Ampeg SVP-Pro valve (tube) swap ?

[stevebasshead]

Hi,

I've got an SVP-Pro preamp (grey hammered finish) with the stock valves in it except for the unbranded ECC82 which I've swapped out for a Jan Phillips ECC82. Thing is, I've got several more lying around unused, so what would happen if I replaced the remaining ECC83's with Jan Phillips ECC82's ? Would it simply sound different (and if so in approximately what way) or just be less efficient, or something else?

I'm not sure what functions the ECC83's perform in the SVP and if I were swapping like for like I'd not hesitate, but going from 83's to 82's I'm not so sure about - I'd rather not experiment in ignorance!

I'd appreciate any advice, thanks in advance.

Steve.

[sharkboy]

It would almost certainly sound different. _Probably_ not in any trouble for the bias, (depending on how it's done) for those tubes. By and large, I find that an ECC83 tends to have more "color", leaving its tonal signature on an amp more than an ECC82- an ECC83 whose character is bright or dark will affect the sound of the amp much more than a 12at7 (but that's just my view.)

An ECC82 (12AU7) is a much lower gain tube than an ECC83 (12AX7), the amplification factor is nominally approximately 20%- but it is a higher output tube- making it a better conduit toward the power stage and less suited bringing up the signal level.

If you are trying to get only a little less gain, an ECC81 (12AT7) might be better for you.

I have also found some of the JAN tubes a little lifeless in some amps, so let your ears be your guide about whether NOS is the right thing in this case.

It would make a lot of sense to me for you to use tube selection after you decide if there is something that your amp should be doing that you want or trying to make it stop doing something you don't like. Lots of us have opinions around here about tubes that can probably help you there.

[johnallg]

Ampeg uses the ECC82/12AU7 tube for a driver tube because of the higher current they can pass over a /ECC83/12AX7. The ECC81/12AT7 is both used as a gain stage like the 12AX7 and as a driver for power stages.

Personally I would stick with same-type tubes as the SVP preamps are known to have a lower output capability than some amps need so as to be driven fully.

There are a lot of new reissue tubes that sound good and don't cost an arm and a leg. I am lucky in that I inherited tubes from here at work and also a deceased uncle who used to repair tvs and radios, so I use NOS in my Ampegs. I've found the older tubes render a more even tonal pallet - darker sounding when compared to the Sovtek tubes Ampeg is using now, which have a brighter sound - probably a slapper's dream tube.

I've also found the 5963 (12AU7 with more current drive) for a bass amp in the driver positions gives more punch/jump factor.

[stevebasshead]

Mark, John - good info, thanks. So long as I'm not going to cause the amp any electrical problems I'll go ahead with the swap and see what it sounds like. Replacing the unbranded ECC82 in the drive position last month was a definite improvement and I've also used the Jan Philips ECC82's to reduce the drive in a valve OD unit I own and liked the sound which is what started me wondering about using them in my Ampeg. Especially as I've several more just sitting around unused.

I'm OK with the lower output level as I've plenty in reserve anyway - my 1000w power amp is a bit of an embarrassment of riches for the pubs and clubs we play!

Regards,
Steve.