Can someone give me some suggestion for a high quality 120V 6.3V-0-6.3V transformer to replace my cheapo radioshack 12.6V CT 1.2A Standard Center Tap Transformer with leads - RadioShack.com (Power transformer, 120VAC step-down to 12VAC, with center-tapped secondary winding (Radio Shack catalog # 273-1365, 273-1352, or 273-1511).
The radioshack cheapo is working fine as filament transformer in my tube amp (for 37 / 76 driver tubes) but running hot to the touch. I need something in compact size that would would well, sounds good and does not cost much (less than $50)
Any pointer is greatly appreciated. Thanks !!!
The radioshack cheapo is working fine as filament transformer in my tube amp (for 37 / 76 driver tubes) but running hot to the touch. I need something in compact size that would would well, sounds good and does not cost much (less than $50)
Any pointer is greatly appreciated. Thanks !!!
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Hammond 166 series for open style
Hammond Mfg. - Power Transformer - Economical Single Primary - (166 Series)
Available from Angela Instruments, Digi-key, etc.
What is your required current draw?
Hammond Mfg. - Power Transformer - Economical Single Primary - (166 Series)
Available from Angela Instruments, Digi-key, etc.
What is your required current draw?
The amp uses a pair of 37 tubes driving a single ended 71a amp. I put 76 in there since I maybe swapping in 76 later on to get different sound flavor. I have not done any measurement to find out what is the exact current.
That Thordason on ebay looks like a good candidate. Thanks
That Thordason on ebay looks like a good candidate. Thanks
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I've used those RS transformers and there's nothing wrong with them. Measure the steady-state temp and let us know.
If it's running too hot either it's defective or there's something wrong in your circuit. You're not going to find a "compact" transformer (i.e. same size) that runs considerably cooler. They need to dissipate. You may also bolt it real well to the metal chassis to help dissipation.
If it's running too hot either it's defective or there's something wrong in your circuit. You're not going to find a "compact" transformer (i.e. same size) that runs considerably cooler. They need to dissipate. You may also bolt it real well to the metal chassis to help dissipation.
So then the current draw is 25% of the transformer rating? Something is amiss; I suspect a wiring problem.
Could also be the flux capacitor orientation, or the positronic charge on the secondary.
on transformers that have rectifier windings, its not advertised usually that the power transformer is gapped nor sometimes they don't tell you that they test the winding (hi pot) to ensure it can float above b+ .
anytime there is significant dc current through the windings of a transformer, it is gapped to lower dc current saturation. That is why se transformers are gapped and is advertised.
basically, get a real power transformer for your application
like this one: http://www.edcorusa.com/products/608-xpwr015_120.aspx
anytime there is significant dc current through the windings of a transformer, it is gapped to lower dc current saturation. That is why se transformers are gapped and is advertised.
basically, get a real power transformer for your application
like this one: http://www.edcorusa.com/products/608-xpwr015_120.aspx
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like this one: http://www.edcorusa.com/products/608-xpwr015_120.aspx
Great suggestion Dave. I will put in my order. Thanks
Great suggestion Dave. I will put in my order. Thanks
What are you on about? As far as I can tell we are talking about AC heaters, and even if it were DC heaters how do you know it is being rectified in a way to put DC on the secondary? And what does cathode current have anything to do with the heater in an indirectly heated tube?
sorry, i'm going by memory, this is a type 5 tube I thought it was a type 4 tube ( like 2a3's)
300 mA of heater current x 4 tubes = 1.2 A of constant current.
It was told to me if you have a constant current draw out of the transformer, add half of the constant current draw to it to find the minimum current rating.
so in the example above, 1.8A transformer minimum.
2A winding on a big transformer ok
I'd go with a 3A and it would run cool if it is just that winding.
300 mA of heater current x 4 tubes = 1.2 A of constant current.
It was told to me if you have a constant current draw out of the transformer, add half of the constant current draw to it to find the minimum current rating.
so in the example above, 1.8A transformer minimum.
2A winding on a big transformer ok
I'd go with a 3A and it would run cool if it is just that winding.
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There are only 2 tubes, not 4. Although not explicitly stated, it sounds like he has wired the 2 6.3V heaters in series and put them across the 12.6 transformer. Therefore, the total draw on the transformer is 0.3A, or 25% of the rating.
I suspect the heater circuit has been referenced to ground in multiple places, it's a common mistake by learners.
I don't think systematically (or deliberately) gapped power transformers are very common, although I have seen a very, very few. Not necessary at all with full wave rectification.. In the case where a center tapped winding is used to power a dht filament and that tap is part of the cathode current path the cathode current appears common mode across the winding and the dc flux component cancels in the windings which are differentially connected relative to the center tap. (Leaves no net dc on the core.)
Please don't confuse SE output transformers with power transformers as the design criteria are obviously different - an SE opt must deal with a DC quiescent current that is normally considerably greater than the average AC current in the winding.
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