SX 1250 FROM SCRATCH

[tarior]

You might have a little more clearance with this one.

https://www.mouser.com/ProductDetai...350ELL102MK20S/?qs=IYueExuAvkq84W%2BQ4rqabA==

 

[rhodus]

You might have a little more clearance with this one.

https://www.mouser.com/ProductDetail/United-Chemi-Con/EKYA350ELL102MK20S/?qs=IYueExuAvkq84W%2BQ4rqabA==

I think that's the one....Thanks!

 

[rhodus]

You might have a little more clearance with this one.

https://www.mouser.com/ProductDetail/United-Chemi-Con/EKYA350ELL102MK20S/?qs=IYueExuAvkq84W%2BQ4rqabA==

You got any nude shots of that BA5000?

 

[tarior]

I do. One of these days, I'll post a thread with them.

 

[rhodus]

Been reworking plug in boards. Replaced all electrolytic caps and transistors on the stabilizer. Rock solid 65 volts. All other voltages in spec. I will post the numbers in the morning. Recapped and replaced relay on Protection board. I used a NOS relay I found a while back. I recapped the amp boards but that's it. I'm having issues with taming DC Offset. Both amps fluctuate as much as +/- 35mv. Idle current is relatively stable. It's late now. Will post pics in the AM

 

[rhodus]

Here's a couple for now...

 

[tarior]

Looks like it's coming together.

 

[rhodus]

Looks like it's coming together.

Yessir, slowly but surely....

 

[rcs16]

I would not be too concerned about DC offset drifting a bit, if it is +/- 35mv, that is fine IMO

 

[rhodus]

I would not be too concerned about DC offset drifting a bit, if it is +/- 35mv, that is fine IMO

Thanks. That's reassuring, but I think I'll go ahead and replace the transistors and diodes while I'm in here and just see if there is an improvement.

 

[tarior]

You really need only change the differential input pair (Q1,2) and the overload detector (Q11).

 

[rhodus]

You really need only change the differential input pair (Q1,2) and the overload detector (Q11).

I tried that first. I even had matching 992s from an AK member but the results were about the same. So I went ahead with the shotgun approach and Voila!! Now the fluctuation is about -2mv/+6mv at worst but mostly hangs around 2-4 mv.

 

[tarior]

That'll do.

 

[rhodus]

I even replaced the stv3 diode with one of the new German units.

 

[rhodus]

Now on to the left amp....

 

[tarior]

Don't throw away your old STV-3 if it is still functional. Those have been obsolete for a long time.

 

[rhodus]

Don't throw away your old STV-3 if it is still functional. Those have been obsolete for a long time.

I got it. and a few others too. One of the horns is broke off but I think its still good. One if these days I'm gonna build a test jig.....

 

[rhodus]

Finished up the left amp with pretty much the same results...DC offset in the single digit range, 2-4mv mostly. That's a wrap for the power supply/amplifier section. Now on to the hard part....the front end boards....now the shits gonna get deep....

 

[merlynski]

I got it. and a few others too. One of the horns is broke off but I think its still good. One if these days I'm gonna build a test jig.....

Suggestion for test jig for STV diodes, works for Zeners also:



You can use just one battery for STVs and low voltage zeners, add a third for higher voltage zeners.

 

[rhodus]

Suggestion for test jig for STV diodes, works for Zeners also:

View attachment 2095442

You can use just one battery for STVs and low voltage zeners, add a third for higher voltage zeners.

Lets say I'm testing an stv4 as in your diagram...One 9v battery...what value R1? And what would the meter read for a good stv4? What would it read for a bad stv4?