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  #1  
Old 5th December 2017, 10:54 PM
Mark Mark is offline
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Default Help Required to Find a Transformer

Hi,

I am looking for a transformer for a simple 2 valve headphone amp. The spec is 2 x 150V 35mA and 1 x 6.3V 3A secondaries. The Hammond 269BX and 369BX from Mouser are the closest I can find and are £45 and £64 respectively. Three questions :

1 Are Hammond transformers the best value-for-money ?
2 Is it worth paying the extra for the 369BX for the Faraday copper primary shield ?
3 The 6.3V secondary is 2A and I need 3A. Do I need 3A for two heaters in parallel or will 2A be OK ?

Thanks

Mark
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  #2  
Old 6th December 2017, 08:25 AM
snowman_al snowman_al is offline
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Default Re: Help Required to Find a Transformer

Hi,
You cannot use the Hammond 269 in the UK, it only has a 115 volt primary for the US market.
The 369BX has dual primaries and can be configured for 240 volt mains. (Specs: http://www.hammondmfg.com/pdf/EDB369BX.pdf)

To know if 2 amps are enough you need to say what valves and or circuit you are going to use. Or have a look at the heater current specs on line.
Alan
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  #3  
Old 6th December 2017, 02:15 PM
Mark Mark is offline
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Default Re: Help Required to Find a Transformer

Hi,

Thanks for the response.

The valves are 1 x 6080 and 1 x 12AU7/ECC82. The datasheet for a 6080 says 2.5A heater current. The datasheet for a 12AU7 says 300mA heater current using 6.3V. This gives a total of 2.5 + 0.3 = 2.8 A. This exceeds the 2A rating of the transformer for the heater secondary, so it looks like a Hammond 369BX is no good.

I will look around some more. Any pointers would be welcome.

Thanks

Mark
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  #4  
Old 6th December 2017, 11:57 PM
colin.hepburn colin.hepburn is offline
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Default Re: Help Required to Find a Transformer

Hi Mark
Hereís a link to antek in the USA I have a pair of there transformers and they are a good buy others on hear have used then too the problem is you will pay the price of the transformer again in shipping cost to uk
The transformer in the link has a better VA rating than the hammond of a 100VA 150-0-150v [so good plus 3A heater x2
Check the spec sheet near bottom of page
Hope this helps
Colin

http://www.antekinc.com/as-1t150-100...v-transformer/
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  #5  
Old 7th December 2017, 09:32 AM
snowman_al snowman_al is offline
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Default Re: Help Required to Find a Transformer

Mark,
Looks as if there is little choice out there other than the AnTek.
Otherwise you could try Terry at Canterbury Windings and have one made?

If you need a 6080 / 6AS7GA, I have a couple doing nothing. Yours for the cost of postage and a small donation to Marie Curie nurses.

Alan
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  #6  
Old 7th December 2017, 06:26 PM
davebms davebms is online now
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Default Re: Help Required to Find a Transformer

hello all http://www.vt4c.com/shop/program/main.php. if the link works
vt4c make some very good R core,, the EU range have a genuine 240 volt
tap so no over spin on voltage (the web page is large takes long time to load)

dave
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  #7  
Old 8th December 2017, 03:24 PM
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pre65 pre65 is offline
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Default Re: Help Required to Find a Transformer

I use Antek toroids in several of my projects and I find them to be of good quality.
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  #8  
Old 11th December 2017, 11:05 PM
Mark Mark is offline
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Default Re: Help Required to Find a Transformer

Alan,

I suspect Canterbury Windings will be way over £100 which would kill the project.


Colin

The AnTek transformer is $34.50 and USPS is $73.50 using the shipping estimator, total $108, or £81, which is more than the Hammond but not a lot more, so it might work. Is that about what you paid for shipping ?


Colin / Pre65

The problem is unknown customs and VAT. What's your experience with customs and VAT on AnTek transformers please ?

It's a toroid so the chassis would need a re-think. The 'traditional' layout is to put the an EI transformer on the top to keep the stray electormagnetic field outside the box ? Can you put a toroid inside the chassis because of the much lower stray EM field ?

Dave

Thanks for the pointer to the vt4c site. An R core is a good idea. There are plenty on eBay I'm never sure if they are good for UK 230/40, so it's good to see some cited as UK spec. I will have a dig around on the site.

Thanks

Mark
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  #9  
Old 12th December 2017, 05:07 PM
colin.hepburn colin.hepburn is offline
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Default Re: Help Required to Find a Transformer

Hi mark
Yes the TXs I got at different times and were bigger 400VA 720CT and at $57.00 plus the shipping at the time canít remember but not much less than the $73.00 today

No customs and VAT charges but you takes your chances there I think
But buying the equivalent Transformers in the UK will cost you more still
Do you need it to be 300v CT you my get away with 230v using two back to back transformers from rapid or some whare?
So 230v in 230v out plus 1,414= 325v
Can you post details on the amp is it based on this h amp
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  #10  
Old 13th December 2017, 11:34 PM
bikerhifinut bikerhifinut is offline
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Default Re: Help Required to Find a Transformer

Don't know if this idea would help, but here goes....

How about a relatively easy to find 2x75V toroid or possibly an EI job if there are commercial ones out there?
You'd use a bridge rectifier in this case, or if you want to use a valve rectifier you could just wire it as a hybrid.
Then use another transformer for the heaters.
Is this for a HT of 150V? In which case you'd get 150V DC from a 110V secondary using silicon rectifiers, and 55-0-55V transformers are fairly common.

Just a thought.

Andy.
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