- Joined
- Mar 21, 2007
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I'm late to the party but I'll chime in anyway. Here's what I'd do:
1) Reverse engineer the circuit. Draw a schematic with all the voltages and currents labeled.
2) Gut it. No matter how bad your layout and soldering skills, it will be better than what you have now.
3) Replace the tube sockets with something of quality. Use some decent audio grade resistors. I like carbon types, such as Kiwame. When you replace the rectifier diodes, go for a safety factor of 5 or 6. Tube filaments have big inrush currents, particularly something like a 6bl7. The power transformer is definately a Hammond 272 type. By getting a rough voltage measurement of the output, and using the physical dimensions given on the Hammond web site, you shouldn't have too much trouble figuring out what you have. You might want to replace it with a 300 series. The 272 is noisy and runs hot. It's a minimalist design. Try the Russian PIO capacitors from Ebay for coupling positions. They are cheap and sound exellent. If that 100mf electrolytic is really simply in parallel with the 220 film cap, leave it out. If you need more filtering, add another RC section with a second film cap. Keep roughly the same operating points, but don't sweat a 5 or 10% difference. The tubes won't care, and I'm sure the designer didn't either
1) Reverse engineer the circuit. Draw a schematic with all the voltages and currents labeled.
2) Gut it. No matter how bad your layout and soldering skills, it will be better than what you have now.
3) Replace the tube sockets with something of quality. Use some decent audio grade resistors. I like carbon types, such as Kiwame. When you replace the rectifier diodes, go for a safety factor of 5 or 6. Tube filaments have big inrush currents, particularly something like a 6bl7. The power transformer is definately a Hammond 272 type. By getting a rough voltage measurement of the output, and using the physical dimensions given on the Hammond web site, you shouldn't have too much trouble figuring out what you have. You might want to replace it with a 300 series. The 272 is noisy and runs hot. It's a minimalist design. Try the Russian PIO capacitors from Ebay for coupling positions. They are cheap and sound exellent. If that 100mf electrolytic is really simply in parallel with the 220 film cap, leave it out. If you need more filtering, add another RC section with a second film cap. Keep roughly the same operating points, but don't sweat a 5 or 10% difference. The tubes won't care, and I'm sure the designer didn't either