Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: jminassi on December 14, 2020, 03:20:34 PM
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Hi Folks,
I solved my resistance check problem, but now I have a voltage issue. I’m following the directions on page 49 of the Crack manual. I plugged the amp into my dim bulb tester and the dim bulb tester into my variac. As I bring the voltage up above 35 volts the dim bulb tester starts to get brighter and brighter. It appears I have a short somewhere. I checked all the connections. Nothing obvious is touching anything it shouldn’t.
Any thoughts?
John
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I must admit that I have not followed this post closely but you stated that you passed the resistance test after re soldering.
If I may ask what wattage lamp are you using? I usually use a 200w lamp as I can't seem to find higher incandescent lamps anymore.
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Ahhh, good point! I used a 60 watt bulb because the last thing I tested drew only 30 watts. What is the Crack’s wattage at idle? I need to size the wattage of the bulb in my tester appropriately.
I do appreciate your help,
J
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Well, you've now passed the 5 post mark, so you should be able to post pics.
Failing that, I'd carefully scrutinize the power supply, looking for miswires, or unclipped leads that may be shorting B+ to ground/chassis. A power supply diode installed backwards would cause a high current short.
cheers, Derek
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I would guess it's aprox 60 watts after warm up and higher at a cold start up. If your resistance tests are good I would not use a dim bulb and only use a variac and look and listen for trouble as you are probably fine. A 60w bulb will glow brightly at 500 ma and you will not get accurate voltage readings.
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Can you plug the amp into the wall and turn it on?
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Ok, thanks to all of you. I will go through the circuit one more time and check the power supply diodes, unclipped leads etc. I can plug it directly into the wall of course. I’m just afraid of blowing something up.
John
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That's what the fuse is for.
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Thank you Paul. I’ll give it a once over look, plug it into the wall and hope for the best. I’ll let you know.
John
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Hi Folks,
I had a transformer diode installed incorrectly (polarity). I corrected it. I put the tubes in place and plugged the Crack into the wall. The tubes are not glowing and neither LED on the 9 pin socket is lit.
I turned off all the lights to make sure. I unplugged the Crack and removed the fuse. It looked good and I tested it for continuity. The fuse is good.
Any suggestions for where to start looking? The Crack passed the glow test on page 31 of the manual when I was at that part of the build.
Any help would be appreciated.
John
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The Crack is no longer passing the glow test. Nothing else matters until you can get the tubes glowing.
The tube heaters (that glow) are fed with the green twisted pair of wires. Since both tubes don't glow, either the green wires going from the power transformer to the B socket aren't well connected, or the power transformer isn't well connected to 120V wall power.
You could recheck the power transformer voltage check on page 29 and let us know what you get. I would also post some build photos while you're at it.
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Hi Paul,
The voltage between terminals 7 and 9 reads 6.39 V AC. The voltage between terminals 11 and 12 reads
173.7 V AC.
So I suppose I’m left with the green twisted pair to check.
I don’t see an “attach†icon that would allow me to attach photos. How do I do this?
Thank you for all your help,
John
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I don’t see an “attach†icon that would allow me to attach photos. How do I do this?
Click "Attachments and other options" -- see attached screenshot.
cheers, Derek
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The green twisted pair of wires leaving the power transformer and going to the octal socket is 100000% the first problem to address. At least one wire in that twisted pair is not properly connected.
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PB,
Transformer lug 7 and 9 have continuity with A4, A5 and A9. Those transformer lugs also have continuity with B7 and B8. Lugs 7 and 8 are effectively connected to each other. Can you confirm this wiring is correct?
The system won't let me attach photos for my ipad even though they are .jpg files. Is there a way to fix this? Then the system would not let me reply via iPad. So I am using my laptop.
John
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In my last post I meant to say that transformer lugs 7 and 9 are effectively connected (not 7 and 8).
Sorry for any confusion.
John
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The winding itself has continuity. In the photos you sent me, B7 and B8 aren't well soldered. The way to check these connections would be to measure the AC voltage between B7 and B8, which is likely to change when you poke it with your meter probes (assuming those connections are loose, the wires on your power transformer looked to be well soldered).
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PB,
I re-flowed all the lugs on the 6080 tube. I read 6.24V AC between lugs B7 and B8. The 6080 tube still does not glow.
Both sides of the 12 AU7 are now lit, but I can’t see the LEDs glowing.
Continuity of the twisted green pairs looks good and measured resistance of each green wire point-to-point is effectively zero ohms.
Any help would be appreciated,
John
PS: I just noticed how many emails/day you deal with. I don’t know how you do it.
