WTB 12ay7, 5751 or similar low gain preamp tube.

4114Effects · November 2014

So, I've just finished my 5e3 amp build, and discovered my EHX 12ay7 gives it a horrible low level hum. Putting a good 12ax7 in there instead cures the hum, but I'd rather use a lower gain tube so it's more authentic. Don't think I'd trust getting another ehx.

A search of ebay brings up very little in the way of low gain preamp tubes, especially 12ay7, so I was wondering if any of you lovely people have a nice spare tube lying about anywhere?

Cheers,

Dan.

simonbeckwith · November 2014

I've got a 12au7 if that's any help? Lower gain than a 12ax7, not sure difference between that and 12ay7?

4114Effects · November 2014

I think the au7 is for higher current like reverb drivers etc. Will look into it though :-)

4114Effects · November 2014

Then again, if the price is right I might just give it a go. Won't damage the amp, might sound alright. Lol.

BowynMadley · November 2014

If you want to buy new. Tube amp doctor 5751s have Never let me down.

4114Effects · November 2014

Ah thanks for the tip. The 5751 is a bit higher gain than ay7, but it might be a good compromise.

rockmonster · November 2014

I may have a brand new unused one I'll have a look when I get home tomorrow night......

4114Effects · November 2014

Thanks mate. :-)

ESchap · November 2014

Possible different take on the hum source. How close is the valve to the speaker magnet? I had the same problem changing from 12AX7 to 12AY7 in a Fender Tweed Twin reissue. If you look at the two valves, you will see that they are made with their Anode plates at a 90 degree orientation to each other when plugged in, with the 12AY7 this geometry difference was enough to induce the hum in the valve and being V1 it gets louder as you push up the volume. An old steel, (not aluminium) screening can reduced the hum substantially i.e. enough that the amp is quite useable.

4114Effects · November 2014

Ahhh, good point. I may buy one of those posh valve sockets with the aluminium screens.

But then again, it's a separate head and cab, so there's a fair amount of distance between the valve and the speaker coil. So probably won't be the issue. Hmmm.

ESchap · November 2014

In the twin, the valve is very close to the speaker's alnico magnet. If it's a head and cab, it's very unlikely, though it could be from a transformer. Thought it was worthwhile sharing though as until I had the problem, I didn't realise that the two valves were oriented differently.

On the valve change front, be careful with 12AU7's they pull quite a lot more current than a 12AX7. Also, it will probably be too low gain, I didn't like the result when I tried them in tweed circuits, sterile sound. As said by others, TAD 5751 is an OK valve. However, in my experience they have a slightly harsh sound to them when the amp is driven.

4114Effects · November 2014

Yep just looked up the 12au7, seems like it would probably be unsuitable. Will look for a nice 5751, unless rock monster comes up trumps.

To be honest, doesn't sound bad with the 12ax7, I just want it to be as authentic as possible. :-)

ESchap · November 2014

I especially like the 12AY7 in the front of a Tweed amp, smother sound clean and driven. But it will still drive, you just need to go a couple of notches up versus the 12ax7. TBH I don't hear too much difference between the 12AX7 and 5751 in the tweed circuits.

Do you have another 12AY7 to try? it could be the one you have is defective, heater insulation breakdown will give a lot of hum. Wouldn't be the first Russian valve I've seen fail right out of the box! I'm sure I've got a spare EH12AY7 or two, known good valves, if you want to try one. PM me if you want it.

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WTB 12ay7, 5751 or similar low gain preamp tube.

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