[BUILD] NU VARIMU 436 build & help thread

[echoplex]

whats the estimate price for all parts, PSU, PCB and case in total?

 

[weiss]

Same question here..
Also are there pcb's in stock?

 

[zayance]

Same question here..
Also are there pcb's in stock?

PCB's are in stock no prob, in terms of pricing, Bernd can maybe give an idea? The answer always depends on what you'll choose and use etc... as you all know.


Best,


T.

 

[zayance]

Hi Bernd,

I found an error on Motherboard  + Control board  components list where R10A-B and R11A-B the value is 10k while on schematic is 18k.
Also R10, R11, R13 has the same Mouser ref code.
Could you please double check on MB + CB list, PSU list and schematics?

Thank you!

Hi There,


Sorry for the long reply time, me and Bernd are pretty busy with life, so having a hard time doing our part on these lately.
Anyway,

R10A & B is 18K
R10-11-13 is just me doing copy paste on refs when doing the BOM, thanks for pointing that out, BOM updated.

Don't hesitate to come back here if you find something wrong on BOM, always nice to have a second view by members.


Thanks a lot.


Best,


T.

 

[Kid Squid]

Gorgeous !

Deffo thinking of doing a case for this Beauty.

 

[Unit-8]

Hi guys,

On control board BOM I found R120 A & B and R9 A & B have their values reversed compared to silkscreen on the boards and also on the schematics.
There is also the HTRLED value on the BOM is 24.9k and on board and diagram is 47k.
No others errors found so far.
I have finished to populate the PCBs and I would like to know about measuring points and voltages readings.

Cheers

 

[bernbrue]

Man, you are fast! Thanks for spotting these errors. I’ll do detailed measurements when I’m back home from holiday in about two weeks.
Cheers
Bernd

 

[zayance]

Hi guys,

On control board BOM I found R120 A & B and R9 A & B have their values reversed compared to silkscreen on the boards and also on the schematics.
There is also the HTRLED value on the BOM is 24.9k and on board and diagram is 47k.
No others errors found so far.
I have finished to populate the PCBs and I would like to know about measuring points and voltages readings.

Cheers

Thanks for that.
Use 24.9K value for LED Resistor, since we need a 250VDC supply, and a 10mA at LED, then you spotted
a minor errata on value for the Schematic PSU & PCB.
47K won't do here....

Best,


T.

 

[Unit-8]

Hi Bernd,

Here are some snippets of the NU436. I'm just waiting for Sowter's trafos I should have next week.
It would be nice now to have all the informations on voltages, calibration and any tip for doing these jobs the right way.
We're just waiting for you, man

Best

 

[Unit-8]

NU436 inside

 

[bernbrue]

Looks great. I’ve listed my measurements in the third post. Please take them as rough reference. Meter and output transformer need to be connected.
Cheers
Bernd

 

[Unit-8]

Hi Bernd,

Thanks so much for the info about measuring  points and voltages readings.
However, my trafo has slight different specs:
1 sec: 220v - 0.2A
2 sec: 9v - 2.5A
3 sec: 12v - 1A
It follows that I will certainly get different readings from the measurements.
So I have to rely on the specifications of the tubes and find a middle ground between minimum and maximum or for this circuit there are precise values (voltages) to observe?
Then I wanted to know something about the eventual modding to do on the release knob that I think changes its timing.

Cheers

 

[bernbrue]

Hi,
your power tx will work fine. The release mod will divide the release time by two. Theoretically it could be done with the attack time as well. I think this has been done before. Just strip a resistor in parallel to the attack pot (same value) and make it switchable.
Best
Bernd

 

[Unit-8]

Hi Bernd,

I’m ready to go, at last. Output trafos installed.
It would be nice if you wrote a sort of mini-tutorial in PDF with all the steps to do to calibrate the NU436, I mean all the tips and/or tricks to do the job as it should be done.

E.G: do the valves have to be on their sockets during the voltage calibration?

Best

 

[petermontg]

Hi,

Will you post some sound samples once you get your build finished.

Best
Peter

 

[bernbrue]

E.G: do the valves have to be on their sockets during the voltage calibration?

Yes, measure the voltages with tubes.
Bernd

 

[Unit-8]

Hi,

Will you post some sound samples once you get your build finished.

Best
Peter

Hi Peter,

I will post some samples for sure

Best

Andrea

 

[bernbrue]

Some basic strategies before powering up the unit the first time.

1) check for shorts. Disconnect the power tx from the pcb and measure for shorts at the AC input terminals. You should have at least some kind of resistance between the power tx terminals on the pcb. When there is a short, something is wrong, don’t power it up and check once again

2) connect the power tx rail by rail. Start with the relay rail and connect the 12VAC (24VAC) first. Very important!!, Isolate the other two secondaries from the power tx. Test the relays.

3) next connect the heater rail and verify that all tubes glow.
4) connect the high voltage secondary and measure B+ at the test point.

5) power up the unit only just for a moment and switch it off immediately.  Check for any unusual noise or smell.
6) leave it on for a few minutes and wait for the meter to rise. Start checking the knobs and switches. Check if it passes audio.

Bernd

 

[Unit-8]

Hi Bernd,

Thanks for the useful tips. This morning I started calibrating the compressor and I encountered the first problem. On test points B, C, D, E, I and J I have the same voltage on both channels between 297 and 300VDC which does not change using the VR103 and VR104 A-B trimpots. On the test points F, G, H the voltages measured are 0VDC and even here the trimpots have no effect. All the tubes do not glow up on both channels. No problem on relays and heater rails where I get 12 and 6.3VDC respectively. The tubes I used in the circuit are: RCA 6AL5, Mullard CV4024 (12AT7) and Brimar 6BQ7A (6BZ7 equivalent). Also, I checked all the components on the PCB to verify the values and their exact place on it and I viewed all the solders. No problems found. Any suggestions?

Ta

Andrea

 

[bernbrue]

Maybe a stupid question, but did you do the heater wiring on the solder side of the pcb?
Bernd