Line 6 Bogner Spider Valve Fault - Dying tubes?

[Sosijdog]

Hi Guys,

I am a newbie to this forum and hope you guys can help me out with an issue I have.
I have a Line 6 Bogner Spider Valve 112 that produces an extremely loud and sudden Blaring noise just a few seconds when standby switch is on.
It occurs usually in the first few seconds (up to a minute) but after this it never does it again?
If you strike the top of the amp the noise will cease which suggested to me it was a bad connection on the main board.
The volume control has no control over the noise either which has me thinking it cannot be an input side fault but more from after the pre-amp stage.
This happens with either a guitar or nothing plugged into it.
I have inspected the main board and found nothing un-toward. I checked the caps with an ESR meter and everything was in spec.
The amp was bought in 2008 and is on the original tubes... but that being said, it has not been used very much at all in that time. (I happen to dislike this amp - but cannot sell it or use it in this state! ). Can this be a sign of dying tubes? I have heard they can make all manner of strange noises when on the way out.

I recorded a video and uploaded it to Youtube so you can hear exactly what it does.
The first video clip - The amp is turned on with no input and approximately 35 seconds later the "blaring" noise happens (You can see the camera flinch as I nearly destroyed my pants )
The second clip - I am playing through the amp and the same thing happens. After the noise the amp functions perfectly afterwards.
The third clip - The amp was turned off and the Noise happened, almost like the caps bleeding off... very strange?



So thats the issue. Have you ever heard of anything like this?
As I say I am not a huge fan of this amp, but cannot get shot of it or even use it in this state.
I would try and replace the tubes if that will cure it but I dont want to throw money at something I kinda hate.

Thanks in advance guys.
Regards,
Stevo

[xtian]

Hi, Steve-man. This issue could be the standby switch--they're not designed to stand up to high voltage switching. You can just connect the two leads that go to the standby switch together to test my theory. Standard disclaimer: HIGH VOLTAGE! Know how to drain your filter caps and check for voltage before touching anything! Danger!

[Sosijdog]

Hi Xtian,

Thanks for your quick reply.
That is a good shout and an easy test to carry out...
This has been a fault for years and I would love to get to the bottom of it. But as I have said I am not really that interested in the amp enough to try and sort it until now.
My son, when he was 2, was attracted by the blue led and being a toddler started poking buttons and flicking switches....

The effect when he flicked the Standby was similar to that scene from back to the future....

I will let you know...

Thanks,
Stevo.

[xtian]

Cool. The other approach, while you have the amp open is to use a wooden chopstick or other non-conductive tool, to wiggle and prod everything while the amp is running to see if you can find the loose or broken connection.

[Sosijdog]

So last night i fitted a jumper cable to bypass the standby switch and amazingly it was worse!

The noise didn’t stop once it started. But i think that is just a coincidence rather than any direct influence of the switch.
I was able to affect the sound slightly using the presence control but volume had no control over the sound. Nothing else made any difference to the sound.

I am going to carry out the prodding test today...

Stevo

[Sosijdog]

Removed the chassis from the amp and tested it today - prodding and tapping all components inside... and it never missed a beat once!

Such an irritating spirious fault.
Any other ideas of what could be going on here?

Thanks again.
Stevo

[Sosijdog]

So I have finally got back around to looking at this fault. I read on another forum a guy that described the exact fault as i have. He said replacing the tubes solved the issue...

I did buy new tubes but i really want to know if it is the fault or not before fitting them. (To satisfy my own curiosity)

So i decided to put my scope onto the output of the Power tubes - however i am totally new to using the scope! I connected 2 probes one to each wire of the primary of the Output transformer (brown wire and blue wire) to try and see if the fault was coming through both power tubes. Now first question - is this the correct way to check the push pull tubes?

There was interference on both the channels on the scope when the fault occurred. Can one tube fault cause interference on the other??
I was hoping to find interference on one channel, then swap the tubes and see if the fault changed channel which indicates a tube fault.
However it was on both... that suggests a fault feeding both the power tubes from a previous stage?

