Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: denti alligator on December 22, 2011, 10:13:28 AM
-
Turned on my SEX today, which I use every day without problems and I got a high pitched screeching that sounded like a teapot that was really, really ready. Turning the volume down did nothing. Power off did.
I unplugged the speakers and turned it on and I can hear a slight sound coming from the amp, like the screeching only much quieter.
I'll be testing resistance and voltage now. What could this be?
-
Sam, could be a microphonic tube or maybe just a dirty pin/contact -- just try resetting the tubes in the sockeets a couple of times as a first pass. Did you bring any new cell phones, or other electrical goodies -- wireless networking, etc. into your listening room lately?
Also, dod you have any shorting plugs -- just to make sure it's not coming from the source?
Sorry can't be more help,
Jim
-
am I the only one snorting my coffee when reading the subject lines of some of these threads
I mean, usually the above costs extra
-
OK, guys. It's not the tubes. Switched them out and used de-oxit on pins.
Resistance readings were funny at 39 and B4, so resoldered and they're fine now. Yeah. But, instead of screeching I get white noise/whooshing in the left channel. Right channel is fine.
Voltage readings are funny now: B5 is 99.3 and B6 is 3.186. These are too high. Shawn troubleshooted this with me on the phone and we couldn't come up with anything. I'm glad it's no longer screeching, but the sound in the left channel is horrible.
Help?
What could be causing this?
-
Sam, Sorry, other than what I suggested, I don't have any more to offer right now.
Chris, and yes, I almost said something like I had a girlfriend like that once... but as you can see, I was being cautious. The operative word here being "was" :-).
-- Jim
-
...
Voltage readings are funny now: B5 is 99.3 and B6 is 3.186. These are too high. Shawn troubleshooted this with me on the phone and we couldn't come up with anything. I'm glad it's no longer screeching, but the sound in the left channel is horrible.
Help?
What could be causing this?
B6 too high (the cathode; should be 2.5v) indicates too much current through the driver section. B5 too high (the plate; should be 70v) indicates not enough current through the driver section. No wonder you and Shawn had a hard time!
Make sure the grid stopper Rstop, (B4 to T39) is 220 ohms - it is somewhat fragile so look for any damage.
If it failed or had a bad connection as you suggested, that might have led to some damage to the cathode and/or plate resistors So ... check those two resistors. Cathode resistor Rkdriver (B6 to T37 ground) should be 1270 ohms, and RL should be 150K (B5 to T36? B+driver). Better check the resistor from T31 to T36 as well.
-
These test out ok, Paul. Except between B5 and 36, which I think is altered with the C4S.
So what else could be causing this? Note that the white noise does not drown out music, and does not change in volume when the volume pot is turned.
-
Oh - didn't know you had the C4S. I assume this is the first stereo SEX version? Sorry for the confusion, we really do need to get clear on the version identifications!
The voltages seem to indicate the C4S is providing a bit too much current. First check is of course whether the LEDs glow properly on both boards. You could swap the C4S feed (just the wires that go to B5 and A5, if they are long enough) and see if the noise moves to the other channel - if it does then it's definitely the C4S board. The bad grid connections could conceivably have resulted in some damage to the MJE350 - but I would just get a whole new board rather than try to figure out which parts are bad.
If swapping the C4S outputs does not swap the noise, then it's somewhere else. Does the volume control have any effect on the noise?
-
Yes, when I switch the C4S boards the sound switches channels. I'm removing the C4S for now and putting the old resistors in until I can get replacement parts from Bottlehead.
Thanks, Paul!
-
C4S boards removed and old resistors in place. Works fine!
I think the screeching may have come from an improperly soldered cap at 34 (to the tube socket). This must have then damaged the C4S board...?
Anyway, thanks for your help everyone.
-
So would BH be willing to send me replacement parts? I left a message at BH HQ. If yes, that would be great. Just let me know if I need to pay for these...
-
After months of no problems and all-day listening yesterday, this happened again this morning.
But I've misplaced my manual, so I can't check resistance and voltage. Anyone willing to give me those figures?
-
Contact cleaner to the tube pins did the trick. I might have spotted a dog hair in there. Damn dog!
Catastrophe averted. For now.
-
And, it's acting up again. Every few days when I start it up in the morning I get feedback from both speakers. Cleaning the tube sockets and pins with contact cleaner works for a few days. This morning it did not work. I've tried cleaning and recleaning. It's oscillating so bad that I don't even need to have the speakers of 'phone plugged in to hear it.
