NAD 402 New traffo compatible with power circuit?

[berthej]

The mains transformer in my NAD 402 tuners died, and I would like to replace it. It is a standard IE48 type, but with a non-standard value of 2x23volts on secondaries.

I thought I could replace it with a 2x24volt one. But while most of the NAD’s power circuits are regulated by 7805 and 7812 type regulators, there is one power circuit that outputs 32v. The schematic is here below. The circuit is feed 23VAC, which is rectified by D11 and D12. Therefore, I believe, 23VAC translates into 32,5VDC, which is then regulated by the zener and transistor to 32VDC.

But what happens if I apply 24VAC, which is 34VDC after rectifying. Can the following regulators handle that, or will they be overloaded.

I greatly appreciate any input on this

berthej

[tvrgeek]

Considering the variance in power line input, you are probably OK. If you were really worried, just add another diode to the rectifier in line to take some of the drop.

[cliffforrest]

That series cap, parallel diode is a voltage doubler, to get enough voltage headroom for the cap-multiplier regulator to work. Presumably it is a low current supply (Tuning diodes ?? ;-)

The downside is that it has a high impedance and poor regulation, ie the voltage ( at Q17-C) will lower as current is drawn.

Given all that, I cannot see any problem at all with using a higher voltage. Measure across C58 when it is working. Make sure it is not wildly above 50V !

[berthej]

Dear tvrgeek and Cliff

Thank you for your input. I will have a go at it, and hopefully not experience any smoke

The old trafo doesn't show the VA rating, but being a IE48-type, these normally have ratings between 8-12VA. Will try a 12VA one.

Thanks again

berthej

[pdul]

I know this is an old thread, but anyway here I go!
The trafo in Nad 402 gives out 16-0-16 vac, Which becomes 21,xx vdc in each rail..
So installing a 23-0-23v trafo will shurely give you much more action than you bargain for, First the smoothening caps rated 25v will pop with a bang.
Etc. etc
Just my ten cents.

[pdul]

I just salvaged one for myself from the dump. The only thing wrong was the bulb for the display light. I replaced it with four white Leds, And Voila, It works Then I replaced all the electrolytic caps with FMs and FCs and Silmics
in the audio signal line.
It is by the way the most simple and at the same time the most sweet sounding FM tuner I ever had