What i have confirmed:
Unplugging input from the solid state side - fault still occurs (fault is on the tube side main board)
Volume set at zero - fault still occurs very loud! Volume has no control over fault.
Presence control DOES affect the tone of the interference noise.
Fault is interfering with both channels (providing my measuring method was correct)

So is this a fault from the inverter tube before the power tubes but after the pre-amp?

Still could just be a tube fault.

Thanks again guys.

[Speedypancake]

I'd be tempted to back here ?..

So last night i fitted a jumper cable to bypass the standby switch and amazingly it was worse! The noise didn’t stop once it started. But i think that is just a coincidence rather than any direct influence of the switch.

[Sosijdog]

After i had bypassed the standby i had the noise all the time, but once it stopped and never came back for a few weeks?

I tried bypassing the switch on another occasion but the fault did not occur again and the amp worked without issue...

So i cannot make the fault appear and if i make a change i cannot guarantee its fixed.

Thats why i want to scope the amp and figure out at what point the interference happens.

[bmx]

Bad standby switches can definitely cause this squealing. I don't know if an alligator switch is a solid enough connection to eliminate the squealing as a squealing standby switch will seem to measure fine. Soldering a jumper across the standby switch is a better test. However, bypassing the standby switch puts full B+ across the entire preamp. So I wold replace the standby switch. It's good to replace parts on old amps imo.

On thing about putting the scope leads on the primary is you will have quite high voltages there. Voltages up to 2x the B+ voltage. Make sure your scope can handle ~940V to 1000V.

Try swapping the Phase inverter tube.

[Sosijdog]

Ok guys thanks for the info.

I will revisit the switch again...
I managed to get the scope across the output of the inverter tube when the fault occured which also had interference on both channels.

I dont believe its the switch as the worst the sound has been was when the switch was completely removed from the circuit and the connector had a jumper cable fitted?

If only the fault was constant then diagnosis would be easier. It seems to rectify itself once it happens... almost like a temperature change inside the tube causing a bad connection. I need to leave the amp almost a day for the fault to re-appear. Very strange.

Thanks for the scope info too bmx.

[Phil_S]

The issue of whether it is the switch or not doesn't make sense to me. I suggest the problem has very little to do with the switch. What does the s/b switch do? It prevents the circuit from being full on, a function that isn't necessary or needed. What I think is going on when you jumper the switch is that your amp is full on at the power switch, so it immediately displays the problem. I'd be inclined to bypass the s/b at least until the trouble is identified and maybe indefinitely, as there should be no reason for this switch. The benefit of this approach is that it eliminates the switch as a causal factor in the problem. Now you can focus on finding the real cause and fix it.

Maybe there is a benefit to taking the basic approach of tube pulling. Pull all of them. Problem exists? Then it is after the power tubes, IOW, the output transformer. Now, put tubes in starting with only the power tubes. Then add the PI. Then add preamp tubes, one at a time working back to the first input tube. Power on each time you add a tube and see if the problem exists. This approach just might isolate where in the circuit the problem originates. From there, you can employ other techniques. There is very little to lose by employing this simple trouble shooting routine. Why not just do it?

[Sosijdog]

Hi Phil, excellent advice.
I am a complete newby to amps but have repaired a lot of welding gear so not completely new to electronics.

As to why i have never done it - i did not think the amp would work with the tubes out and therefor would be pointless. But thanks for the heads up! That is a great diagnostic approach.

I will give it a shot.

[Phil_S]

Well, you say (and demonstrate) the noise happens when you turn on the amp. It has the problem when you have no input. (Is the guitar plugged in and idle or not plugged in?) You should be able to hear the problem when you put in the tube that runs the offending section. It may be a tube or It may be the amp. If it is all 12 AX7's in the preamp, you might try some tube rolling to see if the problem changes position. This would be a dead giveaway that the problem is a bad preamp tube.

[Sosijdog]

Yes the guitar is completely disconnected. The input of this amp goes through a solid state section for the effects before being run into the main tube board. I have completely disconnected this from the tube board and still have the noise.

Thus far I have probed the output of the Pre amp which has no interference, and the output of the PI where i am getting interference.
I immediately swapped out the 2 12ax7’s to see if i then got interference on the output of the Pre-amp which would indicate a faulty tube...

However, since swapping the tubes the fault has not happened again.

I am getting closer...