Transformers 10k:10k vs. 600:600

thomasdf said:

Sorry for digging up.
Been reading a while, still have a question...
I have an Ampex 600 that I am rebuilding. The line input is unbalanced, 10K.
I want to have it transformer balanced, and I have 600:600 Edcors... I'll try them anyway, but should I start looking for 600:10K in order to avoid problems?

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No, you should look at 10k:10k. You don't want gain, so 1:1 and you want the source to see a medium-high impedance. We don't live in a 600 ohms world anymore.

I know transformers acts kind of as a lens,

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??? This analogy is so far-fetched you should wipe it off your memory.

so my guess is that if I feed the input of my tape machine with a modern line level / impedance it should be about fine (approx 10K)

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"modern line impedance is typically 10k input but 100 ohms output.

but if I use the output let's say of my 1176, which is 600 ohms, then the tube will see 600 ohms input and I'll have a sh*tty freq response?

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Not worse than when it sees 100 ohms from a "modern" piece of gear.

thomasdf said:

Sorry for digging up.
Been reading a while, still have a question...
I have an Ampex 600 that I am rebuilding. The line input is unbalanced, 10K.
I want to have it transformer balanced, and I have 600:600 Edcors... I'll try them anyway, but should I start looking for 600:10K in order to avoid problems?
I know transformers acts kind of as a lens, so my guess is that if I feed the input of my tape machine with a modern line level / impedance it should be about fine (approx 10K) but if I use the output let's say of my 1176, which is 600 ohms, then the tube will see 600 ohms input and I'll have a sh*tty freq response?
Sorry if dumb question...

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You should look for a 10K:10K type. This will succesfully reflect the 10K unbalanced input impedance to the primary and make it 'look like' a 10K balanced input.  Modern sources are low impedance and will drive a 10K input impedance without difficulty. A true 600 ohm source will aslo drive it with ease.

Cheers

Ian

You do NOT generally want the 1:4 voltage step-up of a 600:10K. The Ampex is plenty sensitive.

600:600 is fine IF the thing which drives it is happy about 600 Ohms.

The tube sure does not care.

A few modern sources strain in 600 Ohms, even un-loaded (low primary inductance). 10K:10K would be more all-around.

Thanks a lot for your help guys!
I will start looking for a pair of 10k:10k transformers
Maybe I'll try the Edcors!

thomasdf said:

I have an Ampex 600 that I am rebuilding. The line input is unbalanced, 10K.
I want to have it transformer balanced, and I have 600:600 Edcors.

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consider implementing either the Ampex -01 bridging (20k:20k)  or Altec/Peerless 15335 bridging (15k:15k) input transformers.
Most model 600 machines were not fitted with the optional microphone input transformer;
thus with ideal space to mount an octal based  line input unit.
The Ampex and Altec plug-ins have magnetic shielding, which the Edcors sorely lack.
The 600 schematic shows the line input potentiometer as 250k.

To tell you the whole story, I have scored the electronics from an Ampex 600 for pretty cheap.
I gutted it and I am about to rebuild it clean with metal film resistors and without the tape transport / tape playback etc.
I want to keep the mic preamp section pretty straight, add the traditionnal Instrument Input, and make the line amp stereo by adding another half channel and output amp so I can process stereo signals with it. I'll use rotary switches with precision resistors for line input and "rec cal" / output so I can color to taste both channels and maybe use it on my mix bus, or instrument busses.
For the mic input, I have a Gates Yard console mic input transformer (50/150 ohms primary), and for the output a pair of Altec 15095A's (15K:600). I am still looking for a pair of proper Xformers for the line input

I think I still have Altec/Peerless 15335 bridging (15k:15k) transformers listed in the BM......

ruffrecords said:

Maybe we should have a transformers meta?
Cheers

ian

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An Audiotransfers 101, or Audiotransformers for Beginners/Dummies would be something amazing