Hiwatt Lead 30 volume loss

[nhrafan]

Hello all,

I need some help with a problem on my Hiwatt Lead 30. This is a Sterling Imports model made in California. It recently developed a problem where the volume dropped off by probably 80%. There's no overdrive at full gain(pre-amp volume on 10) and the sound is very thin. This amp usually sounds much like a modded Marshall. I ran a good preamp signal into the effects return and volume is normal . . . loud. I hooked the effects send to another power amp and the effect is the same as running through the Hiwatt so I feel that I have narrowed the problem down to preamp. I swapped a good 12ax7 tube into each socket and also swapped the existing 12ax7 tubes around in the sockets. None of the tube changes had an effect so I feel that the preamp tubes are ok. I've used a multimeter to check resistors and caps throughout the amp as much as I am able without removing components. Nothing stands out there. I do not have a schematic to follow so that further complicates the situation as well. I did check the preamp cathode cap and resistor. Any other ideas that I should explore?

Thanks

[mhuss]

Check voltages around the preamp. Does it have a footswitch? If so, those connections or relay could be bad.
Here's a schemo that could be similar.

[nhrafan]

Thanks for the reply.

No option for a footswitch on mine. It is a single input, single channel master volume amp with reverb and effects loop, model cs30. It has 5 12ax7s in it and 4 el84s in the output section. I appreciate the schematic you included. I see some differences looking at it but it might help keep track of the signal path.

The preamp V1 tube only uses one side. I measured 132volts on the plate(pin1) and 1.03volts on the cathode(pin3).