DSL50 Issues

[dpm309]

Working on my bandmates DSL50 that was cutting out intermittently and crackling with the tone shift button out. Found solutions for both of these problems on this forum. Added a ground wire from the 16ohm to 4/8ohm jacks which solved the noise problem. Cut link 27 (near V3) and replaced it with a .022uf 600V orange drop cap and the crackling disappeared. Played through it for a few minutes with no problems. My bandmate was playing through it for about 15 minutes (with his pedal board connected to the effects loop) and then there was a load pop noise and static coming through the speakers. He tried switching cables and tubes with no luck. When he pushed the tone shift button, the amp started making all kind of noise.

I will be getting the amp back in a couple of days and was wondering if any of the mods I did could have caused this. Also could this be related to the effects loop itself? Any suggestions?
Thanks,
Dan

 

[dpm309]

Opened up the amp and rechecked the voltages and everything is in line except for V3. Pin 1- 400vdc, 2- 241vdc, 3- 244vdc, 6 - 241vdc, and 8 -2.4vdc. Pins 1,2, 3 do not look right. Looked all over the internet for voltage charts for the DSL50 with no luck. Voltages on V1, 2, and 4 look correct. Any thing I should be looking for?

 

[mickeydg5]

The problem sounds to be associated with the tone shift circuit.

V3 is a driver and cathode follower stage. The voltages mentioned appear normal, a bit high but again maybe normal for a DSL50.

Hopefully some DSL50 owners will comment.

 

[RickyLee]

V3 voltages on the DSL50/100 and TSL100/122 are high normally. Make sure you run a 12AX7 in V3 that can handle it. Some brands of 12AX7 do not last very long in V3 of these amps. I had even higher than that on my DSL and TSL due to my high wall voltage of around 125VAC. I ended up lowering the voltage a bit by increasing the two first upstream B+ dropping resistor values.

 

[dpm309]

Tried swapping a few 12AX7s I had in V3 with no luck. I removed the .022uf cap and reconnected the link and now have full sound back on the amp but am still getting a minor crackling with the tone shift button out. Ran the amp for a few minutes and it started cutting out intermittently again. Going to pull the board with the speaker jacks and beef up the ground wire that I connected previously from the 16 to 4/8 ohm jacks. I originally used only 1 piece of 22ga buss wire. Hopefully this does the trick.

 

[dpm309]

Well, it's back. Still having the same cutting out issues and I did notice that the heaters on V1 and V2 stopped glowing when it cut out. Tapping on the tubes brings them back up again so I am now thinking cold solder joint or something with the heater power supply for V1 and 2. This amp uses DC voltage for the heaters on 1 and 2 and AC on the rest of the tubes. Anyone ever run into this?

 

[Jazz P Bass]

"Anyone ever run into this?"

What, a bad solder joint?

All the time.

 

[Ken]

I know you did the ground mod; I did too on my DSL 50 due to the same crackling and cutting out. Then a year later, same symptoms as you returned. I found the 16 ohm jack itself was the culprit so I replaced the jack (cleaning is a band aid, not a solution) and now all is well.

You may decide a better quality jack will negate the need for the ground mod but I still have it because I don't trust ANY jack made after 1980.

Ken

 

[dpm309]

Thanks, Ken. I am not using the 16ohm jack, only one of the 4/8 ohm jacks. I think I have it narrowed down to the DC heater circuit for V1 and 2. When the amp cuts out, both V1 and 2 stop glowing. I cannot get the amp to cut out when I have the chassis upside down on my chassis cradle. Put the chassis back in the head cab, and it started cutting out again. The DC heater circuit is made up of a bridge rectifier and 4 e-caps. Since this is an intermittent problem, I doubt that any of those components are bad. Will pull the chassis again and remove the main board to check for cold solder joints.

 

[dpm309]

As I suspected, I found at least one cold joint on the bridge rectifier. Re-soldered all four legs and have been running the amp for about half an hour with no issues. I was able to access the underside of the main board by removing the rectangular cover that the tubes sit in on the top of the chassis. Saved a ton of time by not having to disconnect all of the jumpers and connectors and labeling them.