OPTs of questionable utility

koolatron · 27th February 2008, 03:40 PM

Being the comparative tube newbie (tuwbie?) that I am, I in my zeal for finally figuring things out for myself bought a pair of old telefunken console OPTs off of ebay.

However, this was done at something like 3am, when I wasn't terribly lucid and most certainly shouldn't have been shopping for toys online.

These things are purportedly 12k/4, and were advertised as being acceptable for an EL34 single-ended application. Knowing I had some EL34s kicking around, I pulled the trigger without properly considering that I don't actually have any sort of 4-ohm speakers sitting around to go on the other side of the transformer. So my question to you, dear reader, is what in the world do I do with these? I don't fully understand the process of matching the output stage to the transformer primary (see point #3, below).

Some thing to keep in mind, here:
1- I'm a total tuwbie (totuwbie? God I hope that catches on), but I'm also an EE that knows sort-of what's going on.
2- I've done my best as to due diligence on this before posting. I found some literature on the google, but none of it seemed really authoritative and the explanations seemed aimed slightly above my head.
3- The copy of Jones is in the mail

HollowState · 27th February 2008, 05:44 PM

There was a seller from Germany offering pairs of small open frame Telefunken transformers with these specs. (12K/4) that were said to be used with EL84s....not EL34s. Are these the units you speak of? If so, they probably are not the best match up to your EL34s and they also look a bit under powered.

And I noticed that he claimed to measure the windings with a multimeter to get these numbers. Using this type of meter to measure DC resistance does not relate to the dynamic (AC) impedance. This needs to be done with AC to get the turns ratio and then compute the impedance (N²) or with a bridge measurement. So his numbers may not be correct.

koolatron · 27th February 2008, 05:54 PM

My mistake. That's what I get for trusting my hazy recollection of this happening in the first place. The transformers in question are indeed the ones of which you speak; apparently intended for operation in an EL84 or EL95 SE configuration. Thankfully, I also believe I've got EL84s kicking around.

12k/4 seems like an awfully odd number. But what do I know? NOTHING! That's what.

Since this'd be my first from-scratch project, I'm quite alright with building something on the low end, with regards to power. I have some reasonably sensitive speakers, and huge numbers of amps and volts flying all about the place quite frankly scare the bajeezus out of me.

HollowState · 27th February 2008, 06:24 PM

Ok, if you use these with EL84s (6BQ5s) you'll be fine since that's what they were originally used with. Output tubes have a range of load inpedances they will work into. Somewhere between 8K to 10K is typical for this number, but 12K (if that's what they actually are) is close enough for audio. And a proper measurment may prove them to be a little lower.

Victor

Ty_Bower · 29th February 2008, 12:23 AM

If you have some EL84 tubes, and some single ended output transformers designed for EL84 in the mail, I'd take some time and read this thread:
EL84 SE design recommendations?

The RH84 looks especially promising.

koolatron · 29th February 2008, 02:43 AM

Thanks! I'm *assuming* they're in the mail. I paid for 'em.

planet10 · 29th February 2008, 04:21 AM

Can you post a picture?

10 or 12K to 4 was often used -- EL84s usually like less, EL95s more.

Most of these are quite decent -- especially for a bass limited application.

I'm currently runnin RH84 variants based on 2 grundig consoles.

dave

koolatron · 29th February 2008, 04:32 PM

I'll post pictures as soon as I get them in the post. As they're coming from Germany, and I only paid for them a few days ago, it might be a while. The transformers themselves looked quite decent in the auction picture. Much nicer, at any rate, than anything I've pulled from equipment of similar age.

I think I'll be trying the RH84, since I have most of what's required to make it go. Hooray, learning!

planet10 · 29th February 2008, 04:43 PM

Quote:

Originally posted by koolatron
The transformers themselves looked quite decent in the auction picture.

Got a link to the auction?

dave

koolatron · 29th February 2008, 06:20 PM

http://cgi.ebay.com/ws/eBayISAPI.dll...m=270213577624

Like I said, probably overpaid. Clean, though.

