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

[jefflehiress]

Watch my video.  The meter needs to be retrimmed quite often. Did you tame the pots as suggested in the first post?

https://www.youtube.com/watch?v=0eJVCCYApOw
Very nice unit. Be proud of yourself !
Cheers
Bernd

Thank you very much,
I still need to calibrate all that ....
yes I had already watched your video and the trim pot works the same way home but my meter is not assé sensible (200mA). I have to change.
all the knob is zero and the needle jumps to the max.
I will try to understand what is wrong.

 

[jefflehiress]

Hello everyone,
I have a big problem in calibrating the federal.
I do not really understand what's going on.
I checked everything and everything is well connected: trim = CW and W, thlimit = ratio, current ctrl = threshold, to-out-tx = primary, from-out-tx = secondary, link = pcb right on the spindle of the middle of the switch and pcb left on the right or left pin of the switch two positions ... etc ...).
but I have values ​​at control points that are apparently not the right ones:

B + = 230V

A = 14.54V
B = 223 V
C = 224 V
D = 173V
E = 0.32V
F = 0.33V
G = 230V

- all the tubes are lit except the 12Ax7 whose filaments are not incandescent but heats a little ...
- I always have the two hands of the Vu meters jumping right when the unit is ON.

- what are used to adjust R26, R11 and R9?
- apparently the heating circuit should power the 12ax7 in 6.3V and not in 12.6V.
- Bernbrue, on your first photo of the heating circuit at the beginning of the thread I see a small green cable soldered, that is it indispensable and what it serves it on the rev 1.1.
- Is there a test procedure to be performed without the tubes?

Thank you in advance for your answer because there I am really headed.

 

[bernbrue]

Your voltages are a bit high but not wrong. I wouldn't care too much about that. Try to get the heater wiring right. You need to see the 12AX7  glow, otherwise it won't work. Maybe there is a short somewhere or the tube socket is not soldered correctly. The heater wiring as shown is correct. It's for 6,3 V. The small green wire has no relevance for you. It was just a fix on the prototype.

In case you have a few more 6AS6 tubes, I would test them out. I had a few broken ones, although they were sold as new. They have a big influence on the whole circuit.
R26 is for fine trimming the voltage for the relay. R11 and R9 are trimmers for balancing the two 6BA6 tubes and the two halves of the double triode (12ax7).
Can you adjust the meter with the pot? They should react somehow. Which value did you take for the meter trimmer?
Bernd

 

[jefflehiress]

Your voltages are a bit high but not wrong. I wouldn't care too much about that. Try to get the heater wiring right. You need to see the 12AX7  glow, otherwise it won't work. Maybe there is a short somewhere or the tube socket is not soldered correctly. The heater wiring as shown is correct. It's for 6,3 V. The small green wire has no relevance for you. It was just a fix on the prototype.

In case you have a few more 6AS6 tubes, I would test them out. I had a few broken ones, although they were sold as new. They have a big influence on the whole circuit.
R26 is for fine trimming the voltage for the relay. R11 and R9 are trimmers for balancing the two 6BA6 tubes and the two halves of the double triode (12ax7).
Can you adjust the meter with the pot? They should react somehow. Which value did you take for the meter trimmer?
Bernd

ok I will try to test with new 6BA6 tubes, I have a stock, but not 6AV6.
the 6BA6 and 6AV6 are very bright yet transparent.
when I turn the trim to the right the needle descent to the left and that for both sides.
the needle on the right side only rebonit at the beginning but the left side all the time.
when I activate the link the left needle does not bounce anymore.
and when I push the IN pot all the way to the right the needle of the left channel is also fixed.
when i try to measure the voltage at the trim terminals i have 0.5 mv turned completely to the right and 70mV to the center and 83.9 mV turned completely to the left.
the 12AX7 do not emit light at all.
can this come from a power transformation cable inversion (FIL / AC?) or I would not have the values ​​I tested if it was the case?
whether I am a link or a link, the potentiometer on the left or on the right influences both channels. weird because only the link is the link or the power transformer.
Since I only had two outgoing cables from the transformer for the 9V power supply I took two cables and came out of the 9V powered terminal block to join the other serial PCB ... maybe it was there an influence?

