Combo Preamp Transformer Current Rating

[Drawbar Dave]

I am waiting for a 117 vac 020875 combo preamp to arrive and I will be converting it to run on 230 vac. Both the US and Non US versions of the power supply show 34 vac on the transformer secondary. As I select a replacement power transformer, what current rating would be best? I don’t want to go bigger than I have to!

I already have a couple of 230 vac neons to replace the originals.

I know that the preamplifier design is primitive by today’s standards but I’m mainly going to be running my Farfisa Compact Duo through it and the preamp in the Farfisa is probably just as basic!

Many thanks
Dave

[Jyvoipabo]

Hello,

According to my calculations the power is very low 5mA @ 48VDC ~ 1/4 VA
But you will not find such small transformers.

Example :
https://www.conrad.com/

product N° 609884

Toroidal (Ø) 60 mm
Input voltage (number x voltage) 1 x 230 V
Output voltage (number x voltage) 2 x 15 V AC
Height 39 mm

You must have to wire the outputs in serial to have a 230V / 2x15 = 30V 15VA transformer.
And the no load output voltage will be around 30V + 15% = 35V.
This value is not critical and many other transformers can fit.

JP

[Drawbar Dave]

Thanks JP!

[Jyvoipabo]

check also that it fits in the box.....

[Drawbar Dave]

Well the CPA arrived today and I switched out the transformer and added the 100k resistors in series with the neon pilot lights. My Compact Duo sounds awesome through the 147 and I can finally do that wibbly Farfisa sound on Pink Floyd’s Time!