Transformer technical terms

[Hayman]

Hi,

I'm reading a copy of a UTC-catalog (1962) and I'm trying to figure out what transformers to get for DIY-projects. I have a pair of 0-12's that I plan to use in a 1176-project. The 0-12's are listed under section "Miniature, amateur & public address transformers". There is a section named "Hi-Fi & broadcasting components" and I was thinking...hmmm... are these better transformers? Can I, for example, use a A10 instead of a 0-12 as input for a 1176?

This is where I need to learn the technical terms that are written under "application" in the catalog.

What exactly is:

PL. TO GRID
MIXING
INTERSTAGE
LINE TO GRID
P-P TO LINE
TR. TO LINE

...and when it just says INPUT (primary 50,200,500 sec. 50,200,500), can this be used both as a mic and line input?


Probably have more questions later. :?


Thanks in advance


Richard

 

[rafafredd]

What exactly is:

PL. TO GRID

It wa sdesigned as an output transformers. The primary goes to a tube plate, and the secondary is your low impedance output. Generally 600ohms.

MIXING

Multi primary transformer. You can hook up two or more diferent signals into the tranny, one for each primary winding, and get a mixed signal in the secondary

INTERSTAGE

Most of the time, low turns ratio. 1:1, 1:2 1:3 or 1:4. If it´s a tube interstage, the primary and the secondary are high impedance. Used to get "passive" gain between stages or for better CMRR in push pull circuits.

LINE TO GRID

input transformers with high signal handling. Not necessarily nickel, but most of the time.

P-P TO LINE

output transformers for push pull circuits. It may be described as two plates to line also. The primary is either a center taped high impedance winding, matched, or two high impedance windings, also matched. The B+ is fed to the center tap and gets canceled in the winding. Can be gaped for canceling any DC unbalance, or you will have to use very well matched tubes for the PP pair, or adjust with a trim pot.

TR. TO LINE

Most of the time those are step up output transformer, low impedance primary and secondary. 1:1.5, 1:2, 1:3 or 1:4. Neve, API, etc... all use transformers like this. It´s used as a passive voltage gain in the output of very hot transistor amps. An API for example, can feed a 75ohms line. So, if you use a 1:3 at the output, the impedance goes to 600ohms, and this is considered low enought for line outputs. The good part is that it makes headroom three times bigger in low voltage circuits. In a neve amp that runs at 24v single PSU, you have a 1:1.5 at the output for more headroom.

...and when it just says INPUT (primary 50,200,500 sec. 50,200,500), can this be used both as a mic and line input?

Yes, you can. But you would need to make sure it´s a nickel transformer, and you would want to use it as a 1:1 (200:200, or 500:500) or 1:2 (200:500), into a very quiet solidstate amp. Have a look at the 990 and the forssell discreet opamps for good matches for a low turns input ratio transformer.

 

[CJ]

PL. TO GRID
MIXING
INTERSTAGE
LINE TO GRID
P-P TO LINE
TR. TO LINE

Most of these terms just mean different amounts of impedance, which just translates to different amounts of turns, and different wire gauges.

Plate to grid and innerstage are really the same thing. A typical impedance for these types might be 5,000/20,000 ohms, which is a 1:2 turns ratio. Most of the time, a coupling capacitor is used as a cheaper alternative to this transformer. It just couples two consecutive stages of amplification together, the output of one tube (plate), to the input of the next stage (grid). Two boxes that use an innerstage transformer are the RCA BA6 compressor (UTC Innerstage) and the Pultec EQP-1A (Triad HS-29) Lots of fine wire, many turns.

Mixing/Matching: Most of the time used to adapt a circuit to different mic impedances. It might also be used as a problem solver, such as turning an unbalanced signal into a balanced signal to eliminate hum, etc. Usually 500 or 600 ohms in, and 500-600 out, with multi taps like Raf said. Larger wire gauges and smaller number of turns. 1:1 turns ratio.


Mic/Line to grid, typical impedance would be 500 ohms primary to 50,000 ohms secondary (UTC A10). This translates into a 1:10 turns ratio. The ouncer units are more of a mic to grid due to a smaller core, the A-10 will handle either mic or line signals due to a larger core. The line in transformers usually have more primary inductance so the bass does not distort due to the higher signal levels it has to handle. Usually 49 permalloy, (UTC A-10 Black vintage) or 80 Permalloy (UTC dark gray and later vintages) Pri has big wire and small turns, secondary has smaller wire and lots of turns.

 

[PRR]

>> What exactly is: PL. TO GRID

> It was designed as an output transformers. The primary goes to a tube plate, and the secondary is your low impedance output. Generally 600ohms.

No, "grid" means a tube grid, VERY high impedance. 10K, 50K, not 600.

In fact it is an interstage (from one tube to the next). Dunno why they use both terms.

> "Miniature, amateur & public address transformers". There is a section named "Hi-Fi & broadcasting components" and I was thinking...hmmm... are these better transformers?

Yes. Of course "better" is a matter of taste: some folks like the sound of hard-working iron.

Plate/grid or interstage is high-Z and usually a slight step-up like 1:2. These can also work as input transformers when you need a bridging input to a high-Z amp.

Line/Grid is usually 600:Hi-Z, ratio about 1:10. But it can also be line bridging, 10K or 20K to grid.

Plate to line is 10K or 20K input and will take some DC. Secondary is 600 ohms or something like that.

P-P Plate to line is often 10K center-tapped and should not have DC in it. Secondary is about 600.

Tr:Line is any strange thing that someone custom ordered and UTC thought they could sell a few extras of. Some of those were very strange parts.

I have never seen a mixing transformer in the flesh. If you do, let us know.

In fact the vast majority of the iron in a 1962 UTC catalog was hard to get at the time, most of those models never sold in any quantity, and only a few like the A-10 and some of the P.A. mike trannies are "easy" to find today.