Ghia HISS

[cfidave]

I have a new to me Carmen Ghia, 2007. The amp sounds great but has quite a bit of hiss with volume past 10:00.
There is no hum just an annoying hiss that is volume dependent.  The V1 position seems to be what is causing the hiss.
Going to a 5751 tube in V1 lowers the hiss, as expected, but is is still more then I would like. The guitar nor the cables are the problem as the amp has hiss with nothing plugged in. Any ideas for at a remedy? 

[scottyc13]

Starting with tubes is the best approach. Do you have another amp with a known good 12AX7 for V1? Try that. The phase inverter, V2 would need to have matched sides. It’s basically a process of elimination. Power tubes could also be the culprit.

[colinfromportland]

cfidave did you make any progress with this?
I also have a mild hiss with my Ghia -- it is fine for playing but is just a little too much for recording.
I'm about to start swapping tubes around too...

[cfidave]

Impossible, IMO to get rid of all the hiss. I'm pretty sure the circuit itself has something to do with it.
I have tried any number of different tubes in all positions. I finally settled on NOS 5751s balanced triodes in
both V1 & V2. I put JJ EL84s, again balanced, in V3&V4. That gave me the least amount of hiss. Not really noticeable until about 11:00 on the volume, then it becomes apparent. I think most if not all the hiss is in the pre amp circuit, i.e V1.