Step down trafo to 220v.

[honkytonk]

Hello, looking for a step down trafo from 230v to 220v for my v76 and v72 vintage preamps. Thanks for any advice!

 

[Khron]

Why, exactly?

https://www.se.com/uk/en/faqs/FA144717/

 

[JohnRoberts]

Variac? Technically an auto-former not an isolated transformer.

JR

 

[Khron]

Considering the potential mains variations / tolerances (+10/-6%), i'd argue it's a near pointless exercise / expense, but... What do I know?

 

[honkytonk]

Why...good question. I have been informed by the tech person in Germany who serves and repair my old german modules, that it is important to give them 220v. He knows the v76 inside out. I only use them..))

 

[JohnRoberts]

I recall concerns when 240V and 220V mains voltages were first harmonized to 230V... in some previously 240V regions that 230V was more like 235V.

Conservative design anticipates and manages significant mains voltage variation low or high. Modern gear often accepts universal mains voltages. It is better now than it was decades ago, but this can go with the territory when messing with legacy or vintage designs.

JR

 

[Khron]

Well, speaking from a strictly technical point of view, if a piece of gear can't stand what should be within-normal-tolerances mains voltages, that's a pretty crappy piece of gear.

Maybe i'm a heathen, but i wouldn't worry about it.

 

[JohnRoberts]

The customer is always right, even when wrong...

We can only offer (mostly) good advice.

JR

 

[moamps]

The V72 and V76 are intended for use in studio-controlled conditions, so they are sensitive to overvoltage. The mains voltage is now 230 +/- 10% which means it can also be 250V, what is certainly too much for a V72 or V76.

In several cases, I used a standard 230 / 15V 50VA mains transformer to reduce the mains voltage by 10-15V in such a way that the secondary of the transformer is connected in series with mains but in antiphase. It worked very well.

 

[honkytonk]

Hi moamps,

Thanks for info. Where do I find a transformer like that?

"the secondary of the transformer is connected in series with mains but in antiphase"

Could you pls explain more about this? antiphase?

Would you consider "undervoltage" a problem for the v76, v72? If the voltage goes under 220v.

 

[mjrippe]

Yes, this is an issue that many of us have dealt with. Here in the USA the line voltage is supposed to be 120VAC. Common step-up transformers for European gear are 1:2 and are marked as "110:220". Here in Brooklyn, NY the line voltage is about 125VAC which turns into 250VAC using a step-up transformer. For a vintage V72 which is expecting 220VAC, this is well above 10%.

Moamps solution is a good one, and will certainly work. I have been thinking about having custom transformers wound for 120-220VAC for some time, perhaps someone would do the same for 240-220VAC?

 

[moamps]

Thanks for info. Where do I find a transformer like that?

https://www.tme.eu/de/en/details/tth50_230_11.5v/toroidal-transformers/breve-tufvassons/

"the secondary of the transformer is connected in series with mains but in antiphase"
Could you pls explain more about this? antiphase?

Would you consider "undervoltage" a problem for the v76, v72? If the voltage goes under 220v.

If the mains fluctuates, you can't do much about it without inline conditioners.
Undervoltage isn't so problematic, it usually can't do any harm, except lowering performance (higher noise, THD etc.)

 

[honkytonk]

Very useful info, thanks a lot!

 

[Newmarket]

I recall concerns when 240V and 220V mains voltages were first harmonized to 230V... in some previously 240V regions that 230V was more like 235V.

UK mains was harmonised to 230V some years ago. Last time I looked - and at one time I was looking quite a lot - it still came 'out of the wall' at typically 242V.
+10% / -6% spec obv permits up to 264V so nothing really had to change from a regulatory point of view.

Of course this proper '50Hz' mains which we all know sounds better than that '60Hz' nonsense. Gives smoother more coherent upper mids

 

[abbey road d enfer]

Of course this proper '50Hz' mains which we all know sounds better than that '60Hz' nonsense. Gives smoother more coherent upper mids

Also cures ingrown nails...

 

[Tubetec]

I have a large 1KW isolation transformer made by RS components , its got 240/415 volt primary taps . There are four 60-55-0 volt secondaries so its easy to compensate for a slightly high supply voltage .
That looks like an equivalent model in modern format ,

https://sa.rsdelivers.com/product/r...a-isolation-transformer-0-230-400v-ac/1235703
comes out at about 70 STG .

 

[RuudNL]

Why not simply add a series resistor to obtain a voltage drop of 10 Volts?
How much current will flow? 100 mA?
In that case a 100 Ohm/1 Watt resistor would be sufficient. Take a 5 or 10 Watt one and it will work 'for ever'!

 

[Timjag]

Newmarket! Lol not if you have the misfortune of importing a USA Hammond organ!

As for the power, here in central london it’s always 238 volts on the money!

UK mains was harmonised to 230V some years ago. Last time I looked - and at one time I was looking quite a lot - it still came 'out of the wall' at typically 242V.
+10% / -6% spec obv permits up to 264V so nothing really had to change from a regulatory point of view.

Of course this proper '50Hz' mains which we all know sounds better than that '60Hz' nonsense. Gives smoother more coherent upper mids

 

[Tubetec]

500watts is a bit extravagant for just a couple of preamps ,

that might be more suitable ,

https://sa.rsdelivers.com/product/rs-pro//rs-pro-100va-isolation-transformer-15-400v-ac-115v/1234140
Looks like it would make a usefull HT transformer in its own right as well .

 

[Matt Syson]

The 'autotransformer' as proposed by Moamps is what I would have suggested had he not got in there first. The beauty being that it only needs a relatively small transformer (low VA rating) as it is only supplying the difference and not the full power requirement.
In the wrangling over 'European mains supply harmonisation' I believe a bit of wrangling took place and the former 'plus and minus 10 percent was altered to minus 10 and plus 6 percent (for the UK I think) so that practically everywhere could squeeze into the nominal 230 Volt bracket. Of course some countries and locations manage to hit the target 230 Volts better than others.
with the advance of switchmode 'universal' supplies they claim (and I presume do) function correctly to spec from either 90 or 100 Volts up to 264 ? Volts at 47 Hz to 63 Hz so squeezing in the widest of frequency tolerances.
I have just checked my 'reference book' and under 'battery eliminator' it gives the schematic for a unit that uses 'about 200 Volts DC mains' I can only presume that in the UK DC mains was negative grounded as the unit comprises a 'dropper resistor', 30 millihenry choke and some 4uF capacitors. No rectifier. It would be connected to a lighting circuit using a DC (bayonet cap) power plug.
Since BC lamp sockets can have the bulb fitted either 'way around' I presume making your radio work required you to try both ways until your required programme 'bursts forth.