[BUILD] NU VARIMU 436 build & help thread

[Rob Flinn]

Funny you are saying this : if I turn the Vu trimmers to have 5V at F points, Sounds opens up a bit and get louder a bit, but needle is pegged. If I go to 24V at F points, sounds get thinner and quieter, but needle move to the 1rst number of the scale. Always on that kind of 10khz HP sound.

Rob, did you get your unit working with edcors xsm 10k/600?

I have clamped XLR straight at the secondary of them and same issue, 10khz Hipass sound. Both Channels.

I didn't build with these pcb's, I did an exact RS124 point to point. Therefore my circuit isn't exactly the same as yours, but it's pretty close.  When I was getting my units going I used edcor outs as I happened to have a pair in my spares box & it worked, but I didn't specifically test the HF response, it was more an osc & scope test mainly at 1KHz.  I was only using the edcors on the output anyway because I had some nice Gardners inputs knocking around.  I have subsequently changed the edcor outs to Sowters.

 

[Rob Flinn]

Is anybody tried with 6bc8 tubes?

This is what I've put as they are equivalent to 6bz7...maybe this is why it is not working.

That will make no difference unless your valves are bad, I have a box of about 20 of both types and they all work the same.

 

[labak]

That will make no difference unless your valves are bad, I have a box of about 20 of both types and they all work the same.

That was what I thoughts.

Thank you.

 

[labak]

I didn't build with these pcb's, I did an exact RS124 point to point. Therefore my circuit isn't exactly the same as yours, but it's pretty close.  When I was getting my units going I used edcor outs as I happened to have a pair in my spares box & it worked, but I didn't specifically test the HF response, it was more an osc & scope test mainly at 1KHz.  I was only using the edcors on the output anyway because I had some nice Gardners inputs knocking around.  I have subsequently changed the edcor outs to Sowters.

Ok now I understand...

Need to buy some Output TX.

Thank you.

 

[Rob Flinn]

The thing is if they recommend a 1mA F.S.D meter for their build and you can't get it to behave, then it is likely you have a faulty part or you made a mistake, in which case that may also screw your F response.

 

[labak]

Both Channels are acting the same.

I suspect the Output TX. Looking for another solution...

A to high B+ could also be the problem.

 

[Rob Flinn]

Both Channels are acting the same.

I suspect the Output TX. Looking for another solution...

A to high B+ could also be the problem.

If it's within 10% it should be ok.

 

[labak]

Some news,

B+ was like 370V. I have put a 2k4 resistor 25W at R1 in PSU. Now B+ 270

I managed to have the needles not pegged to the right on the meter. I have to put a 5k trimmer (VR100)+ 10k resistor in serie with the meter,  BUT the needle does not move like there is no compression.

Still this low sound like Hipassed. Same on both Channels.

Seems to be the Edcors XSM10k:600

Sowter is having 12 weeks delay as stated previously...

I did some research and maybe going for a Lundahl 1689 transformers. What you think?

Also waiting on a reply for OEP custom Output transformers 9CT:1

Thank you.

 

[labak]

Are people interested in OEP 9CT:1 Transformers?

Let me know.

 

[petermontg]

The edcors won't work here. Mine lasted 10mins 10k/150 and the bottom went. Both channels too.

I have OEP 9ct/1 on mine.

If you're not using the 1ma your meters will peg fully right with varying voltages.

Your input voltage should be closer to 250volt across B/C. I think 230 will also work here? I had an issue with higher voltages into it I went back to R1 and increased it. Mine is closer to 1k5.

Best
Peter

 

[labak]

Thanks for the infos Pete.

I have ordered some lundahl 1689-PP. Let's see.

Still waiting on OEP to come back with price.

I'm using 1ma meters. I removed the edcors and I was able to move the needles back to left.

Re Voltages : I'm closer to what it should be now...

Edcors are def not made for it.

 

[petermontg]

The edcors can't handle the DC across it. That's it main issue. It's a shame because I kinda like them here and we're responding very good.

Make sure your output tube is balanced also. When it meets the CT and unbalance it will screw your response. I haven't tested tolerances yet, maybe some has?

I wonder are the lundahls rated to handle the DC across them. Never used them CT at all.


Best
Peter

 

[labak]

Those Lundahls 1689-PP are rated :

''Max. current through any primary (“C”) section: 50 mA
Isolation between primary and secondary windings / between windings and core: 4 kV / 2 kV''

After research those are good replacement for Sowter 8650.

 

[petermontg]

Brilliant. Let us know how you get along with them. If you have joy I might grab a pair also to try out.

 

[petermontg]

Those Lundahls 1689-PP are rated :

''Max. current through any primary (“C”) section: 50 mA
Isolation between primary and secondary windings / between windings and core: 4 kV / 2 kV''

After research those are good replacement for Sowter 8650.

I know this will probably break your heart also, but I had to take out my 1540 at the start as it had the problem you described.

I don't think they work here either.i think it's more so to do with impedance matching. I know I got mine working with some 15k/15k edcor. I am going to roll al some more trafos after xmas. I don't like the stauration in those edcors.

Going to try some Carnhill input in the new year. So I'll report back.

OEP's work great in this unit if you can get them. I stayed away from sowter as I didn't want a bright compressor but the OEPs have a certain color (slightly darker) while still maintaining the depth in the unit.

YMMV

Best
Peter

 

[labak]

Thank you Peter,

Happy Holidays. 

Which OEP's are you using? What are the rating?

Best regards.

 

[shabtek]

I am curious what the problem is with edcor and lundahls:
Dc bias? I have chased issues with edcor having intermittent solder joints o the tab terms and even windings out of phase

Did you do autopsy

 

[petermontg]

I am curious what the problem is with edcor and lundahls:
Dc bias? I have chased issues with edcor having intermittent solder joints o the tab terms and even windings out of phase

Did you do autopsy

I am not 100% sure to be honest. Mine were fairly old reused pair of lundahls. They could have been damaged. But acted as previous symptoms. Once I got the unit working I didn't investigate much more than wiping the sweat off my brow.

With the edcors, I thought my output balance was off and it wasn't. I couldn't pin it down as everything was reading 100%. Those edcors went straight to the bin.

The OEPs came from a colleague that had some already stocked from the historical build. Ill try and get some info from him to make it easy to order.

 

[Holger]

I'm currently building a second unit. As you can see, I've did a couple of mods.
I used an external PSU to get rid of the usual power transformer AC hum.
I rewired the tubes for 12.6V heaters, I use an SMPS here.
I'm actually measuring -80 dBu noise floor flat.I omitted the output attenuator section and replaced it with a simple 1k pot (Ian's Neve trick).

In this build I use a Lundahl 1540 which works fine. OP TX is a Sowter 1232. The meter is an old Weston 301 stamped May 1964 on the back.
Note: in an earlier post I wrote that the meter circuit needs to be modified. I was wrong. The meter circuit works well
for the Sifam meter in my first build as well as for the Weston meter when the meter is strapped with a resistor.
I used a 22R which works perfect for both meters.

 

[Holger]

Holger, where did you get the cans? Were they from Sowter when you got the trafos.

...

Sowter, story told here:


https://groupdiy.com/index.php?topic=75702.msg964557#msg964557