Can you run 100w on just 2 tubes?

[willshep]

Hi,

Hope someone can advise; I have a JCM 900 100w combo - recently I had to run on only 2 valves - an opv fuse failed during a practice - I turned up the master volume and realised that the sound was giving some really nice overdrive - presumably because it was driving the two remaining valves harder to achieve a similar volume level - can this be done reliably long-term? I read somewhere you can help reliability, in this situation (which isn't uncommon) by switching the speaker impedance selector to 4ohm and run it on an 8ohm cab?

Any response is appreciated.

thanks

Will.

[stokes]

It is possible to run the amp like this,but you should check the bias to be sure you arent going to fry your power tubes.Also be aware that most Marshall OT's cant tolerate an impedance mismatch as reliably as a Fender or some other amps.Running an 8ohm load in the 4ohm out would be advisable if you use just 2 tubes.

[willshep]

Thanks i'll keep that in mind,

Incidentally, i've heard a lot of bad things about marshall ot's - but i've also heard that if you replace them the amp sounds 'neutered' - is there an OT i can buy and fit to the amp that's more reliable?

Thanks

Will.

[Bruce / Mission Amps]

Thanks i'll keep that in mind,

Incidentally, i've heard a lot of bad things about marshall ot's - but i've also heard that if you replace them the amp sounds 'neutered' - is there an OT i can buy and fit to the amp that's more reliable?

Thanks

Will.

That's funny, I think the 900s sound neutered with the stock iron.
If you have the cash, get some iron from Mercury Magnetics or even the lower cost MOJO Heyboer iron is excellent.

[Chuck H]

FWIW there are a few reasons that Marshall OTs have a bad rep. Some are valid. But no more than for other MFGs. The biggest reason Marshall OTs seem to fail more often is user abuse/neglect. Because most of the Marshall amps in use are heads it is much easier to accidentally not plug in a cabinet, run the wrong impedance or otherwise have a fault in in the connection between the amp and it's speakers. Combine that with the fact that Marshalls are typically played cranked for most of their lives. Oh, and they use EL34s. The quality of which has been very inconsistant compared to 6L6 types esp. in reguard to shorts.

If you don't crank the amp with old, poor quality or mismatched tubes, always make sure you have an appropriate speaker load plugged in with a proper speaker cable and keep the amp properly biased, your Marshall OT should last just fine.

Chuck

[Tiago]

The last abuse of a Marshall amp that I'm aware of, was a friend of mine that was playing live with other band. He let the other player play with is amp and when he was in the audience while the other band was playing, the guitar sound disapeared, when he got to the stage he found the other guy pulling the speaker plug in and out!!
Result?? You might think blown OT...NO!
That was a war tank, a JMP Superlead, melted EL34!!

[nooneknows]

he found the other guy pulling the speaker plug in and out!!

...I could kill for something like this to my Marshall...