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"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
https://www.facebook.com/pg/bartelamps/posts/?ref=page_internal
Think I might give it a go and see if I notice a change. Hoping the plywood will actually be a bit lighter as well!
I think the purpose of them is to increase convection cooling by setting up a cold-in, hot-out path, but the main problem with these amps and heat is that they’re biased far too hot at the factory - the recommended bias setting is 35mA (1.4V measured at the test point), which is nuts - that’s 14W per valve. Set it to 20mA (0.8V or 8W) and it won’t try to cook itself as much! I also increase the cooling gap above the rear of the chassis by adding a couple of rubber grommets around the two top rear bolts, and a heatsink on the filament rectifier.
I expect Martin will do this anyway, it becomes standard practice when you’ve worked on enough of them, as most of us have .
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I’m not sure what bias Martin has set it at but I’m sure it's more sensible than the factory setting! He has also increased the spec of the bridge rec to avoid the overheating issue.
I agree on the metal grilles. I've already been using the amp without them and re-positioned the wooden part to close off the bottom half of the cab. Would do similar if I build a new shell for it.
Certainly way better than 1.4V.