Tubes glow but no one is home: Amp Help.

[PsychoholicSlag]

So I was swapping around some pre amp tubes at practice last night then all of a sudden volume drop then to nothing. All of the tubes (pre and power) were lit but the 12AX7 I swapped was under a sheild and it was a Sovtek LPS so it's hard to know cause they don't light up that much anyways.

Would a pre amp tube that fails do that? Or does it sound more like a power tube problem.

I turned the amp off for a few seconds to let it cool down, the fired it up and it was like nothing happened, played like normal.

Any info would be greatly appreciated.

 

[King Crimson]

What's your setup - you didn't mention the obvious?

You got spare PT PrT then start to swap them 1 by 1. Don't complicate things by swapping more than one at a tme.

 

[glpg80]

What's your setup - you didn't mention the obvious?

You got spare PT PrT then start to swap them 1 by 1. Don't complicate things by swapping more than one at a tme.

+1

the other common misconception is the fact that you see light. the light is simply tungsten heater filaments, that does not show anything or prove anything other than your heater circuit is working properly. the brightness of that glow does not prove anything either - how hot stages are biased or how the tube is designed is nothing you have any control over or any standards to go by.

swap them for a known working preamp tube. if a power tube went under it would be likely you would pop a fuse while your at it, IMHO its time to do a full retube if you're guessing every tube in the amplifier is the cause.

 

[King Crimson]

IMHO its time to do a full retube if you're guessing every tube in the amplifier is the cause.

Can't argue wit-dat; if you got the coin...to a brutha from another mother.

 

[PsychoholicSlag]

Guess that would help huh.

It's a Krank Rev1

V1: cleen
V2: gain
V3: gain
V4: PI

Power tubes: Sovtek 6L6WXT+

The only tube swaped was the V2, but I know I've been hard on my powers lately. They're a year old and I play at least 2-3 times a week, I just don't have any matched spares right now and no one has them in stock. They're all different ratings, I just have some Ruby's and Sovtek 5881 lying around.

If it blew a fuse would it still work?

 

[glpg80]

I just don't have any spares right now and no one has them in stock.

http://www.dougstubes.com or use our own members - Laura www.valvequeen.com for tubes. no excuses for not carrying stock as to not having any spares to troubleshoot or replace worn tubes, there are tons of distributors that exist.

They're all different ratings, I just have some Ruby's and Sovtek 5881 lying around. If it blew a fuse would it still work?

if all you touched was the preamp tubes then do not go looking at the poweramp tubes. No - your amplifier would not even turn on if it blew a mains fuse meaning no power tubes have shorted.

get a full set of tubes for it ASAP and set a few aside that are known to work for testing and future replacement.

 

[PsychoholicSlag]

Doug does have them in stock, just waiting to hear if he has the same bias point (tube depot's rating) or the same plate current.

I really don't want to have to take it in and get it re biased everytime I get a new set of tubes ... I know I know, it's like putting new tires on your car, even though they are the same brand/type they need to be balanced. I would just like to have some spares to pop in when I need to if I'm on the road. I don't want to have to go to a tech I don't know in some bum ass town, that doesn't know what he's doin./rant

I'll send the Valve Queen a message.

I have a shit load of pre's that I'm going to try out this weekend. I have some Sovtek 12AX7 that are bullet proof .. I think the WC ..WB .. something like that. Tone isn't the best but they last.

..... how would I know if my OT is going out? I would hope this wouldn't be the case.

 

[glpg80]

unless you've been abusing your OT by running your bias too high, running improper tube combinations, or running improper secondary impedance settings unmatched to your speakers, your OT should not and will not overheat or short. usually transformers can take quite a beating and usually show signs of stress before going - you're jumping to conclusions and need to make sure it is 100% bit tube related. and since you didnt short a power tube yet because your mains fuse is fine, i would assume you need to retube and bias your poweramp section while you're replacing preamp tubes.

preamp tubes last ~3-5 years under best conditions assuming there are no manufacturer deffects. poweramp tubes last depending on usage and volume and bias, but normally the rule of thump is 6-8 months to at most 1 year with normal every day usage. under heavy gigging and band practices, i was going through poweramp tubes about every 4 months when i played in 3 bands.

tube amplifiers require maintenance. either arrange to pay for shipping insurance to someone that knows what they are doing or prepare to drive a bit to find someone. either way, your amplifier needs regular maintenance to perform correctly. you cannot ignore this

 

[MYLILSS]

laura at valvequeen is awesome to deal with. i would definately recommend her

 

[steve_k]

Careful with the Sovtek LPS as it will not work in a cathode follower position. As a general rule, unless I know exactly how the preamp is set up, I will only run an LPS in V1, which I often do on amps that are too bright or have a little high gain noise and some gain to spare. They will help to knock that down a bit and tighten an amp up.

