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Old 24th January 2012, 01:05 AM   #1
mike567 is offline mike567  United States
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Default Suggestions for 7k output transformers.

I am a looking for a schematic using some cheap output tubes (<$10) for some 7k output transformers.

transformers look like 3~5 watts SE....
power trams 550 vct and 6.3 filament
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Old 24th January 2012, 02:01 AM   #2
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I've seen some single-ended 6BM8/ECL82 schematics with a 7k primary. The Japanese "super triode" ECL82 is one that springs to mind. I've not built that circuit, but I have breadboarded the "Morse's Single Ended" ECL82 schematic found on this forum using 7.5K primary and was impressed enough with the sound to commit it to a chassis.
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Old 24th January 2012, 02:03 AM   #3
rmyauck is offline rmyauck  Canada
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RH84 amp -Said to be well well liked if you google it.

RH 84 - Tube Audio ...... RH DESIGN

I don't think 7K will matter much as some designs as the Decaware ZEN EL84 SE amp is another to look at uses 10K outputs.

Edcor makes good bang for the $ transformers. Even the well regarded Zen uses them.

Just discovered RH has preamp's in google search of rh84 amp

RH 84 - Tube Audio ...... RH DESIGN

Last edited by rmyauck; 24th January 2012 at 02:08 AM.
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Old 24th January 2012, 06:23 AM   #4
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The usual 9W Pentodes use a 7K OPT. ECL86/PCL86 for example. But of course, a pentode can be used with nearly every OPT. EL84 etc. is also possible here.
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Old 24th January 2012, 11:44 AM   #5
mike567 is offline mike567  United States
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thank you all for the fast responses. Bought some iron from ebay and was looking for something easy to build.
I don't have 5 volts availble but can a 12 volt 3 amp rat shack transformer.
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Old 24th January 2012, 03:26 PM   #6
mike567 is offline mike567  United States
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Quote:
Originally Posted by andrew_k View Post
I've seen some single-ended 6BM8/ECL82 schematics with a 7k primary. The Japanese "super triode" ECL82 is one that springs to mind. I've not built that circuit, but I have breadboarded the "Morse's Single Ended" ECL82 schematic found on this forum using 7.5K primary and was impressed enough with the sound to commit it to a chassis.
Do you have a link?
I searched "Morse's Single Ended" with no results
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Old 24th January 2012, 10:53 PM   #7
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Apologies, I thought it would be easy to find. I had the same problem relocating it as you.

Here's the schem:
Click the image to open in full size.

I'm running it triode-connected using 7.5K:8Ω OTs from an epiphone valve junior guitar amp. The little 5W OTs are more than enough iron for this little guy, and triode connected gives me exactly enough power for the speakers I want to use in a small home office environment.
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Old 25th January 2012, 01:47 AM   #8
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Note that Morse's amp is SE Pentodewith no feedback so is going to be a current amplifier so care needs to be taken that the loudspeakers you use are happy with current drive.

From the map i drew that andrew just posted came an RH variation using the (supposedly rare -- i have lots) ECL86.

Click the image to open in full size.

I plan to go ahead with this build, the layout below the scema is for some WE sockets i have that come with attached "tag strip". I haven't had it vetted yet,

Of the greyed out bits, the bypass cap on the output tube is probably a good idea, the screen grid regulation is optional

dave
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File Type: gif ECL86-SE-amp.gif (42.3 KB, 495 views)
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Old 25th January 2012, 12:04 PM   #9
mike567 is offline mike567  United States
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Thanks again!
I am going to see if I can get rid of that big power resistor.
My speakers are rated for about 100 watts max .
I don't listen to stuff very loud any way......neighbors....
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