spi
Well-known member
Just wrapped this up. I took my time building it, also researched a lot both before and during. It has some mods, but nothing to change the tone much, mostly for safety:
Despite going slow and careful I still made a few gaffes:
- Added a RC filter stage of 22uf + 250R before my B+. This was to reduce noise and it also drops the B+ voltage by about 10V.
- Added a 250K bleeder resistor. This was really effective. I also bought a capacitor discharge tool, but turns out that I didn't need it as the bleeder worked wonderfully, but it's nice to have just in case.
- Used 22uf-16uf-8uf filter stages instead of the standard 32uf-8uf-8uf. The 5f1 uses 16uf-8uf-8f. I don't know how much this changes things since I can't compare it to anything else, but I figure it kind of splits the difference between the two.
- Added power tube grid stop (1K5) and screen resistors (470R) to the 6V6. I got this idea from the Hoffman schematics.
- Added rectifier backup diodes for protection. Got this idea from Robrob site.
- Changed feedback from 22K to 33K to account for 8ohm speaker.
- For the grounding I followed tdpri user King Fan's diagram.
Despite going slow and careful I still made a few gaffes:
- I accidently wired the rectifier heater filaments to the pins where the rectifier plates should go. I was using a black-and-white printed wiring diagram and wasn't paying close enough attention to the colors. Luckily I trimmed them with enough length to reach far enough to where they needed to go. I realized it right after soldering.
- I also wired the power transformer to the fuse instead of the switch. This one I trimmed a bit too short, but since I hadn't wired the other end yet, that side could make it to the switch, and the short one was spliced to the power neutral. This too I realized right after soldering.
- After testing the sound on bench and hearing it work, I put the chassis into the cabinet, and tried it again to get no sound--quickly realized I forgot to plug in the speaker. I'm really happy I used a switching jack on the speaker to short it to ground or this could've been bad, but it seems like it came out unscathed.
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