Could it be a flaky adjustment pot? How about installing some new nice multiturn bourns pots. Just an idea---better wait for a more expert opinion though.
steve.
steve.
spind said:
Good thought.. but the bias reading at the emitter is stable during the "events"... so no, dont think so.. If I take these boards apart again (unfortunately highly likely).. I will replace both pots though as you suggest.. they are REALLY hard to adjust.
Mr. Pass, after re-reading my post I see I am not clear on how much I was incrementing the bias.. never did I move more than 15mv upward at a time.. and I waited at least 20 min between.. I used input to raise the temp up a little faster and made sure it dropped slightly after I muted..
Im trying to convince myself I did not cause this.. can you tell? 🙂
I shall wait until you have time to consider my situation.. It cant get any worse with the power disconnected.. LOL! 🙂
Im trying to convince myself I did not cause this.. can you tell? 🙂
I shall wait until you have time to consider my situation.. It cant get any worse with the power disconnected.. LOL! 🙂
Hi Joe, Steve,
Do not use mutiturn pots. Just replace the ones you have with like controls.
Multiturn controls gear down the actuator that moves the wiper. They can oxidize the same as a normal control. The oxide problem can be worse as the wiper is normally smaller, as is the element. Therefore the oxides can have a larger impact. Multiturn controls are also often a lower wattage ratting than the 270° controls originally used.
Remember, there is nothing wrong or cheap about using a 270° control. It happens to be the correct part for the job.
-Chris
Do not use mutiturn pots. Just replace the ones you have with like controls.
Multiturn controls gear down the actuator that moves the wiper. They can oxidize the same as a normal control. The oxide problem can be worse as the wiper is normally smaller, as is the element. Therefore the oxides can have a larger impact. Multiturn controls are also often a lower wattage ratting than the 270° controls originally used.
Remember, there is nothing wrong or cheap about using a 270° control. It happens to be the correct part for the job.
-Chris
anatech said:
Can I try a blast of tube cleaner in it? It might get passed the knob somehow?? maybe.. I hope.. ya think? 🙂
Hi Joe,
Dis be a temporary fix mon!
-Chris
I'm a little unclear here. Use normal metallic contact cleaner on teh metal elements. WD-40 will work great for this. The rotating contact on the back can be a source of trouble, so make sure you get it too.
Dis be a temporary fix mon!
-Chris
anatech said:
Oh I have a can of that tube cleaner stuff that is for potentiometers as well.. I forget what its called.. I used it with EXCELLENT results on my hf-85 tube preamp.. I guess it lubes the stuff too..
Okay I'll shut up now.. Nelson is going to go nuts reading all this. LOL..
barchetta said:
Yes, I think it's a problem.
barchetta said:
Yes.
barchetta said:
Clearly we have a problem on that channel, and we can regard
it as intermittent and possibly thermally related. It is not likely
that the slower outputs are causing it.
There are 3 probable culprits:
1. A bad connection
2. A bad part
3. Intermittent oscillation.
Let's start with #1. I suggest bringing up the amp in "safety
mode" and physically rapping on the bad channel to see if you
can induce the problem with mechanical vibration.
If not #1, then we will want to try a can of "freeze spray" and
cool various parts on the front end to see if that makes the
DC come or go.
If not #2, then take a look at the output with the voltmeter on
DC but with a diode like a 1n914 or similar between the output
of the amp and the +input of the voltmeter, and with a resistor
like 1 KOhm across the meter inputs. If there is high power
oscillation this will detect it as DC at a much higher level than
the simple DC figure you are getting. Of course the alternative
is to borrow an oscilloscope and simply look at the output.
😎
Sorry, update: I was reading (googling) crackling on the net and saw that its common to have a cold solder joint do this. Soooo
I fired it up and tapped once on the right channel board.. ZAP! (arc) tapped again POOF.. fuse blown.
Tear down commences tonight and I will resolder everything.
I will report back.. and I was SOOO confident in my soldering! I suck. lol.
EDIT: HOLY COW the creator replied while I was typing and told me to do the same thing! This is getting fun!
