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Fender Twin Reverb SF135 Distorted
Fender Twin Reverb SF135 Distorted
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Old 20th March 2020, 01:26 PM   #11
Carlosraj is offline Carlosraj  United Kingdom
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Quote:
Originally Posted by Enzo View Post
The Hammond data sheet is clearly a typo.

Your amp was working before, why would we decide the wiring needs to be changed now?

One of my scopes long ago all of a sudden got to a real fuzzy image. I ordered up the manual, and read over the circuit, trying to decide what must be bad with the focus circuit. Ince I actually opened it up and looked, I saw the third anode cup had popped free from the side of the CRT. Snap that back on and clear picture returned. Worth a look.

Thanks for the hint. Now I cannot set the bias using the OT method as the winding resistances are way out and I cannot balance the bias as the voltage drop across the left side cannot get higher then 1.3V. Using the 1 ohm cathode resistor method, I can balance the voltage drop across each resistor. Is this 1 ohm resistor method really more reliable than the other.


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Old 20th March 2020, 02:26 PM   #12
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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To set the bias current, fit a 10R 2W resistor in the cathode of each pair. Measure the voltage and that will give you the quiescent current accurately.
The DC resistance of the transformer looks suspect and definitely not to be trusted to work out the quiescent current.
There should be no hum if the valves are balanced properly.
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Old 20th March 2020, 04:43 PM   #13
Kay Pirinha is offline Kay Pirinha  Germany
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Not too long ago you opened another thread upon your Twin. Finally you confirmed that it was working flawlessly. And now you have another issue with it? What happened to it in the meantime?
Again: Follow my hint given there to confirm that the OT ist connected properly and that this aftermarket thang has the correct colour codes. As said before, I have the suspicion that the plate and screen leads of one side are swapped, most probably because of wrongly colour coded leads.

Best regards and good luck!
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Old 22nd March 2020, 11:26 AM   #14
Carlosraj is offline Carlosraj  United Kingdom
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Quote:
Originally Posted by Kay Pirinha View Post
Not too long ago you opened another thread upon your Twin. Finally you confirmed that it was working flawlessly. And now you have another issue with it? What happened to it in the meantime?
Again: Follow my hint given there to confirm that the OT ist connected properly and that this aftermarket thang has the correct colour codes. As said before, I have the suspicion that the plate and screen leads of one side are swapped, most probably because of wrongly colour coded leads.

Best regards and good luck!

It is the shorted turnings on one side. I manage to get a friend of mine who has the same amp to let me use the OT from his amp for testing. I put in the OT in exactly the same colour sequence. It works perfectly normal. I do not know what to do with this damaged transformer. I dont think the supplier will provide a replacement at no cost. By the way, thanks you all for all the assistance.



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