What tube do you think this OPT matches?

leadbelly · 28th January 2006, 02:40 PM

After reading the other thread on the $17 Edcor OPT, I started looking at this one:
http://www.edcorusa.com/classx/tube_...e25-8-7_6K.htm
Their $27 25W 7.6K SE model. I'm not exactly sure which power tube it is geared towards. I emailed them but didn't get a response yet. I looked at some tube datasheets and searched a bit, but I'm not sure. 8K primary impedance matches with EL84/6V6, but 25W is largely oversized. Of the common power tubes in the 25-ish Watt range it looked like maybe the KT66 came closest.

anatech · 28th January 2006, 02:49 PM

Hi leadbelly,
A single ended 6L6 family tube should give you about 8W in that mode. You do want to oversize the core. I imagine it's even more important to do that with SE amps than it is with P-P types.

-Chris

andyjevans · 28th January 2006, 04:50 PM

Maybe a low power 845?

leadbelly · 28th January 2006, 09:14 PM

I did get a reply: "We don't specify tubes, we leave that up to the experts."

Sort of a comical response, as a new product doesn't arise from primordial sludge. Either Edcor came up with an application on their own, it's meant to compete with another company's specific product, or it's an OEM for a commercial amp. Hmmm.

tubelab.com · 29th January 2006, 02:45 AM

I ordered the cheap SE transformers, and will test them when they show up. When I called them, the person who answered the phone just did sales. She said that no technical people were available and could not tell me the primary inductance or the maximum working voltage.

If this transformer works out (as good as a 125CSE) I will try the larger ones. I believe their wattage ratings might be inflated. Look through the entire catalog and compare transformer size and power to other manufacturers.

Im thinking the 16 ohm version of the 25 watt transformer would present a 3.8K ohm load to the tube with an 8ohm speaker. About right for a 300B or triode wired swep tube.

leadbelly · 29th January 2006, 04:04 AM

I'm planning to buy a couple of the 25W versions. I did think of buying the 16 ohm versions and using a tube suited to 3.8K load. I did a bit more searching and I think I'm right about the KT66 being suited to the 7.6K primary, since I found that Marshall JTM45's paired KT66's with 8K primaries.

richwalters · 29th January 2006, 08:02 AM

Looking at the frequency response......that core looks a bit slack in the low end.
Looking at the 100W p-p core, one notices "hand stacked" cores. It seems doubtful unless someone is paid nominally to do such a boring task and mistakes can be made. A machine can do it much more consistently. The rest is commercial flannel which all manufacturers write. What I would be looking for are the parasitic values of each winding and they don't display them while others do.

Presently I don't have much flavour with US made products without being ripped off or poor quality sent for export.

richj

28th January 2006, 02:40 PM	#1
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	What tube do you think this OPT matches? After reading the other thread on the $17 Edcor OPT, I started looking at this one: http://www.edcorusa.com/classx/tube_...e25-8-7_6K.htm Their $27 25W 7.6K SE model. I'm not exactly sure which power tube it is geared towards. I emailed them but didn't get a response yet. I looked at some tube datasheets and searched a bit, but I'm not sure. 8K primary impedance matches with EL84/6V6, but 25W is largely oversized. Of the common power tubes in the 25-ish Watt range it looked like maybe the KT66 came closest. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

28th January 2006, 09:14 PM	#4
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	I did get a reply: "We don't specify tubes, we leave that up to the experts." Sort of a comical response, as a new product doesn't arise from primordial sludge. Either Edcor came up with an application on their own, it's meant to compete with another company's specific product, or it's an OEM for a commercial amp. Hmmm. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

29th January 2006, 02:45 AM	#5
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	I ordered the cheap SE transformers, and will test them when they show up. When I called them, the person who answered the phone just did sales. She said that no technical people were available and could not tell me the primary inductance or the maximum working voltage. If this transformer works out (as good as a 125CSE) I will try the larger ones. I believe their wattage ratings might be inflated. Look through the entire catalog and compare transformer size and power to other manufacturers. Im thinking the 16 ohm version of the 25 watt transformer would present a 3.8K ohm load to the tube with an 8ohm speaker. About right for a 300B or triode wired swep tube. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

29th January 2006, 04:04 AM	#6
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	I'm planning to buy a couple of the 25W versions. I did think of buying the 16 ohm versions and using a tube suited to 3.8K load. I did a bit more searching and I think I'm right about the KT66 being suited to the 7.6K primary, since I found that Marshall JTM45's paired KT66's with 8K primaries. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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28th January 2006, 02:49 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi leadbelly, A single ended 6L6 family tube should give you about 8W in that mode. You do want to oversize the core. I imagine it's even more important to do that with SE amps than it is with P-P types. -Chris

28th January 2006, 04:50 PM	#3
andyjevans diyAudio Member Join Date: Sep 2003 Location: London	Maybe a low power 845?

29th January 2006, 08:02 AM	#7
richwalters diyAudio Member Join Date: Sep 2003 Location: Alps:Tube amp designs over 150W, SMPS guru.	Looking at the frequency response......that core looks a bit slack in the low end. Looking at the 100W p-p core, one notices "hand stacked" cores. It seems doubtful unless someone is paid nominally to do such a boring task and mistakes can be made. A machine can do it much more consistently. The rest is commercial flannel which all manufacturers write. What I would be looking for are the parasitic values of each winding and they don't display them while others do. Presently I don't have much flavour with US made products without being ripped off or poor quality sent for export. richj

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