Babelfish XA252 / Babelfish XA252 SIT / Babelfish XA252 SET

[Russellc]

Will power down and check BD parts. If they are the two parts sandwiched between heat sink, I was extra careful there, but best laid plans ...I will have to undo the "sandwich" to check those.

 

[Russellc]

No fuse didn't pop, held all the way up to 120V A/C, and that is where meter pics are at. Measuring bias across one of the big resistors,
Offset is with meter on speaker outputs.

 

[Russellc]

Was afraid to push bias higher, is .180 mV the goal?
Or is it 180 mV? If .180 good, otherwise....

 

[Russellc]

I only went little over .100 before I stopped to ask.

 

[Russellc]

Is this channel acting half way normal?

 

[Zen Mod]

No fuse didn't pop, held all the way up to 120V A/C, and that is where meter pics are at. Measuring bias across one of the big resistors,
Offset is with meter on speaker outputs.

no need for further check of components if you actually got that, it actually seems nothing is wrong

now, leave DC Offset trimpot untouched, just increase Iq with Iq trimpot

goal is to have 180mV measured across big resistors

180mV=0.18V

 

[Russellc]

Answered my own question on .180 vs 180, different meters other one shows 103 mV bias right now, off set 2.8 mV. I think I have a good channel?

 

[Russellc]

Up to 125 mV, offset at 1 mV it is decreasing on its own as I raise bias. Outputs @ 30C.

 

[Russellc]

At 170 mV, offset .7 mV. Heatsink on opposite side of puck is 36C. Puck is slightly less. Ambient is 69F.

 

[Russellc]

Out of pot turns at 177.6 mV. Do I need to swap a resistor to go higher, or is this it? Offset .9 mV

 

[Russellc]

Scratch that, variac not quite all the way up...now, 180 mV bias and 6.7 mV offset.
This channel good, now back to old wanky other channel

 

[Russellc]

Other channel, now at 100 mV, 150 and let sit a few seconds...variac at 120 V, well 176 mV is as high as pot will go...

This channel not so good, bias stops at 176, offset at 15 mV. Adding jumper raises it to 127 mV, pot having no effect.

What did I kill now?

Russellc

 

[Russellc]

Wait, more twiddling, off set down to 2.3 mV, good! Bias up to 179.1 mV but I am out of turns

 

[Russellc]

Bias out of pot at 179 mV, offset. Not nearly as stable. Goes from 1-2 up to 13, wanders a bit compared to other channel. Up to 26 mV, turned back to ,
.9. already back to 13, runs down to 9, wanders a bit.

Suggestions?

Other channel rocks.

Russellc

 

[Russellc]

Got it up to 180 mV bias, just don't like the wandering offset. Just climbed from .9 to 20....

What to check?

 

[Russellc]

Removing jumper after setting it down seemed to help. Still wanders a bit but now from 0 to 1.1 mV, so that's good.

Both channels up negligible offset, holding 180 mV bias both sides, devices measure 50C.

I may be ready for speakers

 

[Zen Mod]

and once when you hear it, you can contemplate here aloud, how those fuse popups happened?

 

[Zen Mod]

don't forget one precious rule - fiddle with connections only with amp switched Off, or you'll pay dearly

besides 10Apeak limiting, there is no any other sort of protection

 

[Russellc]

and once when you hear it, you can contemplate here aloud, how those fuse popups happened?

I know. Do you really want to hear this? More silliness caused by crimp connectors on A/C input/fuse dohicky. Bad fit, so intermittent on/off. Solder to the rescue.

Several cycles on off, all good except could use more range on one bias pot. Someone else wrote here with same problem, think a resistor change cured that? Will have to go back and reread. Once warm it was 180 mV.

Dr appointment, then re heat and sit a while followed by test speaker hookup.

russellc

 

[Zen Mod]

Once warm it was 180 mV.

enough