Cinema Engineering Type 735 Attenuator ?

Can any one help with info on this attenuator or how to test it correctly out of circuit with ohm meter ?

I did measure ~600ohm across IN & C  and OUT & C

I have searched cyberpit endlessly without any leads, data sheets, etc , rotary switch seems to rotate smoothly.

I assume these are permanently sealed  , in other words,  ache before break

Positions 21 confirmed , Cinema Engineering , Burbank CA

Info I have been unable to confirm off the beat up label :  Bridged T Pad , 600 ohm , Type 735

pics

Just measure it with a meter across the input terminals and then across the output terminals. It should stay mostly constant over all of the switch positions.

To measure the steps you need at least function generator and a digital RMS multi-meter. Put some known VAC into the input and measure the VAC coming out for each step. Then use one of those online calculators to convert the differences in level of each step into dB.

For example, if you put 10 VAC in and at the second to highest step you get 7.1 VAC, that is 3dB [1].

If you don't have a function generator, you could use a transformer with mains primary and a secondary that is not too high of a voltage or you could damage it. You probably only need maybe 1 VAC to get decent readings depending on the meter but you might need higher to read the lowest steps accurately.

If you really want to get pedantic about it, hook it up between the out / in of your computer audio interface and use software like Room Eq Wizard or ymec dssf3 or one of the countless other programs that will put out a stimulus and then show you a spectrum and look at how the level changes as you switch positions.

[1] http://www.sengpielaudio.com/calculator-db-volt.htm
or use a spreadsheet with formula db = 20 * log(10, vin / vout)

That's the first Cinema label I've ever seen on what looks more like the Langevin package, so I assume later era Cinema production.  (Look up Art Davis)  Langevin may have made this one. 

At what rotation did you measure 600Ω between In/C and Out/C? 
Do it for full on, full off, and 50%.  Also for In/Out.  It'll be obvious what type it is from that. 

If it is a resistive attenuator, you can measure the loss with a 1.5V battery and a DC voltmeter.

Just be sure it does not cleverly short the input for maximum attenuation.

Old catalogs:
http://www.vintagewindings.com/gen%20pop/8299543VW8335/Catalogs/CinemaEngineering-10.pdf
http://www.vintagewindings.com/gen%20pop/8299543VW8335/Catalogs/CinemaEngineering-Cat-18-A.pdf

PRR said:

If it is a resistive attenuator, you can measure the loss with a 1.5V battery and a DC voltmeter.

Click to expand...

Or a 9V battery with a 10K resistor in series.

Thanks for the many responses

so far I measured it with a DMM ohms  2k range  One end Pos 1 shows ~600 ohm other end goes as high as ~1.1k at pos 21 . Measured both IN /C  and Out /C with same results but the DMM jumps around quite a bit from 1.1k to 600 ohm and in between. I'll try running a AC sine/square wave generator at 1 Vac and hook up the DMM .

Remember that often these pots are designed to be fed from a 600 ohm source and loaded with 600 ohms so that when they are turned up full there is a 6dB loss. Attached is a schematic of some 600 ohm Painton stud faders I have that I workd out when I disassembled one of them.

https://drive.google.com/open?id=0B_n67A1hN3qtSkpENGk0MnFIaVk

Note that both the 3K and 680K pots are of course stepped and when set to maximum resistance they are actually open circuit,

Cheers

Ian

Thanks Ian

If I follow you correctly , I measured them with a DMM set to ohms , no source (z 600) , which might explain the difficulty in reading the really jumpy DMM readings. My signal generator is 600 source , so this may solve the source element in measuring difficulty with the DMM, correct ?

I'm finding this a bit tricky

electrochronic said:

Thanks Ian

If I follow you correctly , I measured them with a DMM set to ohms , no source (z 600) , which might explain the difficulty in reading the really jumpy DMM readings. My signal generator is 600 source , so this may solve the source element in measuring difficulty with the DMM, correct ?

I'm finding this a bit tricky

Click to expand...

If it is a 600 ohm device then your 600 ohm generator source is correct. You also need to load the pot output with 600 ohms. Then if you measure the output with a DMM you should see a 6dB loss with the pot full up. You should then see the voltage drop steadily at every other switch position.

Cheers

Ian

Ian ,

Very clearly stated , thanks for helpful info.

if it's a 600Ω ladder:

In/C 800ish Ω full on, 300ish Ω full off
Out/C 600ish Ω full on, off, anything in between
In/Out 600ish Ω full on, 900ish Ω full off

if it's a 600Ω T:

Fully on - In/C and Out/C open , In/Out 0Ω
Fully off - In/C and Out/C 650ish Ω, In/Out 1300ish Ω

Formula and values seems to vary by manufacturer a bit, but not by a lot. 

EmRR said:

if it's a 600Ω ladder:

In/C 800ish Ω full on, 300ish Ω full off
Out/C 600ish Ω full on, off, anything in between
In/Out 600ish Ω full on, 900ish Ω full off

if it's a 600Ω T:

Fully on - In/C and Out/C open , In/Out 0Ω
Fully off - In/C and Out/C 650ish Ω, In/Out 1300ish Ω

Formula and values seems to vary by manufacturer a bit, but not by a lot.

Click to expand...

Just to add the Painton I was referring to is a 600 ohm T type.

Cheers

ian

ruffrecords said:

Just to add the Painton I was referring to is a 600 ohm T type.

Click to expand...

3K, interesting.  Some of the American types are closer to 5K on the final shunting step before they go open.  Maybe those are 1dB/step?

EmRR said:

3K, interesting.  Some of the American types are closer to 5K on the final shunting step before they go open.  Maybe those are 1dB/step?

Click to expand...

It was some time ago but I recall taking one apart an measuring the actual resistor values internally so I am confident the figures are accurate. Looking at pics on line they seem to have about 30 steps so it is not beyond the bounds of possibility that the first few steps were a dB or so. They are in a box somewhere in the garage at the moment. When I get a chance I will look one out and measure the first few steps.

Cheers

Ian

Thanks for the helpful input Ian & Doug , very insightfully de-mystified in a practical sense . I prefer this over a long academic dissertation. But a dissertation has its place too when appropriate.