Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: Dynakitbuilder on March 02, 2020, 10:22:00 AM
-
The static in the R channel has increased to just about all the time set is on. Can hear the static with both phones and speakers. L channel crystal clear.
-
If you knock on the chassis plate with your hand with some reasonable force, does that change the nature of the static? Have you reflowed all of your solder joints?
-
No effect with tapping on chassis. Reflowed all solder joints. Went back and reconfirmed all resistance checks - still the same readings. Set up to do voltage checks; when I plugged in the amp, checked tubes glow; then the inside 680 ohm, 3w (blue, grey, brown, gold, pg 42 in manual)resistor started to smoke and turn red. Unplugged set real quickly and started to call the fire department (not really); then after my blood pressure returned to somewhere near normal wrote this. Assume the resistor is cooked, but don't understand why it went bad. Did I overheat it during reflow?
-
That resistor will go bad because something is drawing excessive current. You would want to start with a resistance check and posting any resistances that are off. Also posting some build photos could be helpful too.
If you soldered the joints on that resistor for 30-60 minutes, then maybe you could do some damage.
-
Thanks once again for the help and support. Even with all this bit of hassle the whole experience had been a blast and convinced me to do other kits in the future. I will post the resistances and photos.
-
Resistance check within stated limits.
Having trouble sending photos. Using png files but they don't load.
-
The files might be too large, data-wise. Try resizing them. If you use Windows, the default pic viewer gives you the option to resize to something suitable for email - I think it's max 2MB. That's fixed the problem of pics not uploading for me.
-
here's some photos: please let me know quality and quantity. Trying to downsize photos to load better.
-
How about a top done shot that looks more like the one at the end of the manual? (In a well lit room)
-
some with , some without flash
-
I would go ahead and do a voltage check on just that side of the amp. That 680 ohm resistor is getting hot, but it's not smoking, so try to limit the amplifier on time to about 90 seconds. Once you perform those voltage checks, pull the 6FJ7 on that side of the amp and power it back up, then report the voltage on terminal 13.
It's still really hard to see much in those photos. These photos are about 1/3 of a megapixel (a current cell phone is 48).
-
I stopped buying "current" cell phones about 4 years ago. 74 years old. Might not get my money's worth out of a new one. I may be able to borrow a current phone from some neighbor that's not quite a luddite like me. Will try.
-
A digital camera made after the year 2000 should be capable of a few MP as well.
-
Not up to checking smoking circuits today. You should go and enjoy a Sunday, too. Will try tomorrow when I am less frustrated.
-
Any Better?
-
Those are all still 640x480 images.
If you run the amp with no tube in the offending side, what's the DC voltage at terminal 13?
-
237.6v
-
Can you reheat the solder joint at 7 and slip the red plate choke wire out, then leave it poking straight up in the air, then recheck the voltage at 13?
-
454.2 v
-
And just to be absolutely positive, if you take the tube that's out of the amp now and swap it with the tube that's still in the amp, does the low power supply voltage follow that particular tube?
What we learned by the voltage popping up when you removed the plate choke wire is that there's something connected on or around where the blue plate choke wire lands that shouldn't be there, or something is touching that shouldn't be, and that's dragging down the whole power supply and heating up the power supply resistor.
-
446.5 v @ #13
Thanks for the explanation. Should I be examining the area around the blue plate choke for anything in particular?
-
There could be a number of problems that would cause this kind of behavior, I'll try to list them all out:
1. Either end of 249K resistor not well connected or the ground wire not well connected to that area.
2. Backwards 1000uF cathode bypass cap.
3. Miswire of the 220 ohm grid stopper from the 0.1uF cap/249K resistor to the 12 pin socket (the resistor is wired to the wrong tube pin).
4. 680 ohm cathode bias resistor is not well connected on one end or the wires on either end are missing or not well connected.
5. Plate choke miswire.
6. Shorted tube (this is why you'd want to test that tube on the other channel).
-PB
-
Is there a particular sequence that these items should be attacked?
-
I listed them in approximately the order I would use.
-
#1: Re-flowed, seemed well-connected
#2:1000 cathode cap attached same as in manual
#3: resistor connected to A 11, not A 12. connections appear solid
#4: re-flowed 680 ohm resistor. appears well-connected
#5: PC-3 - black is heat-shrined ; red unconnected but ready to be re-connected to 7 L; Blue connected, re-flowed and appears solid to 10 L
#6: both tubes OK - assume when we switched tubes that was proved?
-
I would suggest borrowing a phone/digital camera to get some shots of the build. There ought to be something touching that shouldn't be or something out of position on that side of the amp.
-PB
-
//?
-
That's much easier to look at. It looks like there's some kind of debris on the plate choke wires, is this just paint overspray?
Where the 1000uF cap lands, the two white wires heading there should connect to the terminal where the unbanded end of that cap connects. If one of them is connected to the adjacent ground terminal instead, that would explain your problem except that the problem is still there with no tube.
I would check the red wire leaving terminal 10 to be sure it's connected to the correct pin on the 12 pin socket and that it's not touching anything else.
If neither of these suggestions does anything, I would carefully remove the black Solen cap and post another photo so we can have a look at what's going on underneath.
-
1: Yes it's paint
2:attached to 11 L are: one W wire from OT-2 #0 and one W wire from A-7
3: R wire from term 10 connects to 5A. The outside of the black cap may be landing on top of term 5 A.
4: Just found an obvious problem in the area - a blob of solder extended from the bottom of 10 L and touched the chassis plate. Wonder how many times I have re-flowed and checked that area in the last few weeks. One of those times I wish I had someone else to check after me. Wishful thinking. I cleaned the offending blob outa there.
-
Yeah, that'll do it!
-
Ok, so I will re-attach at 7, re-seat the A tube: should I do a recheck voltage check ?
-
Yes, definitely recheck the voltages.
-
All voltages check out! No fires!
Just hooked up the system. Very fine sound. Will start the upgrade after I enjoy some music for a while.
Thanks again for the patience and sage advice.
Looking forward to starting a phono amp kit next.