Altec Lansing 1594A - 1967 [100W Solid State Mono Power Amplifier] BOM + Manual

[Leo_Gnardo]

Kludge a constant current 100mA supply (IŽll draw one for you when I have some free time), feed it from any 9 to 12V wall wart you have, apply test clips across "mystery resistor" and read voltage drop.

1 ohm will give you 100mV , very easy to read.

I'm liking this idea a lot. And TIA for your offer of a CC supply. You got me thinking "hey I have one of those fancy-dan power supplies that has both current and voltage limiting. It can turn out up to 8 amps. That might make a dandy low-resistance meter. Heck I could set the current limit at 1 amp and test very low value resistors, even go up to 8 amps to test super low R's. Hope I don't set any aflame. Would have to make up a pair of fat wire test leads. What think you?

And . . . I forgot to post a couple weeks ago, it is TERRIFIC to see you back on MEF! I appreciate your super body of knowledge & experience. And I hope we don't lose your attention again.

[TelRay]

I love when my posts derail into these kind of things that will benefit more people than the original topic

[g1]

I love when my posts derail into these kind of things that will benefit more people than the original topic

'Derail' to me usually implies an impending train-wreck. I prefer 'off on a tangent'.

[g1]

The specified idle power consumption of 20W suggests an idle current of around 160mA per power transistor. Calculation: 0.16A x 31V x 4 (transistors) = 19.8W.
That would result in a voltage drop of 80mV across each 0.5R emitter resistor.
Did I miss anything?

How about other consumption aside from the output transistors (drivers, etc.) and magnetization current?
I agree they would probably not be significant compared to the outputs though.
But it does seem high idle current to me. I'm used to seeing tens of mA rather than hundreds (through output transistors).
The revision 'C' amp specifies 20mA idle current per output transistor (measured with current meter). Power consumption is same 20W listed.
(section 5(a) on pg.7 of pdf attached)

[Leo_Gnardo]

I love when my posts derail into these kind of things that will benefit more people than the original topic

Thanks for your patience. This is how we learn stuff. Or sometimes, get reminded of what we should already know.

[Helmholtz]

How about other consumption aside from the output transistors (drivers, etc.) and magnetization current?
I agree they would probably not be significant compared to the outputs though.
But it does seem high idle current to me. I'm used to seeing tens of mA rather than hundreds (through output transistors).
The revision 'C' amp specifies 20mA idle current per output transistor (measured with current meter). Power consumption is same 20W listed.
(section 5(a) on pg.7 of pdf attached)

Thanks for your reply and additional info.

First of all I didn't intend to give precise biasing advice. Should have explained better. As I couldn't find useful biasing information in the manual or schematic (emitter voltages are partly wrong), I was looking for something to get in the ballpark or to give an upper limit. Especially as the OP's measurements indicated even higher currents (assuming 0.5R emitter resistors)

You are right, drivers and rest of the circuit may consume another couple of watts. Magnetization current is reactive and doesn't contribute to real power (if measured correctly).

The calculated idle currents do look very high and compared to the revision C manual I have to realise that the specified power consumption is way too vague to be used for idle current calculation.

Referring to the revision C manual's biasing procedure:
The total quiescent current of 40mA per side (method 5 a) doesn't mean that each output transistor draws 20mA. As specified per method 5 b, the voltage across R2 (R3) should be 0.4V. This means that the outputs are practically biased off and that most of the 40mA is used by the driver transistors.