Amp problem! Help!?

[elenore19]

So I was crankin' my SCXD because I finally had the opportunity. Yesterday I played a good 20 minutes with the volume close to full on channel 1. (man, that breakup was amazing)

So I went out there again today, hooked it up, played for about 3/4 minutes and all of the sudden the volume went way down. As if I had it at just below 2 volume. Not loud. But I had the volume at 9/10. Then after playing for a couple more minutes, hoping it would fix itself, it got loud again, only to go back to soft after like 10 seconds.

Any ideas?

I'm hoping burnt out tubes (this is my first "tube" amp and I have no idea what symptoms of blown tubes are)

I checked the fuse. It seemed fine. I checked the two 6v6's and they both seemed the same. I have no idea what to look for. I checked the 12AX7, looked brand new.

Is it maybe the new speaker? I put a Rajin' Cajun in there about 2 weeks ago or so.

Any suggestions?



And if you're wondering due to my other thread... No, I have not tried the organ tubes in the amp yet, this problem happened before that.

Elliot

EDIT:Looking at the two 6v6's there are two "lights" in each one, and in one of them you can barely see one of the lights. It's there, but you have to look closely. Maybe that implies tube breakage?

 

[antichef]

First, I'd check the speaker connection (since you changed it out) -- if any of the connections are loose or compromised, that can cut down on the sound, and it's really bad for the amp to run it that way, usually. Second, if you still have your old speaker, try it with that, just for troubleshooting purposes.

Assuming that's not the problem, do you have replacement 6v6s? Definitely try them out if so. Otherwise, if you want to do something now, maybe try switching them and see if anything changes? (actually, I have no idea whether that last suggestion is helpful at all or not, but I know I'd try it )

Soon, maybe people who know what they're doing will post, but you can try these things in the meantime

 

[elenore19]

First, I'd check the speaker connection (since you changed it out) -- if any of the connections are loose or compromised, that can cut down on the sound, and it's really bad for the amp to run it that way, usually. Second, if you still have your old speaker, try it with that, just for troubleshooting purposes.

Assuming that's not the problem, do you have replacement 6v6s? Definitely try them out if so. Otherwise, if you want to do something now, maybe try switching them and see if anything changes? (actually, I have no idea whether that last suggestion is helpful at all or not, but I know I'd try it )

Soon, maybe people who know what they're doing will post, but you can try these things in the meantime

If I don't have the problem fixed by the time I get back to college, I'll definitely try the speaker swap deal. (The old speaker is in my dorm room)
I just read this thing on a site where it seems that the power tubes have burnt out. So that is most likely the issue. (I hope.)
But I'll be ordering a new set of tubes soon and we'll see for sure in a week or so

 

[elenore19]

Possibly the socket connections to the tube pins may not be making a good connection. With the amp cold and unplugged, gently rock the tubes back and forth in their sockets and make sure they are seated all the way in.

Any chance of a funky guitar cable or plug losing connection?

Does this only happen when you're cranking it or at all volume levels?

Checked the cables..both power and instrument cables.

I made pretty sure that the tubes were in there pretty swell.

All volume levels it happens.

I read somewhere on the internet that mentioned symptoms like my amp is having and apparently it is my power tube dying out on me. So I ordered a new set + a spare set. Should hopefully fix the issue. If not..then I'll be really sad/annoyed.

 

[Anfontan]

I agree that the first place to look would be the new speaker connections-a cold connection with cause volume problems. Is there an effects loop or a line out on this amp? I had and amp years ago that would do the exact same thing-volume would drop so low it was practically silent, and very distorted.
It was the effects loop connections-they were very cheap and very undependable. I found that you could jumper the connections-effect out to effects in- with a short patch cord and you would get the full volume back. Try the patch cord in the loop or just insert into the line out, there might be a dirty connection that the cord will undo.
Hope its something as simple as that!

 

[Anfontan]

Per chance was it a Tech 21 Trademark 60?

I thought of that for the SCXD, but looking at the manual there doesn't appear to be send/return jacks, although there is a line out.

elenore19, if you plug a jack into the line out, does it cutoff the speaker output?

It was actually a 60 watt Crate with a tube driven preamp-a TD-70 I think. The effects loop input/outputs had to be replaced 2 times under warranty, but they always used the same shoddy quality components each time...it's been in retirement for quite a while now, I just don't trust it for playing out anymore.

 

[elenore19]

Per chance was it a Tech 21 Trademark 60?

I thought of that for the SCXD, but looking at the manual there doesn't appear to be send/return jacks, although there is a line out.

elenore19, if you plug a jack into the line out, does it cutoff the speaker output?

I actually don't think it does cut off the speaker. I'll try that out sometime. I'm still hoping that it's the tube.

 

[Gear_Junky]

Per chance was it a Tech 21 Trademark 60?

I thought of that for the SCXD, but looking at the manual there doesn't appear to be send/return jacks, although there is a line out.

elenore19, if you plug a jack into the line out, does it cutoff the speaker output?

no, line-out works together with speaker.

i might add that i also have an upgraded speaker and i played a "gig" (4-5 songs) on full 10 (had to compete with Hot Rod Deluxe) and no problems.

i am no electronics engineer, but if the 2 power tubes don't glow the same, i would guess trivially, that one of them is "not right", no? aren't they supposed to have the same load?

