Help replacing tubes in Ampeg SVP Pro

[Jonesey]

Its got 4 - AX7 and 1 - AU7 no info provided by Ampeg on where the AU7 goes. The board looks like this:


V1xxxxxxxxxxxxxV2xx V3xxx V4xx V5
[---] xxxxxxxxx[---]x[---]x[---]x[---]

I assume V1 is the AU7, but ya never know.

Thanks in advance!

[WailinGuy]

Did you take all the old tubes out before looking at them? If not, then you could look at the tube numbers printed on the glass.

In general, I don't recommend replacing all the preamp tubes in an amp at once. A good preamp tube can last a very long time. If any are still good, you should leave them in there. Only replace ones that are weak, noisy, or have bad tone.

[Jonesey]

An ebay purchase - amp isn't working properly and tubes are not installed so I'm still looking for help.

[vibroverbus]

SLM is pretty good about sending out schematics / service docs, although you usually have to pay for them...

[WailinGuy]

I wouldn't assume V1 is the 12AU7. It could be ANY of them.

Chances are, the amp should function with five 12AX7's, even if the tone isn't quite right (might sound too "gainy", with not enough headroom). If it doesn't, I would be concerned that something is broken.

Ideas:

1) Try contacting Ampeg customer service. Maybe a user manual with tube chart is available online.

2) Go to a bass player oriented BBS and ask around to see if anyone else owns this amp and has the info you need. (Most of us are guitar players here at TGP, I think.)