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Motorboating---Help Please!!
Motorboating---Help Please!!
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Old 17th September 2020, 09:58 PM   #1
Qpiter is offline Qpiter  United States
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Default Motorboating---Help Please!!

I built Leak TL/50 Plus from scratch ,point to point. The only thing I changed
is the layout: Kt88, EF86, 12ax7 KT88 in that order. All voltages appears fine.
The amp is playing wonderful untill I connect the Feedback. Then it started motorboating at a rapid pace. OK I know for sure that is connected right. It's
Edor transformer and it was in another amp. I tried many resistor but it only
stop if I use like 1 or 2 megs.
OK, I am a dilettante and I am working with only a mulitimeter. Any help or
suggestions will be appreciated.http://44bx.com/leak/Leak/Circuits/tl50_ecc83.JPG
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Old 17th September 2020, 10:13 PM   #2
audiowize is offline audiowize  United States
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Motorboating---Help Please!! Send a message via AIM to audiowize
Switch the secondary connections around and try it that way just to be sure.
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Old 17th September 2020, 10:13 PM   #3
rayma is online now rayma  United States
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The primary of the output transformer could be wired wrong; that is,
the upper tube to the lower taps, and the lower tube to the upper taps.
No doubt the secondary is wired ok though.

Last edited by rayma; 17th September 2020 at 10:17 PM.
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Old 17th September 2020, 10:24 PM   #4
Ryssen is offline Ryssen  Sweden
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Location: Sweden--> Here
I just had this problem on a kt77 P-P amp.
I switched the polarity on the secondare and it was solved.
Try it.
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Regards ke
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Old 17th September 2020, 10:25 PM   #5
rayma is online now rayma  United States
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The secondary has an 8 ohm tap and is not symmetrical. It would be symmetrical if there were
only 4 and 16 ohm taps. Here it is not appropriate to switch the 0 and 16 ohm secondary connections.

As an alternative to rewiring the output transformer primary, instead you could exchange the driver
connections to the grids of the output tubes.

Last edited by rayma; 17th September 2020 at 10:37 PM.
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Old 18th September 2020, 01:18 AM   #6
Qpiter is offline Qpiter  United States
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Wow! I am so happy. I don't know if you guys understand how valuable your help is;how
much it is appreciated. Rayma, your are the champ! I did exactly as you stated and there
is no more motorboating. How sweet it is not to hear it.Thank you, thank you and thank
you a million times.
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