Replacing transformer in old floppy drive - UK Vintage Radio Repair and Restoration Discussion Forum

itmustbesid · 15th Jul 2016, 9:55 pm

I have an old (1980's) dual floppy drive which was sold in the UK, but I want to use it in the US. Unfortunately, it has its own power supply. I was hoping I could open it up and replace the transformers (there is one per drive)

The transformers themselves are marked only with:
"VA 13 5 HZ 50"

Which I assume means 13V, 5A, 50Hz. So, if I find a transformer that takes my US 115V AC input, and has the same specs as these, it should work, right?

For example, I found something like this, which looks like a good candidate, although it says 10V, not 13V.

http://www.digikey.com/product-searc...=0&pageSize=25

I'm a total novice at this stuff, hence the basic question. I know I could just get a step-up voltage converter and just plug it in to that, but I thought I'd try something a little more adventurous.

Lucien Nunes · 15th Jul 2016, 10:57 pm

I would definitely go for the external step-up option. It's probably easier, maybe cheaper, doesn't spoil the original construction of the drive and doesn't carry a risk of damage to the rest of it if something were to go wrong in the modification.

That interpretation of the markings on the existing transformers isn't very convincing as it is not a normal way of stating output voltage and current. The output apparent power in VA is sometimes given but it's usually a round figure, often there are numbers that don't give any rating information at all.

What drive is it?

winston_1 · 15th Jul 2016, 11:15 pm

Since houses in the US have a 240V bi phase supply for for cookers, washers etc why not use that?

itmustbesid · 16th Jul 2016, 12:37 am

Thanks for the advice. The drive is a dual Cumana like the one here: http://chrisacorns.computinghistory....deElectron.pdf

I do have a step-up transformer rated for 500W so it should be OK to plug my BBC micro and the drive into it: except it only has one socket so I guess I'll need to have an adapter imported

TonyDuell · 16th Jul 2016, 5:38 am

How many connections are there to this transformer?

Most, if not all, 'classic' 5.25" floppy drivers needed 5V DC and 12V DC inputs. It was common for there to be effectively 2 power supplies -- a single transformer with 2 separate secondary windings, each feeding a bridge rectifier, smoothing capacitor and voltage regulator. The secondaries often had different voltages.

I would be surprised if any floppy drive ran off a single 13V AC output from a transformer. It's possible, but it certainly wasn't the common way to do it.

mike_newcomb · 17th Jul 2016, 11:04 am

Hi Sid, could the difference in cycles UK 50 / USA 60 cause a problem?

Some photos of your drive would be interesting.

Which computer or device will you be using the drive with?

Regards - Mike

Lucien Nunes · 17th Jul 2016, 11:15 am

Most 50Hz electronic equipment works fine on 60Hz. Exceptions are:

* Machines with induction or synchronous motors which run at the wrong speed (e.g. record players and clocks)
* Items using a capacitive dropper that will have a lower reactance at 60Hz resulting in increased current (which might or might not be a problem)
* Items with a choke ballast e.g. fluorescent lights that will have higher reactance resulting in decreased current (ditto)
* Phase-angle controls e.g. dimmers, and other devices that take a timing reference from the mains

The regulated linear supplies in a typical traditional floppy drive should be fine.

The reverse (60Hz equipment on 50Hz) is usually OK too with the same exceptions, although a transformer designed down to a price for 60Hz only might run at or near saturation on 50Hz resulting in increased heat dissipation.

MrBungle · 17th Jul 2016, 1:31 pm

Also add old digital clocks which use the mains frequency as a time reference.

TonyDuell · 17th Jul 2016, 3:34 pm

With regard to floppy drives, most (but not all) 8" ones have induction motors, and you have to change the pulleys/belt if moving from 50Hz to 60Hz or vice versa [1]. All (AFAIK) 5.25", 3.5" and 3" drives have DC-input motors and do not depend on the mains freqnency at all. For completeness many 14" hard drives (the sort of thing I run...) have induction motors and have the same issues are 8" floppy drives. Smaller hard drives again have DC input motors.

As for the mains transformer in the power supply, I doubt there woul be any problems running it on 60Hz. Most small transformers were designed to be fine on 50Hz or 60Hz, for the obvious reason.

[1] I have to mention that Tektronix made a machine with 8" drives where 115V at 60Hz was generated in the power supply, no matter what the mains input frequency was. I believe it was referenced to a divided-down crystal. That uniit can run in the USA or Europe with just a voltage selector switch change.

mhennessy · 17th Jul 2016, 10:35 pm

Those drives are standard 5/12V DC inputs, as was said earlier in post #5.

The disc is spun using a brushless motor, and the heads are positioned using a stepper motor. The Cumana drives used totally generic linear power supplies using 78xx voltage regulators and a simple transformer. I probably still have one in the attic, so finding out the spec of the transformer is possible (if I don't have that particular unit any more, it would have gone to a forum member who might be willing/able to help).

