I must be crazy. To put it simply, I’ve got a lot on my desk at the moment, and here I am digging into a fresh can of worms. But…
Worth it! Totally worth it.
I found this old Grommes stereo amp at an antique shop about a month ago. No idea why I was so drawn to it, but very glad I was. I initially resisted admirably, but after snapping some pix on my phone I returned home and located a schematic for it online. That did it. I returned the next day and took it home.
It’s a model 24PG from the mid to late 1950s. Rated 12 watts per channel (hence the “24”), it’s powered by push-pull 6BQ5s (aka EL84s) with 7025s (similar to 12AX7s) at all earlier gain stages. It’s also tube-rectified with an EZ81.
For the most part, this thing seems like a genuine time capsule. Appears to be untouched inside since it left the factory. I began my refurb with a much-needed cleaning (see photos below – was positively filthy), and testing values of all key components. After that I felt confident enough to place it on some concrete outside and power it on. Happily, it warmed up normally, so I didn’t need the fire extinguisher I was holding. (Never know with power transformers that old.)
Feeling even more encouraged, I then decided to give it a full audio test. A pair of Klipsch 2-ways were attached to the 8 ohm terminals, and I delivered some audio to its auxiliary inputs – to effectively troubleshoot the shortest possible portion of the signal path (skipping the earlier phono and tapehead gain stages).
The good news was that the overall sound quality is glorious! The bad news was that, in stereo, the mix became somewhat ghostly with the balance set at center. I suspected a handful of different causes, and after some further testing, discovered “infinite resistance” between one side of the left output transformer’s primary coil and its center tap. I was hopeful the short was only in the lead, but I’ve now confirmed that it’s an internal failure. Bummer.
So, off to Edcor‘s website I went to find a replacement. Since the right channel’s OT is intact I was able to measure & calculate the primary resistance and find the most suitable replacement. Order placed… so now we wait.
Nevertheless, I’m extremely happy to have had an inspiring taste of this little treasure. It’s definitely a sound that I don’t yet have in any of my listening rooms, and I’m looking forward to nursing it back to 100% health. Will post again once progress resumes