Remove an output tube?

Kalcium

Hi there, I suspect an output tube in my Laney VC-15 has died as tonight it was working fine and then after a while went quite and the best way to describe it is to say i could only hear the preamp. I plugged my gt-8 into the effects loop (send and return) and then plugged headphones into the pedal which gives me a way of hear whats coming from the preamp and the sound in the headphones matches what was coming out of the speaker. The sound responded to gain variation on the drive channel and to the volume control of both channels but was soft enough to not bother anyone in the room next to mine when at normal levels the same setting would be pretty loud. So I assume maybe an output tube or both are dead...

My question is, is it ok to remove 1 of the 2 output tubes and play with only 1 of the output tubes in the amp for a few minutes just to troubleshoot the amp and see if 1 of the tubes is dead? (I dont have any spare tubes lying around to test with...)

I know this is ok with preamp tubes but I've heard you shouldn't remove output valves unless you're removing a pair like 2 out of 4, though I don't know if this was just meant as a kind of dont leave your amp with 1 out of 2 output valves on a permanent basis like you can when u remove 2 of 4 output valves to lower the power.

Any help would be appreciated, thanks ?

MikeM

I'd really recommend against it. I've read some cases of people doing it, but I personally think it's not worth messing with.

Personally I think one should ALWAYS have a spare set of tubes for their amp.. Invest in that, then you don't have to worry about damaging your amp further.

MIKA-the-better-one

Spare tubes... so true..... I need to go get 2 el84s and 2 12ax7s and one at7, or au7......

And I am broke ☹

Kalcium

MikeM wrote: I'd really recommend against it. I've read some cases of people doing it, but I personally think it's not worth messing with.

Personally I think one should ALWAYS have a spare set of tubes for their amp.. Invest in that, then you don't have to worry about damaging your amp further.

Yeah Im gonna get some new tubes and hope it fixes things cause even if that isn't the case, as you say its always good to have a spare set ?

needleshy

it may also be a cap or 2 that has gone on the board as well as a tube, same kinda thing has happened to me in the past with amps, one o my amps are at a Tech at the moment from a power tube that failed which also blew some other things on the board.

if i were you i'd take it to a tech just to make sure everything is still ok on your board, as sometimes tube failure could have negative affect on other components. I'd also try and buy a matched SET of power tubes now cause if you just buy 1 Power Tube, chances are HIgh they are going to be a mismatch, and your amp may not sound as good as it should. You'll also be needing a rebias of the new power tubes,

i would love to keep spare tubes, but these 100 watters really burn a hole into your pocket when it comes to good tubes, and there i have 2 of them, so i'll be saving for a long time to get another 2 sets of tubes,

Gearhead

I don't think the Laney VC-15 is a 100 watter and I would agree with Mike not to remove the one side of the output. Not only is it useless for troubleshooting other than to maybe find out if it is a tube or something else, while risking further damage to this amp. It is completely useless for using the amp as an amp since the sound will be terrible. It might damage the speaker, which will set you back quite a lot more than a set of spare tubes. Etc etc etc.

Kalcium

needleshy wrote: if i were you i'd take it to a tech just to make sure everything is still ok on your board

Its been to 2 -_- the first guy essentially only knows solid state and had a look but saw nothing wrong and suspected a tube fault so he sent me to another guy who does amp repairs to do with tube amps, and when he had the amp it worked 100% ...he couldnt get it to go wrong apparently...which i think is kinda silly cause when i got it back it worked for the first hour then when i turned it on again later that night it went faulty after 30 mins...

Maybe my amp is allergic to me ☹

needleshy

Maybe u got a bad batch of valves.

bottledtone

Pulling valves on a "cathode bias" amp can damage the amp and throw off the bias to the remaining valves. The VC-15 is "fixed bias (grid bias)" so is safe to pull valves. The amp would work with one, just won't really sound the same. The voltage probably would increase a bit now that the load would be less though. Stephenson amps have switches on the back that you can switch out any of the output valves...... even all, and then its like a standby. Some amps come out with a fuse on the cathode, so when it blows, you can carry on gigging on the remaining valve/s (eg. Engl)

Matching isn't too important in guitar amps......its only for Hi-Fi guys. Plus your phase inverter in your amp won't be perfectly balanced! Not even the caps! I can bet you on it. Us guitarists like overtones, and harmonics that come from scew unbalanced signals. ?

Kalcium

bottledtone wrote: Pulling valves on a "cathode bias" amp can damage the amp and throw off the bias to the remaining valves. The VC-15 is "fixed bias (grid bias)" so is safe to pull valves. The amp would work with one, just won't really sound the same. The voltage probably would increase a bit now that the load would be less though. Stephenson amps have switches on the back that you can switch out any of the output valves...... even all, and then its like a standby. Some amps come out with a fuse on the cathode, so when it blows, you can carry on gigging on the remaining valve/s (eg. Engl)

Matching isn't too important in guitar amps......its only for Hi-Fi guys. Plus your phase inverter in your amp won't be perfectly balanced! Not even the caps! I can bet you on it. Us guitarists like overtones, and harmonics that come from scew unbalanced signals. ?

Thanks Bottledtone, I tried removing tubes one at a time and the problem persisted, so it isn't the tubes (though I will still be getting a spare set...)

Basically what happens is the amp is acting like its got a built in noise gate. If the signal is loud enough it goes through perfectly, but if not it fizzes a bit and drops off suddenly. Like when the volume is turned to a point where its just loud enough then if i pick hard it comes through for a while until the note fades a bit (then if drops off suddenly when its faded below the cutoff volume) or if i pick softly i hear nothing, or a bit of fizz if i pick with just enough volume for it to go through for half a second.

Any ideas what it might be? ...Im gonna take it back to the tech this weekend now that its consistently not working maybe he can find out whats wrong.

Gearhead

That sounds like a loose connection or bad solder joint to me. Should be doable, especially if you have a 'scope (like any tech should).

Zulublues

Hi Kalcium

Give Glen Turrell a call. He's a professional sound electronics engineer working out of Westville and understands tube amps and ss amps well. His forte is mixing desks and the like. He sucessfully rescued an old NAD hifi amp for me. Give him a call on 083 360 3579, tell him Mark sent you.

Good luck

Kalcium

Zulublues wrote: Hi Kalcium

Give Glen Turrell a call. He's a professional sound electronics engineer working out of Westville and understands tube amps and ss amps well. His forte is mixing desks and the like. He sucessfully rescued an old NAD hifi amp for me. Give him a call on 083 360 3579, tell him Mark sent you.

Good luck

Thanks I will do that if the guy I took it to now cant fix it...he hasn't really had a chance to see whats wrong cause it was working when he had it...