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Maggie 9304 Amp Threads?

Barton Isaac

Barton Isaac

New Member
Hi Y'all,

I figured instead of me asking a ton of questions, I'd ask if there are threads that y'all know of that you could direct me to. I've done a bunch of searches already without satisfaction.

I'm looking to convert the Magnavox 9304 into an amp to power a CD player, Phone and MP3 via bluetooth. I need to know specifics regarding "do I need a pre-amp and if so, ideas for where to find a schematic". Info on the front end regarding balance and master volume.

I've used my variac to determine that the output transformers are 8ohm....verification would be great as well as thoughts on a speaker set up. I am planning on building the cabinet to house everything.

Thanks in advance!

Bart
 
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Barton Isaac said:
I'm looking to convert the Magnavox 9304 into an amp to power a CD player, Phone and MP3 via bluetooth. I need to know specifics regarding "do I need a pre-amp and if so, ideas for where to find a schematic". Info on the front end regarding balance and master volume.
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Yes you will need a pre-amp.

Am I reading you correctly in that you want to convert a 9304 "Power" amp into an "Integrated" amp (Power + Pre)?

I would start with this thread is a must read, it's long but worth it. The author @dcgillespie is one of THEE main tube guru's here at AK and he took the time to share his knowledge and methodically break down what is needed with these amps.

From there if what I asked is what you're trying to do then this might be a good thread to start

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

https://audiokarma.org/forums/index.php?threads/is-an-integrated-maggie-9300-possible.783223/
 
You can use a phone or CD player directly into the amp, controlling volume from the source. Bluetooth is another matter.
 
Thanks for the links! Yes, I'd like to make an integrated power and pre amp. I don't have the pre-amp that came with the unit so I thought that I would need something. I've seen some of the tube pre-amps on Tube Depot and was curious about trying that out.

Regarding the output transformers--seems like I've done an incorrect calculation because they are clearly stock units.

Thanks for the information!
 
Interesting that magnavox stock transformers arent 8 ohms i always thought they were but then again I leave mine in the console.
 
I wish I could get a bigger pic of that schematic... I think AK unfort down sizes everything in order to save web space.
 
tonyg88 said:
I wish I could get a bigger pic of that schematic... I think AK unfort down sizes everything in order to save web space.
Click to expand...

What I've done int the past is copy them to a thumb drive and then go to my local FedEx Office and the girl there prints them and they come out really nice and easy to read.
 
This is great information; thank so much for everyone's input. I think I'm going to leave the amp as just power and not integrate. I think it would be good as it is to run a CD player. However, for vinyl I'll need to use a pre-amp.

I have an update on my output transformers. I originally did my calculations off of ~6V from my variac but put the load output backwards...this stepped the voltage up from low to high. However, I just took measurements again. This time I put 6.07 volts across the red and brown wires of one of the output transformers. I measured the AC voltage to the output wires, green and black; this measured 0.137 volts. Turns ratio 6.07v/0.137v=44.3 or ~45:1. Squaring of the turns ration gives an Impedance Ratio of 2025. I found a tube data sheet for the 6bq5 in push pull AB effective load resistance, plate to plate of 8000 ohms. So for the output impedience, 8000/2025 yields 3.95 Ohm speakers.

The 4 ohm output transformers seems more consistent with some of the things I've read so far.

Again....thanks for all the information!

Bart
 
Barton Isaac said:
This is great information; thank so much for everyone's input. I think I'm going to leave the amp as just power and not integrate. I think it would be good as it is to run a CD player.

Again....thanks for all the information!

Bart
Click to expand...

That's what I've done in the past and it works quite well. What is really nice if you have one or can acquire one is a CD player with variable output & remote.

I have an old Denon DCD-1500 w/variable outs and the bonus is I have the original remote that acts as my volume control.

FWIW here's a pic of one my tech moddded and friend built the base for, depending on how far down the rabbit hole you go with this amp.

DSCN9927.JPG

DSCN0017.JPG
 
Having done it Dave's way, I can say it works very well. Better power output and reduced distortion. Even with the stock transformers it works pretty well.
 
Huge thanks to @Dswankey and @FlaCharlie....and everyone else. The schematics are great! I had the data I needed to double check the voltages on my power transformer. Seems to check out. Without the tubes installed and 120v on my variac, I measured the following:
314v-0-316v on the Red,
5.7v across the yellow to yellow and
7v across green to green/yellow.

I think that the voltages will be a little lower when all the tubes are in place.

I just ordered some parts today to recap and replace most of the resistors.

As I've continued to read and learn; i'm gonna leave this as a non-integrated set up.
 
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You might also find it helpful to look at photos of completed amps. There are certain things like adding resistors to complete the feedback, transformer bucking..............
 
I've given the top chassis a bit of a clean and polish and have finally got parts and started working on replacing parts. I replaced the power section and added output posts, I broke my only fuse holder and I don't like the power switch. I was going to put the switch in the back but have reconsidered to put it on the top/front/right. Now I've got to order and wait for more parts. I've got a power cord but will wait until I've got everything to add that. I figured I'd use this post as what I'm doing with the amp.
 

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Barton Isaac said:
I don't like the power switch.....have reconsidered to put it on the top/front/right. Now I've got to order and wait for more parts. I've got a power cord but will wait until I've got everything to add that. I figured I'd use this post as what I'm doing with the amp.
Click to expand...

I'm assuming you'll be using a rocker switch? if so and you haven't order it yet I would suggest Parts Express (No Affiliation), they fit perfectly in the "Tuner Pwr" and they light up for when using at night as seen here

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https://www.parts-express.com/cat/rocker-switches/1574

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