how does the 2203 reissue compare as far as specs and components (filter caps, tranny's)?
The original filter caps were made by LCR however LCR went out of business. There is a company that is now making clones/copies of the LCR's. We have not yet tried these those we have a couple dozen in route to us so that we can make some direct A/B comparisons. Hopefully they do sound like the original LCR's.
The coupling caps and bypass caps are different, not necessarily for the better. The transformers are not the same by any means. Your money would be better spent on an original JCM800 2203. As they were in mass production for 10 years there are a lot around and they are more cost effective than the reissues. You can make a reissue sound better by upgrading components, transformers, etc however for some this proves to be cost prohibitive.
what about the silicon diode issue that marshall had starting around the mid-1980's that made the tone worse?
Perhaps you could be more specific? Are you referring to the 2205/2210 series? The only diodes found in the 2203 are the main rectifier and one in the bias supply. With that said using diodes and LED's dooes not make an amp sound bad by default. Just like everything with tube amps and audio, it's how you do it (IE: its all in the design).
is the reissue really the exact same thing as the 1981 original??
To answer your question accurately I would have to say no and then pose the following question to you; Are you referring to a 50 watt or 100 watt model in the year 1981?
It's important to realize that the JCM800 line went through numerous revisions and were not as consistent from year to year as most believe. We have documented a great number of differences and naturally these all effect the tone, feel and frequency response.
The 50 watt 81's did run on lower plate voltage (IE: power transformers were different). If you have a JCM800 that runs on average plate voltage and you want the tone of a 81' you have two options. You can change the power transformer so that it meets the exact same specs or you can lower the voltages to the PI (phase inverter tube). The later is more cost effective and will get you about 80% of the way. Changing the PT will nail the tone. Reissue JCM800's require some more finesse in the circuitry but it's certainly able to be done.
Hope it helps!
Trace