a little something for the effort?"  )