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New Member...Need some help! Schulmerich Amplifier Utility Plugins
Old 14th September 2012
Here for the gear

New Member...Need some help! Schulmerich Amplifier

Hey guys, just recently came across this forum when I was doing some research online.

My father was big into radio when he was younger. Had his own radio station in the attic, and went on to Broadcasting School in I want to say the mid-70s. He has an entirely different career now, but I just discovered his hoard of equipment. I'm now in the music industry, but not in a production capacity. Don't have a ton of knowledge on the technical end and I'm trying to find out exactly what he has.

The big one was a Federal Limiter Compressor AM-864/U. I had this tested at the venue I work at, and it appears to still function correctly. Have been having some trouble finding out much about this next one. It's a tube amplifier made by Schulmerich, Model # 6-123A. Has a Thordarson Transformer in it, Model T-92R21. Powers up, that is as far as I have gotten with testing this one. Here are some pictures if anyone could shed some light on it's scarcity and possible value. Thanks in advance for the help!


Old 14th September 2012
Here for the gear

anybody today??
Old 14th September 2012
Gear Addict

I don't know anything about it, but I do know that if you keep powering it on without a speaker load on it, you're going to kill the output transformer.
Old 14th September 2012
Gear Addict

We had a Schulmerich electronic carillon system installed here once, from the early 50s. Your amp looks older, but when I get to the office, I'll see what we have for paperwork and if anything looks similar. Have you contacted Schulmerich? I'd have no idea about rarity or value.
Old 14th September 2012
Lives for gear

Ask this guy:
Doug is the most knowledgable person I know when it comes to old tube radio gear. He´s known as member emrr at
Old 14th September 2012
Lives for gear
emrr's Avatar
Never heard of them. At a glance looks like a standard multi-input PA amp. Agreed, don't power up without an output load. I wouldn't power up initially without a variac or the lightbulb trick either. Since you already did, prob fine if no smoke, but still might not be passing signal without some cap replacements. I've seen amps like this come up on a variac and be fine for a day or so, and then smoke due to iffy caps. Good luck.
Old 14th September 2012
Gear Addict

Schulmerich is still in business, and known for real bells and carillons as well as electronic ones. The old installation here from the 50s was an electronic carillon with the bell sounds produced by small metal rods pinged by solenoids and picked up by guitar-like pickups. Our paperwork shows designs from the late 40s through early 60s. You unit is apparently a preamp. We had four 6-123AB preamps (I assume yours predates this), and four 6-153 power amps, each with a 6-106B power supply. This ran into an array of outdoor horn speakers.

I could supply a fuzzy scan of a xerox of the 6-123AB schematic.
Old 14th September 2012
Here for the gear

Thanks for the help guys. Schematic isn't really necessary, I was just trying to mainly find out if this was something rare or possibly valuable. I only turned it on because I wanted to be sure it still worked and that the tubes heated up.
Old 14th September 2012
Lives for gear
I dunno, a preamp with a pair of 6L6s for output? I'd be guessing an integrated preamp/amplifier with an output of 30-40w, pretty linear. Cool to be modded for guitar, or possibly for control room if you could find a pair. Likely need caps replaced (all the electrolytics anyway). You really do need a schematic or someone with some knowledge to trace out the circuit and discover the output wiring and the impedance it wants to see. BTW, there's no harm in plugging in a tube amp with no output load AS LONG AS THERE'S NO SIGNAL. What kills the transformer/tube sockets/caps is flyback voltage from the magnetic field around the OT collapsing as the signal passes from negative to positive and back, if there's no signal then there's no significant fluctuation in magnetic field. In fact, several manuals that I've read for setting bias on vintage Fenders, and the factory manual for Groove Tubes amps recommends setting the bias with the speakers unplugged.
Old 14th September 2012
Gear Addict

I don't quite understand the 1948 designs, but these drawings show the model 6-123AB output going to the 6-153 amplifier, which is a pair of 805 transmitter tubes, powered by a "power chassis", the 6-106B, which uses a pair of 866A rectifier tubes to power the 805s. Then the the 6-153 was connected to the speakers, I think multiple driver outdoor horns and likely 70 volt or somesuch.

So the 6-123 probably has a modest power output, and this particular system has a big power booster - it was actually 4 amplifier systems in parallel for 4 multispeaker arrays. There is nothing in the drawings to indicate that it is an option to connect a speaker directly to the 6-123AB. Perhaps the design intent was to always use a booster to get the 30-40W up to a "usable" 200W or so for installs like this.
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