denti alligator
New member
Will run some tests
Where's the best place to get tubes?
Where's the best place to get tubes?
HELP! Screeching from SEX
- Thread starter denti alligator
- Start date
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
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
denti alligator
New member
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?
Any suggestion for finding the faulty solder joint? Is the "chopstick method" the best way to go?
Paul Joppa
Moderator
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! :^)
denti alligator
New member
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
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
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
denti alligator
New member
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!!
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!!
denti alligator
New member
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
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
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
denti alligator
New member
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?
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?
denti alligator
New member
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.
denti alligator
New member
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.
denti alligator
New member
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?
What does this tell you, PB?
denti alligator
New member
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
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.
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.
denti alligator
New member
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?
denti alligator
New member
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.
denti alligator said:
Follow the wires leaving the RCA jacks...
denti alligator
New member
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.
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.
