Phase Linear 200 rebuild

Bias is measured accross R25, NOT R24. Bias is adjustable by changing out R13, values range from 10 ohms to 33 ohms.

Acceptable bias range--10 to 50 mv, anything over 80 mv should be corrected..
 
Ok, you're good there...

The 66430"s were a lower gain RCA 410, the 66546's were a higher gain RCA 410....

The 15022's could also be used in place of the 66546's...
 
laatsch55 said:
Bias is measured accross R25, NOT R24. Bias is adjustable by changing out R13, values range from 10 ohms to 33 ohms.

Acceptable bias range--10 to 50 mv, anything over 80 mv should be corrected..
Click to expand...

Right channel R24: 0.514 VDC
Right channel R25: 64 mV but increased to 72mV VDC so I removed power

Left channel R24: 0.523 VDC (was increasing so I removed power)
Left channel R25: 74 mV but increased to 80mV VDC so I removed power

Bias Measurement Point: R25 (Right Channel Shown)B1B18312-0A95-4B3D-9DA4-072F4FEAC90E.jpeg

Overview of bias test setup:57A62F2D-37B2-4A68-9A3E-BB1C90923006.jpeg
 
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R25 is the one to check bias. 80 mv is is getting close to doing something about it.. Are the outputs cool to the touch?

What value is R13?
 
Argh... It wasn't 80 mV... it wa 8 mv!!! (could not properly see the decimal point on the meter!) It got up to around 11 or so after I let it stay on a bit.

LEFT:
827284D8-1CB5-4565-803B-943F697BCD0B.jpeg

RIGHT:image.jpg
 
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laatsch55 said:
9 and 10 millivolts....you're good...
Click to expand...

Yeah, I hate having old eyes that lead more than myself astray!!! Thanks again. Those measurements were made at 115 VAC applied, no input excitation or attached load, but DBT attached, after a minute or so.
 
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Check again with no DBT and full AC voltage, let it warm up 10 minutes, then measure bias, that should be the final number...
 
laatsch55 said:
Check again with no DBT and full AC voltage, let it warm up 10 minutes, then measure bias, that should be the final number...
Click to expand...

No DBT
10 min soak
Mains voltage: 122 Volts RMS
Mains current: 2-3 mA AC

V(R25) Left: 15.8 15.9 mV DC
V(R25) Right: 12.2 12.3 mV DC
 
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laatsch55 said:
For a 100 watt amp?
Click to expand...
The Service manual calls it out... Ugh.
Screen Shot 2020-07-05 at 11.31.18 PM.png

Trying to decide what I can buy... Mouser doesn't have non-inductive 25 watt parts in stock (was going to buy 10). Now checking ePrey, but see the listing heading and item description fail to match. Heading states "8 ohm 250 watt 1% NH (non-inductive)" while photo of part and text of listing states other values.

I wish I could borrow someones programmable
electronic load box...(Uses a bank of heatsinked transistors instead of wire, and you can just program the value you want.)
 
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29 volts at 8 ohms is 105 watts... a 100 watter would be fine if ya don't leave it on too long..
 
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