grundig: SO390-U/S; Stereo Console

hi,

i inherited this console fron my grandfather, Te power transformer was shot, because the filter caps failed, and someone put a wire in the fuse. 

I sent the trasformer to repair it, but the technician dissapeared with the transfomer.

the console sat for years collecting dust in my house, and now i decided to finish the repair.

i will make a full recap and change the selenium rectifiers.

i started collecting info about it to figure out the specs of the transformer.

i found the schematic for the amplifier(NF2) and with this info i figured out some specs

For the B+:

312V@150Ma after rectifier.

312/1.44=217 

first tap= 220V@150mA, but to be sure 220V@250mA.

If i consider the transformer regulation then 240V@250mA

For heaters the transformer have 2 windings:

first one for tubes in amp section and dial lamps.

The consumption for all tubes is around 4A

so this winding is 6,3V 4A

second one for tubes in pre/tuner section:

the consumption for all tubes is around 3A

So This winding is 6,3V@3A.

For bias

-16V after rectifier.

then it is adjusted with resistors to -11V 

so this winding is 12V@30mA

so far so good, but then i came across the sams photofact for this model and the values are not the same for b+

the specs for the transformer are the following:

Secondary 1: 320V@150mA

secondary 2: 6,3V@2,4A

secondary 3: 6,3V@4A

secondary 4 15V@20mA.

also lists 330V after rectifier.

i'm a little confused. 320VAC is way to high even to get 330V after rectifier and considering the loss in selenium rectifiers and transformer regulation.

also i think 150 mA is too little. 

i'm missing something?

also i'm curious about output trannies.

the sams photofact lists the following

primary: 5Kohms CT

secondary 3-4 ohms

i think 5K ist too little for  2 el84 Push-pull.

maybe is 5k between plate and center tap?, so the transformer is 10K?

 

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Dear Alfonso,

voltage values given in the diagram of the radio here in Radiomuseum appears correct. 220V rms is the proper voltage to have more or less 312V DC across C17 and C18. Unfortunately this transformer is quite complex, with several windings, and is hard to find as of-the-shelf component. If you do not find it, you could give a look at this site. They have some transformers that can be adapted and can even wind a custom transformer.

Regards, Emilio

 

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dear Emilio,

Thank you,

I supposed that will be hard to find an of-the-shelf transformer, but with the specs there are several guys here that can made a custom transformer for me.

Kind regards,

Alfonso López

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Actually Alfonso,  there is a repair shop in the Los Angeles area, USA.  The owner, Jon Pomazi (an RMORG member) can accomodate you with an original transformer.

Telefunken transformers (especially in the Opus series) have shown themselves , to be utter junk (in my opinion), the Grundig transformers, from that era, are the best!

Audio Imports LTD

 

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Thank you Omer,

I will ask him

Kind regards,

Alfonso López

 

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After a long time the console is working.

 didn't posted here because i formatted my computer and lost my password.

I made a custom transformer. i wish i have the original transformer but this works for now. 

the specs are 

secondary 1  230V 250mA

secondary 2  6.3V 5A

Secondary 3 6.3V 4A

secondary 4 15V 30 mA.

i only got 290V in the B+, because the voltage on the transformer is lower when loaded,

i made a full recap, and also changed all the resistors in the nf2 because all of them readed 50 or 100% higher. the only resistors i didn't changed are the 2 big power resistors. Also i changed the tube sockets

when the amplifier was running fine i moved to the tuner. also i made a full recap and changed dome burned resistors. aldo i changes some ceramic caps shorted( the cause of the burned resistors)

also i cleaned all the sockets

the radio works fine on all bands, but distorts on the stronger FM radios.

maybe it will benefit of an alignment, but i don't have yet the tools to do that.

I had to recone the woofers

 

Also i recapped the reverb unit and is working fine after cleaning several times all the sockets.

Also i serviced the record changer (PE66) now everything works, but it turns alittle fast( maybe 36 RPM), don't know why. aso i had to change the cartridge because it skipped on some records. the original cartridge was a PE186, the new cartridge is a PE188. 

Also i experimented putting a shure SC35 with a preamp, but there was a lot of hum.

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I put a dual cds 661 cartridge on the record player. it tracks a lot better and only at 4g and sounds better.

It was almost a drop in replacement.

Here is a video of it working.

I still have a littleproblem with the speed

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