I'm afraid I have at least one bad relay, although the footswitch may have a role to pay here as well.
The amp is a Mark IV-A combo #2425 with a chassis date of 4/24/91 and EV Black Shadow speaker. I've owned it since '96, and it has been well taken care of, largely because I developed all kinds nerve problems in my left arm in music school... Right when I was starting to get session work. Since that injury forced me to get a "real" career path, it has only seen light use. A few months ago, it started buzzing, not through the speaker, but inside the chassis and made all of the channel indicator lights light up dimly with very little sound getting through. Unplugging the FU-3 footswitch helps in that it can operate in any channel in Tweed mode for a minute or so until it fully warms up. In Full power mode, I can run it all day as long as I don't use the footswitch. The buzzing seems to originate from two orange boxes (these have sharp corners and look like relays to IMO) near the front panel, and each has a diode in front of it. While in full power mode, all of the external switches work perfectly. So if part of the remedy is something ugly related to the footswitch, I'm prepared to build my own, since it will give me a few extra options anyways.
I can post pictures/video if needed. If the relays are to blame, I can handle the time consuming surgery although it's likely I will just run this beast in full power mode (which is more fun anyways) as long as I can get away with it. It appears all of my LDRs are the good ones, and they actually show evidence this beast may have gone home to have them changed.
One last thing: my Lead presence pot shaft broke so it turns great but I can't pull on it. Any good sources for a replacement?
Thanks!
The amp is a Mark IV-A combo #2425 with a chassis date of 4/24/91 and EV Black Shadow speaker. I've owned it since '96, and it has been well taken care of, largely because I developed all kinds nerve problems in my left arm in music school... Right when I was starting to get session work. Since that injury forced me to get a "real" career path, it has only seen light use. A few months ago, it started buzzing, not through the speaker, but inside the chassis and made all of the channel indicator lights light up dimly with very little sound getting through. Unplugging the FU-3 footswitch helps in that it can operate in any channel in Tweed mode for a minute or so until it fully warms up. In Full power mode, I can run it all day as long as I don't use the footswitch. The buzzing seems to originate from two orange boxes (these have sharp corners and look like relays to IMO) near the front panel, and each has a diode in front of it. While in full power mode, all of the external switches work perfectly. So if part of the remedy is something ugly related to the footswitch, I'm prepared to build my own, since it will give me a few extra options anyways.
I can post pictures/video if needed. If the relays are to blame, I can handle the time consuming surgery although it's likely I will just run this beast in full power mode (which is more fun anyways) as long as I can get away with it. It appears all of my LDRs are the good ones, and they actually show evidence this beast may have gone home to have them changed.
One last thing: my Lead presence pot shaft broke so it turns great but I can't pull on it. Any good sources for a replacement?
Thanks!
