SANSUII BA-3000 PROBLEMS

BTW you have Ham gear... I assume you are not using it while working on this?
The RF rejection of these amps is not so great
 
Morning Mike
Setting bias...
AMP HAS TO BE UP TO TEMP .. The small signal transistor as it heats or cools will affect this setting, so if you set it with the amp cool.. it will drift.
These amps drift a fair amount anyway.... ~ 10 mv or so... so worry about 40 mv drift, not a 10.
How clean the connectors can affect this is a BIG WAY
ALSO DID YOU SWAP THE DIODE (VD -1212) near TR-05 ?

All of the VD1212 diodes have been replaced by 1N4198 series diodes. I'm not saying that the amp is going to do what it did in the past, I am only saying that the 3 previous times I though the amp was fixed the bias NEVER stopped moving once set. I would wait 15 minutes or longer before setting the bias and it would NEVER settle in. Then when I would finally test the amp like we did last night, all 3 times it went up in smoke within 10 minutes of starting to use it.
 
So, after I hopefully get the bias and dc offset set on the amp with this 2507 board are we ready to try the NEXT 2507 board?
 
The trick is to keep an eye on operating temps and input voltage stability... There has been a bunch wrong , just on this go round...
Stuff breaks.. and that is just the hobby. and that break will dictate your next move
 
NO we have to get this amp semi stable so it can at least lock bias ( within +/- 20 MV ) and can run for OVER 20 min at 10 watts or so
 
R-18 & 22 in the constant current bias section are 120 ohm fuse resistors.. have those been replaced?
Might be a good watchdog move to monitor the regulated +/- 65 volt rails while running ( maybe a bit OCD ) but it might be a " tell".
 
R-18 & 22 in the constant current bias section are 120 ohm fuse resistors.. have those been replaced?
Might be a good watchdog move to monitor the regulated +/- 65 volt rails while running ( maybe a bit OCD ) but it might be a " tell".

I don't remember for sure but I think I have replaced them on ALL of my 2507 boards.
 
After we get the 4-2507 boards that I am fairly confident in tested and set to your satisfaction I want to get all of the resistors changed out in them to MF resistors. I nearly have the last 2-2507 boards with all the resistors changed to MF resistors and good or new components. When I finish these 2-2507 boards I will let you know and then we can get them tested too. I just don't want to put them in the amp until I am fairly confident that they are ready to go.

Right now, I guess I will go over to the shop and fire up the amp. Let it sit for about 10 or 15 minutes while I set the bias and DC offset again and then play some music again to see how the 2507 board acts.
 
Sounds good......Can I get a close shot of the #1 2507 board.....? When this round is done ?

Absolutely. I will take about 4 shots of it 1/4 of the board at a time so the magnification is good enough for you to see everything. I'm headed over right now to start some real test of the 2507 board and setting of the bias.
 
One of my concerns is both your original amps went poof,
I assume we are using the 4 2507's that came out of the 2 old amps first AND you are taking the time to change out the E bay boards to New resistors & other components....
Wouldn't it be BETTER to change out all the passive components on the board we are testing now....?
Seems like a duplication of effort AND testing with older stuff that was put under stress.
The reg board doesn't have to do as much work as the driver, so it wasn't as critical ( in my mind ) .

I would suggest if this 2507 works ( for the most part ) is to do the wholesale change out of "R's" (test) then "C" values.

In addition do you have plenty of heat sink goo on the 2507 TR-10/11 and it's TIGHT ?
Side note if you do screw down the 2507 to chassis it will give you a LITTLE more heat sink... but not as much as you would think.. heat rises..
 
I'm back now. Everything went just SUPER!! I set the DC Offset to +-1 MV without any trouble at all. Then after about 15 minutes I went back and checked it and it was +- 3 MV so I got it back to +-1 MV just because I could. I then set the bias to 15 MV and watched it for another 10 minutes and after that it had went to 14.4 MV. The amp is now settling in with the bias very fast. It would never do that during the past year I have been working on it, and I mean working on it daily for a year. I changed the bulb in the DBT to a 75 Watt from a 55 Watt. After I started playing music (which sounded just great thru my little Infinity speaker) the 75 Watt bulb never got full brightness like the 55 Watt bulb did. I watched the bias for quite a while and it would go from about 14 MV during silence to a high of about 55 MV during louder music. Nothing in the amp came even close to getting hot as I physically touched power transistors and resistors and transistors on both the 2508 and 2507 boards. Everything was running very cool, like the music although I am getting a little tired of John Denver. I'm going to take Janis Joplin over next.

I am going to put the film in the developing tank so you will be getting pictures of everything I thought might be interesting to you (no Playboy or Penthouse magazines). Pictures will follow.
 
One of my concerns is both your original amps went poof,
I assume we are using the 4 2507's that came out of the 2 old amps first AND you are taking the time to change out the E bay boards to New resistors & other components....
Wouldn't it be BETTER to change out all the passive components on the board we are testing now....?
Seems like a duplication of effort AND testing with older stuff that was put under stress.
The reg board doesn't have to do as much work as the driver, so it wasn't as critical ( in my mind ) .

I would suggest if this 2507 works ( for the most part ) is to do the wholesale change out of "R's" (test) then "C" values.

In addition do you have plenty of heat sink goo on the 2507 TR-10/11 and it's TIGHT ?
Side note if you do screw down the 2507 to chassis it will give you a LITTLE more heat sink... but not as much as you would think.. heat rises..

I totally agree about going ahead and changing out the resistors in the 2507 boards before anymore testing. There are a LOT of resistors on these 2507 boards so i will be busy the rest of today and probably all of tomorrow so that I can get all 6 2507 boards changed out with MF resistors AND to finish up the other components on the 2 ebay 2507 boards. I have over half of the MF resistors and probably close to 3/4 of the MF resistors changed out on both of the ebay boards right now so I have a big head start on them.
 
Here are the pics of the #1-2507 board. Sorry for the delay but my wife just came over all upset that our dish tv quit on us. I have been trying to get someone either on phone or chat to no avail. More photos to come. I will start after dinner this evening changing out all the resistors so you won't hear back from me now until probably Sunday.
 

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