Steve

 

[Capulin Overdrive]

ditto on the LPS

 

[PsychoholicSlag]

Not too sure if the Krank has a cathode follower position, I'll look into that.


Hmmmm, guess I'll order some tubes then. None of the places had the Sovtek 6L6WXT+ with a bias point of 34, I have a set of Ruby 6L6GCMSTR's that are still good I'll have someone bias in, then I'll just order a matched set with the same rating from Doug. Don't really have the cash, but you do what you have to do.


Thanks everyone.

 

[steve_k]

If you have volume go to zero and there is no output, the only preamp tube that would do that is V1. Sounds like you replaced it, so you should be getting some output if that was the issue. If the HT fuse blows, you will not get voltage to the power tubes. It has done its job and protect the amp components. I don't know anything about Krank amps though. But, generally in this regard, they are all the same. A mains fuse blows and the amp won't even turn on.

If the HT fuse was good, you could still have a bad tube without a fault, but I would imagine the amp is set up in duets where the outer and inners run as pairs and the amp should make some noise. Try running the amp with a tube in the outer sockets and pull the two inside tubes and see what happens (with known good tubes). Repeat for just the two inner ones. It is best to have some spare fuses when you do this.

Steve

 

[glpg80]

If you have volume go to zero and there is no output, the only preamp tube that would do that is V1

not quite steve, if any tube in the cascaded stages shorts open you will lose all of your signal, its the same as effectively taking the tube out of the amplifier alltogether and trying to play. all of the preamp stages need to be evaluated with a known working preamp tube one by one.

Try running the amp with a tube in the outer sockets and pull the two inside tubes and see what happens (with known good tubes). Repeat for just the two inner ones. It is best to have some spare fuses when you do this.

this would definately be the next step - but dont forget you must half the impedance of the amplifier going to the speaker load when you do this.

if 16 ohm speakers set amp to 8 running two pulled tubes, if speakers are 8 ohms set amplifier to 4 ohms when pulling two tubes (the inside or outside pair)

if after you evaluate all of your tubes and bias is working correctly, you would then need to take the amplifier to a tech to remove the PCB board to evaluate relay's and capacitors.

 

[RoidRage]

Everyone's numbers will be different!!

You must get another set from Tube Depot with the same value!!!

Replace all Preamp Tubes...

If if it were your power tubes then you would blow fuses, and it would make noise...

No Noise = No Input.

Probably V2.

Roid Rage

 

[PsychoholicSlag]

Oh I love you guys.


I'm glad I'm a part of this forum.


So with the V1 debate, since this is a channel switcher, wouldn't the V2 be the "main" tube in a sense since the V1 is just dedicated to the cleen channel?

 

[steve_k]

Oh I love you guys.


I'm glad I'm a part of this forum.


So with the V1 debate, since this is a channel switcher, wouldn't the V2 be the "main" tube in a sense since the V1 is just dedicated to the cleen channel?

V1 is the input tube and affects all channels.

 

[srinivassa]

I'm a little confused. It sounds like you swapped the tube hot? Or in standby? I know you said turning it off and on brought back your volume. I feel like I'm missing something in your description.

Sorry, I'm not expert. I'd like to weigh in, but it sounds a little muddled. Does your amp sound fine now, or do you get no volume?

If you get no volume, yeah, I would say that it might be the V2 tube that you swapped. Also, a lot of amps have multiple fuses for different power section. If you hot swapped a tube, you might have blow a fuse that controls the B+ network to bias your tubes. With that fuse gone, you could still turn on your amp, but you would get no sound because there would be no plate voltages. The tubes would still light because that is caused by a separate power network, the heater network.

Now, if you managed to power down and then everything worked fine, I would think you would be golden. You probably caused a problem by hot swapping the tube (or standby swap), which was corrected when you powercycled the amp.

That's all I've got though. I'm missing what they problem is. If the amp sounds fine now, I would honestly guess that the amp is fine. If you hotswapped a tube, the powercycle could fix the problem. If you didn't hotswap, then it is probably a bad tube in V2. Check your B+ fuse though. If you are getting no sound out, but the tubes light, it is likely your B+ fuse.

Hope that was confusing enough! I would be less roundabout, but I'm not 100% clear on the situation.

 

[PsychoholicSlag]

My life is nothing but confusion.

To let you step by step,

Played the amp, turned it off and let it set for 15 or more minutes, removed the shield cover, removed the tube and replaced with another (nothing was wrong with the amp just wanted to see what the other tube had to offer), turned on the amp, let it warm up, played for about 5 min, then the volume dropped then nothing on both channels, turned it off, let it cool and turned it back on and it was working fine.

I was just wondering would a bad pre amp tube cause this or could it be something else. Could the tube be "ok" then once it warms up all the way BAM! it's gone?

 

[FIREBALL]

try replacing the t1a fuse....if it keeps blowing you need new power tubes