Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dennyg on January 02, 2018, 03:57:30 pm
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I built this board for my TOS and worked out so well that I'll be using on next two builds underway. Thought I'd share for anyone interested.
I've only built 5 amps but they are all quiet as death; all are mid-to-high gain. The board is a combination of little tricks I've picked up - key benefits:
* allows placement of the supplies circuits at opposite end of pre-amp
* all the supply connections are lined up on the right side of the board which simplifies connection of supply wires.
* space efficient - particularly when using term strips for rest of the amp. I just completed the layout for my first 50W amp which is also a 2 channel with relays - which all fits nicely within a 17x8 chassis.
Summary of the board:
* 6V AC to power tubes
* 6V DC to pre-amp tubes - note the .22 dropping across the heater supply which brings the rectified DC down to 6.3 also lowering AC to 5.9V. Connect the neg side to elevation voltage circuit if elevation desired
* single ground pole to connect star grounding scheme
* cap multiplier reduces B+ ripple to less than 2%
* choke is wired up between B+ & +1
* strap 10uf cap across B+1 for further reduction in ripple for screen
* bias voltage circuit on board - simply feed the bias pot
* 5V DC circuit to supply channel switching relays
the component values will support up to 450 B+; you'd need to increase a few caps to 500V for larger B+ requirements (which I'm doing now for the 50W amp).
pic below - let me know if interested and i'll draw up schematic
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I'd like to see a schematic.
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Would also be interested in a schematic!
I've considered transistor designs including the "mosfet gyrator" (may or may not be what you're using), and I read transistors handle barely any power (like 1-2w) if not heatsinked. To make things worse the mounting surface is connected to one of the transistor elements so high voltage would get into the heatsink.
Are your transistors just used for low-current applications (i.e. preamp, but not screens and definitely not plates)? Otherwise the you had any trouble with heat?