Hi all,
I'm new to the site and the hobby and I could use a little help. I've tinkered around with tube type Ham and Shortwave gear off and on for a couple of years, but this is my first attempt at audiophile gear.
I just purchased my first little amp. I got it off eBay for $25 shipped. it even came with the original speakers.
All I know for sure is that it is a Magnavox phono amp using 2 50EH5's and a 12AX7. Aside from the numbers printed on the chassis that you can see in thee pics, the following is stamped on top 636275- 4.
It came with a block diagram but no schematic. On the diagrams lower right corner is: EL 1484-1. I have searched the internet using all these numbers and found nothing. Does anybody have or know where I can get a schematic for this.
It works but of course needs to be recapped (has nasty hum) and I'm trying to avoid having to figure out all the components and hand writing a schematic myself if possible.
Any help would be greatly appreciated. Thanks,
Rob
I'm new to the site and the hobby and I could use a little help. I've tinkered around with tube type Ham and Shortwave gear off and on for a couple of years, but this is my first attempt at audiophile gear.
I just purchased my first little amp. I got it off eBay for $25 shipped. it even came with the original speakers.
All I know for sure is that it is a Magnavox phono amp using 2 50EH5's and a 12AX7. Aside from the numbers printed on the chassis that you can see in thee pics, the following is stamped on top 636275- 4.
It came with a block diagram but no schematic. On the diagrams lower right corner is: EL 1484-1. I have searched the internet using all these numbers and found nothing. Does anybody have or know where I can get a schematic for this.
It works but of course needs to be recapped (has nasty hum) and I'm trying to avoid having to figure out all the components and hand writing a schematic myself if possible.
Any help would be greatly appreciated. Thanks,
Rob
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi Rob,
Welcome to DiyAudio!
You can also look for those phonograph schematics, they should be close. One of the RCA tube manuals should also have a circuit that is close to yours.
Lose the ceramic caps straight off. It will sound better with a different type in there. All coupling caps need to be replaced as well.
-Chris
Welcome to DiyAudio!
You can also look for those phonograph schematics, they should be close. One of the RCA tube manuals should also have a circuit that is close to yours.
Lose the ceramic caps straight off. It will sound better with a different type in there. All coupling caps need to be replaced as well.
-Chris
Dangerous Amplifier Design
Something else needs to be mentioned immediately, and that is the lack of a power transformer to provide isolation from the power line.
Before you even think about plugging this thing in get yourself an inexpensive isolation transformer on eBay. A 100Va rating should be just sufficient.
Do anything else and you may end up electrocuting yourself or someone close to you.
We want to keep you around and healthy, that's how our hobby grows!
Something else needs to be mentioned immediately, and that is the lack of a power transformer to provide isolation from the power line.
Before you even think about plugging this thing in get yourself an inexpensive isolation transformer on eBay. A 100Va rating should be just sufficient.
Do anything else and you may end up electrocuting yourself or someone close to you.
We want to keep you around and healthy, that's how our hobby grows!
YES!!!!!! the popular HOT CHASSIS design has one side of the line cord tied directly to the chassis, usually with a non-polarized plug
. if you use grounded test equipment or connect the device to a preamp, etc... that has a grounded chassis, you will pop a breaker. if you touch the chassis you can get KILLED!!!!!
you MUST use an isolation transformer with this device. if it has a non-polarized plug, you have a 50-50 chance of plugging it in correctly with the chassis connected to the outlet neutral. even if it has a polarized plug, many outlets have been known to be wired backwards. 
. if you use grounded test equipment or connect the device to a preamp, etc... that has a grounded chassis, you will pop a breaker. if you touch the chassis you can get KILLED!!!!! you MUST use an isolation transformer with this device. if it has a non-polarized plug, you have a 50-50 chance of plugging it in correctly with the chassis connected to the outlet neutral. even if it has a polarized plug, many outlets have been known to be wired backwards.
You know what guys?
I knew that but completely missed it. I've repaired so many that these days I sometimes forget about new safety awareness.
Hi Rob,
Use an isolation transformer to make it safe. They are cheap on Eeekbay
-Chris
I knew that but completely missed it. I've repaired so many that these days I sometimes forget about new safety awareness.
Hi Rob,
Use an isolation transformer to make it safe. They are cheap on Eeekbay
-Chris
OH, I forgot to ask, should i go with metal film resistors or are carbon comps sufficient?
and what caps do you guys think are best?
Thanks again,
Rob
and what caps do you guys think are best?
Thanks again,
Rob
Hi Rob,
Carbon composition types are only good in RF work. This includes grid stoppers. I like to use metal oxide types in most places and metal films in the input signal path, and feedback network. Both are easily available from the bigger supply houses.
-Chris
Carbon composition types are only good in RF work. This includes grid stoppers. I like to use metal oxide types in most places and metal films in the input signal path, and feedback network. Both are easily available from the bigger supply houses.
-Chris
anatech said:
In my 1st build i used whatever i had around -- one of the goals was to buy as few parts as possible.
In my next one i'll use Solen PS caps & pay a bit more attention to other parts as well.
Note that my build used no feedback (except degeneration).
dave
i've been bit a few times by HC equipment, as well as the hot baskets of electromagnet speakers on antique radios...... not fun..... even had one time when i was a teenager where i hooked up the UHF tuner in one TV (which had bad IF's) to another TV yhat had no UHF, but had the 47Mhz plug for a UHF tuner. popped the line fuse in the basement as soon as i turned the second one on, twice. i then realized that both TV's were HC, and i had one of the plugs reversed. yes, when i was young, i got blamed for every blown fuse, even if i didn't do it...... later after i moved away from home, my folks got breakers installed.......
Here is my rebuild of a SE 50EH5 Tube Amplifier.
They are fun to play with. Low power and depending on the size of your OPT, you may not get full bass extension.
Yes, and as noted by others, the lack of a isolation transformer on the heaters and a hot chassis is dangerous!
Cheers,
Gio
They are fun to play with. Low power and depending on the size of your OPT, you may not get full bass extension.
Yes, and as noted by others, the lack of a isolation transformer on the heaters and a hot chassis is dangerous!
Cheers,
Gio
Magnavox 50EH5
i have one of these and have also been looking for a schematic and information on rebuilding. It was in a Magnavox Micromatic record player I bought for $10 at a flea market. Mine hums too but does play. I am also aware of the need for the isolation transformer but i really have no idea what to do with mine--I have never rebuilt an amp before. I would love to see a photo documentation of your rebuild.
Than
i have one of these and have also been looking for a schematic and information on rebuilding. It was in a Magnavox Micromatic record player I bought for $10 at a flea market. Mine hums too but does play. I am also aware of the need for the isolation transformer but i really have no idea what to do with mine--I have never rebuilt an amp before. I would love to see a photo documentation of your rebuild.
Than
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