GDS/HEYBOER POWER TRANSFORMER PRIMARY

[ViperDoc]

I'm not sure you've ever seen these, but thought I'd pass this by you guys.

I picked up a few 18-watt GDS/Heyboer PT/OT "Radiospares" sets for some future 18-watt builds.

http://gdsamps.com/parts/

The PT primary is printed only with "0, 110V, 240V", and I have questions:

1) As far as I am aware, there is no option for "110V vs. 120V" on the PT primary, it's just printed as "110V". Do I have the wrong transformer? Or is this intended to spec 110V primary voltage using a variac?

2) I'm sure I could run 120V into the 110V winding, but will my B+ off the 290 VAC HT secondary actually be 290 VAC*(120/110) = 316 VAC?

3) The secondary has a lug labeled "SCN". What is that and what would you recommend I do with that?

Thanks as always.

[martin manning]

The PT primary is printed only with "0, 110V, 240V", and I have questions:

1) As far as I am aware, there is no option for "110V vs. 120V" on the PT primary, it's just printed as "110V". Do I have the wrong transformer? Or is this intended to spec 110V primary voltage using a variac?

I would assume that means that the turns ratio is same as in the original, when the USA line voltage was 110V, give or take.

2) I'm sure I could run 120V into the 110V winding, but will my B+ off the 290 VAC HT secondary actually be 290 VAC*(120/110) = 316 VAC?

Yes.

3) The secondary has a lug labeled "SCN". What is that and what would you recommend I do with that?

See if it's connected to any other winding. If not, it might be a Faraday shield. Perhaps you can ask the seller?

[ViperDoc]

Thanks, Martin. The only SCN reference I could find seemed to refer to a shield, but having never seen that, I wasn't sure what to do with it. The pigeon has been sent, I'll see what comes back.

[ViperDoc]

Indeed, the SCN lug is a screen that is meant to be chassis grounded to “keep the transformer a little quieter”, according to the source.

[RockinRocket]

What's interesting is the original 60's power transformer had lugs for 205 225 245 with the secondary's being 300 300.
Is the GDS making the same voltage?

[ViperDoc]

We calculated that running 120vac through the 110vac primary winding would generate 316 VAC on the HT secondary rated at 290, more or less. I’ll have to fire it up to see for sure.

[Roe]

We calculated that running 120vac through the 110vac primary winding would generate 316 VAC on the HT secondary rated at 290, more or less. I’ll have to fire it up to see for sure.

if its too high, consider using the 240 and 110 windings (240-110=130)

[ViperDoc]

We calculated that running 120vac through the 110vac primary winding would generate 316 VAC on the HT secondary rated at 290, more or less. I’ll have to fire it up to see for sure.

if its too high, consider using the 240 and 110 windings (240-110=130)

If the 110 is too high, methinks the 130 would be higher, no?

[pompeiisneaks]

No a 120v sent into a 130v tap means it's under voltage. Therefore you'll get slightly less than expected.

Think about it, the problem you're having is putting 120+V into a 110V tap (that's expecting 110V)

~Phil

[martin manning]

If the primary is a single coil with 0, 110, and 240V, then the part between the 110 and 240 leads could be called a 130V primary. If you feed that part 120V, then your secondary voltages would be low by 120/130, or 7.7%.

[ViperDoc]

I clearly inverted the math on that, I appreciate the clarification. Makes perfect sense. You guys are crafty. Carry on.

So 120 AC into a 130 VAC primary would generate a 290 (120/130) = 268 VAC secondary? I think I like the idea of a higher B+ that I can lower as needed, either inside the chassis or on a variac.

[wpaulvogel]

What you should do is hook 120 volts to the 110 and 0 lugs and measure the 240 volt lug. If you variac 120 volts in and get 240 your perfect. I spoke to Phil at Heyboer last week about a transformer I got from amp parts direct (18 watt power transformer). He told me that on my particular transformer that the 0-120 volt tap was wound with 22 gauge magnet wire and the 120-240 volt tap is 26 gauge wire. It wouldn’t be a good idea to run the transformer on the 110-240 with 120 volts because it’s current capacity isn’t there. I know many transformer companies that reduce the gauge wire on the lower current taps to reduce cost and to increase space in the winding window.

[martin manning]

Good point! Measuring DC resistances would confirm that.

[wpaulvogel]

The reason I called Phil was because my transformer wire color didn’t match the printed labeling on the transformer. The black/red 240 tap was under the 0 volt location and the black 0 volt wire was under 240. I measured resistance and sure enough 0-120 was about 3.5 ohms and 120-240 was 7.7 ohms. Total from 0-240 was 11.2 ohms.

[ViperDoc]

The DC resistance from 0-110 on my GDS PT is 3.2R. The 110-240 resistance measures at 9R. Good to know! Thanks for the pearl.