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Re: Thanks to everyone ... esp Bruce

5/22/2005 9:03 PM
Chuck	Re: Thanks to everyone ... esp Bruce I built a small guitar amp from the guts of an old 50's phonograph. I used all salvage parts, even the resistors and caps. It sounded great except for a really loud BRRZZZZ!!! that would pop up under heavy overdrive. It sounded like, and I thought it was, a parasitic oscillation. The layout was a little suspect since I was working with salvaged parts in a very small space. But just to be sure I plugged it into an extention cabinet and the noise dissapeared. It took awile to find it but boy does it sound good now. Just wanted so share a sympathetic story FWIW I'd like to share a tip for anyone plagued with that awful rattle from microphonic EL84 tubes. I use heavy heat resistant rubber gasket material. Not the black stuff, it can become conductive (don't ask me how I know ). Use the orange stuff. I cut a circle out about the size of the tube base and poke holes for the pins. Slip this onto the tube pins and snug it against the base before you install the tubes and clip the retainers on. It has helped me to get more life out of a pair of tubes before they start to go microphinic. Chuck

5/22/2005 9:03 PM

Chuck

Re: Thanks to everyone ... esp Bruce

I built a small guitar amp from the guts of an old 50's phonograph. I used all salvage parts, even the resistors and caps. It sounded great except for a really loud BRRZZZZ!!! that would pop up under heavy overdrive. It sounded like, and I thought it was, a parasitic oscillation. The layout was a little suspect since I was working with salvaged parts in a very small space. But just to be sure I plugged it into an extention cabinet and the noise dissapeared. It took awile to find it but boy does it sound good now.

Just wanted so share a sympathetic story

FWIW I'd like to share a tip for anyone plagued with that awful rattle from microphonic EL84 tubes. I use heavy heat resistant rubber gasket material. Not the black stuff, it can become conductive (don't ask me how I know

). Use the orange stuff. I cut a circle out about the size of the tube base and poke holes for the pins. Slip this onto the tube pins and snug it against the base before you install the tubes and clip the retainers on. It has helped me to get more life out of a pair of tubes before they start to go microphinic.

Chuck