Phase Linear 200 rebuild

[laatsch55]

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..

 

[kl0neMan]

What do you have for Q4, Q5?

Q4 is a TIS97.
Q5 is a GES 93.
(both modules have the same parts)

 

[laatsch55]

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...

 

[kl0neMan]

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..

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)

Overview of bias test setup:

 

[laatsch55]

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?

 

[kl0neMan]

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?

Outputs and drivers were cool to the touch on both modules.

What value is R13?

15 ohms on both modules

 

[kl0neMan]

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:


RIGHT:

 

[laatsch55]

9 and 10 millivolts....you're good...

 

[kl0neMan]

9 and 10 millivolts....you're good...

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.

 

[laatsch55]

Check again with no DBT and full AC voltage, let it warm up 10 minutes, then measure bias, that should be the final number...

 

[kl0neMan]

Check again with no DBT and full AC voltage, let it warm up 10 minutes, then measure bias, that should be the final number...

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

 

[laatsch55]

Perfect...

 

[kl0neMan]

Perfect...

I will have to construct a 250 watt 8 ohm resistive load for step 9. Crap!!!!

 

[laatsch55]

For a 100 watt amp?

 

[kl0neMan]

For a 100 watt amp?

The Service manual calls it out... Ugh.


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.)

 

[laatsch55]

29 volts at 8 ohms is 105 watts... a 100 watter would be fine if ya don't leave it on too long..

 

[laatsch55]

Just be sure its non-inductive..

 

[kl0neMan]

29 volts at 8 ohms is 105 watts... a 100 watter would be fine if ya don't leave it on too long..

It's not a Dale NH-250 1%, but may have to pull the trigger on this:
https://www.parts-express.com/8-ohm-200w-non-inductive-dummy-load-resistor--019-030

 

[Gibsonian]

I thought these amps benched out closer to 150 watts/ch?

 

[kl0neMan]

I thought these amps benched out closer to 150 watts/ch?

This is an original model, rated at 100 watts/channel that cannot reliably drive load impedances below 8 ohms.