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Old 20th December 2009, 03:48 AM   #1
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Default Need Some SimpleSE Help

Well got my amp all wired up and double checked out everything, plug it in and in about 20 seconds or less the 5AR4 starts to flicker shut the power of but it blew the fuse already. So anyway double checked everything again and just at the point of scraching my head. I am using edcor xpwr035 for the power and gxse's for the outputs, a 100mfd 370 volt cap and a triad choke. I dont have the solid state diodes in as I don't plan on using that feature. I am running the output in UL with CF right now no switch. I also pulled the tubes and checked the voltage from the power trans and everything was reading as it should but the transformer hums???.... Any help would be great or some suggestions. Thanks
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Old 20th December 2009, 08:31 AM   #2
RDL_AK is offline RDL_AK  United States
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Post pictures of both sides of board and wiring of transformers. With humming of transformer indicates possible shorted/miswired connections.
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Old 20th December 2009, 06:19 PM   #3
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Arc'ing in the rectifier tube could be caused by a number of different things:
  • Too much current draw, caused by a short to ground somewhere downstream of the power supply. It could be stray solder blob, or a wire whisker, or a construction mistake.
  • Too much current draw, caused by power supply caps that are too big or improper biasing on the finals.
  • Low quality rectifier tube. Replace with a better one, but only if you are sure #1 and #2 aren't a problem.
I'll assume the arc'ing does not occur until the rectifier is warmed up? With the amp powered off an unplugged, can you use your ohmmeter to probe for shorts downstream of the rectifier?

The bad thing is that once a rectifier arcs, it is far more likely to arc again. The arc usually jumps between elements near the mica, where carbon tracks will form. This encourages future arc'ing. The only cure is replacement.
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Old 20th December 2009, 06:36 PM   #4
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Well just went over the board again and checked all the resistors and caps along with all the solder joints front and back and all checks out, I unhooked the transformer leads from the board and tested all taps and I am getting all the correct voltages.

Reconnected everything put in the tubes kt88's EH, 5ar4 sovtek and a jj 12at7

Yes the arcing does not happen until the rectifier tube starts to warm up, also when this happens the power transformer growls so I shut the switch off.

Ty were would you suggest to start probing??

Also I noticed that the 150 ohm 3 watt R2 in the schematic looks to have gotten a little warm but it checks out fine with my meter

I will post some pics in a few Thanks for the help
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Old 20th December 2009, 06:46 PM   #5
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Old 20th December 2009, 09:31 PM   #6
rknize is offline rknize  United States
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What happens with just the 5AR4 installed? I assume that you don't own a variac? This would be a good opportunity to use one.
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Old 20th December 2009, 10:02 PM   #7
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What happens with just the 5AR4 installed? I assume that you don't own a variac? This would be a good opportunity to use one.
With the 5ar4 installed it glows and does not arc at all. So is my problem down the line??

And no I do not have a variac, but my father also suggested it would be nice to use in this situation but he is 200 miles away so.....

Earlier I also took the inrush limiter out of the primary and put it in line of the CT but it still arced while warming up.
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Old 20th December 2009, 11:26 PM   #8
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I am going to guess (based on experience) that your amp is OK and you have a bad 5AR4. The Simple SE runs the rectifier near its maximum ratings (especially with the EH KT88's), and the quality of the 5AR4's being produced today varies greatly from batch to batch. Some builders (myself included) have had to try several to find a good one. Other tube amp manufacturers have noticed this too.

The coating on the cathode and the spacing between the cathode and plate must be absolutely uniform or the cathode current will not be evenly distributed along the cathode. If the current flow is concentrated in one small area an arc WILL occur.

You say that there are no sparks with only the 5AR4 installed. Try again with the 5AR4 and the 12AT7. If there are still no sparks, measure the voltage on the plates of the 12AT7 (easilly accessed on the coupling caps). A voltage reading from 150 to 250 volts is OK.

If you got this far without sparks, try adding one KT88. If there are no sparks test to see if the amp is working on that one channel. Try the other channel (one at a time). If both channels work individually but sparks happen when both are used, the rectifier tube is bad.

If the rectifier tube sparks when either KT88 is installed it is likely bad, but this can not be easilly confirmed. If you have some different values of 5 watt resistors available you can set the current through the KT88's to a lower value (higher resistor value) and test again.
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Old 21st December 2009, 12:07 AM   #9
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Sounds like a short downstream of the rectifier.
Use a multimeter on ohms setting to check for shorts.
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Old 21st December 2009, 12:22 AM   #10
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Just tried with the 5ar4 and the 12at7 and I get some arcing

Quote:
Sounds like a short downstream of the rectifier.
Use a multimeter on ohms setting to check for shorts
Are you saying as in a short to ground??
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