Magnovox 2st257

[gadget73]

6EU7 is not a dual voltage tube.

flip it over and get some pics. Not impossible that one side of the 6EU7 is bad, but if its lighting I really doubt it. There are like 6 parts in these things so its probably something simple. Usually just a connection in the wrong spot or a cracked joint.

 

[cademan]

Lol, I just assumed because of what I know about the 6EU7 as a different pinout than the 12AX7.

I think I really did know this and I do have all the data sheets for these tubes but just failed to look at them again. My memory isn't what it used to be. It sucks getting old.

Oh well, sometimes I just get tired and lazy to be looking them up all the time.

 

[Twalt]

Here are some shots of the underbelly.

 

[gadget73]

Check the green wire here. Can't tell if its connected, but if its off you'll get no sound from that channel. Pin 2 is the grid, which is basically signal input to that tube.

 

[Twalt]

Are these capacitors installed in the correct place? The sams photofact shows the .047uf coming off a pin on the 6eu7 socket. I put them where they were as I found them. Something is amiss?

 

[Twalt]

Yes that green wire is attached.

 

[Twalt]

Here is a better picture.

 

[Twalt]

These caps look hinky to me. This is where they were when I replaced them.

 

[gadget73]

related question then, is pin 2 bridged to pin 3 on the 6bq5? New angle makes that look like a possibility. THat would also shut down signal in that channel.


I think the caps around the 6eu7 are right. Its messy but from what I'm able to trace it appears to be connected correctly. The stuff on pin 4 is for channel 2, the stuff on pin 9 is channel 1. Should be an 820 ohm resistor and a 0.047uf to ground and a 150k to one of the power supply cap. There is also a 33k and a 0.1 to a 6.8k that comes off the speaker jack, and a wire goes from that point to the tuner power socket. My guess is that has something to do with the balance control since Magnavox seemed fond of implementing a really goofy balance control system.

The only thing I'm not finding is the 820 ohm from pin 4 to ground. I see the one on pin 9 though.

 

[Twalt]

Pins 2 and 3 on the 6bq5 are not bridged.

 

[Twalt]

Do you think I may have installed a bad capacitor? They were new.

 

[Twalt]

I fixed my sound problem on channel 2. I had a 470 ohm resistor coming off of pin 2 of the 6bq5, instead of a 470k resistor. What a relief, thank everyone for your assistance.

 

[gadget73]

oh, yeah that will do it. Close enough to shorting the grid to ground. The driver doesn't have enough snot to make that work. I've done that more than once myself.

 

[Dandy]

I fixed my sound problem on channel 2. I had a 470 ohm resistor coming off of pin 2 of the 6bq5, instead of a 470k resistor. What a relief, thank everyone for your assistance.

Well spotted. You've just had your first hit of the 'tube amp resto' drug. Welcome to the rabbit hole.

 

[Twalt]

Thanks so much. Looking for more fun on future projects. Just picked up another Maggie, will post some pics soon.

 

[bobabode]

Thanks so much. Looking for more fun on future projects. Just picked up another Maggie, will post some pics soon.

You're doomed, doc. Doomed, I tell ya. Welcome to the club. (grin)

 

[Twalt]

Thanks

 

[Twalt]

This is my new Maggie. If someone can point me to schematics or photofact for this , greatly appreciated. Not sure of the year of manufacture. Model #2st656 s. 9302 00 is the amp number. Tuner# is57-12. Thanks for all your help on my previous project. It is working great.

 

[Twalt]

Forgot my pics. Here they are.

 

[Dswankey]

This is my new Maggie. If someone can point me to schematics or photofact for this , greatly appreciated. 9302 00 is the amp number.

Well well well looks like you've been bitten by the Maggie bug, congrats as they are fun amps and well documented here at AK

A detailed must read by one of AK's preeminent tube guru's

https://audiokarma.org/forums/index.php?threads/more-fun-with-magnavox-the-9300-series.687735/

Schematic attached jpg as seen below and .pdf attached