Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: m17xr2b on February 04, 2013, 06:23:23 AM
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Hi everybody. I have an issue with my crack. For the past few months I have using it with 6080 and 5814 tubes. In that time I have installed speedball and update the output capacitors and installed a bypass on the last cap in the power supply. I used Mundorf Mkp 100uf 250V for the output caps and 2.2uf 250v for the bypass. Today I just got a NOS Chatham 5998. When I played some music I noticed that the volume was very very very low. I have to crank the crack to max just and I'm just able to hear sound. Could this be because of the output caps and the bypass. The rest of my tubes 6080's work as they should and I know the 5998 has different specification. So it is the tube or the crack?
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That's odd. I've done the same thing you have (replaced output caps and bypassed last cap on the power supply), and I'm also running a 5998. No problems at all. With 7 o'clock as my zero position, I usually listen around 9 or 10 o'clock. It sounds like your tube must somehow be bad, although I've never heard of the situation you're describing before. Try cleaning the pins on your 5998, and recheck your RCA connections.
Best regards,
Adam
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I have already cleaned the pins and I don't think that the rca connections are bad because with all my other tubes the amp works as it should, no issues at all. Also the tube lights up so no issues there.
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The rest of my tubes 6080's work as they should and I know the 5998 has different specification. So it is the tube or the crack?
If every tube works except one, then the amplifier is working properly but the tube is not.
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I forgot to say that it worked for the first ten minutes. In that time I felt that my tube search had come to an end. After that the left channel died and after and then the sound faded. I have to place the volume knob at half to just about hear some sound. I do hear both channel.
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If the other tubes work, it is a bad 5998.
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If you want you can check the 5998 pin voltages - I expect pins 3 and 8 will be incorrect (too low) indicating an exhausted cathode.
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Have you tried putting the 6080 back in to see if that is working?
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Yes they all work. I guess I will have to send it back for a replacement and it's a long way from Romania to the US.
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Where did you buy your 5998 from? Oddly enough, I recently (last week) bought a quad of 5998s, and last night I realized I had the same issue with one of them. I bought my tubes from vacuumtubes.net.
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hmmm.... me also :(
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They probably won't make you send it back, but it is obviously annoying to have to wait for the replacement. And I don't get how they send out bad tubes...
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They told me to send the tube back in order to get a replacement.
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Just got my replacement tube from tubemaze. While I did that I ordered another 5998 as a spare. Tested the tubes. I just have to mention that I did not receive 5998 but chatham 2399. So one tube has sound in only one channel. The other tube works good but my god it's microphonic. If i tap the table where the crack is very lite I can clearly hear it in the headphones. Also the microphonics do not start right away as I power on the crack but after about half an hour. The other tube that I use is a CBS 5814WA that I used for a while and I know it's not the culprit. I also noticed that the microphonic effect is intermittent. Is this a known issue with 2399 tubes?
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I have not experienced that with any of my 2399s (or 5998s, which are identical).
I have run into a problem of my own. I was using a Bendix 6080WB and a Tungsram E80CC. E sound was perfect. Today, I received two G.E.C. 6AS7Gs I had been waiting for. The seller tested them at 102% and 104%, respectively. I pulled the 6080WB and inserted one of the G.E.C.s. The sound was very, very low and static-y. I let the tube warm up, but there was no improvement. So I pulled that tube and inserted the other G.E.C. Same problem. I figured I got a pair of bad tubes, so I decided to insert a 7236 I had and knew was good. To my surprise, I had the same problem: low, faint, scratchy sound. I pulled the 7236 and inserted a 2nd 7236. Same problem. Ten I swapped in the 6080WB I had been listening to. Still no improvement. I figured, "O.K., must be that the E80CC went bad." To I pulled it and inserted a spare E80CC. STILL NO IMPROVEMENT. WTF?!?!?
Anybody have any ideas what the problem could be? FWIW, the tubes are all glowing. I also hear sound in both channels, but both are low and scratchy. And last night everything sounded perfectly fine. What is going on?
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AAAAAAAAHHHHHHHHHHHH!!!!!!!!!!
My cup of frustration runneth over. I took today off. My wife is out with the kids. My GEC 6AS7Gs finally arrived. I wanted to sit in my chair, put on my headphones, and relax in bliss while doing some reading. Instead I'm sitting here cursing the world. I love the Crack, but frankly this has been a frustrating process (none of which was due to the Crack per se). The stock 6080 was bad and i had to wait for a replacement. I later ordered a 5998 that turned out to be bad. I bought and struggled to install film caps, then spent many long nights trying to figure out what the problem with the film caps was before I found out one of the leads was bad. I had to wait for, and install the replacement. I wanted to upgrade the volume pot and because the wiring instructions on the sellers website were wrong, I miswired it, then stayed up all night rewiring it. Every time I need to do ANYTHING to the amp, I need to desolder and resolder my film caps. Now this. I know it is my fault because I keep trying to upgrade stuff, but it is getting to be a severe PITA. :-[
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The first suggestion is, as usual:
-redo all voltage measurements and please post any variations from the manual that are more than 15%.
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I figured you were going to say that. Ugh. That mean desoldering my film caps yet again. And with the speedball installed, accessing the terminals to test voltage and resistance is no minor task. Frankly, it makes me uncomfortable, since it is tough to see and I always fear I will short something...
