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Old 14th September 2010, 12:34 AM   #1
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Default Weird issue with tube driver.

Ok, So I started working on a set of normal RH807se mono's, built the first channel, got it up and running (ruff layout, long wires, ect) It sounded like it lacked wattage/volume, ran back to the psu simulator, found out I needed ruffly 75uf on the tail end of my B+ supply (500v) added that, the amp woke up, made tons of usable wattage, and over all impressed the heck out of me.


Later that day I pulled it apart, so I could do the point to point wiring and tidy up all the long wires, did that, and warmed things up for sound test 2, huge issue, preamp needs to be turned to 11 to get ANY sound output, so I took the 807 tube out, disconnected the ECC81 from the 807 grid, turned on the 270v supply (for the screen of the 807, and the plate of the ECC81) and hooked a 1w speaker to the coupling cap's tail end, ground went to chassis ground, and under super high preamp volume levels, got distorted music!


Changed driver tubes about 3 dozen times (not kidding) with known good tubes, everything from telefunken 12at7's to clear top 12au7's, all the way to long plate 3 rib 12ax7's, same condition, took high volume to get anything out of the coupling cap's back end, so then I put a 1m resistor from the coupling caps "out-put" to ground, no change.....


Took the socket out, cleaned it, replaced the 300ohm cathode resistor, new 1m input resistor, new wima 2.2uf coupling cap (also tried a few other coupling caps) and the same issue persisted...





I'm lost...
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Old 14th September 2010, 01:03 AM   #2
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some measurements on a schematic would be helpful...
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Old 14th September 2010, 01:07 AM   #3
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Ill draw the schematic out tomorrow, seams I lied a tad at the start of this topic, I took the PSE807 from Sarris, his take on the RH807 amp, went with 1 tube like the RH807, and used a 5k pri edcor OPT.



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Old 14th September 2010, 01:07 AM   #4
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Hmmm... Is that binding post where you solder the other end of your coupling cap isolated from ground?
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Old 14th September 2010, 01:17 AM   #5
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Indeed it is Wavebourn, even tried with the coupling cap just "hanging" there!

whats weird is when the amp exhibited this problem the first time, a wiggle here or there would resolve the issue, After much thought, and vodka, I think this is coming down to a dirty socket, since a resistor swap, and coupling cap swap did NOTHING for the issue.



Though I might come back tomorrow after a new day has started, only to profess my ignorance!


I am correct in thinking the noise coming out of the coupling cap, should be as high, if not higher then my preamp, correct?
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Old 14th September 2010, 01:21 AM   #6
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I don't know about a noise... Do you have a digital multimeter?
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Old 14th September 2010, 01:23 AM   #7
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By noise, I mean sound, but since my sound is not passing through my output tube, it might as well be noise?
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Old 14th September 2010, 06:59 PM   #8
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Voltage out of the coupling cap was in the range (fluctuating) of +50mv to -170mv, this changed from tube to tube (12au,at,ax7's)


tested a few coupling caps, had a black beauty that was spitting out +50v



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Old 14th September 2010, 07:35 PM   #9
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12au7 bias current is a steady 6.3ma
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Old 14th September 2010, 07:37 PM   #10
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What means +265V -- is it connected directly to the PS, without anode load resistor?
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