step-up travel transformer for small preamp?

aletheian · 26th March 2006, 06:13 AM

I have seen those small 50 watt 120v to 240v transformers floating around, and I have often wondered if that sould be used to power the B+ of a small preamp. 240v*10mA=less than 3 watts, so I dont see why power-wise it would not work. I don't know if they are current-isolated from the mains, but I was hoping someone here might have some more info.

aletheian · 26th March 2006, 06:15 AM

Something like this:

Shoog · 26th March 2006, 10:16 AM

They are usually autotransformers so not suitable.
Check for continuity between the 110V tap and the 240V tap.

Shoog

lndm · 26th March 2006, 10:17 AM

Is that a conventional power xfmr? I used to use something that small for a bias supply.

I guess it would be OK for class A duty. The steady current requirement (especially if used for a class A preamp) would draw little problem from the potentially bad load regulation characteristic of the xfmr. I would probably want a substantial filter capacitance and only ask a few mA from it.

aletheian · 26th March 2006, 06:04 PM

Quote:

Originally posted by lndm
Is that a conventional power xfmr? I used to use something that small for a bias supply.

I guess it would be OK for class A duty. The steady current requirement (especially if used for a class A preamp) would draw little problem from the potentially bad load regulation characteristic of the xfmr. I would probably want a substantial filter capacitance and only ask a few mA from it.

That is what I figured. I am thinking of experimenting with one running a single 12ax7 tube for the preamp and a 12au7 output buffer, so I would not be drawing more than half a dozen milliamps.

I have seen a few advertised as "isolated" so I suppose they would work.. maybe I'll get a few and see which are autotransformers and which ARE actually isolated.

I usually like to run regulated voltage in my preamps anyway, so I am not overly concerned with poor tranny regulation.

tubelab.com · 27th March 2006, 12:40 AM

I have found that the cheapest way to get 240VAC is a Triad N-68X. $11.20 at Mouser and it is good for 50 watts. It has 2 115 volt primaries and 1 115 volt secondary. Turn it around (use the secondary as a primary) and you have a 230 volt center tapped secondary. with a FWB rectifier I get almost 300 volts DC at over 100 mA. They also have a 6.3 VAC 3 amp filament transformer (41FD030) for $6.98.

So you have the power supply iron for $18. With the Edcor $18 output transformers I have all of the iron for a good sounding SE UL amp for $54!

aletheian · 27th March 2006, 05:53 AM

Quote:

Originally posted by tubelab.com
I have found that the cheapest way to get 240VAC is a Triad N-68X. $11.20 at Mouser and it is good for 50 watts. It has 2 115 volt primaries and 1 115 volt secondary. Turn it around (use the secondary as a primary) and you have a 230 volt center tapped secondary. with a FWB rectifier I get almost 300 volts DC at over 100 mA. They also have a 6.3 VAC 3 amp filament transformer (41FD030) for $6.98.

So you have the power supply iron for $18. With the Edcor $18 output transformers I have all of the iron for a good sounding SE UL amp for $54!

that's a great tip. Thanx. I have to do a Dale resistor order @ Mouser anyway, so I may as well toss one of those on.

26th March 2006, 06:13 AM	#1
aletheian diyAudio Member Join Date: Apr 2004 Location: Philly	step-up travel transformer for small preamp? I have seen those small 50 watt 120v to 240v transformers floating around, and I have often wondered if that sould be used to power the B+ of a small preamp. 240v*10mA=less than 3 watts, so I dont see why power-wise it would not work. I don't know if they are current-isolated from the mains, but I was hoping someone here might have some more info. __________________ Heghlu'meH QaQ jajvam!

27th March 2006, 12:40 AM	#6
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	I have found that the cheapest way to get 240VAC is a Triad N-68X. $11.20 at Mouser and it is good for 50 watts. It has 2 115 volt primaries and 1 115 volt secondary. Turn it around (use the secondary as a primary) and you have a 230 volt center tapped secondary. with a FWB rectifier I get almost 300 volts DC at over 100 mA. They also have a 6.3 VAC 3 amp filament transformer (41FD030) for $6.98. So you have the power supply iron for $18. With the Edcor $18 output transformers I have all of the iron for a good sounding SE UL amp for $54! __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
DIY step down transformer	rhapsodee	Parts	4	24th May 2009 03:16 AM
Low-end small portable speakers for travel - build or buy?	larry_long	Full Range	11	30th December 2008 02:52 AM
Step Down Transformer	Ropie	Power Supplies	3	15th October 2006 09:42 AM
Can I use a step-up transformer as step-up?	cviller	Parts	5	6th September 2006 06:32 PM
help design SE preamp with mosfet buffer and step-up transformer.	AudioGeek	Solid State	0	19th January 2005 03:02 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

26th March 2006, 10:16 AM	#3
Shoog diyAudio Member Join Date: Aug 2002 Location: Eire	They are usually autotransformers so not suitable. Check for continuity between the 110V tap and the 240V tap. Shoog

26th March 2006, 10:17 AM	#4
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Is that a conventional power xfmr? I used to use something that small for a bias supply. I guess it would be OK for class A duty. The steady current requirement (especially if used for a class A preamp) would draw little problem from the potentially bad load regulation characteristic of the xfmr. I would probably want a substantial filter capacitance and only ask a few mA from it.