Magnavox Updated 86-01

cephelps

OLD SCHOOL
I saw this magnavox 86-01 update and was wondering has this design been tested? If so where can I get the power transformer?
 

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Does that mean that the stock 86-01 transformer won't work in this circuit? I was thinking of doing this to a spare 86-01 I have lying around...
 
I did a scratch build with this circuit and it was a very good performer. This mod is by Kegger so it is bound to be good. I don't have the amp anymore so I am going on memory but I think it would be well worth it to make this mod. I used the original Maggie trannies. Stan
 
Only thing you may want to tweak on that circuit is that feedback resistor. :)
(edited the schem, it now shows the 20k resistor, you can go to 10k)

Can't remember for sure but I think I ended up about half the value on another
one of those amps, as I wanted it a bit less sensitive and bit better bass "grip".
(think I went from the 39K to 20K, you can experiment for taste, even lower)

(THIS IS BASICALLY JUST A CLEANUP AND STREAMLINE TO THIS AMP)
There are better circuits I would more then likely use instead of the maggie.
 
Thanks so very much for the replies. I am building this amp and want to make sure I have all of the corrected parts. I will post photo progression as I go.
 
I will just take your advice on the feedback resistor and change it to the 20k. I will use the original transformer, I was not sure if the original was used. I all so want to add a volume circuit to this amp, any suggestion?
 
Yep I used the original power and output transformers.

To add volume control, change the 270k resistor on the front to 1meg and
add an 100k audio taper pot like say one of the alps ones from radio shack
to control the volume, no added gain is necessary.
 
Thanks for the volume update. I had it wrong again. I will post photos on this project as I go. If there is any thing you can think of that will improve this my first time SE amp project, please fill free to add your suggestion.
 
Hello,

I have taken the advices all have given me, and this is what it look like. Is it workable? I will soon find out..:music::music:
 

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Not bad, couple things though.

looks like you want to run separate cathode resistors for each output tube.

If so you need to DOUBLE there value and you won't need the 10ohm resistors
either, they were there to measure current in each tube with a shared cathode.

You'll need an 200-220ohm resistor each EL84 cathode if going separate resistors.
(depends on your pwr supply voltage and current draw of your EL84's for optimum)

Also for now loose the cap on the power cord, if your switch makes any noise when
you turn the amp off put the cap across the SWITCH, it then should cure any pops.
 
Yes I want to separate the cathode bias resistors, but was never told of the right values. I will get two 220 ohm 2 or 3 watt resistors. Sure I make any changes to the 150uf caps? I will drop both 10 ohm resistors. I will put the .01 cap across the switch so that I want have to go back into the amp when finish. I added a 3 prong power cord to this amp. I was all so shown a bridge rectifier circuit for the 6.3 volt filaments. Will that help?
 
150-220uf caps are fine for the cathode bypass.

I generally don't use 3 prong cords as you may introduce ground loops,
but if you have no ground loop/humm issues it certainly won't hurt to.

No need for a bridge rectifier circuit, ac heaters is fine here on this amp.
 
The "Sure I make any changes to the 150uf caps" should read, "Should I make any changes to the 150uf caps? in the last post 6. I will start on this amp just as soon as the volume control get here. So far I have put a lot of time into stripping and cleaning the chassis. At this point I have purchased new parts for everything except the transformers. Thanks for your help in designing, what looks like one little jewel for my B&W 602's.
 
Probably not in a build like this, tie all your grounds together at a central
location then connect those to the chassis an you should be just fine. :)

If at all possible I do try an keep the power supply grounds to there area
and the signal ground to another area further away from each other though.
 
I just ordered all of the needed parts, 20k, 1meg, 100k audio taper pot, & 240 ohm 2w. I could not find a 250 ohm 2w.

Thanks
 
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