Reverb input on the other side of long tail pair

[Chipper]

On a scratch build I tryed putting the reverb signal back on the other side of a long tail pair, where you normally put the signal from the negative feedback. Everything works good on the amp except when I turn the reverb up passed halfway (VR1) the total volume starts going down, any thoughts why this is happening and simple fix?   The attached shows the voltages without any signal input,  these voltages don’t change with changing VR1.

[kagliostro]

With my poor knowledge that seems an auto oscillation problem


Franco

[92Volts]

That's an opposite-phase input so it will cancel out the main signal (more or less) if it's in-phase. That's how it actually works as a place to hook up negative feedback. I'm not sure you could even expect reverb to be exactly in or out of phase (since it's delayed by so long) it that might end up happening at some settings.

[sluckey]

It would be more helpful if we could see the entire schematic. Meanwhile, compare your scratch circuit to this known working schematic...

     http://el34world.com/charts/Schematics/files/matchless/matchless_chieftan.pdf

[Willabe]

We need to see the whole schematic to see what could be going on.

 

[Chipper]

Thanks guys.  I think that VR7(VR1) maximum must be about 100k because that’s about where it starts going down hill. I don’t have as much reverb signal coming into the C12 (C31) as the chieftain. So I think that’s where I should start, increasing my Reverb signal so I don’t have to use such a big resister for VR7(VR1). thanks again.

[John]

That's an opposite-phase input so it will cancel out the main signal (more or less) if it's in-phase. That's how it actually works as a place to hook up negative feedback. I'm not sure you could even expect reverb to be exactly in or out of phase (since it's delayed by so long) it that might end up happening at some settings.

This makes the most sense to me, and...


according to your schematic you're not feeding 'verb signal back in past the PI, or at least I don't see it?

[John]

That's an opposite-phase input so it will cancel out the main signal (more or less) if it's in-phase. That's how it actually works as a place to hook up negative feedback. I'm not sure you could even expect reverb to be exactly in or out of phase (since it's delayed by so long) it that might end up happening at some settings.

This makes the most sense to me, and...


according to your schematic you're not feeding 'verb signal back in past the PI, or at least I don't see it?
Wait... I see what you're trying to do. Still think 92V is right.

[tubeswell]

The reverb return signal is probably not as strong as the dry signal on the other LTP grid.