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Dynaco PAS 2 or 3 static with nothing connected and independent of volume

stanko said:
I think B+ is connected to the board via grommets also. The circuit board under the selector switch can be ignored, that is the mag phono board, and the OP said it occurs on all input settings, as well as when the power supply is turned off for 15 or 20 seconds. So, concentrate on the board that is parallel to the front, that's the voltage amplifier that's causing your problem.
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So an update on my progress, I removed all ground connections and will have them resoldered tomorrow. Should have new plate resistors in on m Monday. Just received the shorting caps on the mail today so I'm hoping tomorrow I can rule out the ground connections and can test each input with the shorting caps. I checked all soldered connections on the power supply board and they look good. Looking over the Erhard photos that were posted and will validate those tomorrow as well. Hopefully this will help narrow down the cause. I can't thank all of you enough for the help on this. I've never worked on a PAS before so this has been a crash course and I can't thank this community enough. More to come as I work through this. Not an electrical engineer so it's probably taking me longer than those who have experience with this but thank you again for the direction.
 
So I removed all of the solder of the old ground connections, cleaned the areas and resoldered. Still have the popping sound, however it does sound fainter or maybe it's just my ears hoping for some improvement, but it is still there. Received the shorting plugs and tested those out, still same issue. I should have the new plate resistors in sometime tomorrow so will install those. Looking through the erhard connections and will make sure everything is connected properly.

Regarding the ground connections, should I be using something besides the ear tabs for the can capacitor? I know the capacitor is bypassed with the erhard power supply board, and I cleaned each of the tabs and connected the wires to them ensuring lead went to the chassis. Is there a better way to ensure a solid ground on this?
 
I've experienced that static/popping sound from dirty tube pin contacts.
Did you clean and retension the tube sockets yet?
I'm not familiar with the printed circuit boards in your unit. If it has traces on the top and bottom you should look for a cold or broken solder joint on each side. I would suspect the solder connections around the tube socket pins...they get flexed during tube removal and insertion.
 
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heyraz said:
I've experienced that static/popping sound from dirty tube pin contacts.
Did you clean and retention the tube sockets yet?
I'm not familiar with the printed circuit boards in your unit. If it has traces on the top and bottom you should look for a cold or broken solder joint on each side. I would suspect the solder connections around the tube socket pins...they get flexed during tube removal and insertion.
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I have used this kind of tool to clean the insides of the pin sockets on tube sockets.

https://www.homedepot.com/p/Lincoln...th-12-Stainless-Steel-Reamers-KH575/100341101

Worked well for me.

Shelly_D
 
What is the best method for cleaning? I've heard both ways around using deoxit or not using it. I used a stiff brush in each of the contacts and compressed air so far. I did retension
petercapo said:
Did you rework the solder connections to the riveted eyelets on the PC boards? Sometimes they need to be completely cleared out, including removing flux residue. Then, solder the wire back in.
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I'll do that next. I only did the ground connections on the can. Removed all solder, scraped and cleaned any residue, trimmed and re stripped the wires, and then soldered.
 
In regards to jumping the switches, I haven't found a good instruction on that and want to make sure I understand this correctly. So the top wire on the switch to the bottom center? Just don't want to damage anything by jumping the wrong section.
 
petercapo said:
Deoxit is fine for metal surfaces, in general. However, I am not clear on whether it is okay on soft metals like the cadmium plate found on a lot of tube socket contacts. Deoxit along with any other chemicals should be kept off of any phenolic materials found in pots and switches, including the selector switch. My suggestion is to Google "interdental brushes" and use small ones dampened with 91% or better isopropyl. Try not to let the isopropyl get onto the PC board.



I must have missed this... jumping switches?
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Screenshot_20191124-222447.png
 
petercapo said:
Deoxit is fine for metal surfaces, in general. However, I am not clear on whether it is okay on soft metals like the cadmium plate found on a lot of tube socket contacts. Deoxit along with any other chemicals should be kept off of any phenolic materials found in pots and switches, including the selector switch. My suggestion is to Google "interdental brushes" and use small ones dampened with 91% or better isopropyl. Try not to let the isopropyl get onto the PC board.

.

I must have missed this... jumping switches?
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I copied in the screen shot from the first page of this thread. It was shorting the switches with a jumper wire. Haven't completed it yet as I want to make sure I'm doing it correctly
 
petercapo said:
Sounds like he is talking about bypassing the front panel features as a way to eliminate possible causes of the problem. You don't want to just arbitrarily short out switch contacts.

