Small wiring problem keeps my Magnavox AMP-101B from operating

H2s04

H2s04

auralmicitisis
Hello all,

I posted about this subject earlier in the tube forum, but I feel now that this problem might be a bit easier to solve if more people can see it.

I've been working on this console amp/tuner project for a bit now, and I just received all the parts/tubes I needed to get it running on monday. However, there's a catch. The amp I'm working on shipped with two large field coil speakers inside the cabinet (that I'm missing) but was also designed to accommodate external, non-field coil speakers, via the use of an accessory speaker selector switch that would be plugged into the back of the amp. The amp has a shorting plug in the speaker selector switch socket that allows only the field coil speakers to be used.

So, the point?

I need (with a bit of help from y'all, I hope) to figure out how to rewire the shorting plug so that I can use the external speaker tap, and listen to my project! :) I've also recently realized that the socket for the field coil speakers may need to be filled with some sort of shorting plug, as I am guessing they designed the amp assuming that it would never need to be run with the internal speakers detached. This is important, because I remember someone once telling me that in order for like electronics to work, they need to have their field coil speakers attached in order to turn on/function. I assume this is the case with my amp, in that I tried powering it up with my variac just to see if the unit would light up (I've replaced all the caps/tubes), and nothing took place.

I have a link to the schematic, where it notes the accessory switch's circuitry on the second page ; I just don't have enough experience with this stuff to figure out what to do from here.

Schematic: http://www.nostalgiaair.org/PagesByModel/294/M0010294.pdf

Previous post:

http://audiokarma.org/forums/showthread.php?p=952128#post952128


Thanks all!
 
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Need some sort of choke coil.

Even if you use an external speaker, the field coils of the internal speakers are still connected (they serve to filter the pulsing DC coming from the rectifier tube).

What you need to do is put a choke coil between pins 2 and 6 of the plug (this connects the output transformer center tap to pin 2 of the 5Y3 tubes using the choke, one wire of the choke to the OPT CT, the other to pin 2 of the 5Y3's).

A resistor of the proper value and wattage might work, but it is hard to tell.:scratch2:

Sorry I have no recommended values to give you, others may be of help here.:yes:

As for the speaker wiring, I need further study on this.

Hope this helps.:thmbsp:

Mark T.:music:
 
what kind of choke would you recommend? one that's similar to the coil's 250? rating? i did a bit of research, and it seems like they're measured in terms of "Henries". wtf.

but anyway, thanks for the help so far! I'm really starting to understand it now. regarding the speaker selector switch, i think i should short pins 1 and 4 together. what do you think?
 
Can anyone make out the voltage difference between the two points on the filter capacitor. I'm trying to calculate the power across the substitution resistor.
 
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