[sdiy] Advice?: Powering up a vintage keyboard after several years

[rsdio at audiobanshee.com]

Power resistors are handy things to have around. Just don't touch them (or let anything flammable or meltable touch them) while they're performing their duties as a load. Power resistors also double as a power soak for a guitar amp if you have enough of them and are into that sort of thing.

The trickiest part is estimating the normal load and/or the nominal current. If you can estimate a normal current, then you can calculate the wattage necessary for your power resistors, as well as the total resistance you need.

Of course, having sacrificial loads like an old drum board would work if the board draws approximately the same load. Then again, the load doesn't have to precisely match the synth that you're testing - the primary goal is to avoid running the power supply with no load at all (or with too much of a load that would exceed the current ratings). Just be sure that all of the power supply outputs are loaded. There might be +15V -15V +5V and perhaps others. Swapping in some other piece of electronics might not end up using all of the same voltages.

Brian


On Oct 11, 2016, at 8:36 PM, Tony K <weplar at gmail.com> wrote:
> Good advice. What would you recommend for a dummy load? I used to keep an old drum board around - SCI Drumtrax , but sold it along with my soul to the devil *sigh*
> 
> Back to basics.
> 
> On Oct 11, 2016, at 11:18 PM, rsdio at audiobanshee.com wrote:
>> Never use a Variac on electronics that have a voltage-regulated power supply. That includes most synths because they have linear power supplies that expect a minimum of about 3 VAC above the regulator voltage.
>> 
>> If you're designing electronics and want to find out where things break, a Variac is a great tool.
>> 
>> 
>> Testing the disconnected power supplies is a good idea. Just be sure to put a reasonable load on the power supply to make sure it doesn't fry itself.
>> 
>> Brian
>> 
>> 
>>> On Oct 11, 2016, at 6:19 AM, "Barry Klein" <barryklein at cox.net> wrote:
>>> Well, that’s me....
>>> If the consensus is just plug it in I’m good but if it is check the supplies first....  memorymoogs, prophet 5, lesser synths...  I’d just leave them off – don’t need the added grief right now.
>>> No way am I going to tweak up the memorymoog supplies and go through calibration of them again... at least not now.
>>> Maybe the Variac is just a thing for tube-based things like old ham sets or guitar amps?
>>> I have 2 (transistor(ized) ham tranceivers and a Drake receiver that I need to try too.
>>> 
>>> 
>>> Barry
>>> 
>>> 
>>> From: Synth-diy On Behalf Of Barry Klein
>>> Sent: Tuesday, October 11, 2016 5:14 AM
>>> 
>>> I am going through the stuff in my garage.  I have several vintage synths – some worth quite a bit now – and they haven’t been powered in at least 5 years.
>>> What would you recommend – advancing on a Variac, or just plug it in?
>>> 
>>> Barry