 

[bernbrue]

That's a bit confusing. I suggest to concentrate on setting up a single channel, let's say the left channel.  Please remove any links between the two channels including the wires for 9V power.

Can you make a short video of your Federal? I would like to see, how it behaves. A close up of the inside would be nice. Double check the tube socket of the 12ax7 and also the heater wiring underneath.
Bernd

 

[jefflehiress]

That's a bit confusing. I suggest to concentrate on setting up a single channel, let's say the left channel.  Please remove any links between the two channels including the wires for 9V power.

Can you make a short video of your Federal? I would like to see, how it behaves. A close up of the inside would be nice. Double check the tube socket of the 12ax7 and also the heater wiring underneath.
Bernd

ok i will make a video and cut the links. I will send you a vimeo link.
I also changed all the 6BA6 tubes by a new pack (not pair) and the needles do not hop anymore.
There is a slight light at the end of the anode and catode 12AX7 but it is necessary to put in black to distinguish them.
The others light up a lot.

 

[jefflehiress]

Here is the link to the video you asked me.
you must know that I have not yet replaced the vu meters by 200 micro amper. they are ordered

https://vimeo.com/241967119

 

[skal1]

hi jefflehiress

that last tube has no heater voltage getting to it , check your connection on the bottom of pcb to see if the two wire's are  on pin 4 and pin 5 of that tube .

quick check, pull the tube out  of that socket ,and check from the top  , with your meter , 1 probe to pin 4 and the other to pin 9  , if voltage is their , the tube is naf ,if no voltage  , you may have a dry solder  joint in that part of the circuit.

regards

skal1

 

[jefflehiress]

hi jefflehiress

that last tube has no heater voltage getting to it , check your connection on the bottom of pcb to see if the two wire's are  on pin 4 and pin 5 of that tube .

quick check, pull the tube out  of that socket ,and check from the top  , with your meter , 1 probe to pin 4 and the other to pin 9  , if voltage is their , the tube is naf ,if no voltage  , you may have a dry solder  joint in that part of the circuit.

regards

skal1

I finally received the vu meters of 200 micro ampere.
Skal1, thanks for your answer,
so I just measured and at terminals 4 and 5 I have 0.3V at both terminals, but the voltage is not fixed, it's up to 0.35V and it drops to 0 then goes back ... etc. ..
However all the pins of the base of the tube 12AX7 are soldered neatly.
I'm not sure I understood but basically I have to weld pin 4 and 5 together to properly feed the tube?

 

[jefflehiress]

Your voltages are a bit high but not wrong. I wouldn't care too much about that. Try to get the heater wiring right. You need to see the 12AX7  glow, otherwise it won't work. Maybe there is a short somewhere or the tube socket is not soldered correctly. The heater wiring as shown is correct. It's for 6,3 V. The small green wire has no relevance for you. It was just a fix on the prototype.

In case you have a few more 6AS6 tubes, I would test them out. I had a few broken ones, although they were sold as new. They have a big influence on the whole circuit.
R26 is for fine trimming the voltage for the relay. R11 and R9 are trimmers for balancing the two 6BA6 tubes and the two halves of the double triode (12ax7).
Can you adjust the meter with the pot? They should react somehow. Which value did you take for the meter trimmer?
Bernd

hello bernbrue!
ok I think everything is fine now, would you have a technique or measures at particular points to calibrate step by step so that the entire stereo unit is calibrated at best?

thank you

 

[bernbrue]

There is no real step by step calibration for stereo matching. The best thing you can do is to balance  each single channel for identical voltages at the corresponding measure points. The 6BA6 input tubes are the most important part in terms of matching. Try to find a set of four most identical tubes. Search for "tube matching". Afaik it has been discussed before.
Found it in the sta level build thread:
https://groupdiy.com/index.php?topic=59017.msg807357#msg807357
Bernd

 

[jefflehiress]

