# El 84 Oscillator puzzle

#### Colin Chandler

Joined Oct 2, 2018
37
There are five connections on this oscillator coil, the two on the right hand side are fine but the three on the left have strange readings on the ohm meter, between 1&2 there's 38ohms between 2 & 3 there's 38 ohms , between 1 & 3 there's 5 ohms
Looking at the schematic I can work it out , can you? Sorry I meant to type can't work it out

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#### AlbertHall

Joined Jun 4, 2014
11,222
It would (might?) help if we could relate those pin numbers to the schematic. Maybe two of the transoformer wires are (near) shorted to each other or the two capacitors labelled 21 and 22 are short circuit.

#### Colin Chandler

Joined Oct 2, 2018
37
Thanks for your reply, I have disconnected all the wires from the coil before I took the readings I should have mentioned sorry, do you think the coil is faulty?

#### bertus

Joined Apr 5, 2008
21,319
Hello,

The original unit is pictured at this french page:
http://jacquesg.brun.free.fr/Chambresdechosmeazzi.html
With the schematic:
http://jacquesg.brun.free.fr/schemaechomatic.html

Do you have the name of the unit?
http://meazzi.net/or/schemandlayout1.html

Bertus

#### AlbertHall

Joined Jun 4, 2014
11,222
Is pin 2 the centre tap?

#### Colin Chandler

Joined Oct 2, 2018
37
no it's not a centre tap, I don't understand the resistance readings , I've atttached the readings between the pins , I need help to put the numbers to the pins, based on the schematic
Which is pin 1.
Which is pin 2
Which is pin 3

#### AlbertHall

Joined Jun 4, 2014
11,222
Did you not make a note of the connections when you disconnected it?

My guess would be pin 1 is the tap and pin 3 connects to EL84 anode.

#### prairiemystic

Joined Jun 5, 2018
182
OP you're making it too hard- without telling us what you are calling pin 1,2,3,4,5 etc. on the schematic.
You need ohmeter readings between all FIVE pins to properly ID the windings.

Looking like: Pin 1 to B+, Pin 2 to grid, Pin 3 to plate. Pin 4-pin 5 erase head should be low, around maybe 16 ohms with no continuity to any of pins 1,2,3.

#### Colin Chandler

Joined Oct 2, 2018
37
OP you're making it too hard- without telling us what you are calling pin 1,2,3,4,5 etc. on the schematic.
You need ohmeter readings between all FIVE pins to properly ID the windings.

Looking like: Pin 1 to B+, Pin 2 to grid, Pin 3 to plate. Pin 4-pin 5 erase head should be low, around maybe 16 ohms with no continuity to any of pins 1,2,3.
Ok Thankyou the two pins at right hand side only have continuity to each other and as one is connected to the chassis I managed to work out it’s for the erase head , the other three pins are what’s confusing me , theres a feed in to carry the signal and mix it with the oscillating signal, I just don’t understand the coil 30 ohms 35ohms and 4.6 ohms between the three pins , the coil is drawn in a straight line so I would have thought 30 35 65 ? Does that make sense?

#### AlbertHall

Joined Jun 4, 2014
11,222
One coil of 30Ω and one coil of 4.6Ω So measuring between the ends gets you them in series - 34.6Ω.

#### Colin Chandler

Joined Oct 2, 2018
37

#### bertus

Joined Apr 5, 2008
21,319
Hello,

You could give in the schematic where 1,2 and 3 are:

Bertus

#### Colin Chandler

Joined Oct 2, 2018
37

#### Colin Chandler

Joined Oct 2, 2018
37
Ok Thankyou the two pins at right hand side only have continuity to each other and as one is connected to the chassis I managed to work out it’s for the erase head , the other three pins are what’s confusing me , theres a feed in to carry the signal and mix it with the oscillating signal, I just don’t understand the coil 30 ohms 35ohms and 4.6 ohms between the three pins , the coil is drawn in a straight line so I would have thought 30 35 65 ? Does that make sense?
I see now, it can’t be 65 it is actually 5
Now all I need to know is where on the schematic would 5.3 be and knowing that it tells me where 31.6 goes

#### Colin Chandler

Joined Oct 2, 2018
37
OP you're making it too hard- without telling us what you are calling pin 1,2,3,4,5 etc. on the schematic.
You need ohmeter readings between all FIVE pins to properly ID the windings.

Looking like: Pin 1 to B+, Pin 2 to grid, Pin 3 to plate. Pin 4-pin 5 erase head should be low, around maybe 16 ohms with no continuity to any of pins 1,2,3.

#### Colin Chandler

Joined Oct 2, 2018
37
I’ve got some readings , I need to know what coil on the schematic is 5.3. And 31.6. Thankyou for your help

#### prairiemystic

Joined Jun 5, 2018
182
I think this is correct. Note that the record oscillator is usually tuned- with a trimmer capacitor or moveable slug in the transformer core. I think this is why the schematic shows two series capacitors on the (plate) tank, if you can't get decent AC at 50kHz then change the tuning cap.

#### Colin Chandler

Joined Oct 2, 2018
37
I think this is correct. Note that the record oscillator is usually tuned- with a trimmer capacitor or moveable slug in the transformer core. I think this is why the schematic shows two series capacitors on the (plate) tank, if you can't get decent AC at 50kHz then change the tuning cap.

View attachment 206617
Thankyou very much , would the tuning cap
I think this is correct. Note that the record oscillator is usually tuned- with a trimmer capacitor or moveable slug in the transformer core. I think this is why the schematic shows two series capacitors on the (plate) tank, if you can't get decent AC at 50kHz then change the tuning cap.

View attachment 206617
Thankyou very much, I appreciate your help

#### Colin Chandler

Joined Oct 2, 2018
37
Thankyou very much , would the tuning cap

Thankyou very much, I appreciate your help
I've got it oscillating at 50khz but there's only 90v ptp on the play head and 3 v ptp on the erase, all three pins on the coil have 330v , which cap is the tuning cap?