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Replacing The STV-3H and -4H Diodes

zambrano966 said:
Buenas amigos, soy de Venezuela y me encuentro restaurando una Marantz 300DC, la compre en muy mal estado, pero poco a poco la he ido reparando, ya esta casi lista pero tengo un problema, hay un canal al cual le faltan unos diodos, segun el diagrama electrico dice que son unos varistores MV-1, sabran ustedes cual diodo se puede colocar como sustituto?
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"Good friends, I'm from Venezuela and I'm recovering a Marantz 300DC, I bought it in very bad condition, but little by little I have been repairing it, it is almost ready but I have a problem, there is a channel that is missing some diodes, according to the electrical diagram says that they are MV-1 varistors, will you know which diode can be placed as a substitute?"

(Thanks to Google translate)
 
Te sugiero que comiences tu propio hilo en el foro de Marantz Audio, probablemente obtendrás una mejor respuesta allí.
y bienvenido a Audiokarma
 
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Adding to the data collection, I recently measured two KB369 diodes, 3 junctions. These are DC numbers at room temperature after the reading stabilized.
Code: 
I mA     V sample 1    V sample 2
3          2.0615        2.030
2          2.028         1.994
1          1.969         1.931
.7         1.939         1.898
.5         1.909         1.865
.1         1.762         1.711
.05        1.695         1.639
 
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I am working on a Kenwood amateur transceiver and stumbled across this thread. Yeah, the driver transistors use the STV-3H part to compensate the bias current and I am having issues with the drivers going into runaway.

Very interesting discussion and I would like to add an idea: using surface mount rectifiers in place of leaded diodes. The UF1004 seems to be a good choice for replacing the STV-3H except for the fat leads. I have been comparing leaded vs. SMD diode specs and found that the US1G SMD diode appears to have identical specs to the UF1004.

Seems like it would be fairly easy to solder them together into a flat shape and mount the thing onto the heatsink, or in my case a transistor tab.

Just wondering if anyone has looked at this. I MAY have to go down this path if my STV-3H leads break off and cannot be repaired, and if so I'll let you know what I find.

Thanks.
 
K2AEI said:
I am working on a Kenwood amateur transceiver and stumbled across this thread. Yeah, the driver transistors use the STV-3H part to compensate the bias current and I am having issues with the drivers going into runaway.

Very interesting discussion and I would like to add an idea: using surface mount rectifiers in place of leaded diodes. The UF1004 seems to be a good choice for replacing the STV-3H except for the fat leads. I have been comparing leaded vs. SMD diode specs and found that the US1G SMD diode appears to have identical specs to the UF1004.

Seems like it would be fairly easy to solder them together into a flat shape and mount the thing onto the heatsink, or in my case a transistor tab.

Just wondering if anyone has looked at this. I MAY have to go down this path if my STV-3H leads break off and cannot be repaired, and if so I'll let you know what I find.

Thanks.
Click to expand...

that is an excellent idea!
 
I played with SMD because I wanted to make a smaller package replacement and the specs tend to be more or less equivalent for the relevant models but the problem I had was physical strength of the joint between the SMD diodes.
 
smurfer77 said:
I played with SMD because I wanted to make a smaller package replacement and the specs tend to be more or less equivalent for the relevant models but the problem I had was physical strength of the joint between the SMD diodes.
Click to expand...

Yes, I could see where that would be a problem. But it seems you could JB-weld the diodes upside down onto a terminal or plate, then join the leads with thin gauge wire. Then, put a dab of epoxy over that. Or, maybe this has already been tried.

I have to order other parts anyways so I think I'm going to get some and experiment with them. The full part number, by the way is US1G-13-F, stocked at Mouser.

Joe
 
K2AEI said:
Yes, I could see where that would be a problem. But it seems you could JB-weld the diodes upside down onto a terminal or plate, then join the leads with thin gauge wire. Then, put a dab of epoxy over that. Or, maybe this has already been tried.

I have to order other parts anyways so I think I'm going to get some and experiment with them. The full part number, by the way is US1G-13-F, stocked at Mouser.

Joe
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oh yes, there is definitely a way to do it, and it will be elegant and compact. Just a warning/heads-up
 
Another solution for subbing SV04S diodes (Sony service bulletin).

Attention: this service bulletin forgets to mention to put an electrical isolation (mica/SIL pad) in between the transistors and the surface it is mounted to, in case it has a bare metal back side.
In case bare TO-220 devices are used, then the screw must also be isolated.
Hence, better use a fully molded TO-126 or TO-220 device.
In general, most transistors will do anyway (>50mA)

Bias Circuit Modification.jpg
 
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D'oh, l had already mentioned about that Sony earlier in this thread, two years back is obviously too long ago for me to remember :crazy:.
 
I didn't go through all the pages, but has anybody tried using transistors instead of diodes to replace the STV3-H? Tie the base and collector together and use 3 of these in series. I think the temperature change would track more closely than using diodes. You can get really tiny surface mount ones to make it. Something like the photo.
 

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Ray Brack said:
I didn't go through all the pages, but has anybody tried using transistors instead of diodes to replace the STV3-H? Tie the base and collector together and use 3 of these in series. I think the temperature change would track more closely than using diodes. You can get really tiny surface mount ones to make it. Something like the photo.
Click to expand...

The Vbe multiplier as shown in the Sony service bulletin above follows a simple formula:

Vbe multiplier.JPG

As Vbe is a fixed value of around 0.55V (or measure it with your DVM to know the exact value of the transistor you gonna use), you can play with R1 and R2 to obtain any value needed, such as the forward voltage drop (i.e. Vout in the above formula) across a STV3-H.

The thing to keep in mind is that R1 and R2 in series can (*) play a role in the tail current of the VAS stage where the bias spreader is normally located (in the order of 4 to 8 mA)
Hence, don't play with much larger or much small resistor values, stay in 1 to 5 kOhm range for both resistors.

(*) "can play a role", because the tail current is often controlled by a constant current source/sink in the tail, but some (cheaper) amps only use a string of resistors from positive to negative rail.
 
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