1975 Vibrosonic reverb problem ?

Paul O'Bryan · Post by **Paul O'Bryan** » 31 Aug 2022 2:53 pm

I purchased a very nice 75 Vibrolux reverb that was working fine.
Apparently had all the tubes replaced and capacitors done.
Went to turn it on before and it made a hell of a noise like it was flat out volume with a very loud hum!
I also noticed that one of the bigger tubes glowed very bright purple blue
colour straight away.
Anyone have any clue on might be going on?

Dave Hopping · Post by **Dave Hopping** » 31 Aug 2022 8:10 pm

It might just be a bad tube, but the safest course is to take it to a GOOD tech.

Paul O'Bryan · Post by **Paul O'Bryan** » 1 Sep 2022 2:40 pm

Okay Dave I thought that might be the case but is it okay to take that crook tube out and to still switch amp on to see if that eliminates the noise?

Dave Hopping · Post by **Dave Hopping** » 1 Sep 2022 8:26 pm

Paul, I'm no technician,and while you could try swapping out both power tubes for a matched set of whatever's in there now and seeing whether that solves the problem,there's no guarantee that it will, and it's a fairly expensive proposition anyway.If there's more going on inside, then there's a risk you'll damage your amp(and maybe yourself!)

If one of my amps misbehaved like that I wouldn't even turn it on again; I'd just take it to a professional.

Dave Grafe · Post by **Dave Grafe** » 2 Sep 2022 1:26 am

Check your reverb cables, they can make all kinds of hums and squeals and the volume knob doesn't control the output

Dave Grafe · Post by **Dave Grafe** » 2 Sep 2022 1:27 am

Check your reverb cables, they can make all kinds of hums and squeals and the volume knob doesn't control the output

DON'T turn it on with only one power tube

Jon Light · Post by **Jon Light** » 2 Sep 2022 4:35 am

Not helpful here is the fact that you are asking about removing one of two power tubes on a Vibrolux Reverb but in the title you have a four tube Vibrosonic Reverb on which you technically can remove a pair of tubes (1 & 4 or 2 & 3, eg) without harm (nevermind the impedance issues for the moment).
But the bottom line is that this calls for a tech. The price for mucking around, not knowing what you are doing, is steep.

Shaan Shirazi · Post by **Shaan Shirazi** » 2 Sep 2022 9:16 am

As a longtime Vibrolux Reverb player I would recommend having your tech install those spring tube holders for your power tubes. The sockets get loose at this vintage and that's an inexpensive way to keep them firmly seated. I'm not sure if this would help this particular problem but it definitely helps with eliminating all the problems that are associated with loose tubes and is much cheaper than replacing the sockets.

Donny Hinson · Post by **Donny Hinson** » 2 Sep 2022 4:33 pm

Went to turn it on before and it made a hell of a noise like it was flat out volume with a very loud hum!
I also noticed that one of the bigger tubes glowed very bright purple blue colour straight away.

I suspect the tube has an inter-electrode short. The loud hum is caused by the 6.3v AC (on the filament) getting to the cathode of the tube, where it's amplified and fed to the speaker. Replacing the bad tube will usually fix the problem. If the new tube doesn't correct the problem, it should be obvious almost immediately, and that would indicate that the shorted tube caused some other internal damage.

Paul O'Bryan · Post by **Paul O'Bryan** » 3 Sep 2022 2:13 am

Thanks for all the input and advice, I took the tube out that had a lightning show going on inside it and all was good. I then put one of the others in its place and there was no problem. The tubes are new but they are a cheap brand apparently and obviously just got a dud. Any suggestions on a good brand of tube for this Vibrosonic ? Tubes are a bit hard to come by here in Oz

Jeff Highland · Post by **Jeff Highland** » 3 Sep 2022 1:10 pm

Evatco in QLD are probably your best supplier in Australia for tubes/Valves