Hissing Sound in One Channel

[Joerg Picard]

First of all, thanks to Bottlehead and their kits. I've been listening to my Seduction, Foreplay, Paramour, Straight 8s setup for more than 20 years now and enjoyed it immensely for the past two decades!

For a couple of months now, I have some hissing noise coming out of the left Paramour mono amp. I've swapped input channels, both tubes, the speaker outputs and isolated the issue to the amp itself. It usually takes a couple of minutes (up to 15-20) before the hissing starts. The hissing is a pretty uniform sound with only a little variation in pitch and volume. Here's the weird part, if I disconnect the input RCA from the Paramour and immediately connect it again, the hissing sound is gone but returns within a couple of minutes.

The Paramour has the iron and cap upgrade kit and the C4s upgrade installed. I had a couple of bad solder joints with the connections to the C4S circuit board in the past but I have checked those and they are solid. I have also wiggled around a bunch of connections with pliers when the amp is hot and couldn't detect any issues that way. There's no other electrical device close to the Paramour and I've moved the Paramour to different locations in my room with no improvement.

Does anybody have suggestions on how to troubleshoot further?

Thanks
Joerg

[2wo]

I think it's time to reflow every solder connection in the amplifier, a marginal joint made  20 years ago, you could be hearing now... John

[Paul Birkeland]

The old Paramour (and the other 6x10 power amps) squeeze a whole lot of parts into a very small volume.  Consequently, something like the old Paramour that has been used extensively for any amount of time may have a couple of cooked caps, especially those close to any large wirewound resistors.  These will give themselves away by having tops that are bulged out and not flat, and you may find that a recap resolves your issue. 

[Joerg Picard]

Thanks for the input. Doc also emailed me about checking out transistors on the C4S modules. I'll start poking around some and will report back.

[Joerg Picard]

Wanted to report back, in case somebody has a similar issue.

The culprit was the MJE350 transistor on the C4S board.

Thanks to the folks at Bottlehead for helping me troubleshoot the issue!