Edcor OPT in S5 Electronics K-16LS kit? - diyAudio
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Old 4th May 2008, 09:25 PM   #1
123rmp is offline 123rmp  United States
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Default Edcor OPT in S5 Electronics K-16LS kit?

At the advice of on of the forum members I have ordered two Edcor CXPP25-8-5K output transformers and hope to use them in my kit.

I do need to ask question though and I ask it simply to assure myself. Given the specs of the Edcor transformer, which are:

Pri. Watts: 25W
Plate (Z): 5,000 ohms
Sec. (Z): 8 ohms
Screen Voltage: 40%

Can I simply swap out the OPTs or do I need to do some mods to adapt the amp to receive them? Likely I did not give enough data here; of so let me know what other data I need to give you. I can provide the kit schematic if that helps. My skills just are not up to the level that know this.

Many thanks for any help.
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Old 5th May 2008, 02:08 AM   #2
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Hi,

It uses 2 x 6005 tubes in PP parallel. You need the 2500 ohm primary transformers. Probably why they spec that amp at 4 ohms (5000:8 loaded with 4 = 2500 primary). They should work fine.

Cheers!
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Old 5th May 2008, 02:17 AM   #3
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I see no reason why you can't use the Edcors without modifications as long as you do not use the screen taps. If the amp uses feedback form the speaker secondary, then you might have to adjust the feedback resistor since the Edcors are 8 ohm instead of 4 ohm like the originals. If you desire to use the screen taps an make the amp into an ultra-linear, then other modifications will be necesssary. Perhaps a schematic might help.
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Old 5th May 2008, 03:42 PM   #4
123rmp is offline 123rmp  United States
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Thanks guys. Your reassurance is most appreciated.

I am pretty certian that this is not configured to provide feedback (that's ultra-linear mode, right?). I would be interested for understanding how I might do this for a future modification.

If you have suggestions as to the modifications necessary for the ultra-linear conversion, I would welcome those. Oherwise I plan to drop in the new Edcor OPTs for now.

So you can 1) validate my believe that feedback is not used and 2) provide some suggestions on the future conversion to ultra-linear mode I am providing the schematic.

My scanner is not working so I took a quick pic of the schematic. Hope it is readable.

Thanks Again!
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File Type: jpg k-16ls - schematic.jpg (89.3 KB, 3117 views)
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Old 5th May 2008, 04:41 PM   #5
kevinkr is offline kevinkr  United States
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Feedback is used, take a look at the connection from the secondary of the output transformer back to the cathode of the input voltage amplifier - that is global feedback. Given the moderate loop gain and the high closed loop gain it appears that the amount of global feedback is quite limited. (Without a thorough analysis it is hard to guess, but I would be surprised if was over 6dB.)

Ultralinear connection would just connect the screens to taps on the output transformer primary, and is a form of feedback local to the output stage. It's worth trying, but expect to do a little work to make it stable, which may also be the case with the new Edcor transformers you've purchased.
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Old 5th May 2008, 04:46 PM   #6
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That amp makes me cringe at what it will do to prices of 6AQ5s... I only see PPP as an option if it's already with the biggest tubes available (commercial audio tubes, that is), why not just use a bigger stinkin' tube? (or at least 6V6s which are widely manufactured)
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Old 5th May 2008, 06:24 PM   #7
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Quote:
Originally posted by Boris_The_Blade
That amp makes me cringe at what it will do to prices of 6AQ5s...

I'm not worried...I think that there were a hell of a lot more 6AQ5s made than the 11BM8, 11MS8, 10GV8 that S5 previously used. They're $4-6 at Antique Electronic supply (and the 5AQ5 and 12AQ5 are half that...)

I have about 250 used ones, so I've been considering building a PPP amp myself...
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Old 5th May 2008, 06:43 PM   #8
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Quote:
Originally posted by Tom Bavis
I'm not worried...I think that there were a hell of a lot more 6AQ5s made than the 11BM8, 11MS8, 10GV8 that S5 previously used.
But I never had any interest in those tubes

Quote:
Originally posted by Tom Bavis
I have about 250 used ones, so I've been considering building a PPP amp myself...
As did I at one point (I have maybe 20 of them), but got quickly distracted on other projects. I think I may throw a small office amp together with simple PP pairs and some cheapie line transformers.
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Old 5th May 2008, 10:34 PM   #9
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Hi,

Quote:
Originally posted by Boris_The_Blade
....why not just use a bigger stinkin' tube? (or at least 6V6s which are widely manufactured)
The 6005 is considered by many a "plinker" and can be had by the truckfull for really, really cheap. Probably what S5 did, "fill the pickup"

Cheers!
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Old 12th May 2008, 02:26 AM   #10
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Default edcor pwr trans for k16

Greetings: If you ever wanted to upgrade the pwr. transformer, Edcor has it on file already; therefore, you will not have to pay the 20$ setup fee like I did.
The specs are:

Dual 120 Primary
Sec red= 180 V, 0.2 A
Sec yellow=12.6 V 4A White/yellow CT
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