Input and output transformer

[Quayhog]

While researching transformer choices for a LA-2A project I've discovered a few things.  it's a murky world similar to branding tubes made by other makers.
The original LA-2a used UTC HA-100x transformers on the input.  Ampex 350/400 series recorders also used this tranny.

Ampex put out a specification and UTC filled it with their off the shelf HA-100x, Triad filled it with a transformer that is marked B or C-6299, it also had a p/n of 58-0122-01 and a NSN of 5950-00-545-7765. I've seen the B-6299 on transformers made by UTC, GTC, Triad and Stancor.  My UTC with just that number has some internal CT connections but it otherwise meets the same resistances as the HA-100x.

The output transformers are labeled C6300 and have a part number of 58-0139-01.  My samples are branded Triad and GTC. These were used by Ampex in the 350/400 series and branded by UTC HA-133, and GTC as C-6300.

Like I said its murky.

 

[emrr]

What part of that is murky?  They meet the unknown Ampex spec.  Ampex was known as a maker of tape machines, not as a great maker of audio amplifiers. 

Plenty of other transformers would meet the spec.  Plenty within the spec would sound different. 

 

[Quayhog]

Murky, maybe not. With tubes I see legitimate branding of one maker while actually clearly manufactured by another.  They met the spec and were bought, branded and resold by another.

I've been trying to figure out what the commercial numbers that go along with those odd numbers.  Even Triad historians cannot recognize their number.  I suppose since Ampex used the commercially available UTC transformers I quess I'll just use that spec as a guideline.

 

[emrr]

There aren't necessarily commercial #s that correspond to every custom part #,  there are far more custom #s out there, and there is rarely seen reviving info on custom parts.  Even among known equivalent parts there can be large audible and measurable differences. 

 

[lassoharp]

My UTC with just that number has some internal CT connections but it otherwise meets the same resistances as the HA-100x.

B-6299 is a  ~200:50K and doesn't use the standard UTC primary configuration.    The secondary is a single winding like the A-11, so not like the typical UTC multi tap split secondary  (like the HA 100 and A10).

DCRs often run in the same range for a particular impedance rating.

If making a choice for a suitable input for either LA-2 or Ampex mic amp is confusing, all you really need is a mic to grid of which there are many that will do the job more or less equally well.