weird solid state amp with interstage transformer

**Dulles** · 11-04-2019, 10:52 PM

I got this nearly 40lbs chunk of metal on my table that appears to be some kind of 400W amp. Looks like a Bell Labs creation circa 1970 and described on this page. Does anyone have a schematic for this thing? The one on the page linked above became "404".

**glebert** · 11-05-2019, 09:18 AM

Was it made by Bell Labs or is it a bell ringer (or bell tower) amplifier? Google tells me that Verdin is a bell, carillion, and organ company. Seems many of their amplifiers were made by McIntosh.

**Dulles** · 11-08-2019, 11:27 PM

Your question prompted further sleuthing and I believe you're right. It appears to be a clock tower amp made by Bell Electronics (now possibly Abell Electronics) not Bell Labs. The wiring is very tidy; the conduits are appropriately twisted and the layout is nice and tight. This indicates the designer understood parasitics. I'd like to get it hooked up to hear what it sounds like. Other strange things about this amp beside the interstage tranny are its 4 pin power input and 1V max signal input. It shows 70V on its panel which could either be its rails or its swing. I might be looking at a class A amp. Anyone else have a clue about this thing?

**DrGonz78** · 11-09-2019, 12:48 AM

Isn't 70v the output used for outdoor speakers or something?

**glebert** · 11-09-2019, 01:36 AM

Originally Posted by DrGonz78

Isn't 70v the output used for outdoor speakers or something?

https://www.belden.com/blog/broadcas...peaker-systems

**Dulles** · 11-09-2019, 06:57 PM

Very illuminating, thanks. So is the interstage transformer in the unit a global audio line transformer output that eliminates the need for a speaker to have its own transformer or just the 70V interface that allows the speaker with transformer to connect to it?

**Helmholtz** · 11-09-2019, 07:24 PM

Originally Posted by Dulles

I got this nearly 40lbs chunk of metal on my table that appears to be some kind of 400W amp. Looks like a Bell Labs creation circa 1970 and described on this page. Does anyone have a schematic for this thing? The one on the page linked above became "404".

The link in the other forum doesn't open.
Are you sure that it's an interstage transformer and not an OT? What's its size, can we see pictures? Where is it connected?
A 70V line only makes sense for power distribution - not for signal level. Typically the amp has a step-up OT and each speaker a step-down transformer.

https://en.wikipedia.org/wiki/Consta...speaker_system