- Jul 7, 2014
- Reaction score
Found it. It was a 1.5k and I do need it. So, they got all the resistors right in the order with none missing and none left over.
Very funny, I'm a righty. This amp does not require biasing but I will probably tie the terminals together and ground them like Mojo suggests.Go weber (brown, blue) if you are a lefty guitar player, go Mojotone (blue,brown) if you're a righty. I always attach a 1 ohm to ground through pins 1 and 8 on each tube for biasing, so I can't say.
It looks to me that you have the 100 uF cap for your bias supply fitted back to front in this pic.20uf it is, then. These are a little on the small side. Is that an issue? And what's the deal with those yellow capacitors? Would I be better off buying some orange drops to put in there? By the way, you guys were right about the cost of those Sprague Atom capacitors. It they look to be about $12 apiece
View attachment 265005
View attachment 265006
Wow, good catch. I didn't notice that cap was reversed on the diagram. I'll change it.It looks to me that you have the 100 uF cap for your bias supply fitted back to front in this pic.
It's the cap on the extreme left hand end of the board. It is meant to be connected in reverse polarity. Have another look at your layout diagrams and check it.
What happens is, you hook turn the amp on and get an instant whine... then you reverse these wires. IT doe smatter, but without testing the OT, you'll never know. It's not important... But, leave the wires long enough that once you do turn the amp on, you can reverse them if you need to.Questions re: power tube wiring. Weber and Mojotone reverse the blue and brown OT wires. Does that mean that it does not matter if I switch the wires that go to terminal 6 from the board?
Also, what is the advantage of linking terminals 1 and 8? They are linked on the Mojotone diagram but not on Weber's.
View attachment 265096
View attachment 265097
This amp is fixed bias. That means there's a fixed negative DC voltage applied to the control grids of the power tubes. That's the bias voltage. In modern amps that bias circuit has a little potentiometer in it so you can adjust the bias voltage. Thus they're 'adjustable fixed bias'.I mean that the bias is fixed on this amp, right?
Good to know.What happens is, you hook turn the amp on and get an instant whine... then you reverse these wires. IT doe smatter, but without testing the OT, you'll never know. It's not important... But, leave the wires long enough that once you do turn the amp on, you can reverse them if you need to.
I recently rebuilt a vintage amp... I had to gut it as it had been modded beyond all recognition (okay, so maybe that's an exaggeration, it had gone from 5f8-a to aa270 minus trem). When I turned it on, I got the instant whine... I hadn't changed these wires. Took me a minute to power down, drain the caps and reverse these two wires an voila!