Federal Limiter AM864 thread

[SUPERMAGOO]

http://groupdiy.twin-x.com/displayimage.php?album=40&pos=49

http://groupdiy.twin-x.com/displayimage.php?album=40&pos=50

http://groupdiy.twin-x.com/displayimage.php?album=40&pos=51

 

[kvintus]

Bump?

/Anders

 

[tk@halmi]

I am making my own turret boards today. Maybe this lump will come alive for a few minutes by this evening.
I really like McMaster-Carr. They have all sorts of board materials like fiberglass and garolite. Sourcing turret terminals I like for a particliar board thickness has been more challanging.

 

[Svart]

what would you consider the total cost to build this to be?

I keep meaning to start this project but haven't yet..

 

[tk@halmi]

Here is my BOM so far. This weekend I will update it with part numbers
of suppliers. You should be able to do it for $300 if you get the Edcor transformers.

Qty Item Cost/Ea. Sum Source
1 WSM10K/10K (in) 10 10 Edcor
1 XPP1-600-10K (out) 20 20 Edcor
1 XWPR012 (power) 39 39 Edcor
1 15H 75ma choke 16 16 AES
1 5Y3WGTA 10 10 AES
1 6SN7GT (US Make) 15 15 AES
1 6SQ7GT 6 6 AES
2 6SK7GT 6 12 AES
1 50K Dual LOG Pmeter 3 3 AES
1 500K LOG Pmeter 3 3 AES
1 1K Pmeter 2W 3 3 AES
1 VU Meter 18 18 EPD
1 Resistors 10 10 Digikey
1 Capacitors 15 15 AES
1 Case 3U 60 60 Par-Metal
5 Octal Relay Sockets 3 15 Allelectronics
2 XLR sockets 4 8 Mouser
3 Knobs 3 9 Allelectronics
1 Power Switch 3 3 Allelectronics
1 Fuse Holder 2 2 Allelectronics
2 PS Cap 20u/400V 4 8 Allelectronics

1 Power cord and strain relief 3 3 Allelectronics
1 Garolite turret board material 6 6 McMasterCarr
30 Turret terminals 0.2 6 Mouser
Sum Total $300

If you get fancy with Sowters, pretty VU meter and guilded front panel you can blow $500 to $600 easily.

Abbreviations:
AES=Antique Electronic Supply at www.tubesandmore.com
EPD=Electronic Parts Direct at www.electronicpartsdirect.com

 

[kvintus]

Wonderful! Now I really feel like building something...

/Anders

 

[tk@halmi]

There are two areas others may want to investigate further:
1. I plan to use a 10k/10k input transformer as opposed to the 600/10k one of the original. Many times the are complaints of excess gain in these limiters. I don't know if this is a good decision yet.
2. The Calrad VU meter will not have the right calibration for this limiter as Dave has pointed it out earlier in the thread. I was going to try the Calrad meter without the rectifier and 1.8k resistors that show in the schematics and go from there (Calrad meter has rectifier and resistors inside). I wanted to keep the cost down for this prototype.

For the turret boards I ended up with two separate boards. One that holds two 20u film capacitors for the power supply and the 15k 10W resistor. Another board holds all the other resistors and small capacitors.

 

[Svart]

awesome, this is definately my next DIY project then.

I have not done any in depth research on this.. is there a reason to go with such a high impedence secondary on the input?

I plan on running mine in unbalanced mode from inserts.. I guess 10k to 10k would work for that.

what is the output trafo? 10k:600? I guess i could use another 10k:10k?

 

[tk@halmi]

[quote author="Svart"]I have not done any in depth research on this.. is there a reason to go with such a high impedence secondary on the input?[/quote]
There is a reason in the original plan to get a 12dB step up using a 600/10k transformer. As I understand in those days most mic preamps would give a fixed +40dB or so. They would throw in an attenuator after that and go into a limiter like we are building here. The limiter would have another 30dB gain minus the gain reduction dialed in. Today we prefer the preamp to do most of the gain where it is done cleanly and quietly.

[quote author="Svart"]I plan on running mine in unbalanced mode from inserts.. I guess 10k to 10k would work for that.[/quote]
That would work with most gear. Note that the seconday must be center tapped. If possible balanced as well.

[quote author="Svart"]what is the output trafo? 10k:600?[/quote]
Yes. You could use a 15k:600 as well. You need an output transformer that is balanced so currents cancel each other in the primaries.

[quote author="Svart"]I guess i could use another 10k:10k?[/quote]
If your insert input is high impedance (usually 10k to 100k) then yes.
But you will get 12dB more gain you may not need as these things are reportedly pretty loud already. You can try the low cost XSM10k/600 or for a few more bucks the XPP1-600-10K or the XPP1-600-15K (testing currently).

 

[cannikin]

Awesome TK !!!!!!! :grin: :grin: :grin:

 

[synthi]

:grin: :thumb:

 

[ToobieSnack]

BUMP ...
hehe and pic update please :grin:
later
ts

 

[tk@halmi]

It sounds like you are going to use a non-gapped one. You would need a really, really well balanced output stage to cancel out all DC and avoid saturation.

Let's say that the output triodes are supposed to conduct 10ma each. How much imbalance could there be? Could you really have one triode juiced at 10ma and the other at 5ma? If so the problem is with the tubes, not the transformer. A decent transformer will swallow a couple of ma mismatch.
Gapping is fussy work. Fussy=Expensive. Adding more iron to avoid saturation and making the primary symmetrical is easy. This was common practice in low power tube audio before we were born.
Notice that I had Edcor wind on a large core, the XPP1, as opposed to using the standard XSM core. I posted a picture to demonstrate the difference in sizes. Here is the link again:
http://mysite.verizon.net/res75okq/sitebuildercontent/sitebuilderfiles/edcor_xpp1_10k_600.jpg

 

[tk@halmi]

I am way behind with this project. The power supply is working fine and most of the wiring is done. I am dreading and procrastinating the metal work as usual. I guess I should hang around the forum less and get more done.

 

[cannikin]

Edit -- Confusing Post -- removed :green:

 

[cannikin]

:grin:

 

[penquista]

Hello,

first of all i want to say thanks to all the members of this forum.
After reading all the informations in this forum, i've been able to build a AM-864 clone. I used a regulated 12 volt psu as i got cheap 12sk7 12sx7 and 12sq7 tubes, the edcor xformers i used also sound great.
my problem now is, that i build two units in one box and i don't know how to build the b+ psu to power both units.
i would be really happy if someone could help me.

Christian

 

[Svart]

and of course I assume that a lot of these parts will need to be doubled for a dual mono setup. so we are looking at more like 400-500$ for a 2 channel version of this?

oh and another question, what is the optimum hivoltage (B+) if we plan on building our own sandstate PSU?

 

[penquista]

I'm using a sandstate psu. i have a b+ of 218 volt and it works and sounds fine. in GR mode the meter is in the +3dB position, when i drop the voltage to 200 volts it shows 0dB but as i couldn't notice any change in the sound i took the resistance that dropped the voltage out of the circuit again.

The total cost for both units was about 230 Euro

 

[Svart]

so I don't want a 180-0-180 trafo then right? that would be 360VAC/ 496VDC

so we are looking at 200-250DC B+?

caps 400v ok?
resistors .5W ok?

what power should the 500k pots be? 1/4w?

is C1 a 1uf?