Recently a friend asked me to reacap a Dynakit Stereo 35. Years ago, he'd replaced the output boards with new PC-13 boards from Audio Regenesis but was never able to get it running properly. Well, one thing led to another, and next thing you know I was building Dave Gillespie's EFB board. I cleaned up the wiring best as I could and also installed heatshrink on some of the chafed transformer leads feeding through the chassis. Some of it seems really dried out. Almost crumbling.
Anyway, I stuffed stuffed the PCB and installation was pretty easy. The wires connecting to the EFB Board are mil spec Teflon. Difficult to work with and not really neccessary but looks nice when it's done. After checking my work, I powered it with a dim bulb. The right channel seemed to draw more current than the left. I figured the old tubes were mismatched and removed the dim bulb. The 5W resistor on the EFB board immediately started to overheat. I quickly yanked the plug and reconnected the dim bulb. There was +12V on the EL84 grids of the right channel. I rechecked all my work. There was no continuity to ground from eyelet #2? How could that be? I had connected the input jacks to ground even though someone had replaced the input jacks with fancy gold-plated RCA jacks which were isolated. Turned out to be a bad solder joint due to reusing an old piece of wire. I didn't check the grounds because they looked good. The wires connecting to the EFB Board are mil spec Teflon. I find it difficult to work with and not really neccessary but looks nice when it's done.
It's running well now but the EL84s are old and a bit mismatched. I was able get a closer match by swapping a couple tubes between channels. Now I measure .27v on one channel and .25v on the other. I connected the amp to my Belle Klipsch speakers. This amp can go loud and clear. Definitely better than any Dynaco EL84 amp before modification. Although it seem a bit rolled off. Not a criticism. I do have some age-related hearing loss which is disappointing. Maybe new tubes would improve the high frequency response for me.
Thanks to David Gillespie who never fails to amaze with his great designs and vast knowledge of ways to improve this old tube equipment.
Anyway, I stuffed stuffed the PCB and installation was pretty easy. The wires connecting to the EFB Board are mil spec Teflon. Difficult to work with and not really neccessary but looks nice when it's done. After checking my work, I powered it with a dim bulb. The right channel seemed to draw more current than the left. I figured the old tubes were mismatched and removed the dim bulb. The 5W resistor on the EFB board immediately started to overheat. I quickly yanked the plug and reconnected the dim bulb. There was +12V on the EL84 grids of the right channel. I rechecked all my work. There was no continuity to ground from eyelet #2? How could that be? I had connected the input jacks to ground even though someone had replaced the input jacks with fancy gold-plated RCA jacks which were isolated. Turned out to be a bad solder joint due to reusing an old piece of wire. I didn't check the grounds because they looked good. The wires connecting to the EFB Board are mil spec Teflon. I find it difficult to work with and not really neccessary but looks nice when it's done.
It's running well now but the EL84s are old and a bit mismatched. I was able get a closer match by swapping a couple tubes between channels. Now I measure .27v on one channel and .25v on the other. I connected the amp to my Belle Klipsch speakers. This amp can go loud and clear. Definitely better than any Dynaco EL84 amp before modification. Although it seem a bit rolled off. Not a criticism. I do have some age-related hearing loss which is disappointing. Maybe new tubes would improve the high frequency response for me.
Thanks to David Gillespie who never fails to amaze with his great designs and vast knowledge of ways to improve this old tube equipment.
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