Flux! I may be able to find some of the old style stuff on town. I have always used flux cored solder. Not cleaning or using flux when resoldering is probably an neb kind of error.
I do have good tip tinner and I use it.
I do have good tip tinner and I use it.
One other thing to check for - if you’re using twisted pairs from Comm cabling (I can’t tell for sure), it might be worth checking an inch or two up from each wired solder joint and see if the insulation has melted/bridged. I’ve used some comm wire with dialectric that melted quite easily, and Ive had this happen on more than one occasion.
Hi all, thanks for your ideas. I am currently waiting until my flux paste comes in and then I will work through these suggestions. I have a feeling the problem is that ground pin on the tube. I will get back to you with my results later one week.
I'm Back again, I obtained some flux paste and spent a lot of time cleaning and resoldering and I still have the buzz. When I turn up the volume, it has a staccato buzz with a background deeper hum. I need to replace one of my R1 resistors. I know they are matched to the transistors. With that said, they are just resistors, right? So if I replace the one suspect resistor with one that matches the other 3, it should work just fine, i think. I have not yet found any breaks or melted insulation in my com wire. I do not know what to do next. I hae not found any obvious bad solders. I welcome ideas or suggestions.
Thanks
Thanks
Sorry to hear that. But at least you have excluded a few possibilities.
The resistors are matched, but against each other. They are matched with the JFET, to provide a specific ampunt of current. Unless you make a jig and desolder JFET, or order a bunch of new ones along with various resistor values, I would consider ordering a new matched set from the store.
Also, have you checked CodyT’s suggestions?
The resistors are matched, but against each other. They are matched with the JFET, to provide a specific ampunt of current. Unless you make a jig and desolder JFET, or order a bunch of new ones along with various resistor values, I would consider ordering a new matched set from the store.
Also, have you checked CodyT’s suggestions?
You have two separate problems:
First - The Hum/Buzz
Second, T7 & T8 voltage of 13v
On the T7 & T8 voltage issue, check to make sure you have the 33.2K resistor in the correct place and not 332K. Since both channels have this voltage issue, check all the 332K and 33.2K resistor placements.
For the Hum/Buzz, use your DVM from the G2 pin on the nutube to the negative pin on the 10uF cap and one side of the 33.2K resistor.
I would avoid adding any more heat to the G2 pin and the PCB at that spot until you know if you have good contact from the G2 pin to the the two parts connected to it.
G2 is the grid pin.
Regarding your R1 issue, don't they have color codes on them? The three kits I bought all had resistors with color codes on them. Find a resistor color code chart and print it. I have one in front of me on my work bench at all times. Don't guess on the resistor value on R1.
Hi all, I have a piece of information to add. The buzz gets louder as the preamp warms up.
I have ordered the transistors, matched resistors, and another board is included.
I have ordered the transistors, matched resistors, and another board is included.
I'm going to try to get this post to take for a second time. I have gone through the offending channel again. I have replaced all of the transistors and R1 resistors. I have cleaned the darn thing and reworked all solders that looked like they might be weak. I have replaced the output wires and RCA jack on the offending channel. The buzz is still present. It seems to be getting louder every time I turn the preamp on. I need to Check on the 332 and 33.2 resistors as noted above. The connections to the G2 pins have been rechecked and are good.
Thanks you Elwood625 I found 2 335k resistors where 33.5 resistors should have been Voltage is corrected. Buzz is still there but is quieter. nutube is if anything, more microphonic.
On the ACA mini I deliberately chose different digits on resistor values to reduce that sort of error.
Tyerkey, if you want to try another nutube and don’t mind a bit of desoldering, Id be happy to send you my completed board. I had to rob it’s jfets, but it does work and sound great (no hum). Just PM if interested - no money necessary.
I already ordered a new nutube. I also changed out all of the capacitors on the offending channel and it made no difference.
Thanks for the offer though.
Thanks for the offer though.
So I installed the new korg nutube. Still had buzz. Hmm. I had refine cleaned or adjusted everything on the board. So I really focused on the ground circuit. The hum as barely audible, and both channels sound the same. I can only hear it if I lean close to the speakers with nothing playing. I may chase it further, but as of now I am done. I probably need to buy some higher quality RCAs. I really had to fiddle with them to get to 0 ohm resistance on the ground. There was one pole on my old nutube that has some melted plastic or some other material where it attached to the tube only visible from the bottom side. I do not think that was it. At any rate I’m sitting here listening to Robert plant and Allison Kraus. Life is good enough.
Suggestions on good RCAs are welcome.
Thanks for everyones’ efforts to help.
Suggestions on good RCAs are welcome.
Thanks for everyones’ efforts to help.
Congratulations! That is a great album to listen to, they have a new one coming out later this year.
I'm not very good at diagnosing ground hum issues, so far I haven't had that issue, yet. Either I'm blessed or lucky with grounds, however, I always follow this diagram for grounds.
I was just notified the new Alison Krauss, Robert Plant LP just shipped. The album name is "Raise the Roof", it's 2 LP's.
I was just notified the new Alison Krauss, Robert Plant LP just shipped. The album name is "Raise the Roof", it's 2 LP's.
