STV-3 Bias Diode Testing

[aldena007]

I am in the process of repairing a pair of F2624 Driver Circuit Boards from a QRX-9001. As part of my repair I decided to test the STV-3 diodes on both boards. The expected voltage drop on my test rig was 1.5 ~ 1.8 vdc. The voltage drop I measured was 2.2 vdc. I got this on all four of the diodes off of the two boards. To verify my test rig I tested a diode from the supplier in Germany who is selling on eBay. This diode did test good with a 1.6 vdc voltage drop. The OEM diodes off of the F2624 boards are marked with the yellow dot but the body is reddish brown. The one from Germany has the yellow dot [cathode] but the body is black.

Are the brown diodes really STV-3? If not, should I switch to the black bodied diodes in my restoration?

 

[avionic]

I've used the black ones without issue. I think the body color distinguishes different variants . ie. STV-3H-Y or some other lettered suffix. It looks like there is at least 4 variations

 

[aldena007]

I think that I will reuse the originals. All four were identical in their voltage drops at 2.2 and are OEM.

 

[kevzep]

I've never had a STV fail in all the years I have been working on Sansui's, I've only ever had the legs broken on them.
They are as tough as old boots..

 

[aldena007]

Thanks for the information on these diodes guys. I do have some of the STV-3H-Y from Germany [sh-halbeiter/eBay] to use with the v2 builds. I did notice his inventory is steadily diminishing so I thought on the OEM rebuilds if the diodes were testing good that I would reuse them. Like "kevzep" says I have not yet found one STV-3 diodes that failed to give the rated voltage drop. I do not usually reuse OEM parts that test good during trouble shooting the F2624 since most components are relatively inexpensive and available. I am certainly glad to see new STV-3 diodes available for now, but sole sources give me some concerns so I will reuse the ones I have.

 

[bktheking]

Worked on a g33000 a few years ago that would bias up nicely, run for about a minute and happily blow the entire channel- culprit, stv3. For the cost of the ones in Germany I replaced all 4 in my last g33000 rebuild with no issue. Owner wanted a full rebuild so I gave it to him, stv3’s included. That’s not to say I haven’t reused them in the past of other builds. Ever since that g33000 went boom I can’t say I’ve never run across a bad one. Now I’m giving the option since they are available.

 

[Kale]

Just wish to say one detail, brown STV diode is STV-4H, black STV diode is STV-3H... I had some NOS STV-4H... look
https://www.sansui-vintage.com/product_info.php?cPath=15_17&products_id=128
they are really rare today...