Of course, the drives can be powered from the BBC Micro itself. Many people cautioned against this, but I ran dual drives from a model B for many years with no issues. The Master PSU has more headroom, so is even more likely to be fine with this (this is how I use my Master today). I think the folk who ran into trouble were either unlucky with their drives, or had expansion options installed in their machines.

However, the best advice has already been given - just use the step-up transformer

I've yet to see an induction motor in a floppy (the 8" drives pre-date me), but this reminds me that I did once see a full height 5.25 drive that had a brushed DC motor driving the rotation of the disc via a belt, and the "turntable" had a strobe pattern printed on it for checking the speed - that had 50 and 60Hz options. Didn't keep it as it was only 40T, single side IIRC...

Maarten · 18th Jul 2016, 3:42 am

Quote:

Originally Posted by itmustbesid

I have an old (1980's) dual floppy drive which was sold in the UK, but I want to use it in the US. Unfortunately, it has its own power supply. I was hoping I could open it up and replace the transformers (there is one per drive)

The transformers themselves are marked only with:
"VA 13 5 HZ 50"

Which I assume means 13V, 5A, 50Hz. So, if I find a transformer that takes my US 115V AC input, and has the same specs as these, it should work, right?

Almost certainly not. 13V 5A is quite a lot of power to supply a single floppy drive. If anything, it probably means 13.5VA (13.5W) at an unknown voltage. I would avoid the problem alltogether and use an external step up transformer as suggested.

bluepilot · 18th Jul 2016, 10:08 pm

Quote:

Originally Posted by Maarten

Almost certainly not. 13V 5A is quite a lot of power to supply a single floppy drive. If anything, it probably means 13.5VA (13.5W) at an unknown voltage. I would avoid the problem alltogether and use an external step up transformer as suggested.

VA is used to specify wattage when current and voltage aren't necessarily in phase. The transformers are almost certainly 13.5 "Watts". (Perhaps there's a dot there that you haven't noticed). Measure the output voltages and perhaps you'll be lucky and find a suitable replacement transformer. Be very careful using a 500W step-up transformer. It will be designed to produce the correct output voltage with a 500W load. If you're only loading it with 13.5W you might get quite an over-voltage.

arjoll · 19th Jul 2016, 2:18 am

Quote:

Originally Posted by mhennessy

but this reminds me that I did once see a full height 5.25 drive that had a brushed DC motor driving the rotation of the disc via a belt, and the "turntable" had a strobe pattern printed on it for checking the speed - that had 50 and 60Hz options. Didn't keep it as it was only 40T, single side IIRC...

The 100tpi (SSQD) Teac ones that SORD used were like that.

(if anyone has some they don't need please let me know, they are rather scarce and two of the four drives I have a pretty dodgy; a project for the coming weeks is to try to get an HxC floppy emulator working with SORD FDOS

)

Okto1984 · 25th Jul 2016, 10:42 pm

I've discovered that some (maybe all?) BBC micros appear to be pretty easy to convert to 120v with a wire inside the power supply (all mine have it near the fuse, and clearly printed on the PCB). As for floppy disc drives, all of the ones I've encountered for the BBC micro so far plugged in to the BBC micro itself via an auxiliary power supply on the underside of the computer. It outputs 5V and 12V, which I have found to be the commonly needed voltages for floppy disc drives.

15th Jul 2016, 9:55 pm	#1
itmustbesid Retired Dormant Member Join Date: Jul 2016 Location: Auburn, California, USA. Posts: 8	Replacing transformer in old floppy drive I have an old (1980's) dual floppy drive which was sold in the UK, but I want to use it in the US. Unfortunately, it has its own power supply. I was hoping I could open it up and replace the transformers (there is one per drive) The transformers themselves are marked only with: "VA 13 5 HZ 50" Which I assume means 13V, 5A, 50Hz. So, if I find a transformer that takes my US 115V AC input, and has the same specs as these, it should work, right? For example, I found something like this, which looks like a good candidate, although it says 10V, not 13V. http://www.digikey.com/product-searc...=0&pageSize=25 I'm a total novice at this stuff, hence the basic question. I know I could just get a step-up voltage converter and just plug it in to that, but I thought I'd try something a little more adventurous.

15th Jul 2016, 10:57 pm	#2
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Replacing transformer in old floppy drive I would definitely go for the external step-up option. It's probably easier, maybe cheaper, doesn't spoil the original construction of the drive and doesn't carry a risk of damage to the rest of it if something were to go wrong in the modification. That interpretation of the markings on the existing transformers isn't very convincing as it is not a normal way of stating output voltage and current. The output apparent power in VA is sometimes given but it's usually a round figure, often there are numbers that don't give any rating information at all. What drive is it?

15th Jul 2016, 11:15 pm	#3
winston_1 Heptode Join Date: Oct 2012 Location: London, UK. Posts: 500	Re: Replacing transformer in old floppy drive Since houses in the US have a 240V bi phase supply for for cookers, washers etc why not use that?