I fired it up and tapped once on the right channel board.. ZAP! (arc) tapped again POOF.. fuse blown.
Tear down commences tonight and I will resolder everything.
I will report back.. and I was SOOO confident in my soldering! I suck. lol.
EDIT: HOLY COW the creator replied while I was typing and told me to do the same thing! This is getting fun!
I'm following this thread with great interest and believe that a good soldering session will cure the current problem. May I add to pay great attention to a solder joint, being that parts should be shiny clean (not corroded) and the solder should melt like peanut-butter and chocolate. 🙂
Great job so far, Joe.
/Hugo
Great job so far, Joe.
/Hugo
Nelson Pass said:
I hate puzzles.. but this is still fun! THANKS AGAIN!!!! I will check everything you mentioned and am eyeing up oscilloscopes.
Netlist said:
Thanks.. I wish I had cleaned all the parts first.. I did not, didn't know I should.. but now I read I should have cleaned them a bit.. but I will try my best to get it resolved. Whats scary is I usually really careful to make sure the parts do not move when the solder is molten.. so I dont know where I went wrong.. but hopefully I will find it by resoldering every single connection.. I'll just add a little more solder to each one.. unless you have a better idea.
EDIT: Also; I really appreciate all you guys hanging in here with me.. as I mentioned very early on; I am very tenatious.. I do not give up.. call it a fault.. I am sure this is sorta boreing for you guys so I really appreciate the support!
It's you being persistent that makes it funny for all of us. 🙂
As for the parts that eventually would need cleaning:
That's an easy job. With a good iron and good solder, tin should stick almost immediately to a loose resistor wire - as an example. Try a corroded one and you'll notice its almost impossible to get the tin attached.
A bit of worn sandpaper is your friend.
/Hugo
As for the parts that eventually would need cleaning:
That's an easy job. With a good iron and good solder, tin should stick almost immediately to a loose resistor wire - as an example. Try a corroded one and you'll notice its almost impossible to get the tin attached.
A bit of worn sandpaper is your friend.
/Hugo
Hi Joe,
Liquid solder flux and clean up afterwards. Failing that, remove the solder, clean up the lead and then resolder using only a little (enough to do the job). Clean up afterwards. I like Electrowash PX and a toothbrush.
Hugo is right though. An oxidized lead will not accept solder easily.
-Chris
Liquid solder flux and clean up afterwards. Failing that, remove the solder, clean up the lead and then resolder using only a little (enough to do the job). Clean up afterwards. I like Electrowash PX and a toothbrush.
Hugo is right though. An oxidized lead will not accept solder easily.
-Chris
Netlist said:
Good solder? Man, I bought some from Radio Hack that is supposedly 4% silver but it looks so DULL when it hardens.. I dont get it.. I am concerned now. I also have another roll, just standard stuff from RS and it looks dull when it hardens as well.. I hate the way it looks.. but dont care if its doing its job.. any reason to believe that this solder should be replaced?
I can tell you all of the joints had a nice "creep" affect where the solder would look as if it was creeping up the wire.. thats why I dont get where I went wrong.. but who knows.. maybe I missed one..
I have some paste flux.. shall I dab a little on each joint and heat it up?? I bet that would do the trick nice???
Hi Joe,
-Chris
Exactly the way it should look. Those joints are fine. Ball should be treated with deep suspicion.
Unless it is for electronic soldering, NO! Electronic flux is typically a yellow liquid.
-Chris
You worry too much. 🙂
Your solder is fine. As Anatech said, rather remove what seems too much and restart with a bit of fresh solder.
/Hugo
Your solder is fine. As Anatech said, rather remove what seems too much and restart with a bit of fresh solder.
/Hugo
Netlist said:
Normally I would get angry about someone telling me what I am.. but in this case you are correct.. I worry way too much.. OKAY ON THE FLUX! I WAS GOING TO USE PLUMBERS FLUX! 🙂
I'm gonna stop by radio hack and treat myself to a new solder iron 🙂 I have 3, one for each temp range.. but it sucks managing all 3 of them.. 🙂