Looking for Info: WWII era U.S. Navy Electronics Lab, Non-Linear Amplifier?

[AardvarkBry]

I picked this thing up because it was cheap, and looked like it does something awesome, but I don’t really know what it is? It says:

Non-Linear Amplifier
Bandpass: 200~20kc
For general labratiry use

it’s got input and interstate gain controls, and a headphone Jack. It has a Hollytran 500-60,000ohm input transformer, and an output transformer that looks like a Peerless, but it doesn’t have any info written on it. It’s got 4 - 6SJ7 tubes, and 1 - 6V6 tube. The back, there is a remote power supply hookup that asks for 180 volts, and 6.3 heater hook up.
Any info is much appreciated.

 

[JohnRoberts]

The way you spelled laboratory (labratiry) I thought maybe it was a Chinese knock off...

Looks almost too clean to be that old, but specifying frequency bandwidth in cycles per second instead of Hertz which came into popular use in the 1960s, suggests it is pretty old.

JR

PS; I remember that spaghetti insulation slipped over bare wires in point to point wiring.

 

[AardvarkBry]

Haha! That’s a weird auto correct!

 

[AardvarkBry]

The way you spelled laboratory (labratiry) I thought maybe it was a Chinese knock off...

Looks almost too clean to be that old, but specifying frequency bandwidth in cycles per second instead of Hertz which came into popular use in the 1960s, suggests it is pretty old.

JR

PS; I remember that spaghetti insulation slipped over bare wires in point to point wiring.

I don’t really know what a non-linear amplifier does? The limited info I could find suggests it either creates distortion, or it does some sort of limiting? I kind of just looks like a pretty standard preamp though?

 

[JohnRoberts]

I don’t really know what a non-linear amplifier does? The limited info I could find suggests it either creates distortion, or it does some sort of limiting? I kind of just looks like a pretty standard preamp though?

Back then nobody would make distortion on purpose so perhaps some kind of early dynamics processor (gain modulation).

Try to find a model number and keep searching...

The "linear" way would be to trace out the schematic and analyze the circuit.

JR

 

[AardvarkBry]

Back then nobody would make distortion on purpose so perhaps some kind of early dynamics processor (gain modulation).

Try to find a model number and keep searching...

The "linear" way would be to trace out the schematic and analyze the circuit.

JR

The terminals on the back say 180 volts. I have one of those Lambda power supplies, but it only goes down to 220 volts. Do you think that will be alright? 6SJ7 has a plate max of 300v, and 6v6 is like 315v.

 

[JohnRoberts]

IDK (I don't know)

JR

 

[rock soderstrom]

Beautiful device! John is right, I would also follow the wiring to find out the schematic. A nice exercise to understand what is going on.

About the supply voltage, the capacitors are the limiting components. If there's little clearance there, you can use a resistor to bring B+ down to the right voltage. (via Ohms law) If you suddenly apply B+ after all this time, the risk that a capacitor explodes is very high. Check the caps and go slowly with a variac. You will probably have to replace some because they are dried out or leaky.

I think it's some kind of compressor/limiter for radio communication. If you're lucky the bandwidth limiting is realized at the low end by the coupling capacitors and the transformers give full bandwidth.

You might be able to use it in modern studio with a few mods or it can be a very good basis base
for your own mic pre or limiter project.

 

[abbey road d enfer]

Any info is much appreciated.

Well, the lay out is pretty clear and accessible. Why not trace the schemo?

 

[AardvarkBry]

I’ve started tracing the schematic out. It’s so nicely laid out, it’s not that difficult, just a fair amount of work. I guess I won’t know what kind of impedance the output x-former is putting out until I get some electricity on it. Although, I imagine that with just the 1 6V6, it seems likely it’s more of a line level output, and not trying to drive a voice coil?

 

[AardvarkBry]

Beautiful device! John is right, I would also follow the wiring to find out the schematic. A nice exercise to understand what is going on.

About the supply voltage, the capacitors are the limiting components. If there's little clearance there, you can use a resistor to bring B+ down to the right voltage. (via Ohms law) If you suddenly apply B+ after all this time, the risk that a capacitor explodes is very high. Check the caps and go slowly with a variac. You will probably have to replace some because they are dried out or leaky.

I think it's some kind of compressor/limiter for radio communication. If you're lucky the bandwidth limiting is realized at the low end by the coupling capacitors and the transformers give full bandwidth.

You might be able to use it in modern studio with a few mods or it can be a very good basis base
for your own mic pre or limiter project.

Thank you for all the info. When I bought it, I was really hoping it was some kind of dynamics processor, so I’ll be psyched if that’s the case. I’ll do the math, and figure out what kind of resistor I need to put on it.

 

[abbey road d enfer]

I’ve started tracing the schematic out. It’s so nicely laid out, it’s not that difficult, just a fair amount of work. I guess I won’t know what kind of impedance the output x-former is putting out until I get some electricity on it. Although, I imagine that with just the 1 6V6, it seems likely it’s more of a line level output, and not trying to drive a voice coil?

A single 6V6 can output 4W, and the output xfmr is big enough to handle it.

 

[emrr]

I guess I won’t know what kind of impedance the output x-former is putting out until I get some electricity on it.

Resistance measurement will tell you

At least one Hollytran transformer, may be band limited or may be really high quality. They made many of the transformers on one era of RCA Photophone amps for film recording work.

I feel like the old magazine stacks from the 1940's will tell you what they meant by non-linear amplifier, I recall articles.

 

[mjrippe]

Without an "AN-" number it will be hard to find info from the usual military sources. I love the shaft extenders on the pots rather than running wires to the front panel!

 

[rock soderstrom]

I love the shaft extenders on the pots rather than running wires to the front panel

+1