GDS POWER TRANSFORMER PRIMARY

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ViperDoc
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GDS POWER TRANSFORMER PRIMARY

Post by ViperDoc »

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

http://gdsamps.com/parts/

The PT primary is printed 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?

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?

I must say, every transformer I've ever purchased with the exception of Hammond gives no indication of what the wires are. Methinks precedent-Elvis left that building more than a few days ago...
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Re: GDS POWER TRANSFORMER PRIMARY

Post by ViperDoc »

I heard back from Graydon at GDS. The SCN lug is a screen that is meant to be chassis grounded for quieter operation.
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Re: GDS POWER TRANSFORMER PRIMARY

Post by TriodeLuvr »

ViperDoc wrote:
Sun 01/10/21 11:22 pm
I heard back from Graydon at GDS. The SCN lug is a screen that is meant to be chassis grounded for quieter operation.
Did they say why there's no 115/120V primary winding? Line voltage in my area never goes below 120V and is often 125V. Transformers with 115V primaries can get pretty hot, and I wouldn't even consider using one that's actually wound for 110V. If that's a real specification, and you're in the U.S., they should have told you up front before taking the order.

Jack
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Re: GDS POWER TRANSFORMER PRIMARY

Post by JMPGuitars »

ViperDoc wrote:
Sat 01/09/21 11:14 pm
I picked up a few 18-watt GDS/Heyboer PT/OT sets for some future builds.

http://gdsamps.com/parts/

The PT primary is printed 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?

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?

I must say, every transformer I've ever purchased with the exception of Hammond gives no indication of what the wires are. Methinks precedent-Elvis left that building more than a few days ago...

The transformer is made to vintage spec. That's why it doesn't say 120 on it. Your loaded HT will be around 300-0-300 instead of 290-0-290. If your B+ is too high, check the zener voltage dropping thread in my signature.

As you now know, SCN is screen/shielding that goes to your power amp star ground.

The GDS / Heyboer PT is my favorite. I also like the Mercury PT because it too has solder lugs, but the price point is a lot more wallet friendly for the GDS. Both have about the same unloaded HT.
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Re: GDS POWER TRANSFORMER PRIMARY

Post by ViperDoc »

I've never used one of these, but I think I might prefer the higher B+. If not, I can always knock the AC back with a Brown Box.
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Re: GDS POWER TRANSFORMER PRIMARY

Post by TriodeLuvr »

JMPGuitars wrote:
Mon 01/11/21 6:52 am

The transformer is made to vintage spec. That's why it doesn't say 120 on it. Your loaded HT will be around 300-0-300 instead of 290-0-290. If your B+ is too high, check the zener voltage dropping thread in my signature.
Have you used this specific transformer on our line voltages? The issue isn't only the rise in B+, it's the increase in dissipation in the primary winding. The difference between 110 and 120 (let alone 125) is huge. At my location, Hammond transformers with 115V primaries get extremely hot, even with no load. After years of complaints, the company finally started offering primaries suited to the U.S. market. Just sayin'.

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Re: GDS POWER TRANSFORMER PRIMARY

Post by JMPGuitars »

TriodeLuvr wrote:
Mon 01/11/21 2:34 pm
Have you used this specific transformer on our line voltages? The issue isn't only the rise in B+, it's the increase in dissipation in the primary winding. The difference between 110 and 120 (let alone 125) is huge. At my location, Hammond transformers with 115V primaries get extremely hot, even with no load. After years of complaints, the company finally started offering primaries suited to the U.S. market. Just sayin'.

Jack
Yes, I've used plenty of his 18W and 36W sets with a line voltage around 120. Sometimes slightly higher. I test my voltages with a variac set to 120.

I've definitely not had any heat issues. I've grabbed amps by the transformers after bench testing them with no problem, or noticeable heat.
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Re: GDS POWER TRANSFORMER PRIMARY

Post by ViperDoc »

That's a good question: when you load up the Superlite TMB schematic, the HT secondary off the transformer is listed as 290 VAC in BLACK--that is the spec'd, not "tested" secondary voltage like the other power supply voltages listed in RED, is that correct? Point being, the GDS PT ran at 120V will produce the RED voltages on the schematic using the component values as listed, give or take?
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Re: GDS POWER TRANSFORMER PRIMARY

Post by JMPGuitars »

ViperDoc wrote:
Mon 01/11/21 3:37 pm
That's a good question: when you load up the Superlite TMB schematic, the HT secondary off the transformer is listed as 290 VAC in BLACK--that is the spec'd, not "tested" secondary voltage like the other power supply voltages listed in RED, is that correct? Point being, the GDS PT ran at 120V will produce the RED voltages on the schematic using the component values as listed, give or take?
You might need to drop the B+ to hit the target values on any of the projects. With a SS rectifier, you will most likely need to drop it. But listen to the amp first and then decide, assuming you're not too far off.
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