OPT impedance

[el156]

Hi !

If i have a opt like in the photo, that i inject 5.3 v in the 8 ohm output, and i have the voltages shown in the pic, what can i know more about this opt? is it possible to know the impedance with this data ? sorry but my mathematics are very low level.

thanks

 

[Sorento]

You have a Push-Pull Transformer with Ultra Linear Taps. The turns ratio between the full primary and the secondary is (2*58v)/5.3v=21.89The primary impedance plate-to-plate is calculated from the square of the turns-ratio which is 479 21.89*21.89*8=3833ohms or approx. 3.8 kohm plate-to-plate when you use 8 ohm speakers on the secondary. The taps on the primary are to connect to the screens in case of UL operation with pentode outputs.

 

[el156]

Thanks a lot !

 

[cerrem]

I would speculate it's more like a 4K plate load with 40% Ultra-Linear taps.. Typically 43% is the standard... The reason I say this is due to measurement error from the magnetizing current the plate load will typically calculate out a tiny bit lower than actual..

 

[grovergardner]

I would suggest applying voltage to the primary and then measure the output on the secondary. It's a better way to check. If you have a variac, try applying 58 volts to the primary and make sure you get 5.3 volts on the secondary.

 

[6A3sUMMER]

Use the 58V from the variac, and read the open circuit voltage at the 8 Ohm tap (Vopen). Then load the 8 Ohm secondary with an 8 Ohm resistor and find the closed circuit voltage (VLoaded).

Now, the loss of the transformer is:
20 x Log(VLoaded/Vopen) dB.

If you get 5.3 Vopen, and 4.7 VLoaded, that is -1dB (loss) if yu get 5.3 Vopen, and 5.0 VLoaded, that is 0.5dB (loss)

 

[el156]

Use the 58V from the variac, and read the open circuit voltage at the 8 Ohm tap (Vopen). Then load the 8 Ohm secondary with an 8 Ohm resistor and find the closed circuit voltage (VLoaded).

Now, the loss of the transformer is:
20 x Log(VLoaded/Vopen) dB.

If you get 5.3 Vopen, and 4.7 VLoaded, that is -1dB (loss) if yu get 5.3 Vopen, and 5.0 VLoaded, that is 0.5dB (loss)

Thank you very much ,i will do that, because i would like to know everything possible about this OPTs, because i would like to use them in a amp project, and i know they are very good quality. i know they are c core and were made by Partridge and have 5 Kilos each (very heavy).

 

[6A3sUMMER]

Sorento,

Good.
There are Pentode output tubes in UL . . .
And don't forget Beam Power output tubes in UL mode.

Hmmm, now you have got me thinking, has anyone used a true tetrode tube in UL?
I have at least one 4-65 tetrode, but I bet it won't do good in UL because the max screen voltage is only 600V, but the max plate voltage is 3000V.
Maybe with series resistor and capacitor coupling to the screen from the UL tap, and a screen resistor to 600V to activate the screen?

Has anybody out there done transmitting tetrodes in UL mode?

Thanks!