Geloso tape machine voltage question

[snk]

Hello,
I have an old Geloso 600 tape recorder. It's a cheap italian stuff, using tubes. I would like to use it for various (lofi, obviously) recordings, but it features only one single MIC input, and it uses an old kind of plug (which is neither jack, cinch, or din).

My goal was :
1 - to make a little box to lower the volume coming from instruments or mixer to the tape machine (well, or use a DI) ;
2- change the plug to either jack or cinch (depending on the size inside) ;

BUT, while browsing the internet, one post caught my attention :
https://www.vintage-radio.net/forum/showthread.php?t=46668

« I just restored a mid 50s Geloso G255 open reel recorder and was horrified to see that the chassis in these recorders (and also in the later G600 and other valve models) has U-series valves and is LIVE at full mains potential including the mic socket ground!
The user was somewhat protected from electrocution by recessed jack sockets and a well insulated microphone.
Of course it would be extremely dangerous to connect anything other than the original INTACT, undamaged microphone to this recorder, don't even think about making an extension lead to record from a PC or anything! «

Here is the schematic of the unit : https://www.doctsf.com/geloso-g-600/f41328

Am I right understanding that :
- You can die if you touch the steel chassis when the unit is powered on ;
- and high voltage is running through the ground wire... which could « go out » in a harmful way if I try to plug the tape machine mic input to a DI ?

Is there any solution to « fix » that, so I could safely plug a jack (coming from an instrument, a DI or a mixer) into the mic input ?
Would a DI with « ground lift » do the job, or is it something else ?

Thank you !

[PRR]

You can die

Unlikely--- a string of dead customers is bad for business.

But don't listen to strangers on the internet. Get a dry wood or plastic table, outlet, voltmeter, clip-leads, and a 10k resistor. Clip a resistor from chassis to electrical "ground". Clip (don't hold!) voltmeter leads across the 10k resistor. Meter on 300V AC. Now plug-in. That quote says you get 230V. If that schematic is right, there is ONLY trace leakage, and the 10K (approximate human body) will bleed most of it off.

[Rob Strand]

I'm with PRR the schematic and the comments in the post don't agree.

The unit in the post could have had a fault - simple as that.  Any part involving the mains could have developed a short to ground.    A fault to ground in the transformer, motor, power switch, fuse wiring could have done it.  Old wire insulation can rot over time and short to the chassis - be particularly careful with old rubber insulation.   In the post the restoration process itself could have even promoted one of these, or other, failures.

As a side note: old products do not comply with modern product build standards - especially for safety.  Some of the old practices definitely allow for more bad things to happen.   When you use old devices with aged insulation you have to be aware there could be a danger of fire or electrocution - it's a real possibility.   If your country doesn't enforce earthing of the chassis then you are at even higher risk.

These days I don't really like using old transformers with over-wound windings.   Maybe after 60 years the insulation between the primary and secondary cannot be trusted.

[PRR]

I've added a cleaned-up schem in my above post.

transformers with over-wound windings

For more fun: I read it as the motor is also the transformer. (Put another pound of metal in it, avoid a separate part.) Which makes replacing leaky parts trickier.

[Rob Strand]

For more fun: I read it as the motor is also the transformer. (Put another pound of metal in it, avoid a separate part.) Which makes replacing leaky parts trickier.

You could be onto something there.   I kind of filtered out the funky symbol but now you mentioned it  ... hmmm, what is that all about.  (Didn't spend enough time to find a good gut shot of the unit.)

[PRR]

a good gut shot

It's not that much bigger than a cassette Walkman (well, 2.5X, but still teeny for a reel machine).
The motor is like many cheap-cheap fans, rotisseries, and phonographs, a winding on an H-core with shaded poles.

[drdn0]

I would be shocked (heh, what a pun) if the issue here wasn't that old mate 'restoring' it has flipped active/neutral in the mains connection.

Either way, get a sparky to take a look at it (especially if you're not confident with mains), and install a new plug with an earth connection bonded to the chassis as a precaution.

[Rob Strand]

It's not that much bigger than a cassette Walkman (well, 2.5X, but still teeny for a reel machine).
The motor is like many cheap-cheap fans, rotisseries, and phonographs, a winding on an H-core with shaded poles

Now combining the transformer and motor makes a lot of sense.   Saves a lot of space, even simplifies the wiring a bit.    Quite a clever step for that product.

[PRR]

flipped active/neutral in the mains connection.

Any device which depends on one line wire being "less hot" than the other is already unsafe.

There are places where residential outlets are fed in Delta, both live wires equally hot to dirt.

However IF that schematic is to be believed, there is no galvanic connection across the transformer(/motor), and safety is as good as the insulation.

[snk]

Hello,
Thank you all for the advices.

But don't listen to strangers on the internet.

Yes, this is why I wanted to ask here. What I had read surprised me, but I wanted to be sure.

For more fun: I read it as the motor is also the transformer.

Yes, indeed.

install a new plug with an earth connection bonded to the chassis as a precaution.

It looks like a wise advice. I need to figure out how to do that (I mean, space wise : the original plug socket is unusual (by today standards), and the molded plastic enclosure doesn't really allow for a clean mod.

From what I understand, and if the test PRR suggested above succeeds, I can safely change the mic socket and use it with anything?

[Lino22]

Unlikely--- a string of dead customers is bad for business.

    

[antonis]

Those old-time schematic drawings could drive an unfamiliar repairman nuts..!~!  

e.g. those non-polarized caps with "K" after number (1000 x μF, or pF or what..??) or those polarized caps 16+16μF are set in parallel (32μF) or in series (8μF)..??

[diffeq]

Those old-time schematic drawings could drive an unfamiliar repairman nuts..!~!  

e.g. those non-polarized caps with "K" after number (1000 x μF, or pF or what..??) or those polarized caps 16+16μF are set in parallel (32μF) or in series (8μF)..??

Glad that at least 05E volume pot didn't disturb you. 

[drdn0]

flipped active/neutral in the mains connection.

Any device which depends on one line wire being "less hot" than the other is already unsafe.

Isn't that mains in the US/UK/Aus though?