Help Identifying Diode on Sharp SA 306

[dlPeter]

Hello everyone, my name is Peter. Before I continue, I just gotta say you guys have a lovely community. I've been reading up on this site for a while until now I decided to register. You guys have lovely recievers too!! OMG! I mean I thought mine was the bomb until I saw some others. Looking back at mine...I'm realizing that Sharp no doubt got into the Receiver business a bit later either that or their quality isn't really high end. I recently decided to start using my Dad's Sharp SA 306 Receiver.

So here's my problem. I've recently started using this receiver again and I notice the bulbs started blowing on them. Which I'm not totally surprised since the original Bulb is 6.3v 250ma while. I replace some with lower much amps but same voltage (those were a bit cheaper from where I live) The two 250ma that I actually got is lasting so far. The dial pointer bulb is also blown. It uses the wheat grain bulb. But since it's connected directly to the same circuit as the other bulbs I assume the bulb is of the same specs as the others. Measured the leads and got 6v. The closest I've seen is 2.6mm 6.3v 60ma. Should I give this a shot?

Also I've been flirting with the idea of replacing the dial pointer bulb with a 3mm orange led if I cannot get a bulb for it, although I've been worried about how well the led will disperse into the pointer. Looking around the receiver. I noticed that the blue and purple wiring leading directly from this transformer goes to this little circuit for the lights. The transformer produces 6.1v AC (it fluctuates on my meter between 7 and 6.1 sometimes 6) It also produces 76v AC in series which powers the rest of the radio.

Does anyone have any idea what sorta diode this is? The one marked with the H connected to the capacitor? I tested it an I got 6v DC so I assume this converts AC to DC in a crude way. Should I consider replacing that grey capacitor that is connected in series with the 'H' looking diode?

I drew the circuit in LT Spice. Just to give a clear description. The stereo indicator negative wire (if that's how you would describe it) leads to the radio section on the board while the positive is connected before the diode. I just need help figuring out of if D1 is a zener diode or some special type of diode that isn't zener.

Also...would an led work in this circuit?

I'm capable of taking constructive criticisms since I'm new to this board and my electrical experience isn't at great as others here.

 

[petehall347]

what is V1 ?
i would think its just a rectifier diode and the cap is for smoothing .
wheat grain is small and might not get as hot as incandescent .. but not too sure on that one .

 

[goat67]

This may help. V1 in voltage in BTW the diode is not a zeener as you have drawn it is a normal diode you would need a 1/2 or 1 watt I woulde imagine

http://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/rectifier-circuits/
Rectifier Circuits
Chapter 3 - Diodes and Rectifiers
Now we come to the most popular application of the diode: rectification. Simply defined, rectification is the conversion of alternating current (AC) to direct current (DC). This involves a device that only allows one-way flow of electrons. As we have seen, this is exactly what a semiconductor diode does. The simplest kind of rectifier circuit is the half-wave rectifier. It only allows one half of an AC waveform to pass through to the load. (Figure below)

Half-wave rectifier circuit.

For most power applications, half-wave rectification is insufficient for the task. The harmonic content of the rectifier’s output waveform is very large and consequently difficult to filter. Furthermore, the AC power source only supplies power to the load one half every full cycle, meaning that half of its capacity is unused. Half-wave rectification is, however, a very simple way to reduce power to a resistive load. Some two-position lamp dimmer switches apply full AC power to the lamp filament for “full” brightness and then half-wave rectify it for a lesser light output. (Figure below)

Half-wave rectifier application: Two level lamp dimmer.

In the “Dim” switch position, the incandescent lamp receives approximately one-half the power it would normally receive operating on full-wave AC. Because the half-wave rectified power pulses far more rapidly than the filament has time to heat up and cool down, the lamp does not blink. Instead, its filament merely operates at a lesser temperature than normal, providing less light output. This principle of “pulsing” power rapidly to a slow-responding load device to control the electrical power sent to it is common in the world of industrial electronics. Since the controlling device (the diode, in this case) is either fully conducting or fully nonconducting at any given time, it dissipates little heat energy while controlling load power, making this method of power control very energy-efficient. This circuit is perhaps the crudest possible method of pulsing power to a load, but it suffices as a proof-of-concept application.

 

[dlPeter]

This may help. V1 in voltage in BTW the diode is not a zeener as you have drawn it is a normal diode you would need a 1/2 or 1 watt I woulde imagine.

Thank you for the article. Now I'm 99% confident in what is going on in this circuit. You mentioned need 1/2 or 1 watt. Are you answering the question about wanting to add an led? or what value the diode is?

 

[Oldsansui441]

Welcome Peter, a grain of wheat globe in the 50mA region is ideal for the pointer (like the one you have found). A 6v globe will be fine if the circuit stays around 6v but any higher and the globe won't last. If this is the case an 8v globe would be ideal. An AC voltage supply directly from the transformer for the lighting circuits is normal in this vintage stuff, mostly in the 6-8vac range.
I would recommend a standard incandescent globe over an led as it will emit plenty of light and you won't have to mess around with dropping resistors.

 

[dlPeter]

Welcome Peter, a grain of wheat globe in the 50mA region is ideal for the pointer (like the one you have found). A 6v globe will be fine if the circuit stays around 6v but any higher and the globe won't last. If this is the case an 8v globe would be ideal. An AC voltage supply directly from the transformer for the lighting circuits is normal in this vintage stuff, mostly in the 6-8vac range.
I would recommend a standard incandescent globe over an led as it will emit plenty of light and you won't have to mess around with dropping resistors.

Thank you! So would a 8v bulb still be bright even though the circuit is 6v?

 

[Oldsansui441]

Yes an 8v will still be bright enough. I have had to use 12v grain of wheat in 8v circuits because this is all l can source locally and they are bright enough.

By all means though that 6.3v globe you found will be fine if your circuit stays around 6-6.5v

 

[dlPeter]

Yes an 8v will still be bright enough. I have had to use 12v grain of wheat in 8v circuits because this is all l can source locally and they are bright enough.

By all means though that 6.3v globe you found will be fine if your circuit stays around 6-6.5v

Thank you!

 

[dlPeter]

Sights...now I have another problem. In trying to remove the FM Stereo bulb from the holder I snapped it :'( The bulb got so hot that the rubber holder melted around it. Now I'm left with this...

I don't know what type of bulb it is. I placed it beside a US 1 dime on an envelope. Just to give a good idea of the size. The black around the broken bulb is from the melted bulb holder.