2008 SOLDANO SLO 100 MK1 - noisy mains transformer and another surprise

[Overtone85]

I recently purchased a mint condition 2008 SLO 100 Mk1, almost unused, with the stock Sovtek 5881 tubes in it. I tested it with the seller in his recording studio, in the rehearsal room. In the excitement ( and the loudness! ) I didn't notice that the mains transformer has mechanical noise/buzz ( at bedroom volume it's almost worse than an old plexi). You can't hear it in the speaker so the signal is fine, it's sounds awesome.

Is this normal for these supposedly magic DeYoung transformers everybody raves about?

Also I pulled out the power tubes for inspection because one of them was glowing blue with the volume at whisper level, gently of course, and for every tube, the contacts for pins 2 and 3 got partially pulled out of the socket.
I noticed that the tubes had some solder on the tips of the pins, almost as if someone tried to thicken the tips on the pins slightly.
I opened the amp for inspection and luckily there was no damage. Because of the way Soldano wires the sockets, by twisting the lugs, the tabs that keep the contact from pulling got flattened a little bit and it made them easier to slip out. I just needed to push them back in, all good, no shorts visible, no wires bent.

But it is very strange that the tubes had that 'thickening' on. Have you ever seen anything like that?

 

[Rocker68]

Normal manufacturing process. Every power tube I've looked at had that. I always power down to remove tubes. Blue is good color.

 

[Bronco]

I recently purchased a mint condition 2008 SLO 100 Mk1, almost unused, with the stock Sovtek 5881 tubes in it. I tested it with the seller in his recording studio, in the rehearsal room. In the excitement ( and the loudness! ) I didn't notice that the mains transformer has mechanical noise/buzz ( at bedroom volume it's almost worse than an old plexi). You can't hear it in the speaker so the signal is fine, it's sounds awesome.

Is this normal for these supposedly magic DeYoung transformers everybody raves about?

Sounds exactly like mine, which is a 1990. Normal as far as I know.

 

[Chubbs]

Have you checked the bias and mains current and fuses? It’s probably fine but I’d hate to see you pop a discontinued transformer. Only time I’ve ever had a transformer buzz was when I was drawing a ton of current, but I’ve never had an SLO.

 

[Overtone85]

Have you checked the bias and mains current and fuses? It’s probably fine but I’d hate to see you pop a discontinued transformer. Only time I’ve ever had a transformer buzz was when I was drawing a ton of current, but I’ve never had an SLO.

It was doing the same thing after i pulled all the power tubes. I will try again pulling all tubes and taking measurements.

 

[zewango]

SLO's I owned also had hum

 

[Overtone85]

Have you checked the bias and mains current and fuses? It’s probably fine but I’d hate to see you pop a discontinued transformer. Only time I’ve ever had a transformer buzz was when I was drawing a ton of current, but I’ve never had an SLO.

I checked the voltages with all tubes pulled out. Transformer still humming.
Mains: 231vac (i'm in Europe).
Unloaded heater voltages on tube sockets: 6.6vac
B+ secondary: 345vac on each side before the rectifier.
Bias tap: 57vac
I have no tools to measure current at the moment. But the mechanical hum doesn't change when the amp is loaded. Must be simply vibration noise. Transformer doesn't seem to get warm quickly, stays cooler than an idle Plexi for sure

On a side note though I just found that this amp has 100hz hum in the Phase inverter as well, which you can hear in the speaker in a silent room. with all the preamp tubes removed except the PI, the hum is still there. If I pull out the PI but leave the power tubes, the 100hz hum goes away and i hear just a very quiet hiss in the speaker. the transformer hum of course is still there. Changing PI tube doesn't help.
I made a quick search and it seems this is not uncommon in SLO circuits. Does it depend on the Heater winding artificial center tap? Is this the reason why people implement elevated heaters in SLO clones and does it really help?

 

[Overtone85]

I also found a way to push the crimp tab of the output socket contacts back in so that the tubes won't pull them out anymore. I filed the solder buildup off the tube pins and everything works like in a normal amp when replacing tubes

 

[glpg80]

Bad filter caps. Time for a re-cap.

 

[Fusionbear]

Bad filter caps. Time for a re-cap.

To the OP: Do you have a picture of the guts?
That will tell a lot...
I think glpg80 is onto something...

 

[CrystalSky]

Bad filter caps. Time for a re-cap.

Mine did hum a little bit after turning on after sitting couple years untouched, but after couple minutes I guess it warmed up and no hum. Is that okay or should I check something too?

 

[glpg80]

Mine did hum a little bit after turning on after sitting couple years untouched, but after couple minutes I guess it warmed up and no hum. Is that okay or should I check something too?

The hum is the PT itself. You should check Bias caps. Excessive current is from power tubes being wide open until negative voltage is negative enough. The slew rate degrades with cap age.

 

[CrystalSky]

The hum is the PT itself. You should check Bias caps. Excessive current is from power tubes being wide open until negative voltage is negative enough. The slew rate degrades with cap age.

Amp was built in 2014. Do they go bad so fast?

I can’t check anything, I am a noob

 

[glpg80]

Amp was built in 2014. Do they go bad so fast?

I can’t check anything, I am a noob

If you haven’t checked the bias in a while then start there. As tubes wear, bias will need adjustment. It could be a sign of worn tubes as well as a need for bias.

 

[glpg80]

Amp was built in 2014. Do they go bad so fast?

I can’t check anything, I am a noob

Depends on the date code of the cap and not when the amp itself was built

 

[CrystalSky]

Depends on the date code of the cap and not when the amp itself was built

I just thought Mike wouldn’t have kept caps for a decade before installing them, but will have to check it out somehow. Same goes for the tubes.

The hard part is there is literally NO professional amp tech in my whole country

Will look for that noise when turning the amp on next time.

 

[Overtone85]

To the OP: Do you have a picture of the guts?
That will tell a lot...
I think glpg80 is onto something...

When the PI is removed the power tubes have no hum, so I am assuming the filtering in the first stage is still good. The hum doesn't in crease with volume. it's stays quiet and it gets drowned when bringing the master volume up. Makes me thing it is more related to heaters rather than filtering.

As far as I've been told this amp belonged to a lawyer who bought it new and kept it in his office, rarely playing it, then the guy I bought it from took it from him 2 years ago.

 

[Chubbs]

Have you tried checked the Pi voltages or tried touching the pins with a meter? I find that to be a decent way to narrow down noise.

 

[mikey]

I have an '02, it has a little mechanical hum from the transformers, it's always been that way. I suspect it's more noticeable when you have an open headshell like Soldanos, as opposed to a shell that has far less venting.