SVT-VR tube layout / map???

[smo]

Hi everyone,

I'm hoping for some help. I've been looking for hours without any luck.

I've been looking for a layout or map of which tube is which, and what each tube actually does, for the Ampeg SVT-VR, made in Vietnam.
Think something like the picture attached, except relating to the VR instead.

Thanks

 

[coreyfyfe]

Preamp arrangement from the numbering on the schematics/pcb, the preamp tubes are all in the upper chassis.

V1A/B 12AX7 - A channel 1 input gain, B side unused

V2 12AU7 - cathode buffer before volume control on channel 1, gain stage before bass/treble stack in channel 1

V3 12AX7 - active midrange circuit

V4 12AU7 - preamp output buffer

V5 12AX7 - channel 2 input and eq

Power amp is the same as above with a 12AX7 instead of the 12DW7 and 12AU7s in place of the 12BH7s.

 

[smo]

Thank you very much!!!

 

[smo]

Power amp is the same as above with a 12AX7 instead of the 12DW7 and 12AU7s in place of the 12BH7s.

Would this 12AX7 be the phase inverter?

 

[coreyfyfe]

Yes, 12AU7s are the drivers for each side of the power amp

 

[smo]

Yes, 12AU7s are the drivers for each side of the power amp

Thanks again for the help.

I have just one more question relating to the phase inverter 12AX7;
I'd be aiming for a balanced tube of course, but should I also aim for a long-plate version, or will a regular 12ax7 do the job just fine?

 

[coreyfyfe]

No need for a balanced tube at all, usually people cite some benefit of balanced PI tubes in a long tailed pair design but that’s not the type of PI used in the SVT nor is it really that beneficial.

On an SVT it can be good to have matched (not matched triodes but a matched pair) for the driver 12AU7 tubes, but the VR has the balance control which allows you to adjust and compensate for not getting a matched pair here.

 

[smo]

No need for a balanced tube at all, usually people cite some benefit of balanced PI tubes in a long tailed pair design but that’s not the type of PI used in the SVT nor is it really that beneficial.

On an SVT it can be good to have matched (not matched triodes but a matched pair) for the driver 12AU7 tubes, but the VR has the balance control which allows you to adjust and compensate for not getting a matched pair here.

You sir, are an absolute champion. Thank you very much!