Preliminary readings on transformer voltages slightly out

[PS2500]

I've just installed the transformer, tube sockets and RCA terminals to my chassis and done all the wiring up to the first stage of voltage testing (transformer input and output voltages, p. 42 in my manual).

My readings are 100V across terminals 1 and 2 (mains voltage in Japan is 100V), 7.7V across 4 and 5 (which should be reading at 9V) and 118V across 6 and 7 (which should be reading at 130V).

Are these readings acceptable, or too far outside the range? I assume it's a result of 100V input.

[Paul Birkeland]

Go ahead and install and test the power supply PC board and let us know what DC voltages are coming out.  I suspect you will be within the acceptable range, but on the very low end.

[PS2500]

Thanks. I hope to get to that tomorrow. Do you think those low readings are because of the 100V (instead of 120) local mains input?

[Paul Birkeland]

Yes, low mains voltage will reduce all of the winding voltages on the power transformer.

[PS2500]

After a much more late-evening session than I intended, I've got the power supply PC board installed and ran the test on it just now.

The DC readings specified in the manual are 375V +/-15%, and 6.3V.

My actual readings were 314V and 6.27V. By my calculation, -15% of the specified reading would be 318.75V, so I'm several volts short of that.

Am I going to be okay with these? I can't see an easy way around it, as the Japan mains voltage is, from what I understand, used by no other country. I guess if the worst comes to the worst, I could use a stepup transformer, but I'd much prefer not to if I can avoid it.

[Paul Birkeland]

You mean 214V?  This would definitely be an issue.

The 6.3V is not an issue at least. 

Is there any possibility of obtaining a small 100:110 step-up transformer to put ahead of the Eros?

If not I have an idea for a workaround for you, but it will be a little strange.

[PS2500]

Yes, I can do it if I have to. Certainly small is better than large, if I can get away with that - on grounds of both cost and size.

[Paul Birkeland]

The other option would involve you finding a 9V wall transformer of reasonable size and using that for the heaters, then we can wire the heater winding on the Eros transformer in series with the high voltage primary (I'll help you with that) to boost up the available B+.  PJ may have another idea too on how to do this and some recommendations on potential performance issues with doing this, so hopefully he'll weigh in.

Many of the adapters for the original Nintendo NES would work for this purpose oddly enough.

[PS2500]

Thanks. I'll need to digest that info; it didn't take first time round!

Maybe it will just be simpler to use the stepup, though.

[Paul Birkeland]

Yes, it would be my first recommendation!

[PS2500]

You mean 214V?  This would definitely be an issue.

Sorry, I misread this question yesterday. The answer is no; my DC voltage test result was 314V.

In other words:

375V +/-15% was specified in the manual. 15% lower than 375 would be 318.75, so my actual reading is just 4.75V less than the lowest value in the specified range. In percentage terms, it's only 1.26% short of an acceptable value (and 16.26% short of 375V).

[Paul Birkeland]

Ah, I would proceed to building the shunt regulator.  You should still have adequate DC compliance.

[PS2500]

Thanks, will do. I was hoping those values might be acceptable.