There is no real step by step calibration for stereo matching. The best thing you can do is to balance  each single channel for identical voltages at the corresponding measure points. The 6BA6 input tubes are the most important part in terms of matching. Try to find a set of four most identical tubes. Search for "tube matching". Afaik it has been discussed before.
Found it in the sta level build thread:
https://groupdiy.com/index.php?topic=59017.msg807357#msg807357
Bernd

Hi Bernd
yes I had seen this topic on the 4 tube peers. and it's done for me.
notice you could watch the video I made? what do you think ?
ok, so I tested the unit with a drum, and I have a big problem of interferences and buzz. I always have the left and the right which have an influence on one another while the link is not welded. I will try to order another pair of 6AV6 just in case ...
Do you have an idea about the worries?
I will try to make a video with the sound to give an idea.
thank you.

 

[jefflehiress]

Hi Bernd and everybody,
Here is as expected the video of the Federal with audio.
I unsoldered the link, so normally there is no link between the left and the right apart from the 9V power supply connected in series.
In the video we see very well that the left channel has an influence on the right, especially when I activate the threshold.
Can you give me advice on what you hear ... the compression works well but there are some things that go beyond me like the action of the pot IN which is incoherent ...
Thank you

https://vimeo.com/244089212

 

[bernbrue]

The input pot is not wired correctly. Turned fully counterclockwise there should be any signal at all. Your unit starts to motorboat, so I assume you haven't tamed the pot range of threshold and ratio, as I described in the first post. The output pot is also not wired correctly. It is just an attenuator, I.e. there is always a signal even when turned fully counterclockwise. Check your wiring!!
Bernd

 

[jefflehiress]

The input pot is not wired correctly. Turned fully counterclockwise there should be any signal at all. Your unit starts to motorboat, so I assume you haven't tamed the pot range of threshold and ratio, as I described in the first post. The output pot is also not wired correctly. It is just an attenuator, I.e. there is always a signal even when turned fully counterclockwise. Check your wiring!!
Bernd

actually, for the IN I reversed deck 1 and deck 2 and I did not tam the threshold with the 1K3 between 1 and 3 ... for the rest everything is ok, except that having unsoldered the 9V and the link I always have the signal sent in the left unit that goes in the right ... very strange since nothing is connected ... I'll see everything if it's not the XLR sockets that create a contact.
thank you for your follow in any case.

 

[Eliani]

Hey Guys!!

I just finished my Dual/Stereo unit! Or at least almost, but it's all very functional!!

• I have yet to connect the link-switch because I wanted to make sure both channels were working properly on their own!
• I received Aaron's 200mA meters, they look and work great, the meter-lights still need to get hooked up to the relay rail@12v.
• I've ordered a uTracer3+ impuls power tube-tester kit so I can find the best Quad matched pair out of a bunch of Russian 6K4P NOS tubes!
• For true stereo compatibility I'll probably try to match all tubes as close as possible including the 6AV6 and the Russian 6N2P-EV tubes (12AX7/ECC83).

So It's a shame I'm sitting in a boring conference about health-care (wich great in Belgium, it's practically free, but still some guy says in these harsh times we should do better!) , but at least I'm working with audio all day, every day!!

 

[bernbrue]

What a fantastic build! Congratulations!
Bernd

 

[Eliani]

Thanks Bernd,

Although I do have a few issues!
When modding the ratio pot (Threshold Limit@100k) with the 400k resistor on solder lug 1 (CCW) and the 1.3k resistor Paralleled over the Threshold (Current Control, Lug 1 end 3) the meter trimmer (1k with 240R on R10) just isn't cutting it! Even with both knobs fully CCW the needle barely goes past zero on the 200uA meter. I've upped the B+ voltage to be around 200V and that improves the situation slightly. Adding another resistor in series just lowers the range of the trimmer... So how do I get this needle up, or what's wrong here?

 

[bernbrue]

Try reducing the 400K to 330K.  Test another pair of 6K4P.
Bernd

 

[Eliani]

Test another pair of 6K4P.
Bernd

That's going to be it!
Since I did not yet receive my uTracer Tube-tester kit, I can't really tell which tubes are good, But when I searched my stock for some 6BA6 tubes I remember using last time, I found some new RSD EF93 tubes and those made the needle shoot past the 0dB mark!

So let's get better tubes!