Old transformer ID

[richfoub]

Hi, found three old transformers while having a clean up, two are ? Partridge 1428 and the other has 48R08 printed on top. Does anyone know what they might be from or have any specs available for them?

Richard

 

[gingertube]

It seems that the Partridge 1428 are 6K Primary Single Ended Output Trannies.
According to this:
PARTRIDGE 1428 VARNISH-DIPPED VALVE/TUBE AMP OUTPUT TRANSFORMERS EL84/EL34/KT66 | #268888599
Cheers,
Ian

 

[trobbins]

I just got the audio amplifier sub-chassis from a Ferrograph 2N reel deck (circa 1955) that uses the 1428 in single ended mode with an EL84 operating with a 220R cathode bias (9V or circa 35mA anode), and 260V B+ (and screen) for a rated 2.5W into 15 ohm, with 2.3 and 15 ohm output taps. The 6BQ5/EL84 datasheet SE pentode rating is 7k impedance for 4W output.

 

[lhzsl]

I just got the audio amplifier sub-chassis from a Ferrograph 2N reel deck (circa 1955) that uses the 1428 in single ended mode with an EL84 operating with a 220R cathode bias (9V or circa 35mA anode), and 260V B+ (and screen) for a rated 2.5W into 15 ohm, with 2.3 and 15 ohm output taps. The 6BQ5/EL84 datasheet SE pentode rating is 7k impedance for 4W output.

Can you take a look at your 1428 machine, thank you

 

[trobbins]

I renovated the Ferrograph 2N audio amplifier sub-chassis last year, https://dalmura.com.au/static/Ferrograph 2A-N amp.pdf

I just had time to go through the power amp stage in more detail, and determine its stability given it uses global feedback. With a few minor tweaks it is unconditionally stable with 11dB global feedback, and flat frequency response with -1dB from 10Hz to 30kHz at 1W, contracting to 20Hz to 28kHz at 3W, given it starts to clip above about 3.6W. So very pleased with the T1428 OPT, given its first significant HF resonance is about 35kHz, and gain/phase is pretty benign above that.