Geloso G600 tape recorded issues & questions

[snk]

Hello,
I have a Geloso G600 tape recorder (made in Italy in early 60s).

Here is the schematic :
https://archives.doctsf.com/documents/feuilleter_document.php?num_doc=65796&ref=41328#lg=1&slide=0


It works quite well (tape runs smoothly, etc), but it produces a lot of noise and hum.
I will clean all the mechanical parts, but I am also considering changing some capacitors in hope to help killing the hum and noise.

I have a couple questions :

1- it features two dual capacitors (16+16µF 350V).
I can't find a similar modern replacement, but I think I can use two 16µF electro caps (with the right voltage, of course), and wire their ground together, right ?
Would it be a good thing to try capacitors with higher values (like 33µF) for a better noise protection ?


2- I have read on several forums that many Geloso tape recorders featured selenium diode rectifiers which might cause hum and noise, and would require replacement.
From the schematic, it's a B250-C75 (600/20). I think « 250 » is the voltage, and « 75 » the milliamps, right ?
So am I right assuming that this diode rectifier could be a good replacement ?


3- I have seen this little component, looking a bit like a transistor, but with two legs. What is it ?





Thank you in advance for any kind of help !

[duck_arse]

your little thing seems to show markings of "E30 C25", which would make it the diode shown just above the DM70.

[snk]

your little thing seems to show markings of "E30 C25", which would make it the diode shown just above the DM70.

Oh, yes, that makes perfect sense (since the diode bridge is selenium type, and this "little thing" is marked "sel", so it could be a selenium diode I guess).
Thank you!

[snk]

By the way, this is how that lovely cheap plasticy tape machine looks :

[Rob Strand]

2- I have read on several forums that many Geloso tape recorders featured selenium diode rectifiers which might cause hum and noise, and would require replacement.
From the schematic, it's a B250-C75 (600/20). I think « 250 » is the voltage, and « 75 » the milliamps, right ?
So am I right assuming that this diode rectifier could be a good replacement ?

According to this page, B250 C75 is a selenium rectifier,

https://www.vintage-radio.net/forum/showthread.php?t=56093

Usually the selenium rectifiers where a complete set of 4 diodes.  Which you can see in some of the links off that page.

Your part looks like a silicon diode.   I didn't find any info in a hurry.   Short story is it's likely you can just use 1N4007's and that's it.   I'm assuming the diode you have shown is factory.

When replacing selenium rectifiers with silicons it's common to add a low valued series resistor, the value needs to be tweaked.   That's also mentioned in the link.  However there's a good chance you don't need the series resistor.   Unfortunately there's no test voltages on the schematic.

[PRR]

The main cap-pack can be two 22uFd 450V. Mild overkill.

The seleniums won't add "noise". If one of the bridge is blown it adds buzz. I'm sure this one is fine with a stock 400V 1A fullwave (Silicon) bridge. There's enough added resistance in this rig that lowered diode loss is no big deal.

The single diode may be the meter-tube rectifier and that will never fail.

> this is how that lovely cheap plasticy tape machine looks :

That's how they all looked in 1965. This Geloso is odd mainly that it was The Age Of Transistors but Geloso could still do it cheaper in tubes.

[snk]

Short story is it's likely you can just use 1N4007's and that's it.

Thank you!
So 4 diodes, wired like on the schematic, and it would replace the selenium diode bridge? There is nothing fancy in the diode enclosure, just 4 diodes?

[snk]

The main cap-pack can be two 22uFd 450V. Mild overkill.

Perfect, thank you PRR!

This Geloso is odd mainly that it was The Age Of Transistors but Geloso could still do it cheaper in tubes.

Yes, that's strange indeed!

[Rob Strand]

So 4 diodes, wired like on the schematic, and it would replace the selenium diode bridge? There is nothing fancy in the diode enclosure, just 4 diodes?

Yes that's it, it's just a bridge rectifier.   On the schematic it's drawn as 4 diode. but the physical device is a single unit.   (FYI: Quite often Selenium rectifiers had five terminals and you had to join two to form a bridge rectifier.)

[snk]

Hello,
I received the electrolytic capacitors, and changed them. With the new one, the tape machine is much, much more quieter 
Thank you for the help!

The only thing is that now, I still can here hum coming from "somewhere", caused by a ground loop. Sometimes, if I touch a component leg, or the tube shielding (but it's quite hot!), the hum goes away. I guess it is because the unit only features a 2 prong plug (and no earth), and when I touch the unit I am "making" the ground?

[Rob Strand]

The only thing is that now, I still can here hum coming from "somewhere", caused by a ground loop. Sometimes, if I touch a component leg, or the tube shielding (but it's quite hot!), the hum goes away. I guess it is because the unit only features a 2 prong plug (and no earth), and when I touch the unit I am "making" the ground?

Yes, with a 2-prong cord you can get hum/buzz which goes away when you touch something (it's really annoying!).   In equipment with plastic/wood enclosures you will find some parts of the circuit aren't shielded and adding a metal plate grounded to the circuit's 0V rail can help.   Sometimes you can put your open hand in certain places around the enclosure to find the weak point but often it doesn't generate enough noise.

[PRR]

> the unit only features a 2 prong plug (and no earth)

Do you have earth terminals in your rooms? Put a properly earthed appliance next to this Geloso. Take a clip-lead and tap it to metal on the appliance and the earphone/Uscita jack's shell. That should reduce hum/buzz. Or if there is old-age breakdown in the Geloso insulation, it will spark and blow house fuse (that's why I say start with tapping a clip lead). If temporary earthing helps, then figure how to change to a 3-contact earthing wall-plug.

[snk]

Put a properly earthed appliance next to this Geloso. Take a clip-lead and tap it to metal on the appliance and the earphone/Uscita jack's shell. That should reduce hum/buzz.

Tried, and confirmed 
Thank you, PRR!
(Now I only have to figure out how to add a 3 prong plug to the custom vintage plug socket featured on that Geloso  )

[amptramp]

Sometimes with old equipment that has a 2-prong plug, the level of noise or hum can be dramatically different when the plug is reversed in the wall socket.

In an audio system, only one component, usually the amplifier, should be grounded through a 3-prong plug if there is any connection to ground from the ground pin of the plug.  Otherwise, if you have multiple pieces of equipment using 3-prong plugs, you may get a current loop through the grounds.  If you have 3-prong plugs on more than one item connected through audio cable, only one item should have continuity between the signal return and the power ground.

[PRR]

Me, I would just carry a clip-lead rather than do it right, until I'd shown that this Geloso was an important part of my life.


Make a short 3-pin to 2-pin cable. The two power leads just go through. Use locally accepted wiring materials. The earth lead comes out to the side. You could connect it to the Shell of a 1/4" plug in the Uscita jack. If you don't want to break the (switched jack) speaker signal, hack off the end of the plug. If you need to take signal for further use, find the 1/4" Male-to-Female adapter and cut it up.

[snk]

Thank you!
I just replaced the original sockets by regular 1/4 jacks (well, a regular jack at the input, and a switched jack at the output, so the speaker can still work as expected).
When using jacks, the noise is gone (I guess the hum goes to ground through the jack's ground).

For sure, this thing isn't a Studer reel to reel, but it's a fun tape machine and I am glad to have made it work better