PT questions

[uki]

Hey guys !

I got this PT from a Geloso 268 reel to reel. Schematic attached.
The PT itself is confusing as you can see in the picture, heaters wires in the same side of primary wires.

The insulation on the wires are crumbling but the windings give readings.
Except for the purple wire, not even connected with the core.

I got some questions:

1- The HT winding(orange) read 35k ohms, is this right? readings attached

2 - What is the grey and blue windings for ?

3 - Advice replacing the wires ?

Thanks in advance !

[sluckey]

I got some questions:

1- The HT winding(orange) read 35k ohms, is this right? readings attached That's bad!

2 - What is the grey and blue windings for ? Grey is for a lamp bulb. Blue is to power three solenoids.

3 - Advice replacing the wires ? Run like hell!

Actually I have a good idea how to replace the wires but since the HT winding is shot, why bother?

[uki]

I got some questions:

1- The HT winding(orange) read 35k ohms, is this right? readings attached That's bad!

3 - Advice replacing the wires ? Run like hell!

 

Actually I have a good idea how to replace the wires but since the HT winding is shot, why bother?

Please tell me, 

after seen this video , i may try to fix the PT.

Thanks

[shooter]

i may try to fix the PT.

insure your fire extinguisher is electrical fire rated 

[sluckey]

i may try to fix the PT.

Why? The HT winding is bad or has a bad connection to those rotten wires. 35K is ridiculously high. That winding should read 200Ω or less.

Put some voltage on the primary and measure the secondary voltages before doing anything else.

[uki]

Put some voltage on the primary and measure the secondary voltages before doing anything else.

I did that !!  After some caring with the wires we dont want things to explode right!! 

My line was giving 117vac at the test moment.

Through a down step PT 120 to 12v

into the 110v primary of the PT.

The HT was giving 21.3v output !

Heater across wires 0.8v and sides with CT about 0.4v

The grey wind 2.3v

and the blue wind 0.78v


Is it good ?

Thanks

[johnnyreece]

Is it good ?

Thanks

Hard to say.  Is there any indication what the HT winding is supposed to be? 

[sluckey]

The voltages appear normal. I'm still concerned about that high resistance reading on the HT winding. Could you measure that again?

[uki]

The voltages appear normal. I'm still concerned about that high resistance reading on the HT winding. Could you measure that again?

I did, several times, all times the voltage was the same 21.3v on HT...

But,  the resistance did change almost every time it was plugged/unplugged   
2.7k at the first reading today!!  I was really surprised, what happened to that 35k
it was the result after reading more than once yesterday...

So 2.7k at fist then 6.5k , 8.6k , 9.5k, then back to 6.5k and changed again...
The PT was unplugged between ohms and volts read.

I did read with three different multi meters to make sure. 

thoughts ?

Thanks !

[sluckey]

All of those DCR reading are way high. Most likely a bad connection where the tiny winding wire is soldered to the external lead. You would still get a correct voltage reading, but as soon as you connect some load to the winding the voltage will likely go way down. I suggest connecting 120VAC to the primary and measure the HT winding voltage. Then connect a 10K 10W resistor across the winding and see what happens to the voltage.

[uki]

Reading the PT voltage connected to 115vac, without the resistor the output is  161v
with the resistor output is 156v

Now the surprising part, after unplugging and reading ohms it does give way less now, i did repeat the process a few times

readings are: 471r , 431r , 444r , 454r

thoughts?

Thanks!

[tubeswell]

Reading the PT voltage connected to 115vac, without the resistor the output is  161v
with the resistor output is 156v

Now the surprising part, after unplugging and reading ohms it does give way less now, i did repeat the process a few times

readings are: 471r , 431r , 444r , 454r

thoughts?

Thanks!

Meter battery?

[uki]

Meter battery?

Well

....I did read with three different multi meters to make sure. 

One with new battery, This variation only happen with the HT wind.

... Most likely a bad connection where the tiny winding wire is soldered to the external lead. You would still get a correct voltage reading, but as soon as you connect some load to the winding the voltage will likely go way down.

Ain't 161v and 154 with 10k/10w resistor, too low for the HT?

Thanks !

