Big Vern

Hi Guys,
I'm new to the forum, so firstly hi to everyone,
I've already got loads of good info from this site- so thanks already!!.
Now to my current problem, I switched on my rack this morning, just playing away when I realised that one channel was hardly audible.(I run it as a stereo rack)
A quick check of all connections etc - but still Channel A is fine, Channel B is only just audible. I have 2 preamps in the rack feeding a rack mounted mixer with the FX returns from each going to its own input on the mixer (so I can keep dry/wet signals separate) so I tried with both of them, still the same. All of the valves light up - normal colour, but one thing I did notice was that if I increased the gain it did become louder but even when on full it wasn't as loud as Channel A at half gain?
I have to admit to being a bit of a novice when it comes to tube amps so I would welcome any advice as to what the problem may be.

David

Adwex

Are you sure it's the power amp?
Did you swap the left and right inputs to see if the problem moves with it?

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Big Vern

Hi, yes I tried that - the fault is on Channel B
The amp still has the original tubes that were in it when I acquired it (no saying how long they've been in) Maybe I should change them anyway??

Adwex

Yes, I would imagine it's time to re-tube that baby. You might get away with only replacing the smaller tubes (12AX7).

Try swapping the tubes around (A to B, B to A), see if the problem moves.

I used a 9005 for years, still have it. It's a great power amp, well worth the cost of new tubes. I put Svetlana's in mine.

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Big Vern

Yes, I love mine, I think youre right, it deserves a complete retube - I'm currently running it with a Rocktron Pirahna and Digitech 2120. I'll have a look around to see whats available. I guess I could change the 12ax7 valves, but what about the EL34's - will they need rebiasing? - It may be easier just to drop it off at my local shop and let their amp tech do it.

Thanks, David

Adwex

Yes, if you replace the EL34's, the bias will need to be adjusted/checked.

Just to satisfy my own curiosity, I would still swap the tubes around to see if that really is the problem.

I also installed 2 small cooling fans on mine. Without them, it's like having an oven inside your rack...nowhere for the heat to go, and it gets HOT!! Whatever component is installed in the space above it will eventually melt.

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Big Vern

Hi, I'll try swapping the valves round too see if it makes any difference, but like you advised I think a complete re-tube is probably long over due.
As I only play for my own amusement I have the 9005 at the bottom of my 14U rack with the top cover removed and a 1U ventilation grill above that.
The items directly above the amp are only half depth (alesis 3630, BBE 422, EQ) so there's quite a lot of space for the warm air to circulate - seems to be ok
Thanks again for your advice.

David