6AH4 preamp
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Author:  SoundMods [ March 12th, 2023, 11:32 am ]
Post subject:  Re: 6AH4 preamp

dberning wrote:
Speaking of cathode bypass caps, has anyone tried polymer types? I just got some for a power supply application. They are rated for 4 volts and 560 uF, in a package 5/16 inch tall and same in diameter. Seems perfect for a 12AX7. The impressive thing, and is why I got them, is the fantastic ripple-current rating of 6 A. I know that you are not putting 6A through a 12AX7, but to have that rating they have extraordinarily low ESR and ESL. Higher-voltage types are available that could be used for the likes of a 6V6.

Like the caps from Japan shown in the attached data sheet?

TK Poly PPSO Capacitors.pdf [142.29 KiB]
Downloaded 696 times

Author:  GaryB [ March 12th, 2023, 12:12 pm ]
Post subject:  Re: 6AH4 preamp

Perhaps something more like this. They work very well in decoupling power supply noise in digital circuits. I haven't tried them as cathode bypass caps.

AAB8000C250.pdf [849.46 KiB]
Downloaded 671 times

Author:  Grover Gardner [ March 17th, 2023, 12:21 pm ]
Post subject:  Re: 6AH4 preamp

Well, I'm about done here. The preamp is quiet and sounds great. I purchased some Bendix 5992s on eBay for a good price, and they are excellent. The last piece is a 6.3 in > 6.3 out filament regulator board from a fellow at DIY Audio. Hoping to squash that last miniscule bit of noise. ;-) I've got a fancy Hammond chassis on the way, and a can for the toroid, which I hope will shield it enough to place it on the main chassis. If not, I'll outboard the raw DC supplies. It wasn't a cheap project--someone more skilled at building reg'd supplies etc. could do it much cheaper, but honestly the Neurochrome board is kind of key to the excellence of the sound, IMO, as well as keeping the power supply fast and light-weight. Looking forward to it sounding even better when I get it off the sprawling breadboard.

Author:  David McGown [ March 17th, 2023, 2:05 pm ]
Post subject:  Re: 6AH4 preamp


Congratulations on the successful project! I may end up trying this out sometime on my 12SN7 Aikido preamp...all I need is a new top plate, desolder a few connections and it is a blank slate. I have a couple Pete Millett Maida regulators built and ready to go (with heat sinks).


Author:  Guy [ March 21st, 2023, 11:44 am ]
Post subject:  Re: 6AH4 preamp


Thank you for posting your progress and changes! It has stirred my juices and sent me looking at HV regulators.

Your success with the modified Maida regulator gives me hope that we will all soon have quieter systems. If mine are now noisy, then I have a good direction to pursue if the noise is from the HV.

I'm looking forward to new projects: mine and everyone else's!

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