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Have you tried measuring the continuity of the heater in the 6080? Pull the tube out and measure ohms from pin 7 to pin 8. Should be very low, like an ohm or so.
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The 6080 also takes some time to start glowing, so if you aren't leaving the amp powered up long enough, it may not have enough time to glow. Another thing that can happen is sometimes the plastic keyway on the base breaks off, then you have to be careful not to insert the tube into the socket improperly. Lastly the tube socket can be installed improperly (not the case based on the photos you sent me), and that will also cause glowing problems.
Since the 6080 did pass a glow test originally, I would be betting on time or a broken keyway being part of the problem.
Since the 12AU7 is glowing, you can run the amp and check DC voltages at least.
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Doc,
The reading between pin B7 and B8 is 0.1 ohm.
PB,
I set the chassis plate on the base right side up, plugged it in, and both tubes were glowing after a few minutes. However, when I removed the chassis from the wood base and turned it on its side, only the 6080 glowed. The socket appears to be installed correctly and I can assure you that the plastic keyway is fully intact. The wires going to the 9 pin socket appear to be securely soldered in place. The LEDs are not lit.
I measured the voltages and they are way off as follows:
1. 205.1 V
2. 205.5 V
3. 96.6 V
4. 205.3 V
5. 197.2 V
6. .3 mV
7. .3 mV
8. 0 V
9. 92.6 V
10. 92.7 V
I disconnected the test lead and put the chassis back into the wood base. The 12AU7 is not glowing. The 6080 glows when first turned on and then goes dark after about 30 seconds.
Let me know what you think. I do appreciate your help.
John
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I set the chassis plate on the base right side up, plugged it in, and both tubes were glowing after a few minutes. However, when I removed the chassis from the wood base and turned it on its side, only the 6080 glowed.
A loose solder joint will do that.
Since you have tubes lighting and not lighting, there is still an issue with the green twisted wires and their connections.
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Ok, it was a loose solder joint just like PB said. Tubes are glowing. LEDs are glowing. All voltages look good except Terminal 7. I have floating millivolts where I should have 90-115 V.
Any idea what I should be looking at?
John
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Double check that your meter is set to measure DC volts (parallel dashed and straight lines), not AC.
cheers, Derek
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Hi Derek,
Thanks for getting back to me. I am definitely on DC. All the other voltages measure correctly.
Here's a picture of my wiring of the octal tube.
Best,
John
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Hmm. Just a shot in the dark. With the amp unplugged and cooled down, what resistance (ohms) do you get between terminals 7 and 3, when touching the probes to the terminal lugs themselves (not the leads of the 3K resistor)?
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Yikes, what did I do? Everything was working except for one voltage reading. I plugged the Crack in and I saw a small flash where the UF4007 rectifiers are. I shut it down and looked for shorts. Not finding anything I powered back up. The 270 ohm 5 watt wire wound resistor between 15U and 21U gets very, very hot. I shut it down.
Is it possible one or more of the rectifiers failed? I did initially have the polarity of one of them reversed.
Help!
John
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Deke,
I get 2.971k ohms between lugs 3 and 7 with amp cooled down and unplugged. That reading is done by just touching the lugs.
John
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Post lots of detailed pics - overhead and from different sides.
If the first 270 ohm 5W resistor is getting super hot, but not the second one, then that seems to point to a short immediately after the first one - my bet would be between T15 and one of (a) chassis, (b) T16, or (c) T14.
A rectifier diode shouldn't be affected by being installed backwards - unless you ran a lot of current through it - but I think the fuse would prevent that.
cheers, Derek
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Look for leads poking through that should have been trimmed off, but are now touching the chassis. Trim them off.
Consider also posting some fresh build photos.
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I can't see any leads touching the chassis. Here are photos. Let me know if you want more.
Best,
John
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Some ideas:
(1) I think you could use some more heat on the 8 pin socket - and quite possibly on other joints. What solder are you using? If it's Cardas Quad, you should see brown flux come out of the joint and settle on the surface of the solder. If it doesn't rise to the surface, it's insulating the inside of the joint. If you have an adjustable soldering station, try cranking it up to at least 750F.
(2) You've painted the bottom of the chassis and I see that you've scraped the paint away from at least some of the terminal strip attachment points. But I can't tell the full extent of the scraping. I would make sure that the paint is scraped away from any terminal-strip-to chassis connection to which a black wire attaches. But I doubt that's what causing your negligible voltage at T7 since you have the correct voltage at T9.
(3) Purely for the sake of future reliability, I suggest pushing the leads of the "internal" diodes (the ones closest to the power transformer) farther into the terminal lugs and then trimming the excess on the other side.
