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In Reply to: RE: Magnavox 9302-00 Schematic posted by Eli Duttman on December 11, 2014 at 21:13:49
Yes, dual log-taper pot will be needed - 500K is probably best, as the phono stage has a high output impedance. If the 750 Ohm balance control R117 is installed, leave it as-is - if not, you need to add two 390 ohm resistors in its place to use the amp stand-alone. If you have the Molex harness from the console, it can supply the power to the preamp as Eli described - if not, ask around the forums - most haven't used it, and eliminated the connector on the amp. A 5V4 can be used in place of the 5U4, giving slow warm-up and less load on the transformer heater winding.
Edits: 12/12/14Follow Ups:
nt
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare
I'm not sanguine about using a 5V4. Check the data sheet out. Current capability is 175 mA., which should be enough for the power amp, but may be problematic if ancillary equipment's B+ is to be provided. Another thing to watch out for is the small 1st filter cap. value limit.
A 5AR4, like the 5V4, draws only 2 A. of heater current, but like the 5U4, the type is good for 250 mA. Also, the 1st filter cap. limit is greater than that of a 5U4. Therefore, the 5AR4 is the vacuum rectifier type I'd look at, IF a change was to be made.
If either rectifier with a cathode sleeve is installed, B+ has to be taken from pin 8, not pin 2. Both the 5V4 and the 5AR4 will raise the B+ rail voltage, with the 5AR4 raising it more.
Eli D.
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