More Amp Construction

Yes, these were her amps. I suggested to the new owner that we reuse the remnants of the purple heart wood from the bases for the side panels, then make the chassis plates purple. It just so happens that in one spot in the circuit I need to burn off 150V, so there will also be an 0D3 letting off its pinkish-purple glow.
That Bottlehead member now has beautiful Purple stained Jager speakers as well!
 

paulbottlehead

Active Member
And the last pair of these.
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I had to paint some panels for a prior project in bright orange, so I did up a pair of these panels as well. Since I figured nobody would ever buy these, I put film caps in the HV supply and set them up with 572B tubes that let the amps make a little more power (21W). The sides are marine grade bright white HDPE.
 

fmena

Junior Member
Question if I may.... what plate voltages do the 572B's see in your amp? ... ....I'm guessing they are higher than what one would see in your typical SET amp? and what driver tube are you using.... they look fantastic
Cheers
FM
 

paulbottlehead

Active Member
Yes, 572Bs are in production. They are essentially an 811A with a carbon plate, so plate dissipation increases from 40W to over 200W.
 

paulbottlehead

Active Member
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These are some full throttle 300B amps I made for a local customer. They make 20W, but they should also burn through a pair of 300Bs about every 12-24 months!
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Here's a photo from when I was doing some testing before the wood sides went on. To make this kind of amp function, you need a driver that's directly coupled to the 300B grid to push into A2 on peaks to get that extra power. You can see the little choke on the left side of the amp and that's connected to a negative rail and feeds a 6J5W wired up as a cathode follower. That arrangement gets its B+ dropped way down with some cold cathode VR tubes, and the majority of the bias voltage is supplied from the negative rail. An IXYS CCS chip with a cap across it sits between the 300B filament and ground to set the standing current and adjust the ground to filament bias voltage to maintain the proper operating current. There's a 6AB4 triode as the first stage to get a hefty amount of voltage gain to get this to work.
 
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