Lol, hi, this is Drewski_Brewski, and I found your post of my post while searching for articles relating to the Allen Type 90, so I joined the group! (I'm very excited to find others discussing this) The original input jacks on these amplifiers are an old-style threaded coaxial Amphenol connector, and it is completely insulated from the surrounding chassis. If a person converts over to RCA, they must isolate the RCA jacks and return the ground in the same manner as the original circuit. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
A note about the amp I own above: From day one, the B+ was much higher than the schematic indicated it should be, and I checked and double-checked the circuit, capacitors, resistors, choke, etc, until I finally measured the open-circuit voltage of the AC transformer, and found it to be about 250 volts higher than my other Allen 90's. Then, I looked at the notes on the schematic, and noticed that the serial numbers for the Type 90 start at 5000, and I own number 5005! Several of the components differ from the other '90's that I own and I suspect this one was built using substitute parts before Allen got their supply chain in full swing. I could be wrong, but it's a great theory.
I didn't scrutinize this string... did the subject amp ever get fixed?