Tube swap in a Marshall Valvestate failed...

[Gold star]

I have a 2005 Marshall Valvestste 2000. the amp suffers from a certain amount of hum especially in the overdrive channel. recently I changed the standard single 12AX7 for a JJ 5751 tube which is slightly lower gain as a way of 'cleaning up' the sound. As soon as I plugged in the amp emitted a lot of hum, was unplayable so i switched off and put the old one back. Now it's OK. Either the circuit will not function with that tube or the tube is faulty. I believe the 5751 and 12AX7/ ECC83 are constructed the same .. but the 5751 has shorter plates...any ideas?

[Gtrjunior]

Re: Tube swap in a Marshall Valvestate failed...

Try another tube. The two you swapped should both function.

[Aceman]

Re: Tube swap in a Marshall Valvestate failed...

Which Valvestate amp?

[Gold star]

Re: Tube swap in a Marshall Valvestate failed...

Valvestate 2000 50 watts..could be a fault with the valve , the noise was there even with the volumes right down

[Aceman]

Re: Tube swap in a Marshall Valvestate failed...

The head? Or the combo? The head was a pretty super underrated amp....

[Gold star]

Re: Tube swap in a Marshall Valvestate failed...

Combo..any thoughts ?

[AlexR]

Re: Tube swap in a Marshall Valvestate failed...

Tube is faulty, or the pins have corrosion.

[Gold star]

Re: Tube swap in a Marshall Valvestate failed...

Ok thanks .. its a brand new tube, JJbrand ..and it is still a pre-amp tube .just different. i'll check with the seller

[Gtrjunior]

Re: Tube swap in a Marshall Valvestate failed...

Although it’s fairly uncommon, even brand new tubes can be faulty.

[Phantasmagoria]

Re: Tube swap in a Marshall Valvestate failed...

Could be a faulty/dirty socket/bent or misaligned tube pins too. Either way I'd try a new tube first..

[NegativeEase]

Re: Tube swap in a Marshall Valvestate failed...

The head was a pretty super underrated amp....

Cool to hear, someone else on hear said these amps got pretty strong too -because the early 90s ones were kind of the laughing stock of the amp industry. In fairness, Marshall had literally just started their solid state amplifier department.

[NegativeEase]

Re: Tube swap in a Marshall Valvestate failed...

Good chance the tube is bad, 12AX7s are relatively rugged, so usually a bad one is from nice drop or jolt from handling and transport

However, it's also likely that one of the tube pin's dimensions is off or the tinned contact surface was not annealed correctly which can create a connection issue in the sprung sprocket. I've seen this in Chinese ones in the 90s a lot -and because Tubes are vacuum sealed and good for who knows, you can still buy tubes new today that were made decades ago in new packaging -especially with all of the mergers and acquisitions and rebranding buying and unused tube thats 10-30 years old but that has been repackaged into new modern packaging is possible.

[Gold star]

Re: Tube swap in a Marshall Valvestate failed...

or it could just be that type of tube does not suit the circuit design in that amp...all I know is the 5751 is a pre amp tube and in theory should work..but with less gain output...

[chadd]

Re: Tube swap in a Marshall Valvestate failed...

Cool to hear, someone else on hear said these amps got pretty strong too -because the early 90s ones were kind of the laughing stock of the amp industry. In fairness, Marshall had literally just started their solid state amplifier department.

The early ones were awful. I melted a couple of those heads and rack power amps back in the 90s.

[NegativeEase]

Re: Tube swap in a Marshall Valvestate failed...

The early ones were awful. I melted a couple of those heads and rack power amps back in the 90s.

I never melted one, but I did A/B comparisons of them in the Studio and they were criminally short on anything resembling a Marshall -lacked full sound, brittle, and uninspired.