I have a pair of Tango FE-25-8 transformers that I bought more than 3 years ago in the hope of building a Dynaco Stereo 35 clone around them.
Now that She Who Must Be Obeyed expressed her preference for not having idle items (i.e. the items in my precious Nice to Have These Parts for Some Non-specific Future Projects pile) in the house, I was compelled to get started on the project.
Tango FE-25-8s are potted, Ultra Linear, push-pull, 8K Ohm primary, 4-8-16 Ohm secondary, 25W capacity output transformers with silver-gray Hammertone finish:
The "owner's manual" is a single page data sheet. These transformers have a good wide frequency response:
![Image](http://home.comcast.net/~BrikMA/ST35_Tango/FE_25_8_Resp.png)
One vital piece of information I could not find in the data sheet, however, was the screen grid winding ratio.
Since it is easy to measure the turns ratio of the screen grid winding vs. the total number of turns in the plate winding, I decided to measure the ratios using the trusty old Heathkit Model IG-18 signal generator.
While I was at it, I decided to measure the plate-to-plate inductance of the primary as well, since the only additional piece of "equipment" I needed was a reasonably precise resistor.
(See http://www.daycounter.com/Articles/How- ... ance.phtml )
Then, I decided to measure the same set of output transformer parameters of the units in some of the tube amplifiers I had on hand.
In all I have the following transformers measured:
1. Tango FE-25-8s
2. Dynaco Z565s in an old Dynaco SCA-35 : Measured in circuit, with speaker load "open", NFB connected.
3. Dynaclone Z565-48 in a Dynaco ST-35 clone : Measured in circuit, with speaker load "open", NFB connected.
4. Triode TF110-48 Deluxe in the "Poor Man's ST-35" : Measured in circuit, with speaker load "open", NFB connected.
Some scenes from the measurements:
![Image](http://home.comcast.net/~BrikMA/ST35_Tango/ST35PM.jpg)
![Image](http://home.comcast.net/~BrikMA/ST35_Tango/SCA35.jpg)
![Image](http://home.comcast.net/~BrikMA/ST35_Tango/ST35C.jpg)
Here are the tabulated results:
I have the following observations:
- 1) The Tango transformers have SG winding of 40-42% which is the standard value I expected to see.
These Tangos are very well matched in all respects: DC resistance, Sg winding ratio, and inductance.
2) Both the Dynaco Z565s and the Triode Dynaclone Z565s have SG winding ratio of 22-24% which I did not expect. Are these optimized for 6BQ5s / EL84s?
Would a "standard" output transformer with SG of 40% give an optimal performance with EL84s?
3) Both the Dynaco Z565s and the Triode Dynaclone Z565s have exceptionally high inductance that is unmatched by the Tangos.
Would Tangos sound as good as the Z565s with EL84s
All in all, I renewed my respect for the Dynaco Z565 designs, both old and new.
Note: I had to use the fairly high resistor value of 330K Ohms since the Z656s have such a high inductance that I had trouble measuring with lower valued resistors. As a consequence, the inductance was measured using miniscule currents which may result in higher inductance values.