Help Me Identify This Preamp: Audio Radio Corporation - ARC 15

[SirCVH]

Hello
I picked up some tube stuff last week from a recycle/junk shop, one was an Ampex 403 preamp unit with UTC transformers and all the tubes and power supply! But I also picked up another preamp that I can't come up with anything on the internet and was hoping you guys can help.

It is labeled as a "ARC 15" by Audio Radio Corporation
- Input Transformer: UTC CG-134
- Output Transformer: UTC A24
- Power Transformer: UTC HP-123
- Tubes: 12AY7 and 12AU7 with 6X4 Rectifier

I am trying to figure out what kind of preamp this would be?

Who was Audio Radio Corporation?
Any other info, similar schematic, etc are much appreciated.

Pics Below....
Thank you!

 

[emrr]

Put new filter caps in and fire it up, put it to work.  Should be a nice piece.    Not a lot to know. 

 

[Bo Deadly]

Radio Museum is a good site for info about old electronics. If you're going to find something about it, it would be there (although I did a quick search for "ARC 15" and didn't find anything).

You can tell a lot by the input transformer. CG-134 is a Consumer Grade line input transformer. So it's basically just an entry level line amplifier.

 

[SirCVH]

The UTC docs call the CG line "Commercial Grade" so hopefully decent quality. Wondering if this will have enough gain and reasonable impedance for a microphone? The primary can be 50, 200, 500 ohms, secondary is 80k to the tube.
Maybe I should wire a three way switch on the primary to give some input options?

 

[Bo Deadly]

Unfortunately no. It doesn't have the impedance, the frequency response and most importantly the gain will not be nearly enough for a mic pre.

 

[emrr]

Unfortunately no. It doesn't have the impedance, the frequency response and most importantly the gain will not be nearly enough for a mic pre.

I'm not sure if we're reading the same thread, or if you're trolling.  It is very close to a mic pre.  The only thing that would make it NOT one would be if it's eq'd for tape or phono use, which is easily undone. 

 

[Bo Deadly]

Ok. Well my apologies then. The UTC catalog says it's a "consumer grade" line input transformer that's only good up to 10kHz. That didn't sound like it would make a good mic pre.

 

[SirCVH]

"Commercial Grade" not "Consumer Grade"! ;D

I did see that it is linear from 40Hz-10kHz, I'm wondering if this was mainly used for radio and maybe the higher register wasn't as important for that purpose? Interesting...

I am excited to get the Ampex 403 in shape, it has the UTC HA-100x and UTC HA-133 on it. I will probably use that for the Mic pre and maybe try this one for a color box (maybe for bass?). Will still try mics on it, and maybe will try to swap the 12ay7 with a 12ax7 or something too.

Thanks for your input guys!

 

[Bo Deadly]

"Commercial Grade" not "Consumer Grade"! ;D

True. Again, apologies. Actually a 10kHz roll off is not necessarily a bad thing. There's not a whole lot going on above 10kHz honestly.

 

[emrr]

Those are frequently better than the catalog spec, they just weren't making promises with that line.  Kinda like Edcor not testing their transformers before they ship them.......

 

[Dmichel123]

I picked up one of those CG-134 input transformers at a surplus place for $5. Mine performs better than 40Hz on the bottom and better than 10Khz on the top....

 

[Conviction]

Are you sure it's Audio Radio Corporation? Aircraft Radio Corporation made a whole lot of gear. I've never seen a LF amp though.

 

[PRR]

Are you sure it's Audio Radio Corporation? Aircraft Radio Corporation made a whole lot of gear.

It looks clear in the picture.

Also Aircraft** was Boonton NJ, this Audio** lump says Los Angeles, Calif(?).

(They may look close from your house but they were a world apart. Before internet and overnight shipping, LA had a distinct electronic subculture, very different from the near-NYC shops.)

It's an utterly mundane utility amp. Microphone, mix make-up, in-house line driver. (Driving audio across Los Angeles wants something bigger than a 12AU7.) LA was full of radio, recording, film-sound studios who needed stuff like this. And small shops doing military and lab gear assembly. Somebody got a contract to do a few. Maybe cheaper than Langevin, or needed it fast. Probably just a few or we would find more traces.

 

[Conviction]

It looks clear in the picture.

Also Aircraft** was Boonton NJ, this Audio** lump says Los Angeles, Calif(?).

You're right, sorry. I didn't see the print.

 

[ruffrecords]

The only internet reference I can find is on a quiz site: Who invented the vacuum tube: de Forest: aka Audio Radio Corporation.

Cheers

Ian

 

[cyrano]

Started in 1955. Suspended now:

https://californiacheck.com/company/C0299794/audio-radio-corporation

That's about all.

 

[Dmichel123]

Did you ever try this thing out? Interested in selling?

 

[SirCVH]

After 2 years I am finally getting to this project, and I wanted to document the circuit here. I have started the schematic, but I have a question regarding the circuit.

- The circuit is a UTC-CG134 into the first half of a 12AY7, then 100k gain pot, into the second half of the 12AY7
-This gain stage is followed by a 12AU7 (to drive the output transformer, I think) and out through a UTC A-24
-My assumption until now is that this was used as a line level amplifier, possibly a mic pre where possible

My question is this:
The plate of the 12AY7 (pin 6) is connected through a blocking cap to the grid of the 12AU7 (pins 2&7). But ALSO, the cathode of the 12AY7 (pin 8) is connected to the plates of the 12AU7 (pins 6&1) through a cap and resistor. These are points "D" on my schematic that I have squared in red. Is this a normal arrangement for a line amplifier gain stage? The only places I can find with this arrangement of using both signals from the preamp tube (plate and cathode) have been "parafeed" circuits, phase inverter circuits, and RIAA phono correction circuits. Should I be able to use this circuit for recording as-is, or is this a phono preamp or other that I will need to make circuit changes for? If so, could I just disconnect connection "D" to correct for this? Are there any improvements or modifications I should make to the circuit for recording purposes?

Any insight is much appreciated!
I will clean up the schematic and post a final version as I work through the project.
Thanks!

 

[PRR]

There's resistors. They do not have any Ohms in them?? Most circuits are a LOT about resistors and especially resistor-ratios.

 

[mjrippe]

"D" is a feedback connection.  Try the preamp with and without it, see how it sounds, see how it measures, see Spot run.  Run, Spot, run!  ;D