All that said, I think your best and fastest route to a working amp is to reflow all the joints, making sure that they get a good heating, and adding just a small dab of solder (unless there's a solder blob there already, in which case don't add any -- or better yet, remove most of it with a sucker or wick and redo the joint).
That's all I can think of. PB may have some better pinpoint suggestions.
cheers and good luck, Derek
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Hi Derek,
I’m using Kester 60/40 leaded solder. I had the chassis powder coated. The guy wouldn’t mask the underside for the $50 he needed to do it and the bell housing. I saw PB’s instructions to someone else who had the plate powder coated. I removed paint with a Dremel tool at the ground lug next to the IEC power inlet, and where the screw that holds the 5 lug terminal strip closest to the 9 pin tube is. I also removed paint under both screws that hold in the octal socket. I removed paint from the underside of the transformer bell housing where it meets the transformer too.
Thanks for your suggestions,
John
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What's your DC voltage at 21?
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PB,
DC Volts at lug 21 is 219.6. Let me know if this is significant.
Thanks and have a great holiday,
John
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How about 15?
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PB,
0.3 mV at lug 15.
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Are you certain about that? If this was the case, the 270 ohm resistor that runs across your power transformer either isn't connected on one end or would be burned up into pieces.
Because you have appropriately high voltage at terminal 21, I would suspect maybe you measured 16 or 14, both of which would be 0V.
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Sorry PB, I was on lug 16. But I only get 27.1 mV at lug 15.
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Are you certain about that? 220V on one side of that resistor and 0V on the other side of that resistor would dissipate 180 watts and it would get so hot that it would fail quickly and horribly, your fuse would blow, etc.
It's possible that one end of the 270 ohm resistor that crosses over the power transformer isn't well connected on one end or the other, or that one of the black wires running around the 6 lug terminal strips isn't well connected.
Can you power down the amp and let the DC voltage bleed out, then try measuring the DC resistance of the 270 ohm resistor that crosses over the power transformer?
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Whoops, that last reading on lug 15 was my error....I didn’t have the power connected.
I get 211.0 V at lug 15.
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I’m getting 252.9 ohms across that resistor.
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OK, the resistor isn't getting too hot. It will actually be about twice as hot when the amp is working.
Could I see some tighter shots of the 6-10 terminal strip?
You have the correct resistance at 7 which should allow the 6080 to draw current on that side, but it isn't. Can you carefully measure the voltage at B1?
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The voltage at B1 is 98.1 V DC. When I first turned on the amp the voltage was as high as 250 V and then it came down.
One side of the 6080 tube lights up.
I’ll take some tight pictures and send them via my computer as the forum’s system doesn’t recognize photos from my iPad as .jpg files.
Thanks,
John
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If only one side of the 6080 is glowing, I would seek out a different 6080.
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Ok, I'll have to buy a couple of new ones.
I tired posting pictures, but the system keeps giving me an error http500 or something. I'll try later.
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Pictures
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Picture
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Another photo
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Last photo
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Paul,
I am ordering a couple of different brand 6080 tube and a couple of different brand 12AU7 tubes from Tube Depot (Digikey).
I repeated the resistance checks and it all checks out. Because the flash/puff I experienced came from the side with the rectifier diodes, I have removed all four of them from the circuit. They all measure between .501 and .504 Volts. Is this the value that you would expect? If so, I’ll put them back in the circuit.. If not, let me know and I’ll order new ones.
Thanks,
John
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No, I didn't give up and stop the build. It took this long to get a new 6080 tube (NOS RCA 6080). I also bought a new 12AU7 (EH). I also decided to replace the four rectifier diodes with Vishay diodes UF4007.
At this point my resistance checks are all good.
My voltages look good to me. Here they are:
Terminal
1. 81 VDC
2. 177.8
3. 0.5mVDC
4. 172.7
5. 80.4
6 0.4mVDC
7. 106.0
8. 0.6mVDC
9. 106.3
10. 0.4mVDC
Please confirm I am good to go to plug a pair of headphones into this thing.
Many thanks,
John Minassian
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That's a working set of voltages.
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Success! Holy moly, this thing sounds awesome! I just plugged my Ah! Njoe Tjoeb CD player into and played Trower's Bridge of Sighs. Complete silence between tracks even with the volume up at eleven o'clock. It's driving those Drop/Sennheiser 6xx's like it owns them. I can't wait to get one of my DACs into the mix or my phono stage. Next step is the constant current source upgrade. I am going to start the build, but I will listen to the Crack in its present form for weeks before installing one of the new boards.
A special shout out to PB for your patience with me (I will get better), and to Deke for the help.
Let me know if there is something I need to do to close this thread.
Many thanks,
John