Federal Limiter AM864 thread

[penquista]

I used a 175-0-175 trafo and replaced the rectifier tube with 2 diodes, as its half wave rectified the voltage should be around 248 volt but i measure 218 volt at CT of the output trafo.

the pot i used is a normal stereo pot 1/4w, resistors 1/2 W and C1 is 1uF. i used Solen Fast 630v for all the caps

 

[Svart]

??

6sn7gt, they range from 6$ to 50$. which one should i get and why?

 

[Svart]

Secondary: 190-0-190 V, 65 mA
Filament winding: 6.3 V, 2.5 A
Mounting centers: 1.75" x 1.56" vertical mount

work good for a PSU trafo?

 

[Svart]

ok 95% of my stuff ordered now.

back to ordering!

i think i can do this for less than 300$ for two channels.

 

[penquista]

Any idea how to build the B+ psu to power 2 units?

If not i will just build 2 identical psu's but it would be great to use only 1 choke.

thanks

 

[Svart]

I'm building mine with a solid state PSU. I believe that some diodes would be enough to separate the two?

 

[tk@halmi]

[quote author="penquista"]Any idea how to build the B+ psu to power 2 units?
If not i will just build 2 identical psu's but it would be great to use only 1 choke.[/quote]

Since you are using silicon rectification you should have no problem running two channels off a single supply. However, the power transformer must be able to supply at least 50ma without drooping too much. The choke should be rated at 75ma at least.
Simply double the values of the capacitors in the power supply. Better yet, try hanging 100uF/400V capacitors before AND after the choke. Do NOT apply this mod to the tube rectifier version though!

 

[penquista]

thanks tk@halmi, i will try the 100uF caps.
but my main problem is that i don`t know at which point to connect both units. til the moment every version i tried made me some trouble with paralel or serial resistances. conecting each unit separately works fine but at the moment i connect both, none of them will work.

 

[Svart]

ok, firebottles, PSU trafo, Rs, Cs, pots, octal bases and diodes are all in. Now i just need a case/frontpanel and I/O trafos.

Time to start wiring!

One more question, what would happen if I ran this in unbalanced mode? I assume this cannot be done because of the current flow in the primary of the output trafo?

 

[Svart]

also, since the DC in the primary of the output is balanced, can't I just use a regular 10k:600?

 

[tk@halmi]

You must have the input transformer in there like shown on the schematics with a center tapped secondary. The output transformer must have a center tapped and balanced primary. Not all 10k:600 have that.

 

[Svart]

does the wsm10k:10k have a CT secondary? I assume so since you are using it..?

 

[tk@halmi]

[quote author="Svart"]does the wsm10k:10k have a CT secondary?[/quote]

Yes, Sir.

 

[Svart]

ok, done deal.. calling them to order now!

thanks TK!

 

[Svart]

ok got my trafos today. will attempt to finish this soon!

 

[gary o]

I DIYed one a these a while back and had a strange problem, I accidently made totally the wrong value input attenuator but it worked, I corrected my mistake then it didnt work so I left it alone, I will dig it out of the shed and have another play with it be very interested to hear how yours turns out.


Cheers .........Gary O.

 

[penquista]

i`m still working on my 2-channel version. How do i have to connect the units to the psu? both units are seeing the 15k resistor of the other unit. how can i make sure one unit is only "seeing" the 15k resistor and 1k pot that corresponds to that unit? i completely rebuild both units trying to separte the gnd connections but the result is still the same.

 

[Svart]

ok so i am attempting to finish these, and see that the output trafos do NOT have secondary center taps.. :? I ordered the special wound ones that TK specified.
now what? use ground for the centertap?

 

[NewYorkDave]

Why do you need a centertap on the output xfmr?

 

[tk@halmi]

[quote author="Svart"]ok so i am attempting to finish these, and see that the output trafos do NOT have secondary center taps.. :? I ordered the special wound ones that TK specified.
now what? use ground for the centertap?[/quote]

The secondary is a 600 ohm balanced output like you have on modern gear. One lead goes to pin 2 the other to pin 3 and pin 1 goes to ground on the XLR output.
What would you do with the center tap on the secondary in a modern studio?

Edit: Retarded pin mix up.