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Old 11th March 2007, 10:45 AM   #1
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Default transformer questions

Problem: getting the likes of a hammond PX to me costs a fortune. Talking $100 for the PX and at least another $50 for shipping and thats assuming you can get one with 230V primary (or 115-0-115)


Possible solution: Use 2 separate traffos:

Use 63VA 230V primary 230V sec to give B+. Use voltage doubler to get higher voltage.

Use 100VA 230V primary 9V sec for heaters. Use SS rectification with CRC (or even a regulator) to get it down to 6-6.3V (or similar traffo except with 12V or 15V sec where 12V heaters are needed) Ratings give this TX as around 5A IIRC.

Could also use third traffo for 5V heater for tube rectification if you want.

Total cost for all 3 transformers is about $75.

What am I missing here?


Fran
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Old 11th March 2007, 12:01 PM   #2
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Default Re: transformer questions

Quote:
Originally posted by woodturner-fran
What am I missing here?
Nothing except convenience.

I think separate heater and B+ transformers are a great idea. Besides adding the ability to easily power up the heaters without B+, you also are better able to keep diode switching noise out of your heater circuit.

Except for the fact that you need to deal with two or three transformers, it's a wonderful thing.

-- Dave
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Old 11th March 2007, 10:35 PM   #3
kevinkr is offline kevinkr  United States
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Hammond 300 series have primaries that can be configured for any voltage from 100V - 250V.. I would suspect that someone probably stocks these somewhere in Europe/UK for considerably less than it would cost to ship from the US or Canada.

Also there are vendors in the UK like Sowter that make great transformers to order. There are also several German vendors that specialize in this market, although I have no names to hand..
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Old 11th March 2007, 10:51 PM   #4
brianco is offline brianco  Ireland
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Quote:
Originally posted by kevinkr
Hammond 300 series have primaries that can be configured for any voltage from 100V - 250V.. I would suspect that someone probably stocks these somewhere in Europe/UK for considerably less than it would cost to ship from the US or Canada.

Also there are vendors in the UK like Sowter that make great transformers to order. There are also several German vendors that specialize in this market, although I have no names to hand..
You are right...Hammond have a very helpful company in S.England. You will find it on Google.

Sowter - check them on Google - have a big range of off- the- shelf Tx. Something for virtually any audio application.

Brianco
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Old 11th March 2007, 10:52 PM   #5
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I get my power transformers custom wound at a local shop, it's far more convenient and about the same price (or less, at least here) as Hammond transformers. Besides, I get to specify all the voltages myself instead of choosing a specific model (which may not suit my needs).
I'm sure there are some transformer companies in Ireland that can do this for you... there are at least 5 - 6 here in Norway, and luckily two of them are in the same town as me
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Old 12th March 2007, 12:39 AM   #6
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OK, thanks to all. I'll check out the yellow pages for manufacturers.

I'll also look up sowter and I saw a few references to allied transformers too - I'll check them.

You'd think the postage from the UK to Ireland would be reasonable - but its not! Costs just as much as if it were coming from the USA. Only thing is that there are no import duties/taxes to worry about if it comes from the EU.


Fran
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Old 12th March 2007, 09:13 AM   #7
EspenE is offline EspenE  Norway
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Quote:
Originally posted by showdown
I get my power transformers custom wound at a local shop, it's far more convenient and about the same price......

Hi, showdown. I live in Norway too. Can you recommend one or two transformer shops for me?

Thanks, Espen
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Old 12th March 2007, 09:48 AM   #8
ulibub is offline ulibub  France
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Hi kevinkr

Quote:
Originally posted by kevinkr
Also there are vendors in the UK like Sowter that make great transformers to order. There are also several German vendors that specialize in this market, although I have no names to hand..
yes, I can recommend Sowter from own experience, I have had wound several trafos there over the years. They offer a perfect service (you can place your orders on a web form on their home page) and quality, but I also found them to be quite expensive.

In Germany I can recommend Experience Electronics, Mr. Haas (www.experience-electronics.de) where I have had wound several custom made trafos, too. Also very recommendable, also home page in English. They widely use MD-cores, which are quite close in their performance to toroidals and allow for conspicously smaller trafos than with ordinary EI cores.

The other one is Mr. Reinhöfer of www.roehrentechnik.de who also offers custom winding service. Have no experience with him, but he is very much endorsed in many amateur projects on a german tube forum (www.jogis-roehrenbude.de).

There are still several others, but I don't have their names present acutally

Uli
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Old 12th March 2007, 05:12 PM   #9
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Quote:
Originally posted by EspenE

Hi, showdown. I live in Norway too. Can you recommend one or two transformer shops for me?

Thanks, Espen
Vi tar det på engelsk :
I get my transformers from SEKO or Lanne here i Stavanger. Noratel in Hamar can also make transformers to order, including toroids.
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Old 12th March 2007, 09:09 PM   #10
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OK, here are some results:

Sowter, jeez they better be making those TX from gold cos they cost a fortune! STG£140 plus VAT (17%) that must equate to >$300!

So thats not an option. I rang one transformer maker here today but it was too small for them to do (ie industrial winder) I'll try some more soon.

So its still looking like going the route of 3 separate Tx.

2 more Qs:

I've been reading MJs valve amplifiers and he reckons that a 230V secondary rectified (SS bridge) will give approx 325V. After regulator etc, that could end up at about 285VDC as B+. Will this be OK for your EL84 PP amp eg red light district?

If the answer to the above is no, then could I get a Tx with 0-230V primary and 110-0-110 secondary but connect it in reverse. (bearing in mind this would only be for B+ so current demand would be low)

Thanks,

Fran
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