Any clue where to start locating the source of this problem? Why is it always late December when it starts acting up? Weather? Nothing else has changed. I haven't moved the amp one inch.
The only thing I can think of that's I've done differently recently is that I've been using the amp 3 to 4 times more each day. Last night it was on from 6 to 11 or so. Maybe it's gotten heated up with this long usage and this has somehow had an effect ...?
EDIT: I forgot about the volume pot. In each case it was turned all the way down. However, I had forgotten to use the contact cleaner on it. So I did that. Not sure how to clean the inside, so I just drop some of the cleaner into it and moved the pot several times back and forth. Turned on the amp and it made a brief squeak (remember, I don't have speakers or phones plugged in!) and then was silent. I've moved the pot around a bit, turned it off, and will return later. Maybe this was the source of the problem?
-
So, it seems like every morning I wake up and the SEX starts oscillating when I turn it on. I then go on to clean the tube pin contacts and volume pot, and then it's fine until the next day. This just doesn't seem right. What could be going on here?
-
Have you tried different tubes?
-
The thread has gotten too long to figure out what has already been checked, and it's unclear whether the C4S has been replaced or not. (At one time the noise was thought to have originated in the C4S?) So maybe a status summary would help. Is it in one channel or both?
From the description, it seems most likely to be a mechanical connection problem, such as a bad solder joint, bad tube socket connection, bad pot, broken part, etc. Nothing bad enough to be obvious, just enough that the connection comes and goes. It might be time for the chopstick test.
-
C4S has been replaced. LED lights on those boards still light up, so they appear to be fine.
I only have these tubes, so I can't switch them out. I can't tell for sure (because I don't let the squealing continue for more than a split second, if I can help it) which channel, but it appears to be both.
What's a chopstick test?
The question is: what would work fine for a year and then without any changes, suddenly act up again? Surely not a solder joint? I'm wonder if the heat has anything to do with it: since when it's cold in the morning it acts up; but when it's warmed up it appears to work fine. Could that be affecting something.
-
Solder, unlike a diamond, is not forever. Funny things happen, especially if the joint has a hidden flaw.
Chopstick test is to poke each joint and component with a non-conductive stick such as a chopstick, while the amp is running and you are listening. This helps detect anything that is mechanicall sensitive, indicating a possible bad connection or damaged component. You have to be careful, since all the dangerous high voltages are exposed, and it's a bit of a pain to get everything connected correctly with the amp upside down so you can do the test - it has to be stable enough to actually push the component, not just touch it as for a voltage test.
-
Might be worth acquiring a spare set of tubes...John
-
Will run some tests
Where's the best place to get tubes?
-
It sounds like a bad joint or a bad cap. Did you melt any of the film caps while building the amp?
You never mentioned if it is one channel, or both channels?
It would be most likely that this is a bad joint, flipping the amp over restores connection for a while, and everything is OK.
Cleaning a tube socket or a pot every day will just wear them out, I wouldn't consider that a solution or an indicator that the problem is in either of those components.
-PB
-
I left it on today with the oscillation and it subsided after a couple seconds. Not sure if that helps explain the source.
Any suggestion for finding the faulty solder joint? Is the "chopstick method" the best way to go?
-
I thought the tubes had been cleared of guilt - I have heard such a noise from tubes warming up, though not often. Pick up a spare pair from Antique at http://www.tubesandmore.com/ - they are usually inexpensive and reliable. I don't think anybody offers tested matched gold-pin cryo'd 6DN7s anyhow, an it would be overkill for a SEX amp anyhow! :^)
-
So I turned it over and turned it on and let the oscillation subside (after 1 1/2 seconds) and plugged in my phones and began prodding. I immediately found a problem at 36 and 37, both of which make loud unpleasant sounds when prodded. So I reflowed the solder. Same problem. I then reflowed and added some fresh solder: same problem. Could it be the cap? How to check?
I need someone to be so kind as to post the resistance and voltage readings for the SEX 2.0 (the one before the newest version) so I can check these. Or I can just check them all and post them here and hopefully get some feedback. Thanks, and merry Xmas! I got a ton of vinyl (or, as we call them, because of their shape: wall calendars), but with my wounded SEX I'm not able to enjoy them :(
-
Hello Sam,
PJ and I have asked several pointed questions, and I would recommend answering those first before going any further. The answers to these questions will help determine if the cap at 36/37 might be the problem.
