Advice on build the classic 300W Ampeg SVT

[Steve Conner]

Need more info, can you post schematics?

[dpacek]

Need more info, can you post schematics?

OK, i snipped out the parts of the schematics that seem relevant

here is the last stage of the stock SVT Pre-amp


and here is the input to the splitter of the simplified SVT power amp


note the 100n 400V coupling cap from the anode of the previous pre-amp

do I attach the stock pre amp out put to the front of that cap ?
do I leave out that cap and a attach directy from stock pre-amp out to the 220k res in to the splitter ?
do I add another coupling cap between them ?

[Steve Conner]

The capacitor is just there to block DC. One capacitor will do that fine, you don't need two in a row with a resistor to ground in between. You can just sling a capacitor straight from V5 cathode to V2's 220k grid resistor.

Someone with more knowledge of the SVT might know better, but I think V5 is just there to provide a low impedance drive to the preamp out jack, and can be left out if you're not planning to have a preamp out jack.

[Enzo]

I'd agree with Steve about V5.

[dpacek]

The capacitor is just there to block DC. One capacitor will do that fine, you don't need two in a row with a resistor to ground in between. You can just sling a capacitor straight from V5 cathode to V2's 220k grid resistor.

Someone with more knowledge of the SVT might know better, but I think V5 is just there to provide a low impedance drive to the preamp out jack, and can be left out if you're not planning to have a preamp out jack.

Yep I had the same thought but KOC also suggested that it would be useful to use that tube as a gain stage since his simplified PA has less gain. than stock PA.
Although I'm not quite sure the safest way to do that or perhaps I would get OK gain by removing V5 and using the output of V4
See attached Joe Piazza SVT-Preamp drawing for reference.


Or perhaps leave CF as is and just lower the value of the grid stop resistor to the input of the splitter ?