I have Blues Deluxe Reissue.
Did not find this in the FAQ's, so.....

After how many hours should I change the tubes?

Thanks.

There is no time frame as to how long tubes last. Thats said by the post on how to use a standby I can see many don't use correct so they are burning them out faster then they should.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.

Thomas Jefferson

my marshall still has it's original tubes , it was made in 81

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but if you have a problem change the valves and if that don't work change the valves and if that don't work change the valves .
that said don't forget the bias setting / adjust .

Wow! That's pretty good going.

I got my current Marshall new about ten years ago and it's been revalved/retubed twice. Pricey!

Cheers - C

'have a Cyber-Twin (2-12AX7 preamp tubes) bought used, tubes were iffy when it was purchased.

Changed them in August '08 and they are sounding a little furry, of late.

I changed the tubes in my 83 Marshall JCM800 2204 and had it rebiased about 10 yrs ago and it's still sounding great.The tubes didn't have to be changed but some other guitarist friends were raving about the difference Groove Tubes would make so I changed them but didn't find a noticeable difference from the tubes that it came with.My 84 JCM 800 4210 still has the original tubes and is still singing sweetly.

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'65 Strat,65 Mustang,65 Jaguar,4 more Strats,3 vintage Vox guitars,5 Vox amps,'69 Bassman with a '68 2-15 Bassman cab,36 guitars total-15asst'd amps total,2 vintage '60s Hammond organs & a myriad of effects-with a few rare vintage ones.

MY 1971 JMP-50 still has the original tubes.
If you play at 10 constantly, the tubes will not last as long. Many NOS tubes cant take more juice than current production tubes.

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Current Gear: Ron Kirn Barnbuster Tele,
Marshall: 1971 SuperLead 100>1997 1960-TV, bunch of pedals
and a 1987 Porsche 911 Carrera coupe named Veronica