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PostPosted: 26 Dec 2013, 19:16 
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Output Edcor CXPP25. Regulated B+

Working about 12 hours and power transformer only 60 deg Cel

Below a few more pictures

Image

Image

Regards
Alex


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PostPosted: 26 Dec 2013, 20:17 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
The blue of the meters nicely matches the blue (from the residual gas in the tubes) glow of the tubes. The temperature is in the expected range. The CXPP25 transformers are rather excellent and very reasonable in cost. Then too I designed the circuit around them so they should work well in it :idea:

Good listening
Bruce

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PostPosted: 03 Jan 2014, 02:03 
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Joined: 31 Oct 2010, 20:46
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Location: Calgary, Alberta.
Hello there.
Ive been using my self build Oddblocks for about a year and a half. Everything sounded great until this evening.

Considering ive cheched the wiring for something broken between the two output tubes like a resistor or the pot to the current reg. What would cause one tube to hog all but 7ma out of 180ma? Shorted tube?


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PostPosted: 03 Jan 2014, 17:06 
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Hi, possibly, but I would first look at the grid circuits to see if one is open. Also check the connections on the screen and anode of the tube not working. You might also look for corrosion in the tube sockets/ on the tube pins. Another possibility is a failed coupling capacitor allowing dc on the one grid.

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Bruce

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PostPosted: 03 Jan 2014, 17:53 
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I did end up checking all of the above as well as checking the tubes out. After about a minute or so of warmup time, I end up with a short between two elements inside the tube. Looks like I was one of the lucky ones. Nothing else happened to the amplifier. Although I now have two Gold lion KT88 that are garbage after about 500 hours. Good thing I have some SED 6L6GC on the way.

Thank you for your time Bruce.


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PostPosted: 03 Jan 2014, 23:05 
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Strange that the GLs went bad. They have been one of the most reliable ones in the amps. Class A operation tends to stress tubes so I design for a comfortable margin in dissipation. But then again tube specs and the actual tube performance are not always the same. Ask pretty much anyone who has tried KT88 Psvanes in the amps. They might be great tubes, but they don't behave well in the amps.

Good listening
Bruce

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PostPosted: 07 Jan 2014, 20:22 
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gofar99 wrote:
Strange that the GLs went bad. They have been one of the most reliable ones in the amps. Class A operation tends to stress tubes so I design for a comfortable margin in dissipation. But then again tube specs and the actual tube performance are not always the same. Ask pretty much anyone who has tried KT88 Psvanes in the amps. They might be great tubes, but they don't behave well in the amps.

Good listening
Bruce



It is strange that these have shorted elements inside. But really not as strange as to what is going on with the Amp now. Resistors were checked, pins and solder joints were checked. I threw in a Pair of JJ KT88 that I had on hand and I was able to even out the current between the two. I kept my meter on the tubes and left it in logging mode. A couple of hours later I hear the meter beeping and go take a look. The balance had shifted about 10ma, so one tube at 100 the other at 80. I had to swing the pot all the way to the other extreme to keep in in balance. While trouble shooting the issue, I had no music on, they were just idling. I could hear some audible white noise and a little crackling, at this point I unhooked the input to the amp and the noise remained. Upon very close inspection of the 1R resistors, one had looked like it was "wet" compared to the other 1W Carbon films. It had a light film of oil on the resistor. All the others do not have this. I am wondering if this 1R resistor is breaking down for some reason and went really high, and then now its back down to 1R? Is that possible? Im not sure what came first, the chicken or the egg.

At this point, there are so few resistors in the tube circuits, Im really leaning towards replacing those 1R Carbon films with 2W, Metal films. The 1W Carbon films I used were only good for 250V :eek: I shouldnt have assumed that they were good for 350V


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PostPosted: 07 Jan 2014, 22:26 
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Hi, My experience is that the JJs stay balanced for a long time. The resistors should not show any film. I would replace the two 1 ohm ones with metal films and see if it behaves. Can you send a photo of the insides of the amp so I can look it over and see if anything else might cause the issues. BTW do you have a scope? If so check the output. It is possible that it is oscillating at an above band frequency. It would explain the hiss.

Good listening
Bruce

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PostPosted: 08 Jan 2014, 00:15 
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Location: Calgary, Alberta.
I plan on replacing the 1 ohm resistors with metal films pretty quick. I actually do have a scope. I forgot all about it. Its and oldie. A Heathkit IO-12 restored and works nice. I dont know why I did not think of it. I will check out that channel and see whats out there. Here is a picture of the underside.


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PostPosted: 08 Jan 2014, 22:05 
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Joined: 12 Sep 2013, 22:15
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Hi everyone, i'm currently wiring up my first oddblock and i'm having a little trouble with my heater voltages.

I'm using the edcore xpwr002-120 power tranny, so have series wired the 6.3v and 5v coils, but i'm getting a much higher output than expected. I've got 11.8VAC going into the bridge with 15.3VDC coming out, even with two series rectifiers (6A 100PIV were all i could get at short notice) the DC only drops to 14.0VDC. I guess i could keep adding rec's in series until i get all the way down, but i've a feeling that's not a great idea.

For reference i'm powering the amp from a 100v-115v step-up transformer (live in japan), though even running it straight out of the 100v ac i'm still quite a bit over.

I'd be very grateful for any tips or ideas,
Cheers very much
Josh


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