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PostPosted: September 19th, 2019, 11:29 am 
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Joined: February 28th, 2013, 1:19 pm
Posts: 332
Agree about fuse, starting with a 3 amp slow-blow would be best.

If the DJH mod added a PS capacitor in series to improve reliability, retaining the original capacitor as part of the series stack (like the photo appears to show), then it is possible that the older capacitor was overstressed prior to the mod and finally failed. I bet the original cap was only a 350 to 400 V rated cap, and operating right at the top of its voltage rating. I also note that AE-25 is based on a 115V mains voltage, and I find that local voltage tends to be 120V (or even a little higher). This can result in a 4 to 5% higher B+ voltage than rated. This is all idle speculation on my part, but not unusual practice. It also explains why it was deemed necessary to add the extra cap.

David


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PostPosted: September 20th, 2019, 12:14 pm 
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Joined: July 17th, 2016, 6:24 am
Posts: 637
Found this description of DJH version on the web. When I got it upgraded, DJH version was not yet introduced. Remember talking to Dennis Had and sending the unit for upgrade. Don't remember the details.

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The Audio Electronic Supply AE-25 Super Amp DJH is a power amplifier in the valve amplifier category.

Audio Electronic Supply web site (April 2004): The Super Amp DJH is a substantial upgrade from the standard and the Signature version. The output power is 35 watts through each channel in the triode mode, utilizing KT-88 s, EL-34 s or KT-90 s. You may wish to operate with KT-66 s, 6L6 s or even 6V6 s. The output power with these lower dissipation tubes will yield from 20 to 25 watts output power. Speaking of output power, the DJH Super Amp has a peak envelope power of 57 watts into an average loudspeaker load. There are many fabulous features incorporated in the DJH version. First is the larger power transformer.

Secondly, the replacement of electrolytics in the power supply with film and foil capacitors. A third feature is the dual negative DC bias supply that incorporates a filter choke for less ripple voltage. Continuing on, the DC voltage supplied to the two 6922 drivers is regulated with separate supplies for each tube. No matter how loud or soft the amplifier is played the voltage is rock steady on the 6922's yielding incredible speed and dynamics. The DJH comes standard with Jensen, copper and foil oil filled coupling capacitors. The Super Amp DJH has an incredible minus 80 dB noise floor. This low noise floor yields dark spaces between instruments in the sound stage.
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Amazon is delivering the assortment of fuses today. I will try with another set of power tubes (6n3ce) and 3A fuse first. BTW, I did not fine any pins shorted in the current tubes.

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Shashi


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PostPosted: September 29th, 2019, 10:03 am 
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Joined: July 17th, 2016, 6:24 am
Posts: 637
Yesterday, David Berning traced the problem to a shorted coupling capacitor in the output stage, one of the PIO caps.

Thanks everyone for the help and Thanks David.

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