What type of audio transformers to use for tubes / valves

sco1t · 3rd April 2010, 05:38 PM

Hiya all, i've made a amplifier useing a pcl84 valve useing this plan

http://www.diyaudio.com/forums/attac...4&d=1152603590
and it goes pretty loud

and sounds really good

but i don't have a proper audio transformer so i'm useing a mains transformer insted that only works well with 16 ohm speakers

I was wondering if one of these transfomers would work well. what do you think???
--|P037T|100V TRANSFORMER 8W | CPC

600-OHM INPUT AUDIO TRANSFORMER FOR R390 R390A RECEIVER on eBay (end time 03-May-10 14:18:26 BST)

Thanks for looking

Salas · 3rd April 2010, 06:01 PM

First one is for commercial sound speakers tapping off 100V lines. Each roof or wall speaker in large buildings has one inside. Bad quality, mainly for the vocal range. Primary voltage I don't think they can take safely over 100V.

The second one is milspec. Very low primary impedance. I don't see the circuit for your link.

sco1t · 3rd April 2010, 06:39 PM

Hi, thanks for the help

and oops. this is the circuit i used.
http://www.diyaudio.com/forums/attac...udio-ecl84.jpg (if this link works)

Salas · 3rd April 2010, 07:14 PM

Save some Quid for a proper one at a point. SE needs a good core and a gap. I don't think proper quality goes much lower than this example though. Can be cheaper for less mA maybe.

rotaspec · 3rd April 2010, 07:37 PM

Do a search on output transformer. This is what I spotted, and it would be fine for your amp when used with an 8 ohm speaker:
1 OUTPUT TRANSFORMER 5.6 K - 4 OHM 3.5 WATT 6V6 on eBay (end time 05-Apr-10 13:19:05 BST)

rotaspec · 3rd April 2010, 07:39 PM

Or find someone who restores old valve radios, and talk them into letting you have an output transformer (I'll bet the one in the auction comes from a radio)

sco1t · 3rd April 2010, 08:27 PM

Hi thanks Salsa and Rotaspec for the tips and help.
I'm new to valve amplifiers

. You know on the pri side of the audio transformers they seem to have about 2000-5000 ohms. does that mean if i mesuerd it with a ohm meter the ohm meter would read the same????? E.g A output transformer saying 5k would read 5k on a ohm meter????

anatech · 3rd April 2010, 09:04 PM

Hi sco1t,
No, it wouldn't.
Transformers and things like speakers are measured for an AC impedance, not a DC resistance. Normally the impedance is rated in mid-band. If you were to measure the resistance of a speaker, it would only be about 75% of the rated Impedance of the speaker.

For instance, a power transformer may only have a resistance of a few ohms. Yet if you calculate how much current it would draw connected to the AC mains, it's clear that the working impedance must be a lot higher (it is).

Instruments that measure inductance, capacitance and impedance (an LCR meter or impedance bridge) use an AC voltage or current to develop a voltage drop across the component. They calculate the impedance from that. Often the test frequency has several values to cover a larger range.

-Chris

Tekko · 3rd April 2010, 09:12 PM

Edcor make good audio transformers to resanable prices.

jrenkin · 3rd April 2010, 09:16 PM

Maybe this helps? It describes how to determine the output impedance of your OPT.

Output Transformer Impedance

3rd April 2010, 05:38 PM	#1
sco1t diyAudio Member Join Date: Mar 2010 Location: Northeat England	What type of audio transformers to use for tubes / valves Hiya all, i've made a amplifier useing a pcl84 valve useing this plan http://www.diyaudio.com/forums/attac...4&d=1152603590 and it goes pretty loud and sounds really good but i don't have a proper audio transformer so i'm useing a mains transformer insted that only works well with 16 ohm speakers I was wondering if one of these transfomers would work well. what do you think??? --\|P037T\|100V TRANSFORMER 8W \| CPC 600-OHM INPUT AUDIO TRANSFORMER FOR R390 R390A RECEIVER on eBay (end time 03-May-10 14:18:26 BST) Thanks for looking

3rd April 2010, 09:04 PM	#8
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi sco1t, No, it wouldn't. Transformers and things like speakers are measured for an AC impedance, not a DC resistance. Normally the impedance is rated in mid-band. If you were to measure the resistance of a speaker, it would only be about 75% of the rated Impedance of the speaker. For instance, a power transformer may only have a resistance of a few ohms. Yet if you calculate how much current it would draw connected to the AC mains, it's clear that the working impedance must be a lot higher (it is). Instruments that measure inductance, capacitance and impedance (an LCR meter or impedance bridge) use an AC voltage or current to develop a voltage drop across the component. They calculate the impedance from that. Often the test frequency has several values to cover a larger range. -Chris __________________ "Just because you can, doesn't mean you should" © my Wife

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
Testing valves/tubes	Joe of Loath	Tubes / Valves	4	18th January 2010 06:53 PM
CCS for tubes/valves: PCBs	SY	Tubes / Valves	340	20th October 2009 02:43 AM
Techtube valves/tubes	geoff4valves	Tubes / Valves	10	21st October 2008 05:01 PM
10,000+ AUDIO Type tubes for sale or trade	DrRick	Swap Meet	25	20th June 2008 06:39 PM
Valves-tubes-mosfets-	Graeme	Tubes / Valves	0	21st February 2002 04:47 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

3rd April 2010, 06:01 PM	#2
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	First one is for commercial sound speakers tapping off 100V lines. Each roof or wall speaker in large buildings has one inside. Bad quality, mainly for the vocal range. Primary voltage I don't think they can take safely over 100V. The second one is milspec. Very low primary impedance. I don't see the circuit for your link.

3rd April 2010, 06:39 PM	#3
sco1t diyAudio Member Join Date: Mar 2010 Location: Northeat England	Hi, thanks for the help and oops. this is the circuit i used. http://www.diyaudio.com/forums/attac...udio-ecl84.jpg (if this link works)

3rd April 2010, 07:14 PM	#4
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Save some Quid for a proper one at a point. SE needs a good core and a gap. I don't think proper quality goes much lower than this example though. Can be cheaper for less mA maybe.

3rd April 2010, 07:37 PM	#5
rotaspec diyAudio Member Join Date: Nov 2007	Do a search on output transformer. This is what I spotted, and it would be fine for your amp when used with an 8 ohm speaker: 1 OUTPUT TRANSFORMER 5.6 K - 4 OHM 3.5 WATT 6V6 on eBay (end time 05-Apr-10 13:19:05 BST)

3rd April 2010, 07:39 PM	#6
rotaspec diyAudio Member Join Date: Nov 2007	Or find someone who restores old valve radios, and talk them into letting you have an output transformer (I'll bet the one in the auction comes from a radio)

3rd April 2010, 08:27 PM	#7
sco1t diyAudio Member Join Date: Mar 2010 Location: Northeat England	Hi thanks Salsa and Rotaspec for the tips and help. I'm new to valve amplifiers . You know on the pri side of the audio transformers they seem to have about 2000-5000 ohms. does that mean if i mesuerd it with a ohm meter the ohm meter would read the same????? E.g A output transformer saying 5k would read 5k on a ohm meter????

3rd April 2010, 09:12 PM	#9
Tekko diyAudio Member Join Date: Jan 2005	Edcor make good audio transformers to resanable prices.

3rd April 2010, 09:16 PM	#10
jrenkin diyAudio Member Join Date: Nov 2007 Location: Denver, Colorado	Maybe this helps? It describes how to determine the output impedance of your OPT. Output Transformer Impedance

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)