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Some Marshall history (to the best of my knowledge):
In the first half of 1965 the JTM45 received a Drake OT having an Raa of 8k, resulting in a 2k loadline per KT66.
This was a clear "mismatch" resulting in only up to 30W output with a B+ of 450V.
Used with an Raa of 4k to 5k those amps would give at least 40W clean.
The first 4xKT66 amp from the same year used 2 of those JTM45 OTs wired in parallel and was named JTM45/100.
Soon after, the 2 OTs were replaced by the single, larger Drake 1202-84 OT having an Raa of 4k (again meaning a 2k loadline) and the amp was renamed JTM100.
The JTM100 also used 4xKT66s and had a B+ of 560V acc. to original schematic.
Those early 4xKT66s amps were very short-lived (hardly longer than 1 year in production).
I don't have info on actual power output, but I'd expect less than 80W depending on PT sag.
Now, the later 4xEL34 Plexi Marshalls (starting from end of '66?) received a 1.75k OT and had a B+ of around 500V.
They easily deliver 100W clean.
I own two 100W Plexis from that era (both around '68).
In the first half of 1965 the JTM45 received a Drake OT having an Raa of 8k, resulting in a 2k loadline per KT66.
This was a clear "mismatch" resulting in only up to 30W output with a B+ of 450V.
Used with an Raa of 4k to 5k those amps would give at least 40W clean.
The first 4xKT66 amp from the same year used 2 of those JTM45 OTs wired in parallel and was named JTM45/100.
Soon after, the 2 OTs were replaced by the single, larger Drake 1202-84 OT having an Raa of 4k (again meaning a 2k loadline) and the amp was renamed JTM100.
The JTM100 also used 4xKT66s and had a B+ of 560V acc. to original schematic.
Those early 4xKT66s amps were very short-lived (hardly longer than 1 year in production).
I don't have info on actual power output, but I'd expect less than 80W depending on PT sag.
Now, the later 4xEL34 Plexi Marshalls (starting from end of '66?) received a 1.75k OT and had a B+ of around 500V.
They easily deliver 100W clean.
I own two 100W Plexis from that era (both around '68).
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