AZ41 supply AC voltage?

[Diniz Diniz]

Dear all,
Can anyone inform me what is the supposed AC supply voltage and the expected (typical) DC output voltage?

Thanks in advance!
Diniz from Portugal

[snowman_al]

There is no real typical...
But if your transformer gives you 250-0-250 volts (AC) expect about 350 volts DC.
If you have 300-0-300 volts AC expect about 420 volts DC.
These figures assume you are using a 32 or 50uF capacitor as first smoother ie. connected to the cathode of the AZ41.
The standard figure is 1.41 times the AC voltage gives the unloaded DC voltage into a capacitor.

[Gabe001]

It depends on various factors, including plate voltage and output current. Valves are not quite as efficient as modern day recitfiers so you need to refer to the valve's datasheet which is available online.

The way I interpret the datasheet graph is that with a 50uf capacitor and in a set consuming 50mA of direct current:

300v AC per plate will give 325v DC
400v gives 450v DC
500v (rated maximum) gives 580v DC

Happy to be corrected if I made a mistake

Gabriel

[Diniz Diniz]

Thank you for the replies.
@snowman: can you explain better the “300-0-300” meaning (sorry if it is a dummy question).
I am reading 645 Vac drop across pins 2 and 6 of AZ41, is it normal?
Thank you in advance.
Diniz from Portugal

[Gabe001]

Sounds about right, almost 325V AC per plate (325-0-325 from the transformer). Should give you about 350DC

[broadgage]

300-0-300 is generaly understood to mean a transformer with a 600 volt secondary winding that has a center tap.

Very often used in vintage equipment with a valve "double diode" rectifier as this is a cheap and simple circuit.

(modern tranistorised equipment more often uses a single transformer winding and four solid state diodes in a full wave bridge circuit. Modern silicon diodes are very cheap and use of four such components is affordable. Back in the day, valves were expensive and a circuit that used only one valve was preffered)

[snowman_al]

Originally Posted by Diniz Diniz

... @snowman: can you explain better the “300-0-300” meaning (sorry if it is a dummy question).
I am reading 645 Vac drop across pins 2 and 6 of AZ41, is it normal?
...

The AZ41 is a 'Full Wave Rectifier'. It is 2 diodes that share a single cathode (the filament in this valve). Pins 2 and 6 are the two anodes.
A two diode full wave rectifier requires a transformer with a centre tap to work. The centre tap (the -0- in the example) is the negative (or ground) reference for the rectifier circuit.
You measure 645 volts end to end of your transformer, but if you measure from pin 2 to the chassis (-ve or ground) you will get 322 volts AC. Same for pin 6.
So your transformer is a 322-0-322 volt ac transformer. And yes quite normal.
The actual 'working' DC voltage you get at the AZ41 cathode will depend on the current drawn by the circuit, the internal resistance of the transformer (how much current it can deliver) the 'sag' in the valve (how many volts it looses in operation) the age of the valve, the value of the capacitor and so on...

Have a search for 'Full Wave' rectifier and look for an explanation of the two diode type.

Alan

[Diniz Diniz]

Thank you all for your clear and detailed explanations.
The reason of my initial doubt was because (thinking that AZ41 was killed) I replaced it for a new (old stock in box) mullard AZ41. I had the opportunity to have a very amazing but expensive experience seeing blue rays inside the AZ41 until the filaments burn

After a analysis of the wiring I do not understand the reason of one wire connecting the anode of AZ41 and the output transformer. I thought such connection should be in the DC side of AZ41 (pin 7 or pin 8).

Attached you can find an image or the wiring. The yellow wires go from the transformer to AZ41 anodes, and blue and red go back to the transformer. And there is that green wire connecting one yellow wire to the output transformer.

Anyone can advise me on this. I I said previously I believe this set has been in other hands before it came to mines.

Thanks in advance,
Diniz from Portugal

[ms660]

Pins 7 and 8 of the rectifier should be connected to the 4 volts winding on the mains transformer and one side of the rectifiers filament (pin 7 or pin 8) should connect to the reservoir capacitor and probably the HT side of the primary of the audio output transformer, the anode pins of the rectifier (pin 2 and pin 6) should be connected to the HT winding on the mains transformer with the center tap of that winding being connected to chassis, can you check the wiring and pin connections and numbering again as found?

Lawrence.

[snowman_al]

Originally Posted by Diniz Diniz

...After a analysis of the wiring I do not understand the reason of one wire connecting the anode of AZ41 and the output transformer. I thought such connection should be in the DC side of AZ41 (pin 7 or pin 8).

Attached you can find an image or the wiring. The yellow wires go from the transformer to AZ41 anodes, and blue and red go back to the transformer. And there is that green wire connecting one yellow wire to the output transformer.

