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MAGNAVOX 294H Help

The originals in my AMP-150 are actually working currently. I wouldn't trust them long term but I was able to bring it up without trouble to do some testing to see if it had signs of life, and to figure out what the crossover points actually were. Its from the same time period, so you might get lucky. I would dump the paper caps underneath though, mine were only slightly leaky, which is better than I was expecting but they were bad. Film caps are cheaper than tubes are anyway.
 
I hope they are good enough to test with, but judging by the level of dust and crud that was laying on the power amp and tuner I'd say this thing has not seen power in many many years. If it does power on after all of that I would say that is a wonderful example of Made in America at its finest. I mean really anything made from back then and still working is amazing. Imagine our landfills in a few decades from the junk that is made today.
 
Sorry Tom, I'm not sure why I didn't get a notification of your post. I appreciate the offer. I ended up finding the tuner section, and have been getting by with the AMP142AB schematic even though I have AMP142CC.

I replaced most all of the filer caps with the exception of 1 half of the 30/30uF@475VDC in the tuner. I screwed up my shopping list and shorted myself (1) 30uF@500vDC cap. I also replaced the (2) .1uF and a .022uF poly caps and (2) 470K resistors that tested strange. I serviced the turntable and my dad gave me this awesome rubber renewer that took all of the wobble out of the drive idler. The turntable runs about as well as I can expect it to for 62-63 years old. The power amp is working the best, and the tuner the worst. FM and AM reception is spotty and somewhat weak for the most part. About 75% of the tubes were bad. Without really looking at it I found that the one 5Y3 that was in the socket was actually a 5U4. I need to replace 6U8A, 6BZ6, and 6CY5. They tested really weak on a Triplett 3444 tester. 3 out of 4 6V6's were weak, the tuner had a 12AT7 instead of a 12AX7 (what is that a gain factor of 40 vs. 100???) and needed both 5Y3's. My dad had all of them and they are on loan. Having said that everything DOES work. I just need to get those tubes, do more cleaning, and if my 2 prong isn't causing it or the one remaining 30uF, figure out the ground loop issue I have. It is coming from the tuner because if I remove the single RCA input cable from the amp the hum is gone. That is it for now. Thank you everyone.
 
pull and clean the tube pins and sockets in the tuner. The CR-730 paired with mine had some random drops in sensitivity that were caused by crusty sockets.


12ax7 makes more sense if its in the audio portion, 12at7 if its in the tuner section. The 12at7 works vastly better at radio frequencies. They got used a lot as the mixer/oscillator in FM tuners.
 
gadget73 said:
pull and clean the tube pins and sockets in the tuner. The CR-730 paired with mine had some random drops in sensitivity that were caused by crusty sockets.


12ax7 makes more sense if its in the audio portion, 12at7 if its in the tuner section. The 12at7 works vastly better at radio frequencies. They got used a lot as the mixer/oscillator in FM tuners.
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I did spray out some of the tube sockets, but I need to hit them better. The SAMS I have for the tuner has versions 52-01, 52-02, and 52-03. The block section for the 52-03 shows the 12AT7 in circuit. I'm curious if someone at one point was working on this unit with the wrong schematic? Like I said there was the 12AT7, but I have the 52-02 which calls for the 12AX7. How does the 12AT7 work better in the tuner? I'm curious as they are essentially the same tube except the gain factor. Do you feel the 12AX7 makes the radio signal too hot? I do admit that for the channels I can get on AM the signal is strong and loud. FM comes and goes. I can sometime slap the radio on the side and the reception comes in, but then shortly after fades again. Man, that slapping the set thing sure does bring back memories as a kid. I forgot having to do that from time-to-time.
 
depends what its doing. If its used as a mixer/oscillator there isn't much gain going on, but the lower internal capacitance and higher plate dissipation is an advantage. If it was being used as a mixer/oscillator I'd expect to find it tucked in right next to the tuning condenser and probably under a shield.
 
gadget73 said:
depends what its doing. If its used as a mixer/oscillator there isn't much gain going on, but the lower internal capacitance and higher plate dissipation is an advantage. If it was being used as a mixer/oscillator I'd expect to find it tucked in right next to the tuning condenser and probably under a shield.
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I guess I'm not following you. Are you saying use the 12AT7 in place of a 6U8A? In my tuner the 6U8A performs the mixer/oscillator function, and its also close to the tuning condenser.
 
no. Just saying that if the mixer/oscillator was supposed to be a 12AT7, it probably would not perform well with a 12AX7 in that spot. A 6U8 is a completely different tube and not compatible with either of the 12A*7 types.
 
gadget73 said:
no. Just saying that if the mixer/oscillator was supposed to be a 12AT7, it probably would not perform well with a 12AX7 in that spot. A 6U8 is a completely different tube and not compatible with either of the 12A*7 types.
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OK good. You had me scared there for a moment. I was totally not getting you there for a moment. I got it now.
 
I've redone a few Magnavox's with the 54 series tuner, which is the stereo version of the 52. The Sams will call for a 12AT7 but the tube layout sticker that Magnavox applies to the inside of the cabinet has always called for a 12AX7 in the preamp section. I believe Magnavox would use the 12AT7 tubes in lower output consoles and that 12AX7 in the higher output consoles.
 
MotoTJ said:
I've redone a few Magnavox's with the 54 series tuner, which is the stereo version of the 52. The Sams will call for a 12AT7 but the tube layout sticker that Magnavox applies to the inside of the cabinet has always called for a 12AX7 in the preamp section. I believe Magnavox would use the 12AT7 tubes in lower output consoles and that 12AX7 in the higher output consoles.
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Interesting information. Thanks.
 
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