amp builders or diy guys ?

[seti]

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.

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?

I delivered the amps to my brother three weeks ago. He is contacting a tech in Tulsa to examine them for him. Thank you for the information. I will be forwarding your comments to him. If my brother makes any progress on the amps I'll send you a message. These are actually made by webster electric for Allen before they started making them themselves. The name on the side is Webster Electric.

Thank you very much for the information!

[drewski_brewski]

The same rules should apply to the Webster models. From the pictures, it appears that there is a ground bus on that one, as well, and all the grounds should be returned there. It seems to me that the ground for the inputs was returned to the pre-amp tube, and not to the bus at all, but I'd have to check on that. Another thing I forgot about was that I bought some Russian tubes that were suppoed to be a substitue for the 6sn7, but when I tried it in the pre-amp, it caused hum. I never did a side-by side spec comparison to see what the difference was. The Russian tube worked fine for the phase splitter.

I own a couple of Allen/Websters myself, two chennel models with 6L6 output tubes.Mighty fine amps.

Thanks for the chat, have fun, and keep me posted on the saga.