[sluckey]

Ain't 161v and 154 with 10k/10w resistor, too low for the HT?

160vac can make 226vdc with a fwb. Might be just right for that recorder.

[uki]

Actually I have a good idea how to replace the wires

How would you do it ?!

Thanks!

[uki]

Back to this PT, giving a go on restoring the wires connections.

it is been a surgical procedure! 

Maybe someone have some advice/ideas.

Thanks in advance!

[kagliostro]

Some time ago It happened to me to change the wires of a PT, they were chewed by mice, but honestly situation was way better than what I see in your photo

Franco

[uki]

Some update !

I got the wires fixed !  There is that purple wire but it isn't connect to anything... 

1- what to do with the purple wire? (the one between the orange and grey in the pic)

2- what would be a good way to now insulate the transformer wires, before reassembling?

Thanks

[kagliostro]

Nice job but ....... I'm not sure it is also a good job, why I say so ? Because joining the insulated wires to the windings in that way you enlarged the structure

If when covered with some paper turns all fit on laminations, you are fine but if the thickness is too, the risk is your windings don't fit in lamination (EDIT: I forgot to add End Bells) space

The doubt is here because whey they builded the transormer they connected the wires in a way to prevent the insulation was under the paper

Franco

[Merlin]

1- what to do with the purple wire? (the one between the orange and grey in the pic)

Is it an internal screen?
You orange wire solder joint looks like it could use some more solder

2- what would be a good way to now insulate the transformer wires, before reassembling?

Maybe a spear of epoxy glue?

[uki]

Thanks Merlin and Franco!
I did a recheck on the solders!

1- what to do with the purple wire? (the one between the orange and grey in the pic)

Is it an internal screen?

I don't know, in the schematic looks like the purple goes to the core of the PT, am I reading it right?


Another thing that i don't get it, the supposed filament wires, in the schematic are on the secondary side. They read on the PT 3.4v on each side,
but on the PT the supposed filament wires on the primary side, and on the secondary there is two wires without center tap that read 6.5v
Which ones should be used for filaments ?

[kagliostro]

You say there are wires on the primary that you suppose to be heater wires

Are those wires connected to the primary windings ?

If they are they are not heater windings, the purpose is to adapt the primary to the voltage of your line, but 3.4v is a low adjustment, so seems this isn't the pourpose

If they are stand alone (not connected to the primary) they are for heaters and the connections are near the primary windings simply for space reasons

The other windings (6.5v) are also at heater level

Assuming both windings are not connected to other windings, as you measure 3.4v-0-3.4v (6.8v) and 6.5v it may be that at the windings that measure the higher voltage there is more current available

Observe the thickness of the wires of the windings and/or connect a load to see which ore has more current

Franco

[Merlin]

I don't know, in the schematic looks like the purple goes to the core of the PT, am I reading it right?

That is certainly possible.

Another thing that i don't get it, the supposed filament wires, in the schematic are on the secondary side. They read on the PT 3.4v on each side,
but on the PT the supposed filament wires on the primary side, and on the secondary there is two wires without center tap that read 6.5v
Which ones should be used for filaments ?

It looks like the PT has two HT windings, and two heater windings. One HT winding and one heater winding are for the amp in the schematic, and the other pair go to a separate preamp unit that would be plugged into that octal socket. So I guess you can use whichever heater winding you like. Brown-brown probably has a higher current rating since it supplies the power tube.

[uki]

Some update!

The wires are insulated, the core is back in place. Tests tomorrow.
Only have done ohms reading it is the same as before.

What is the purpose of the purple wire?

[Merlin]

What is the purpose of the purple wire?

If you have tested it correctly, it is to ground the core. It may also be connected to an internal screen.

[AlNewman]

That looks really good.  I hope your tests go well.

[uki]

Thanks Merlin !

That looks really good.  I hope your tests go well.

Thanks

Yeah it is now giving solid readings

brown/blue/brown - 6.6vac

oranges - 164vac

greys - 19vac   what is this for?

blues(no CT) 6.4vac

some pics of how it was when it was in the device, wires dried out, crumbled, melted, it is really surprising it does still work!


Next step is to build an amp