Author Topic: Shaking Power Transformer?  (Read 266 times)

Offline Swabian_Keys

  • Pre-Piano
  • *
  • Posts: 8
    • View Profile
Shaking Power Transformer?
« on: October 08, 2020, 11:21:36 AM »
Hey,
I just got myself a wurli 200! Timestamp beneath the keyboard says its from 1972.  Yay. Now the first thing i want to do, probably like everyone, is trying to get rid of the hum.
I just ordered that pickup shields. While waiting for them, i wanted to isolate the Powercables from audio cables etc..
Now i just recognized, that the entire wurli is softly vibrating. It feels a little like a Purring cat, just not that heavily, very very sublte:D
I plugged in headphones to make sure that the speakers are not the vibrating part, so it has to be the Power Transformer i guess. Which also makes totally sense to me.
Seems like the transformer slowly vibrating itself apart? I wouldn't mind, as its somehow cool (and cheaper) than replacing it, but i could imagine that that introduces hum? Do you also feel your wurli to softly vibrating?

i also checked the transformer, which seems not to be isolated on the bottom. Would it make sense to try isolating it with layers of copper and rubber to not be part of the grounding to reduce hum? (heat/grounding problems)

Also one thing im wondering about is, that the Power Transformer is obviously a 220v/50hz (big stamp on top:D). Buuuut they changed the Voltage in germany to 230v back in the 80s. Anyone has experience with that?
The pre-owner just used it like that...
Some Pictures included:
https://imgur.com/a/rncfgZg

« Last Edit: October 09, 2020, 06:06:25 AM by Swabian_Keys »

Offline Major Bloodnok

  • Pre-Piano
  • *
  • Posts: 6
    • View Profile
Re: Shaking Power Transformer?
« Reply #1 on: October 10, 2020, 01:01:28 PM »
As for voltage, I think that you will find the actual domestic supply in Germany is closer to 220V. Some while back, it was decided that countries across the EU should pretend to harmonise supply voltages; so they hit upon the idea of using a declared voltage of 230V. The catch is that in the formerly 220V countries the adopted tolerance was 230V -10% +6%, whereas here in the UK (formerly a nominal 240V) the new standard is 230V -6% +10%. But the supply voltages did not actually change (hence the jiggery-pokery with tolerances), for the simple reason that such a change would entail an enormous cost in re-equipping the distribution infrastructure (new transformers at all the local substations), not to mention problems with some (mainly industrial) machines which are designed to run within narrower voltage tolerances.
That is not to say that your supply will be spot on 220V - it will vary according to the state of your local distribution grid, and with the time of day (due to fluctuations in total load). I find anything between about 238V and 247V here in south-west England.
This is not a problem for most new domestic electric appliances - those made for the EU market must be able to work over the range 230V ┬▒10%. If I buy a Euro-standard electric kettle in my local Lidl, it will come to the boil faster here than it would in Germany (incidentally affording us a marginal saving in heat loss, thus saving the planet or some such nonsense). Most modern electronic gear working with an internal low voltage from a regulated step-down unit will automatically adapt to a much broader mains supply voltage range. Older kit, which just relies on a fixed transformer winding turns ratio for its internal voltages, is often equipped with mains voltage selectors, jumpers, or requires some soldering to adjust to the local supply voltage. If your tranny is marked 220V, then you are probably OK. But if you are worried, I would first suggest putting a voltmeter on your wall socket at the times when you typically play the Wurli, in order to see what your actual supply voltage is.
Where supply voltage can be a problem is exemplified by the Twin Reverb amp I use with my Fender Rhodes. This twin is a reissue (i.e. modern), and labelled 230V for the European (including UK) market. Now I know that the power transformer has multiple taps on the primary windings to cater for 220V, 240V etc., which suggests that this order of internal voltage accuracy is regarded as important; but the only schematic I can get for it is some years out of date, so I cannot check/adjust the primary connections to suit my 240V supply. In theory, if I am putting 240V across the 230V taps, the B+ and all the related plate voltages are going to be 4.3% too high. Happily, my grid voltages will also be correspondingly more negative, affording some correction, so the set-up is probably near enough to avoid red-plating the output valves (tubes); but goodness knows how Fender set the bias at the factory. Do they anyway use for this a bench supply which gives exactly 230V anyway, or is it 230V ┬▒lots, close enough for those weird folk across the Atlantic?
The moral of this story - take nothing for granted.
Growing old disgracefully with a 1972 MkI Stage 73, a Prophet '08+Tetr4 and a Korg SP250.

Offline Jenzz

  • Mark I
  • ****
  • Posts: 103
    • View Profile
    • http://www.tasteundtechnik.de
Re: Shaking Power Transformer?
« Reply #2 on: October 10, 2020, 02:53:35 PM »
Hi .-)

You should measure the voltage across the 1000uF filter cap... If you are at roundabout 44 to 46 volts, it's allright.

The '220' stamp only indicates that this is a 4-wire primary EU-Transformer which can be wired for 115V or 230V. The US models have a '115V only' 2-wire primary.

Jenzz
« Last Edit: October 11, 2020, 12:27:01 PM by Jenzz »
Rhodes tech in Germany
www.tasteundtechnik.de
www.spontaneousstorytelling.net

VintageVibe 64 ACL + DOD FX25B, Tone City Sweet Cream, Rocktek PHR-01, Boss BF-2
Adams Solist 3.1 Vibraphone

Offline Swabian_Keys

  • Pre-Piano
  • *
  • Posts: 8
    • View Profile
Re: Shaking Power Transformer?
« Reply #3 on: October 11, 2020, 08:32:33 AM »
Hey, i just measured the Voltage of the 1000uF Filter Cap and i'm just getting 42V, which is okay i guess?
Did i measured it right? I attached a photo. I know you can't measure caps while being build in, but i did it, and it seems to work as it got a 1600uF.

Any suggestions for the shaking power transformer? is it normal? Its the same feeling as touching the electricity meter in my flat.

Also somebody modified the the amp i guess? The aux cable is connected to the yellow poti on the board which is numbered as 48 in the manuals, but i can't find out what its good for.

Still waiting for the pickup shields. I hope this will fix all the hum. I read that the hum can only be from the reedbar, as when the rca is unplugged the amp isn't humming to much. I checked for dirt or shortings and bad groundings but i dindn't found a problem... i thing i'll just take the pickups out and clean them.
 In the meantime i twisted the power cords ans wrapped them in copper. Didn't change nothing.





« Last Edit: October 11, 2020, 08:43:43 AM by Swabian_Keys »

Offline Jenzz

  • Mark I
  • ****
  • Posts: 103
    • View Profile
    • http://www.tasteundtechnik.de
Re: Shaking Power Transformer?
« Reply #4 on: October 11, 2020, 12:25:08 PM »
Hi .-)

Do you have the 200 schematic?

42V is ok.

The 1600uF is a 'fake' measurement, but makes kind of sense, because there is another 470 /500 uF filter cap after a 10 Ohms resistor... So nothing wrong here :-)

Jenzz
Rhodes tech in Germany
www.tasteundtechnik.de
www.spontaneousstorytelling.net

VintageVibe 64 ACL + DOD FX25B, Tone City Sweet Cream, Rocktek PHR-01, Boss BF-2
Adams Solist 3.1 Vibraphone

Offline Swabian_Keys

  • Pre-Piano
  • *
  • Posts: 8
    • View Profile
Re: Shaking Power Transformer?
« Reply #5 on: October 11, 2020, 02:33:47 PM »
Jens, thank you very much for your support:)
Yes i have the schematics!