It would require a carefully considered procedure. I believe I previously posted a link to a document that offers a complete procedure for bypassing the tone controls, but I don't have anything handy for bypassing everything else. There was at one time a post by Joe Curcio in Dynaco Doctor forum where he posted a diagram showing how to bypass some of the front panel features, but you'd have to go look for it - sorry I don't have it handy. You certainly don't want to bypass the volume control, in any case.
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No problem. I've been reading up on his forum. Most of my front panel are already bypassed I'm just down to the volume, balance, stereo/mono, and input selector. If the problem is still there after cleaning the sockets, replacing the plate resistors, cleaning the selector contacts, then I'm going to replace the two pots. At this point I think it's narrowed down enough that those might be the ultimate culprits.
 
If I jumper the wiper of the volume pot with the signal high side, I will eliminate any noise due to a faulty carbon trace or wiper, if I further remove the ground side of the pot, I will end any current flow through the carbon in the pot, which also can be noisy. Taking out the pot will cause full gain, so I can't have any signal connected, but the procedure will determine if the problem is with the pot.
 
To Dave OP:

Noticed in your photo(s) that some of the AC wires to the rectifier don’t look to be twisted, it’s always a good practice to twist wires for noise reduction...not saying that’s the problem, but could contribute.

Also when it’s making static, if you reach a hand in like your gonna remove the rectifier tube*, does the static change?

*I’m not saying touch anything* Something like a wide piece of plastic would also work for the test....

BTW it’s a nice looking preamp, with a considerable amount of time and money invested even before you got your hands on it...Keep at it (-:

Andy



 
adnick said:
To Dave OP:

Noticed in your photo(s) that some of the AC wires to the rectifier don’t look to be twisted, it’s always a good practice to twist wires for noise reduction...not saying that’s the problem, but could contribute.

Also when it’s making static, if you reach a hand in like your gonna remove the rectifier tube*, does the static change?

*I’m not saying touch anything* Something like a wide piece of plastic would also work for the test....

BTW it’s a nice looking preamp, with a considerable amount of time and money invested even before you got your hands on it...Keep at it (-:

Andy


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I'll check that when I get home tonight. I'll also look at twisting the wires. Everything in the photos was how I received it and I'm still a noob at understanding the circuit of this device. Thank you for the suggestions I truly appreciate it
 
I'm interested in the outcome of this issue. My thoughts are a bad carbon resistor or a bad cap in the power supply. Since it's always generating noise you should be able to interrupt the signal path at different points and see if you can locate the section that's generating the noise. You can also run it with different tubes pulled to see if that helps isolate the problem.
 
JohnT123 said:
I'm interested in the outcome of this issue. My thoughts are a bad carbon resistor or a bad cap in the power supply. Since it's always generating noise you should be able to interrupt the signal path at different points and see if you can locate the section that's generating the noise. You can also run it with different tubes pulled to see if that helps isolate the problem.
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I'll update this thread this weekend. Unfortunately my resistors are now showing delivered tomorrow and we'll be leaving for the week for the holiday so won't be able to test the resistor until Saturday. I'm going to pull some tubes tonight as well as testing to see if a change in sound happens by reaching towards the rectifier tube. More to come
 
So the holiday weekend away was longer than I thought and yesterday was quite busy getting caught up. I replaced the two 100k plate resistors today and the popping sound is still there. I also used a plastic tool to move the tubes and wires while it was on and was unable to hear a difference at all throughout the testing. I also cleaned the tube pin sockets again, still have the popping sound.
 
where does the circuit board ground connect? Is that a solid contact? How about the heater supply leads? Those should go to the PS board.
 
Peter has tremendous powers of observation, i’d double check everything.....With that said, the new switch is probably because of the faceplate change, and most of the deeper replacements are 6 lug, but the ones I used had the same amp rating, just used 2 lugs, but did replace the disc capacitor.
 
Just go home from work. Going to hit the bench and check all soldered eyelet ground points, the disc capacitor near the switch, and I will get the voltage checks. I've been iffy on those. Am I removing the tubes and checking the voltages from pin locations where the tube was installed or am I leaving the tubes in and checking the voltages from the underside of the board? I cannot find any info in the manual other than which pins to check to ground and what they should be. I also cannot find any info online. Like I said previously I'm a newb on this device and just recently got into tube gear so a lot of this is uncharted territory for me. My AC mains are measuring at 123V.
 
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