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« Last post by Soundmasterg on April 10, 2024, 11:39:19 pm »
That's in the earlier range of the completely self contained in one chassis 200S. The grille cloth is the early style. Dynaco transformers most likely, with slightly lower voltages than the later Schumacher transformers. I personally like the Dynaco transformer amps better. That is probably from around 1967.
The 5U4 rectifier lowers the voltages in the amp below stock, which is probably why the 6L6's haven't blown out yet. 6L6GC are robust tubes, but getting above 500V and unless top notch vintage quality they will struggle to survive, especially in a UL circuit like the Sunn, and will certainly give less power than the 6550 or KT88 with the proper 5AR4/GZ34 rectifier.
It looks like a decent amp though. I'd replace all electrolytic caps in the amp, and in the first two filter stages, you should use series connected caps with parallel resistors to give it 700V capability for each stage. Something like two 60uF and 350V connected in series with 220k resistors in parallel with each cap to share voltage load will give the equivalent of 30uF and 700V. Then the second stage set up the same way could be two 47uF caps at 350V for the equivalent of 23.5uF and 700V. Mouser sells some in those values. You may be tempted to use the CE Distribution can cap that is like the originals, but it is overvoltaged with today's wall voltages, and doesn't have the best reliablity as a result, and it will also be more expensive than the solution I mentioned. Drill a couple holes in the chassis and mount some terminal strips and secure the series connected caps and parallel resistors to those. Ground in the same place as stock. Replace any 2 wire power cords with a 3 wire setup and get rid of the 'death' cap. Replace the tubes and set the bias properly, and you should be good for many years.
Greg
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