• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Dynakit ST-35 - quiet static (popping noise) in one channel. Help!

Brice,
IIRC, someone ran tests ,new v. old . The new iron is electrically identical. They are accurate reproductions and the new PTs are better.
 
I was running a minds eye exercise, thinking about a build, buying parts, or a complete kit. If you got a deal on an old one at a ham fest or a flea market, or garage sale you could do a restore. If you're paying auction site prices, I think it's a better deal to do new kit. I would recommend Dave's EFB PS board in any build. Many believe this was Dynaco's best sounding amp. I have no first hand experience with one. Keep in mind , you're talking 17wpc so you need reasonably efficient speakers. I'll be waiting to see your build and your impressions.
 
And....


Success! Hooray! It took a while for the new resistors to arrive but it is well worth the wait to have my sweet little tube amp working again! Thanks to all who helped... this is why this is my favourite community on the internets.

Check out those cool new red 300k resistors.
 

Attachments

  • IMG_3836.jpg
    IMG_3836.jpg
    67.2 KB · Views: 53
Alright. The bad news is that I'm back. And the worse news is that I'm back because the static is back. Still an intermittent static that seems to build in intensity quickly to a quiet snap and then nothing for a few (5-10) more minutes. Repeat. UGG. Been getting worse over the last month or so.

Here's what I've done:

Contacted Kevin at Dynakit to ask for further help. Sadly, it seems that Kevin is having health issues and the business is (hopefully only temporarily) on hold.
Rotated tubes. No improvement, the issue stays in the left channel.
Tested all components on the board with a multimeter and compared to the other side. No differences found. This is how I found the bad resistor the first time.
Swapped the 3 large capacitors on both boards (to try to see if the issue moved to the other channel). No improvement nor change.
Replaced (again) the resistor that was an issue (although measured fine this time). No improvement nor change.

Theoretically, I can continue to do the swap of parts from one side to the other and test after each move to see if I can identify the problem. Time consuming and unpleasant but possible.

Anyone got any suggestions as to what to try next?
 
Brice said:
Hum, this is not fun.

Have you changed the small caps, looks like silver mica on your board?
Click to expand...

Yup. Did that initially on the suggestion from Kevin at Dynakit. No dice. :(

Edit to give a quick update on what has been done:

Ensured the Russian coupling capacitors are not contacting the chassis.

Replaced the solder trace with a jumper from Solder Pad 10.

Cleaned each pin socket with De-Oxit and a small dental brush.

Tightened each socket with a dental pick.

Traded around tubes and tried rocking them gently in place while on.

Replaced the black silver mica caps on the boards.

Tested all components on the board with a multimeter and compared to the other side. I found one resistor (R5) that measured differently (basically no resistance) from the same on the good board. Replaced and this seemed to make the issue go away for a couple months.

Now the static is back.
 
Last edited:
Maybe I state the obvious, do you have spare coupling caps to try?

Else the last measure would be to swap the boards around to see if the pop follows...
 
I've read of people getting bad Russian coupling caps though it's rare. You could also try swapping the OPT's from side to side to rule them out.
 
Never had a bad one. But I also think it's capacitor related. The silver mica do fail, by DC leak. I did not know that before.
 
I've had similar problems with carbon comp resistors - usually 60s vintage, though - where hair line cracks were introduced while recapping an amp. I almost always showed up as a sizzling, scratchy sounds. You'd see them in any application where the high voltage was sufficient to support arcing at close distance.

In one case, I was able to identify them by turning off all the lights and actually observing the arcing that showed up as a faint colored light that got worse when I flexed the board the resistor was mounted to.

They're rather nasty because they measured resistance ok with an ohm meter but acted out under power.

Key things:

- Constant sizzling sound

- Might be influenced by flexing of the board.

Hope that might provide a hint.

Cheers,

David
 
I was thinking some kind of arcing event too. Would it be possible to set up with the cover off and to view bottom in dark room. Watch while popping occurs. Good chance it'll show itself
 
Early on in this thread, I suggested that you remove the 7247 driver tube from the channel that is making the noise, to help isolate whether the problem is in the driver stages, or the output stage -- but I never saw any results of you trying this. I would again strongly suggest this simple test (which will hurt nothing) to help focus your search in finding the critter!

Dave
 
Thanks for all the help!

I've replaced all the small silver mica caps and I've swapped the Russian coupling caps to the other board and the problem has not changed.

Resistors do seem like a likely culprit as replacing the one that measured bad did seem to fix it for a couple months.

Dave - check out post 22:

TravAndAlex said:
As Dave suggested early on and I foolishly forgot to do it when I was trying everything else...

Just tried it without the front 7247 tube on the left side and NO popping noise. Swapped the tubes and put them both back in and the popping is back! Does this mean it is one of the mica caps next to the the 7247 tube?
Click to expand...
 
Ah! Thank-you! I missed that on my look back. If you have any spare power supply electrolytic cap available -- say about a 20 uF at 400 vdc -- you can further isolate where the problem is by grounding the negative side, and connecting the positive side to pin 6 of the 7247 driver tube. Do this BEFORE you turn the power on, and do not disconnect it until after the unit is turned off. While it is connected and on however, listen for the noise. If it is still there, then the problem is in the inverter section of the driver tube, and if gone, then the problem will be in the AF Amplifier section.

I hope this helps!

Dave
 
dcgillespie said:
Ah! Thank-you! I missed that on my look back. If you have any spare power supply electrolytic cap available -- say about a 20 uF at 400 vdc -- you can further isolate where the problem is by grounding the negative side, and connecting the positive side to pin 6 of the 7247 driver tube. Do this BEFORE you turn the power on, and do not disconnect it until after the unit is turned off. While it is connected and on however, listen for the noise. If it is still there, then the problem is in the inverter section of the driver tube, and if gone, then the problem will be in the AF Amplifier section.

I hope this helps!

Dave
Click to expand...

THANKS! I'll see what I've got around and give it a try!
 
Just priced out changing all the remaining resistors. I think I'll give that a try. For $10.24, metal film here I come.


Quantity

Image

Name

SKU

Each

Total

2


PRP Resistor_76598 1K3 / 0.5 (1/2) Watt, Metal Film, 1%, 100ppm, Non-Magnetic, Each

PRP-76598

$0.45

$0.90

2


PRP Resistor_68627 47K / 0.5 (1/2) Watt, Metal Film, 1%, 100ppm, Non-Magnetic, Each

PRP-68627

$0.45

$0.90

2


PRP Resistor_68629 150K / 0.5 (1/2) Watt, Metal Film, 1%, 100ppm, Non-Magnetic, Each

PRP-68629

$0.45

$0.90

6


PRP Resistor_50251 470K / 0.5 (1/2) Watt, Metal Film, 1%, 100ppm, Non-Magnetic, Each

PRP-50251

$0.45

$2.70

2


PRP Resistor_50196 27K / 0.5 (1/2) Watt, Metal Film, 1%, 100ppm, Non-Magnetic, Each

PRP-50196

$0.45

$0.90

2


PRP Resistor_62520 27K / 1 Watt , Metal Film, 1%, 100ppm, Non-Magnetic, Each

PRP-62520

$0.65

$1.30

2


PRP Resistor_70175 33K / 1 Watt , Metal Film, 1%, 100ppm, Non-Magnetic, Each

PRP-70175

$0.65

$1.30

Subtotal

$8.90

Tax Total: NS (15.00%)

$1.34

Total

$10.24
 
You must log in or register to reply here.
Back
Top Bottom