16th Jul 2016, 12:37 am	#4
itmustbesid Retired Dormant Member Join Date: Jul 2016 Location: Auburn, California, USA. Posts: 8	Re: Replacing transformer in old floppy drive Thanks for the advice. The drive is a dual Cumana like the one here: http://chrisacorns.computinghistory....deElectron.pdf I do have a step-up transformer rated for 500W so it should be OK to plug my BBC micro and the drive into it: except it only has one socket so I guess I'll need to have an adapter imported

17th Jul 2016, 11:04 am	#6
mike_newcomb Rest in Peace Join Date: Apr 2012 Location: West London, UK. Posts: 665	Re: Replacing transformer in old floppy drive Hi Sid, could the difference in cycles UK 50 / USA 60 cause a problem? Some photos of your drive would be interesting. Which computer or device will you be using the drive with? Regards - Mike

16th Jul 2016, 5:38 am	#5
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,222	Re: Replacing transformer in old floppy drive How many connections are there to this transformer? Most, if not all, 'classic' 5.25" floppy drivers needed 5V DC and 12V DC inputs. It was common for there to be effectively 2 power supplies -- a single transformer with 2 separate secondary windings, each feeding a bridge rectifier, smoothing capacitor and voltage regulator. The secondaries often had different voltages. I would be surprised if any floppy drive ran off a single 13V AC output from a transformer. It's possible, but it certainly wasn't the common way to do it.

17th Jul 2016, 11:15 am	#7
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Replacing transformer in old floppy drive Most 50Hz electronic equipment works fine on 60Hz. Exceptions are: * Machines with induction or synchronous motors which run at the wrong speed (e.g. record players and clocks) * Items using a capacitive dropper that will have a lower reactance at 60Hz resulting in increased current (which might or might not be a problem) * Items with a choke ballast e.g. fluorescent lights that will have higher reactance resulting in decreased current (ditto) * Phase-angle controls e.g. dimmers, and other devices that take a timing reference from the mains The regulated linear supplies in a typical traditional floppy drive should be fine. The reverse (60Hz equipment on 50Hz) is usually OK too with the same exceptions, although a transformer designed down to a price for 60Hz only might run at or near saturation on 50Hz resulting in increased heat dissipation.

17th Jul 2016, 1:31 pm	#8
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Replacing transformer in old floppy drive Also add old digital clocks which use the mains frequency as a time reference.

17th Jul 2016, 3:34 pm	#9
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,222	Re: Replacing transformer in old floppy drive With regard to floppy drives, most (but not all) 8" ones have induction motors, and you have to change the pulleys/belt if moving from 50Hz to 60Hz or vice versa [1]. All (AFAIK) 5.25", 3.5" and 3" drives have DC-input motors and do not depend on the mains freqnency at all. For completeness many 14" hard drives (the sort of thing I run...) have induction motors and have the same issues are 8" floppy drives. Smaller hard drives again have DC input motors. As for the mains transformer in the power supply, I doubt there woul be any problems running it on 60Hz. Most small transformers were designed to be fine on 50Hz or 60Hz, for the obvious reason. [1] I have to mention that Tektronix made a machine with 8" drives where 115V at 60Hz was generated in the power supply, no matter what the mains input frequency was. I believe it was referenced to a divided-down crystal. That uniit can run in the USA or Europe with just a voltage selector switch change.

17th Jul 2016, 10:35 pm	#10
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Replacing transformer in old floppy drive Those drives are standard 5/12V DC inputs, as was said earlier in post #5. The disc is spun using a brushless motor, and the heads are positioned using a stepper motor. The Cumana drives used totally generic linear power supplies using 78xx voltage regulators and a simple transformer. I probably still have one in the attic, so finding out the spec of the transformer is possible (if I don't have that particular unit any more, it would have gone to a forum member who might be willing/able to help). Of course, the drives can be powered from the BBC Micro itself. Many people cautioned against this, but I ran dual drives from a model B for many years with no issues. The Master PSU has more headroom, so is even more likely to be fine with this (this is how I use my Master today). I think the folk who ran into trouble were either unlucky with their drives, or had expansion options installed in their machines. However, the best advice has already been given - just use the step-up transformer I've yet to see an induction motor in a floppy (the 8" drives pre-date me), but this reminds me that I did once see a full height 5.25 drive that had a brushed DC motor driving the rotation of the disc via a belt, and the "turntable" had a strobe pattern printed on it for checking the speed - that had 50 and 60Hz options. Didn't keep it as it was only 40T, single side IIRC...

25th Jul 2016, 10:42 pm	#14
Okto1984 Retired Dormant Member Join Date: Dec 2013 Location: Winchester, Hampshire, UK Posts: 288	Re: Replacing transformer in old floppy drive I've discovered that some (maybe all?) BBC micros appear to be pretty easy to convert to 120v with a wire inside the power supply (all mine have it near the fuse, and clearly printed on the PCB). As for floppy disc drives, all of the ones I've encountered for the BBC micro so far plugged in to the BBC micro itself via an auxiliary power supply on the underside of the computer. It outputs 5V and 12V, which I have found to be the commonly needed voltages for floppy disc drives.