[BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD

[jefflehiress]

Hi bernb,

I have some questions about wiring:
- For the 400k resistor in series on the ratio pot. It is necessary to solder on the cable connecting CW, W or CCW?
The deck 1 of input pot is the one on top or bottom (closest to the front - panel)?
- for the attack and the release is there a meaning for the cabling of W and CCW? Because I do not see any indication on the PCB.
- For the link should I connect each point "link" of the pcb with each other with a cable?

thank you very much

 

[bernbrue]

Hi,
Turn the pot with shaft towards you, solder pins downwards.  Solder the 400k to the pin fully ccw, so it's the pin on the left. Solder the wire to the open side of the resistor.

Deck 1 is the closest to the frontpanel.

Attack/release should at least be wire the same. It's up to your taste/frontpanel design whether turning cw wil reduce or increase attack/release times.

Link is as you described. Make it switchable.

Cheers
Bernd

 

[jefflehiress]

Ok thank you for your answer,
For the attack and the release the front panel is the 3U from don audio.
When I face the frontpanel, slow is to the left and fast to the right.

 

[bernbrue]

So it is wiper/cw !
Bernd

 

[dogvoid]

Hi!
Edcor WSM600/600 work well as input transformer (without HPad)?

 

[Tubetec]

Re Edcor as input tx .
Im working on a point to point version of the fed at the moment , any way to loose some gain sounds like a good plan . Even though theres some dc on the secondary my guess is ungapped would do fine here . Ive decided to go with a 2x50k input pot too ,wouldnt 2x500k on the secondary of the input transformer severely limit high frequencies ?

 

[Tubetec]

Using a chunky line transformer on the front end would be good in that you could drive a proper line level signal into it ,lack of mu metal sheilding might mean more problems with induced noise though if you have a mains tx in close proximity .

 

[ChrioN]

How come you guys use 6BA6s instead of 6SK7s used in the original? (Reason I ask is I got a crapload of 6SK7s)

 

[bernbrue]

We searched for a "modern" glass tube alternative. Since the 6BA6 is the successor of the 6SK7 and already worked fine as sub for the 6386 in the sta level, we thought it might work fine the NU Federal as well. Indeed it does.
Bernd

 

[sr1200]

Quick question, in the BOM there are two R21s listed.  One of them is on the board next to the "from Out TX"  and is 160r. The other is a 15 K 10 W resistor which I'm not sure where it  goes.  Thoughts?

 

[bernbrue]

The 15K 10W resistor is on the mainboard and is needed for the bias voltage. See schematic. The 160R is part of the input/output pad. Buy both.
Bernd

 

[Tubetec]

Hi Bern,
Just wondering how would the Federal circuit work with triode connected 6BA6's or 6SK7's at the front end. If anyone has attempted such a mod Id be very interested to hear what the results were .
Thanks again for all the info in this post on pot values and attack/release mods, you've really made a silk purse out of a sows ear .

 

[sr1200]

OK got it.  Thanks  ;D

Any further reading on what NOT to populate for a stereo build? I notice in the pics that the PS section is pretty sparse with the exception of a bunch of the bigger caps.  The only mention i saw was in one of the docs that says only populate one board, but didn't mention what exactly.  The pics of the board lead me to believe its just the V supply portion, but I'd like to confirm that.  Also, where are the connections between the two made?

 

[bernbrue]

Hi,
You need to stuff both boards though you only need a single power supply for the relays of both boards (See picture attached to the very first post). There is a stereo link between both boards. Make it switchable. That's it.
Cheers
Bernd

 

[jefflehiress]

hi bernbrue.
I have some questions about the editing:
the first concerns the wiring of the EDCOR output transformer:
- this is an EDPOR XPP1:
on the primary input I have 1 = flat, 3 = B + and 5 = flat
on the secondary output I have 7 - 9 = 600 ohms
how should I wrap all this on the to-out-tx and the from-out-tx knowing that on the PCB there is a "point", "CT" and a location with no indications.

my second question concerns the wiring of the power transformer:
I have B +, AC and V +, AC on the PCB. On which I have to wook the 180V the 6,3V and the 9V of the transformer.

thank you very much

 

[jefflehiress]

on the primary input I have 1 = plate, 3 = B + and 5 = plate  ;D
sorry

 

[bernbrue]

Please have a look at the datasheet of your transformers. I'm quite shure that you will find the answers to your questions yourself. Don't get me wrong, but it's better to understand what you do than being told which wire goes where.

The 180V is B+, 6,3V is filament and 9V is V+ for relays.
Bernd

 

[jefflehiress]

ok thank you I will try to find the data sheet of the transformer

 

[jefflehiress]

I understand your point of view but I do not understand what "CT" and "point" mean on the PCB for the audio transformer?
thank you.

 

[bernbrue]

CT= Centertap ! It  indicates where the centertap of the output transformer is connected. The dot is for polarity. So connect the + or *  side of the input/output  transformer to this terminal.

Bernd