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Quick question: should the octal socket connections be my primary focus, since the only thing that changed between when the amp worked, and when it didn't, was installing the new 6AS7G?
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Are all of the LEDs lighting up?
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Adam,
Get some jumpers, alligator clips on each end. Clip them to the test points then turn the amp on. You can safely get the voltage readings.
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Just realized....I can't check voltages, at least not tonight. I have to desolder my film caps to open the case, and I can't attach them when the case is open without a pair of leads with clips. Grrrrrrrr......
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Adam,
This sounds to me a lot like your new tubes may have had some crap (wax?) on the pins and when you first inserted the one and then the other, you gunked up your socket pins. Get some pipe cleaners, some round wood toothpicks and some kind of solvent like mineral spirits or 409 or something and try a good, deep cleaning on the sockets and then on the pins themselves. If this is what happened the trick of pulling and inserting the tubes will do nothing.
Also, when using pipecleaners, have the unit off and unplugged and all charge drained off -- they are metal spines and you don't want to be zapped when doing this.
This is assuming that the LEDs are all glowing and that there is no obvious damage to rectifieers, etc.
HTH,
Jim
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First,
Apologies to everyone for my rant yesterday. I was frustrated, and although I'm still frustrated for reasons explained below, I've calmed down a bit.
So....the issue wasn't the Crack at all. I went out, bought some pipe cleaners, cleaned the socket, and then tested the Crack with a portable source. It worked fine. So I put it back into my rack and hooked it up to my system via a line router. Only low sound again. I'll spare you the 20 intermediate steps used to diagnose the problem, but the bottom line is that the balanced outputs on my DAC work just fine, but the unbalanced RCA outs are only putting out a very, very, very low signal. I'll open it up to see what the problem might be, but if anyone has any ideas, I'm all ears. Could using signal attenuators have caused a problem?
Best regards,
Adam
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OK, now I'm totally stumped. I opened e DAC. The unbalanced RCA outputs are just connected to the balanced XLR outputs and the wiring is all perfectly fine and intact. The balanced outputs work without any problem. The unbalanced don't. How is that possible? I even checked the unbalanced interconnects in a different setup. How is it possible for both channels to suddenly not work (or rather only work at very low volume), when the balanced outputs are fine? They are connected. If one works, the other should, too. I'm totally flabbergasted and have no idea what to do next.
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That's an AudioGD dac, correct? Do you have the ACSS engaged by any chance?
-- Jim
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Yes, it is. Good thinking...unfortunately, this model doesn't have a button to select between ACSS and other outputs -- all outputs are active all the time. You can only select gain and input. Besides, since the unbalanced outputs are wired to the balanced outputs, if one works, the other should, too.
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If the unbalanced is wired to one balanced hot and ground you get 1/2 of the voltage out there.
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Try turning the ACSS off -- it may have an effect as ACSS is a current loop interface.
-- Jim
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The unbalanced outs are indeed wired to one balanced hot and ground. But the DAC puts out 5V balanced and 2.5V unbalanced. I've never had a problem using it this way before. The signal was plenty strong. If anything, it was too strong.
As for ACSS, I can't turn it off. I have other Audio-Gd DACs where you push a button for ACSS vs. RCA, but the Ref. 5.32 doesn't work that way. ACSS is always on, as are the balanced and unbalanced outputs. And again, I don't really see how it is possible that the unbalanced outs wouldn't work if the balanced outs do.
I thought maybe there was a cold solder joint or something, but everything looked fine and it isn't that the unbalanced outs don't work at all - if I turn the Crack or one of my other amps up all the way, I can hear a signal, but it is very, very faint. It's not 1/2 as strong as the balanced output - it is more like 1/50th or 1/100th. And I have this faint sound in both channels, not just one. None of this makes sense to me.
Please understand that I appreciate your help and brainstorming here. I just don't think we have hit upon the answer yet.
Signed,
Confused in Connecticut
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Perhaps it's time to talk to Qing-Hua? Sounds like maybe something went kahput with the dac's output section -- possibly.
Sorry it's so frustrating but at this point I really don't think it't the crack.
-- Jim
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Yeah, it's definitely not the Crack. I'll contact him...
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Your logic is perfectly good, so it is very likely one of your assumptions is wrong. Sorry that's not as much help as one would hope!
Is the interconnect good? Does it actually connect to the jacks at each end? With no shorts? Perhaps you could find a source of constant-voltage sine wave, and measure the output voltage between the balanced outs (should be 5vFS), from ground to each of the balanced outs, and ground to the RCA "hot". Repeat at every stage - DAC jacks, cable ends, connectors inside each target device, ...
Having seen a zillion of these kinds of question, I am confident you will find the answer eventually!
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Question: if one of the hot signal lines to the balanced outputs were to have a really weak signal (e.g., if L+ and R+ were both weak, but L- and R- were both normal), would the balanced outputs sound odd when feeding a balanced amp? Would the signal be weaker, wonky or would there be no sound at all? I'm wondering if maybe that is what happened and the hot signal to the unbalanced outputs is somehow defective, which is why the unbalanced outs sound weird, but because the other hot signal is fine, the balanced signal still works and appears fairly normal?
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Play a 60Hz tone through the DAC, measure the AC voltage between the hot and cold pins on the XLR jack, then between hot and ground and cold and ground.
This would be a nice way to verify that things are in order.