Otherwise, you are chasing your tail (and we are too).
-PB
-
I can't tell what channel, because the feedback is so loud and strong I'm trying to turn it off so as not to destroy my speaker or phones drivers. But I'll go ahead and see if I can identify it.
And no, I didn't melt any film caps during the build. At least I don't think I did.
I'll get back to you with resistance and voltage readings and (I hope) channel ID. In the meantime, are there any other questions I forgot to address?
Thanks!!
-
resistance:
1 1.65M and steadily decreasing
2 1.50M and steadily decreasing
3 0.2
4 0.614M and slowly rising
5 0.4
6 2.484M
7
8 0.3
9 622
10 0.2
11 1.70M and steadily increasing
12 622
13
14 249.4k
15 0.3
16 1.59M and steadily increasing
17 0.3
18 0.2
19 1447
20 can
-
I'd recheck 39/B4 while you are turning the pot.
Can you describe the nature of "all over the place"? Do you have any spare resistors around in the 100-500K resistance range? (any wattage will do), we can do a little experiment to narrow the suspects down.
-PB
-
I think I have some spare resistors.
Now I'm getting fine readings at 39 and B4. Goes up steadily with the pot until it reaches 2.075 (same at both places), which is about 12 noon on the pot, and then drops out (no reading).
I find the complete lack of readings at B2, 40, and 36 very odd. There's an earlier thread from about a year ago when I had this same reading, and thought it might be connected to the problem. Could it be?
-
I have a couple 152k resistors on some old C4S boards, but they have really short leads. I guess I could make them longer with some wire. The other resistors I have are much lower.
-
Temporarily resolder this resistor between 38 and 39, then see if the screeching persists at startup.
-
Alright, I'm trying that now. You know what you're doing better than I, but keep in mind that the noise when prodding solder joints was at 36 and 37.
-
OK, resistor in place. I turned it on without phones or speakers plugged in and I'm not hearing the screeching (which was completely audible even WITHOUT phones or speakers attached). So I guess I'll test with speakers next.
What does this tell you, PB?
-
Tried it with phones: no screeching. Hardly any sound in the left channel, but I'm assuming that's the resistor's fault. So what next?
By the way: THANK YOU for helping me on Xmas day. I'll try not have this solved by tomorrow, so you can celebrate Kwanzaa in peace :)
-
Remove the resistor, turn the volume pot all the way down, measure the resistance between 38 and 39.
You either have a bad solder joint in the wiring between the input jack(s) and each tube (running through the volume pot), or the pot is defective.
There is no reason to assume that the pot is defective without measuring it to check (they generally take a long, long time to wear out).
If the resistance between 38 and 39 is not zero when the pot is all the way down, let us know.
-
It's definitely not zero. Depending on where I put the MM leads, it reads between 1.7 and 1M. I can't seem to get a stable reading. What does this tell you?
-
Does it help to know that the screeching in unaffected by the volume pot (turning it up or down)? Also, it happens whether or not there is anything coming from (or even plugged in to) the inputs?
If I need to recheck the solder joints from the input to the tube, what path is that so I can start reflowing? Thanks.
-
If I need to recheck the solder joints from the input to the tube, what path is that so I can start reflowing? Thanks.
Follow the wires leaving the RCA jacks...
-
I'm afraid I'll need a little guidance. I see the left input going to the headphone jack and from there it appears to go to 25 and 30, but the trail ends there for me. I see the wires coming from the transformers, and I see the ground buss. But that's it. I'll start with 25 and 30, but I'm assuming the path is longer than this.
Is it not possible that the cap at 36 and 37 is somehow to blame? It's the one that makes horrible noise when I jab at those joints.
-
Lots of screeching sex talk here! Sorry, I guess I'm being insensitive to those with the issue.... Couldn't help it. Well maybe I could have. Who fucking cares. Ok, I'm done.
-
Reflowed 25 and 30 and then 37 and 38 again. Now getting a resistance reading of 3 between 37 and 38. No screeching. So I'm at least able to listen to some tunes. I'll guess I'll wait til it starts screeching again to post here, unless someone has advice before that (inevitably?) happens again.
-
Sounds like there was a bad solder joint, keep us posted.
-PB
-
agreed - bad solder joint is frequently the prob. I have been calling the police for a couple of week because 'someone' has been ringing my doorbell. Well, duhh, its a bad connection!