I do not see your analysis? I see the red and green (blue) wires going to pins 2 and 6, so assume they are the 322 volt AC for the anodes.
I see the yellow wires going to pins 7 and 8, the filament so should be 4 volts AC. As the filament is also the cathode, (and therefore the +ve HT) one side has to be connected to the smoothing capacitor and likely the output transformer.

Before going further, check the AC voltages on the valve base, with no valve inserted and confirm they match the picture. Then with the set off and disconnected, measure the resistance from the output transformer HT connection to the chassis/ ground. Let us know what you find.

Blue flashes in the rectifier can be caused by a faulty valve or short across the +HT supply (possibly from a failed cap) drawing too much current through the rectifier.
Alan

[Gabe001]

Some sets use the output transformer as an HT choke so having DC connection from one of the heaters (the cathode) of your valve to the output transformer is not unreasonable.

[ms660]

Here's the link again for the one I posted in the other thread about identifying the receiver:

https://archives.doctsf.com/document...2990&ref=18394

If you enlarge the 1st page you can see that the rectifier and transformer appears to be connected the same as the OP's is.

Lawrence.

[Diniz Diniz]

Thank you all for your comments.
Later tonight I will re-measure all the voltages of main transformer output, and re-confirm the connections to AZ41 socket.
I must add, that the 2 40uF elect. capacitor previously (by me) been replaced for 2 50uF new ones.
I'll let you know my results asap.
Thanks once more for all your patience.

BR
Diniz from Portugal

[Gabe001]

Diniz, the 321z is rated to work at a maximum of 150v AC according to the service sheet Lawrence posted. The HT rail is 155v DC.

If this is indeed your set, you're not running it at 220v AC by any chance, are you?

[Diniz Diniz]

Originally Posted by Gabe001

Diniz, the 321z is rated to work at a maximum of 150v AC according to the service sheet Lawrence posted. The HT rail is 155v DC.

If this is indeed your set, you're not running it at 220v AC by any chance, are you?

Thank you Gabe for pointing this out. My set is a Mediator m379z which have huge similarities with Philips - BE 321 Z. But it has a voltage selector in the rear side, set to 220. So, I am running it with 220V (since portuguese grid supplies 230vac.
See attached image.

Thank you.

[Diniz Diniz]

Hello to all,
Here I have the measurements I get and I apologize for any misunderstanding regarding previous measurements (somehow I get the wrong picture).

@main tranformer:
- yellow wire (from mains to pin 8): 4,61 Vac against chassis;
-yellow wire (from mains to pin 7) and green wire (from mains to OP transformer): 0.039 Vac against chassis;
- blue wire (from mains to pin 2): 295.6 Vac against chassis;
-black wire (from mains to ground): 0.039 Vac against chassis;
- red wire (from mains to pin 6): 295.0 Vac against chassis;

@output transformer:
- resistance between HT++ and ground: 7ohm
- resistance between positive lead of C1 and ground: 7ohm (just to check).

After that measurement (7ohm) I noticed that one of the wires coming from the loudspeaker was directly connected to HT++ (I mean, connected to the primary of OP transformer), so I disconnected that wire (from speaker to OP transformer) and I repeated the measurement. I now get infinite resistance (O.L.) between HT++ and ground.

I believe this was the cause of AZ41 failure (to much current being drawn) and I am wondering why this was not enough to cause a short-circuit...!?!

I would like to have your opinion, and advices in further actions before replacing AZ41 for a new one (I only have one more AZ41!!).

Many thanks in advance,
Diniz from Portugal

[Gabe001]

If you had a wired connection between s23 and the speaker it would explain your 7ohm reading imo, and you've done well removing it

Voltages look good to me except that filament voltages are meant to be taken relative to each other not to chassis, but that's academic now.

What I'd do now is turn it on with a lamp limiter and if the bulb remains dim I think youre probably ok. I'm happy to be corrected by others if any of my advice is incorrect.

[Diniz Diniz]

Originally Posted by Gabe001

If you had a wired connection between s23 and the speaker it would explain your 7ohm reading imo, and you've done well removing it

Voltages look good to me except that filament voltages are meant to be taken relative to each other not to chassis, but that's academic now.

What I'd do now is turn it on with a lamp limiter and if the bulb remains dim I think youre probably ok. I'm happy to be corrected by others if any of my advice is incorrect.

Can I use a 100mA fuse instead of a lamp limiter? (I am not familiar with this concept of lamp limiter but I would be glad that someone explain me how to build it).

Thanks once more!

[Diniz Diniz]

Guess you're talking about this:
https://www.vintage-radio.com/projec...p-limiter.html
Right?

Thanks!

[Gabe001]

Yes that's the one. It's a current limiting device (to keep the rest of your components safe in case of a short) and a diagnostic device too (using the brightness of the bulb)