Funkwerk Leipzig MVT 4050 T tube mic preamp

[rock soderstrom]

.input transformer looks like UI30 lamination used.

I'm curious to see how it measures up and how it sounds.

Here are some more detailed photos:



Here the OPT:

 

[moamps]

View attachment 118293

Don't be mad at me for telling you this, but you're drawing electrolytic capacitors upside down.

View attachment 118299
Could it be that this "capacitor" is a combination type, with a parallel rectifier diode that is dead? That would explain a lot, I'm about to cut this thing open...

What do you think?

Edit: The capacitor is polarised, quite unusual for a 0.01uF type. It also has this marking on the anode side:
View attachment 118294
No max. voltage markings...

That's the selenium rectifier.
https://www.eevblog.com/forum/projects/diodes-die-pictures/50/

 

[rock soderstrom]

Don't be mad at me for telling you this, but you're drawing electrolytic capacitors upside down.

No problem, what's wrong is wrong ...I was affected by the stink of the amp last night

That's the selenium rectifier.

Thanks! That makes perfect sense. I will kick em out...it has no continuity, no matter from which side RIP

Edit: So far I have only seen the West German selenium rectifiers...ich bin Wessi!

 

[rock soderstrom]

The 0.01 marking therefore means 10mA nominal current at which the diode should be operated or maximum current?

 

[Cqwet Dbdfte]

Don't need max voltage marking, just follow the smoke trails...
Is it soderstrom or Söderström?

 

[Cqwet Dbdfte]

I see little value in old parts, except tubes,and paper/oil/glass caps.
Terrible tolerances, bad specs, short life. The HP200AB manual from '53 brags about electrolytic life of "five to ten years".
I know guys who restore old car radios, they hide new parts inside old ones.
I had paper capa catch fire and burn smelling as an autumn leaf burn. Happy days

 

[rock soderstrom]

Don't need max voltage marking, just follow the smoke trails...

Is it soderstrom or Söderström?

It doesn't matter, but it looks cooler with German umlauts. I was given this name years ago by a game engine... where does your name come from? I'm trying to imagine how to pronounce it! LOL

 

[rock soderstrom]

I see little value in old parts, except tubes,and paper/oil/glass caps.
Terrible tolerances, bad specs, short life. The HP200AB manual from '53 brags about electrolytic life of "five to ten years"

I'm going to throw out almost all the capacitors, they're all leaking. For instance, oil and a black sludge comes out of the square (MP??) capacitor...together with the smell, that's certainly not so healthy.


The stuff is really old now, built in 1957, it's time to retire.

 

[Cqwet Dbdfte]

Check the Swedish phone book, you'll find a few. ,
My pseudonym is just a random keyboard attack.

 

[rock soderstrom]

Check the Swedish phone book, you'll find a few. ,
My pseudonym is just a random keyboard attack

I had already guessed that the Soderstroms, probably with a ø, come from Scandinavia.

In my head you are named Cigwet from now on.

 

[amplexus]

I'm going to throw out almost all the capacitors, they're all leaking. For instance, oil and a black sludge comes out of the square (MP??) capacitor...together with the smell, that's certainly not so healthy.
View attachment 118303
View attachment 118304
The stuff is really old now, built in 1957, it's time to retire.

There is a greater than zero chance given the era that that’s got one of the various PCB oil formations inside it. Use gloves, avoid touching any leaked fluid and wash hands extremely well after! If any fluid has spilled elsewhere, clean well with isopropyl.

If possible, don’t just throw in trash, but take to a depot that handles hazardous wastes.

 

[rock soderstrom]

There is a greater than zero chance given the era that that’s got one of the various PCB oil formations inside it. Use gloves, avoid touching any leaked fluid and wash hands extremely well after! If any fluid has spilled elsewhere, clean well with isopropyl.

If possible, don’t just throw in trash, but take to a depot that handles hazardous wastes.

Without wanting to panic, but I think you're right! I'm washing my hands a lot at the moment, more so than during the coronavirus pandemic. It's no exaggeration to point this out. Make sure you have good ventilation! Washing your hands is mandatory!

I have no idea where the irritating odour comes from, an open window and a fan are a minimum. No joke!

I am collecting all the affected parts in a zip bag and will hand them in at an appropriate disposal point.

 

[Cqwet Dbdfte]

Chances are that old oil caps had Polychlorinated Biphenyls (PCB) which was banned in 1977.

 

[rock soderstrom]

Chances are that old oil caps had Polychlorinated Biphenyls (PCB) which was banned in 1977.

I've heard that too and that's why I always treat old capacitors that emit liquids and snot with a lot of respect.

The decision has been made that I will modify the amp considerably and completely rebuild certain parts (e.g. PSU). All the capacitors and parts of the resistors are going in the bin. (=appropriate disposal point)

I will open a dedicated project thread for it, it will be fun.

 

[Tubetec]

I was going to add a warning about PCB in caps , but I see other have chimed in about it already ,
use gloves ,especially if your using solvents to clean up the black goo .

 

[rock soderstrom]

It is also interesting to note the significant differences in size between old and new capacitors.

Here the toxic 2uf MP capacitor compared to the modern 2.7uf MKP model.

 

[amplexus]

It is also interesting to note the significant differences in size between old and new capacitors.

Here the toxic 2uf MP capacitor compared to the modern 2.7uf MKP model.

View attachment 118601

100%. I replaced this a few weeks ago and its really insane to see the size difference

On the left 10u/700V completely inert, on the right 8u/600V and full of highly carcinogenic PCB laced Dykanol.

 

[rock soderstrom]

100%. I replaced this a few weeks ago and its really insane to see the size difference

Ho ho, that's really an impressive difference in size!

Here is another candidate from the Funkwerk amp. A 1.6nF non-polarized capacitor also with a considerable size for its max. voltage.
It was one of two capacitors that was within tolerance, the rest were KIA.


However, not using it for a long time can damage the capacitors and especially the electrolytic caps more than continuous operation.

Some of them looked like new, but were totally blown.

Even this cathode resistor bypass cap has four times the nominal capacity. That is never a good sign. At least he didn't leak like most of the others.