Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: [email protected] on June 29, 2020, 06:32:33 AM
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Greetings! First time build here. Everything has gone fine so far in terms of testing required in the manual, but I can't resolve a curious problem.
About 90 seconds after powering on, the LED attached to A3 will start to blink, then increase in brightness while voltage at T5 and T9 rise to about 140V and stay there. All other measurements are within spec until the LED blinks and T5 and T9 spike.
I've done all the obvious/routinely suggested trouble shooting, so I'm at a dead end. Can anyone help me out?
I have a three minute video of what happens which I'll try to attach or can send to those interested.
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Can you unplug the 6080 and recheck this behavior? How about posting some build photos?
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Not sure if my photos went through. Maybe there's a MB limit? Lemme know if they don't show.
Removing the 6080 stopped the voltage spike to T5.
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I would definitely be interested in seeing the build photos. You may need to reduce them in size slightly if they aren't posting.
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Ok. I'll try one at a time.
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photo 9 pin
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What voltage do you get at A3? If the LED is blinking or off it will either be 12V or 0V usually.
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With the 6080 removed, A3 is 1.573V, which from what I understand, is in spec.
With 6080 removed, it stops blinking. T5 stays steady at 94V.
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photo transformer
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I would suggest resoldering all of the connections in the amp. You can leave the ones alone where the LEDs are, as those look pretty solid. Everything else needs more heat and more solder.
On the UF4007 diode bridge, that one that you have going up and over the black wire may cause some problems down the road and I would recommend going back to the manual and reviewing the installation instructions for that part. It should not go over the black wire and the way it is installed allows for the possibility that the leads of it and the diode next to it can touch and short out the high voltage power supply.
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OK. I'll give it a shot.
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I basically re-soldered the entire amp, and moved the diode, yet the problem still persists. Could it be a tube?
Short of dismantling it and rebuilding it, what are some options?
Updated pics enclosed.
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Can you wrap the wires on the octal socket? A loose connection on the octal socket could cause issues like that up at terminal 5. This is very unlikely to be a bad tube.
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My apologies, but I'm not entirely sure what you mean by 'wrap the wires'. B4 is very loose, though.
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The voltage at T5 and T9 are identical @136.5V, if that offers any clues.
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Wrap the wire around the tube socket contacts rather than just letting it pass through. This makes a solid mechanical connection before soldering.
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The voltage at T5 and T9 are identical @136.5V, if that offers any clues.
That would likely point to a loose wire on the octal socket or potentially the 3K resistor feeding that half of the circuit just not being well enough connected to work.
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Re-soldered the resistor twice now. No luck.
Re-soldered and crimped as best i can all terminals on the octal. No change.
T5 and T9 still around 140V.
I'm starting to be concerned my 'repairs' are making matters worse. T3 has a LOT of solder on it.
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And you're 100% certain that your resistance readings are OK?
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Yes. I've checked them at least 4 times now. They're always in spec.
I'll check again now though.
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Checking with tubes out, just to clarify.
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Everything checks out.
The wanderers wander into the mega OHMs.
0 OHMs read 0.
2.9K's read at 2.9.
RCA jack, right = 94 left = 102
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Just for fun, i checked temps on the resistors.
The side that is malfunctioning, the resistor is at around 300F.
On the side that seems to be functioning properly, the temp is around 250F.
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You could try a different 6080. They are relatively inexpensive at Antique Electronic Supply. What you are experiencing would be an unusual failure mode for a 6080.
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I don't know if this is sound reasoning as far as electrical circuitry goes, but I tested resistance (I think) across the 22.1K resistors on 1-2 and 4-5.
The one from T1-T2 measured right at 22K, with no wandering (this is the side where voltage measures in spec). Resistance between T4-T5 wandered all over the place and never settled (this is the side where voltage is way too high).
Is this coincidental to the overall circuit layout, or does it possibly mean something, like the resistor is bad?
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You would I have I think the second bad resistor that I can remember in 25 years. Are you measuring across the terminals or the actual leads of the resistors? A bad solder joint could create this issue, or if the resistor was pulled super tight against the terminal strip, it's possible that it was damaged, but physical damage is usually pretty visible.
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I'm putting the probes on the leads.
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Rub the tips of the probes back and forth on the leads. If there is any contamination from flux or a little oxidation that will cut through it and give a more solid reading.
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I put some sand paper to each lead and it still wanders all over the place. (T4-T5)
If I remove the 6080 (and keep in the 12au7), it lands on 22 immediately and stops. Wandering stops with both tubes removed.
Wandering of T4-T5 resumes with 6080 in and 12au7 out.
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Is there corrosion/oxidation on the bottom of the 6080? If you are running a load of dishes in a dishwasher sometime in the near future, go ahead and throw the 6080 in there and give it a wash cycle.
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Got it functioning properly finally (sounds great!).
It is a loose connection in the octal socket. I don't yet know if it is the socket itself, the tube or bad connections/solders on the pins.
It is presently stable, though, which is a relief. Are better octal sockets available which are recommended?
Thanks!
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There are many octal sockets that I don't recommend, like the teflon ones, PC pin ones, etc. You can get the same socket with solder cups, though I like how easily the fork pins in the ones we use can be tensioned if necessary.
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Ah, good to know! I'll explore tensioning if need be.
Thanks!