Question: JVM 410H Plexi Cap Mod

[smarsh]

So I successfully completed the anti-compression, negative feedback, and choke mods this last weekend and love the results. I also swapped in and biased a quartet of KT77 power tubes at 68mV per side.

I attempted to do the Plexi cap mod using a Solen "Fast" Cap 630V 0.68uF non-polarized capacitor that I purchased from Tube Depot.

Once completed I did noticed that the mod had changed the tone and all seemed good, but I chose to just check the bias once more to be sure all was still good. What I found was that one side was now at 113mV while the other side was still hanging around 68mV.

I'm kinda of new to modifying amps though I've built 3D printers and other things in the past for fun. The issue I encountered is sort of perplexing to me. Perhaps I bought the wrong cap?

Thanks for reading. What does everyone think? Any advice?

 

[Dogs of Doom]

just bias it...

it might have been off. IDK why any of your mod's would have unbalanced it, but, it's a possibility, I suppose.

shoot for around 72-78 per side... Try to get them pretty close, to matched, as close as you can. Do note that when you turn one side up, the other will drop, & vise-versa, so they'll teeter-totter back & forth as you adjust...

 

[Spanngitter]

The cap added for the Plexi mode doesn’t have anything to do with the Bias, if installed correctly…I hope you put it across R97?

 

[smarsh]

I hope you put it across R97?

Yes I put it across R97. It's removed atm, but I am considering retrying when my v1 tubes arrives.