P.S. If it IS the power tubes, el19, you must let us know how the new ones sound

 

[elenore19]

no, line-out works together with speaker.

i might add that i also have an upgraded speaker and i played a "gig" (4-5 songs) on full 10 (had to compete with Hot Rod Deluxe) and no problems.

i am no electronics engineer, but if the 2 power tubes don't glow the same, i would guess trivially, that one of them is "not right", no? aren't they supposed to have the same load?

P.S. If it IS the power tubes, el19, you must let us know how the new ones sound

I really was just focusing on fixing my amp...so to avoid any issues really with biasing or anything of the sorts. I ordered the same tubes. So sorry to disappoint.
BUT!
When I get my new power tubes, I'll definitely be working with the 12ax7's from the organ. (my other thread..there are pics in it too!) But otherwise..I'll have to wait for a couple of years to buy different power tubes.

As far as them not glowing the same..that's what I always thought too...although I just remember reading somewhere that the glow really doesn't matter Too much in telling if the tubes are messed up or not. I can't remember specifically. But yeah.

 

[dgatwood]

i am no electronics engineer, but if the 2 power tubes don't glow the same, i would guess trivially, that one of them is "not right", no? aren't they supposed to have the same load?

The glow is caused by the filament (heater). I would expect it to be approximately the same on every tube, assuming that they are the same brand/model/style of tube. It is just a resistor between a constant 6V or 12V supply and ground, so it should draw roughly a constant wattage and output roughly a constant amount of light. If two tubes of the same model/manufacturer/style are of dramatically different brightness, it likely means one of two things:

1. One of the two filament elements burned out. Years of not letting the tube cool before moving the unit around can do that.... Remember that the tube heater is basically just like a light bulb. Some circuits wire the filaments in series, in which case it should either be lit or dark unless the part is just about to fail and is glowing excessively brightly, but if they're wired in parallel, you could have one lit and one not. You could also have hot spots on the filament caused by them being thinner at various spots. That is likely to be a sign of imminent tube death. (It's also a sign that your power supply is providing too much inrush current to the filament, IIRC, though I'm not sure how you'd cure that without either using a very small DC power supply that provides just the bare minimum amount of current or designing a custom power supply that ramps up the supply voltage gradually, which is something that AFAIK nobody actually does.)

2. The power or ground to the darker tube is bad. This is probably a cold solder joint on the tube socket, but I suppose it could be farther down the wire. Worth inspecting the solder joints just to make sure. (Be sure to do any inspection with the device unplugged, and be sure to turn it on for a minute or so while unplugged to discharge the power supply capacitors.)

 

[elenore19]

The glow is caused by the filament (heater). I would expect it to be approximately the same on every tube, assuming that they are the same brand/model/style of tube. It is just a resistor between a constant 6V or 12V supply and ground, so it should draw roughly a constant wattage and output roughly a constant amount of light. If two tubes of the same model/manufacturer/style are of dramatically different brightness, it likely means one of two things:

1. One of the two filament elements burned out. Years of not letting the tube cool before moving the unit around can do that.... Remember that the tube heater is basically just like a light bulb. Some circuits wire the filaments in series, in which case it should either be lit or dark unless the part is just about to fail and is glowing excessively brightly, but if they're wired in parallel, you could have one lit and one not. You could also have hot spots on the filament caused by them being thinner at various spots. That is likely to be a sign of imminent tube death. (It's also a sign that your power supply is providing too much inrush current to the filament, IIRC.)

2. The power or ground to the darker tube is bad. This is probably a cold solder joint on the tube socket, but I suppose it could be farther down the wire. Worth inspecting the solder joints just to make sure. (Be sure to do any inspection with the device unplugged, and be sure to turn it on for a minute or so while unplugged to discharge the power supply capacitors.)

Hmm, alright. Well the thing is, both tubes all have the same lights. Just one of the lights in one tube looks really cloudy...I guess that'd be the best way to describe it. I ordered new tubes, I'll try them out, I'll try switching out preamp tubes, and switching back in the old speaker. Otherwise, I think I'll take advantage of my 5 year warranty and send it in to fender.

Thanks for the help though! It's greatly appreciated!

Elliot

 

[dementedchord]

intermitent problems almost always come down to connection issues... in this case i'ld be taking a serious look at the sockets... and just jiggling them aint gonna do it... you need to take the tubes out and look at the sockets... each of those little tabs in there have to grip the thing tight... use a small screw driver (i use a dental pick) to close them up a bit ... if you simply try to reseat with out doing this... then one could be bad and feel good if the other are tight... make sense???

 

[dgatwood]

Hopefully the power supply caps have discharged when he does this.

It kind of does sound like as the tube heats up it may lose contact with the connection.

Yeah, the "comes back again" part does hint at a thermal issue, which usually means a cold solder joint somewhere, though I suppose it could be a tube socket expansion issue as well. A little DeoxIT on the tube pins would probably help (or steel wool if you're really really careful not to touch the glass).

 

[elenore19]

Yeah, the "comes back again" part does hint at a thermal issue, which usually means a cold solder joint somewhere, though I suppose it could be a tube socket expansion issue as well. A little DeoxIT on the tube pins would probably help (or steel wool if you're really really careful not to touch the glass).

Thanks for all the help guys, but I believe that if it is a connection like that somewhere in the amp...Definitely able to take advantage of the 5 year warranty on this sucka.