Can power tubes test as good but not be?

tekbow

In the continuing saga of my not being happy with the sound of my SLO anymore.

Its currently got a set of JJ 6L6GC in there, which tested good toward the end of last year when I had it in to check a funky bias that turned out to be the bias meter.

They gave it a general Once over and said it was fine.

But I think there's something weird going on with it. OD channel Sounds a bit lifeless to me, with a weird almost mildly comb filtered thing going on in the midrange, splashy/scratchy might be a good overall description.

I've changed all my preamp tubes out one at a time and no dramatic difference, so it's not a preamp tube.

Just wondering before I end up sending it in for a full check against a schematic.

Chester

The JJ's may have checked within bias, but be near the end of their useful lives. Worth swapping them before going through an expensive check up. Dull or noisy response is usually a tube issue

tekbow

Chester said:

The JJ's may have checked within bias, but be near the end of their useful lives. Worth swapping them before going through an expensive check up. Dull or noisy response is usually a tube issue

Sorry, should have mentioned, they were checked on an actual tube tester, and not one if the Orange ones, an Avo VCM MKIII

ICBM

Valves can easily test good on a tester and fail or not sound good under real amplifier conditions, which are usually at much higher voltages than the tester applies and often at power dissipations well outside what the designers originally intended.

In fact, for guitar amp valves a 'proper' tester is almost useless other than for matching - it will tell you if the valve is definitely no good, but not if it's noisy, microphonic, poor-sounding or likely to fail when subjected to the sort of stress in a real amp.

tekbow

ICBM said:

Valves can easily test good on a tester and fail or not sound good under real amplifier conditions, which are usually at much higher voltages than the tester applies and often at power dissipations well outside what the designers originally intended.

In fact, for guitar amp valves a 'proper' tester is almost useless other than for matching - it will tell you if the valve is definitely no good, but not if it's noisy, microphonic, poor-sounding or likely to fail when subjected to the sort of stress in a real amp.

Grand, so the power tubes could explain the perceived lacklustre sound? I'll order a new set of 5881s. Never did like those JJs anyway.

Modulus_Amps

The OD channel and the clean channel both share the same power amp, does the clean sound have the same dullness? or do you not use it enough to know?

tekbow

Modulus_Amps said:

The OD channel and the clean channel both share the same power amp, does the clean sound have the same dullness? or do you not use it enough to know?

Guilty

I do use the crunch mode and feel its lacking some oomph, but less noticeable because I usually boost it with an SD1 or the like.

Put it this way, if you use the SRV/mid cut (700hz) switch on the crunch channel, it gets scratchy and thin to my ears.

That's what the lead channel is sounding like. I cannot find an IR Setup I like. Also feels like it's not as gainy as it used to be.

I'd switched out all pre-amp tube positions, one at a time, with a known good tube, actually a couple of good tubes to be sure.

Paid most attention to V2 as that's the extra gain stage for the OD Channel as far as I'm aware. But no difference.

I'm ruling out a phase switch being in the wrong position somewhere in my signal chain because this is with the SLO On it's own.