27th February 2008, 03:40 PM	#1
koolatron diyAudio Member Join Date: Jul 2006	OPTs of questionable utility Being the comparative tube newbie (tuwbie?) that I am, I in my zeal for finally figuring things out for myself bought a pair of old telefunken console OPTs off of ebay. However, this was done at something like 3am, when I wasn't terribly lucid and most certainly shouldn't have been shopping for toys online. These things are purportedly 12k/4, and were advertised as being acceptable for an EL34 single-ended application. Knowing I had some EL34s kicking around, I pulled the trigger without properly considering that I don't actually have any sort of 4-ohm speakers sitting around to go on the other side of the transformer. So my question to you, dear reader, is what in the world do I do with these? I don't fully understand the process of matching the output stage to the transformer primary (see point #3, below). Some thing to keep in mind, here: 1- I'm a total tuwbie (totuwbie? God I hope that catches on), but I'm also an EE that knows sort-of what's going on. 2- I've done my best as to due diligence on this before posting. I found some literature on the google, but none of it seemed really authoritative and the explanations seemed aimed slightly above my head. 3- The copy of Jones is in the mail

27th February 2008, 05:44 PM	#2
HollowState diyAudio Member Join Date: Aug 2006 Location: Taxland, New Jersey	There was a seller from Germany offering pairs of small open frame Telefunken transformers with these specs. (12K/4) that were said to be used with EL84s....not EL34s. Are these the units you speak of? If so, they probably are not the best match up to your EL34s and they also look a bit under powered. And I noticed that he claimed to measure the windings with a multimeter to get these numbers. Using this type of meter to measure DC resistance does not relate to the dynamic (AC) impedance. This needs to be done with AC to get the turns ratio and then compute the impedance (N²) or with a bridge measurement. So his numbers may not be correct. __________________ "The supercomputer is technologically impossible. It would take all of the water that flows over Niagara Falls to cool the heat generated by the number of vacuum tubes required." ~ Professor of Electrical Engineering, New York University

27th February 2008, 06:24 PM	#4
HollowState diyAudio Member Join Date: Aug 2006 Location: Taxland, New Jersey	Ok, if you use these with EL84s (6BQ5s) you'll be fine since that's what they were originally used with. Output tubes have a range of load inpedances they will work into. Somewhere between 8K to 10K is typical for this number, but 12K (if that's what they actually are) is close enough for audio. And a proper measurment may prove them to be a little lower. Victor __________________ "The supercomputer is technologically impossible. It would take all of the water that flows over Niagara Falls to cool the heat generated by the number of vacuum tubes required." ~ Professor of Electrical Engineering, New York University

29th February 2008, 04:21 AM	#7
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	Can you post a picture? 10 or 12K to 4 was often used -- EL84s usually like less, EL95s more. Most of these are quite decent -- especially for a bass limited application. I'm currently runnin RH84 variants based on 2 grundig consoles. dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

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27th February 2008, 05:54 PM	#3
koolatron diyAudio Member Join Date: Jul 2006	My mistake. That's what I get for trusting my hazy recollection of this happening in the first place. The transformers in question are indeed the ones of which you speak; apparently intended for operation in an EL84 or EL95 SE configuration. Thankfully, I also believe I've got EL84s kicking around. 12k/4 seems like an awfully odd number. But what do I know? NOTHING! That's what. Since this'd be my first from-scratch project, I'm quite alright with building something on the low end, with regards to power. I have some reasonably sensitive speakers, and huge numbers of amps and volts flying all about the place quite frankly scare the bajeezus out of me.

29th February 2008, 12:23 AM	#5
Ty_Bower diyAudio Member Join Date: Mar 2007 Location: Newark, DE	If you have some EL84 tubes, and some single ended output transformers designed for EL84 in the mail, I'd take some time and read this thread: EL84 SE design recommendations? The RH84 looks especially promising.

29th February 2008, 02:43 AM	#6
koolatron diyAudio Member Join Date: Jul 2006	Thanks! I'm assuming they're in the mail. I paid for 'em.

29th February 2008, 04:32 PM	#8
koolatron diyAudio Member Join Date: Jul 2006	I'll post pictures as soon as I get them in the post. As they're coming from Germany, and I only paid for them a few days ago, it might be a while. The transformers themselves looked quite decent in the auction picture. Much nicer, at any rate, than anything I've pulled from equipment of similar age. I think I'll be trying the RH84, since I have most of what's required to make it go. Hooray, learning!

29th February 2008, 06:20 PM	#10
koolatron diyAudio Member Join Date: Jul 2006	http://cgi.ebay.com/ws/eBayISAPI.dll...m=270213577624 Like I said, probably overpaid. Clean, though.

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