[BUILD] NU VARIMU 436 build & help thread

[Grooveteer]

I managed to get my noise floor close to -100. I had to ground my heaters for those wondering.

Best
Peter

Hi Peter,

That's a nice improvement.  How exactly did you ground the heaters if you don't mind me asking?

I'm getting close to finishing this one myself.  Might be a good idea to try once I get the stock version working.

Thanks.

Stefan

 

[petermontg]

Hi Peter,

That's a nice improvement.  How exactly did you ground the heaters if you don't mind me asking?

I'm getting close to finishing this one myself.  Might be a good idea to try once I get the stock version working.

Thanks.

Stefan

Hi Stefan,

I tied F- to common ground.

Best
Peter

 

[Perm0]

In old tube radio's you'll often find this small "Humm" pot on the back, it simply balances to a ground reference;

 

[rock soderstrom]

In old tube radio's you'll often find this small "Humm" pot on the back, it simply balances to a ground reference;

This guy is called humdinger!  ;D

 

[Perm0]

I had to google that LOL  ;D

 

[Ayman59]

Hello folks, I hope this message will find each of you in great shape ;-)

I need your lights please, my B channel won't pass audio when engaged...

Channel A seems working properly. Unit built with sowter xfmrs, 1,2mA meters (but I'm looking to get some nice 1mA). I made the tubes heaters wiring modification.

I already tried to swap one by one the tubes, the xfmrs, the cabling (internal and external), but nothing... I tested the relays and they work fine. Now I'm stuck !!

I tried to trace the signal with the same test tone on each bypassed/engaged channel with a DMM to compare them and found a strange behavior on B channel: The signal is getting very low at the input when I engage the B channel. Looks like a short somewhere in my circuit ?
When comparing I also found that for all tubes plates pins I had greatly lower voltages than the ones on A channel when the unit is engaged (like 230V vs. 150V).

If this symptoms tells you something, or if you can point me the right way to debug this channel, that would be wonderfull

Thx in advance.

Jerome

 

[zayance]

Hello folks, I hope this message will find each of you in great shape ;-)

I need your lights please, my B channel won't pass audio when engaged...

Channel A seems working properly. Unit built with sowter xfmrs, 1,2mA meters (but I'm looking to get some nice 1mA). I made the tubes heaters wiring modification.

I already tried to swap one by one the tubes, the xfmrs, the cabling (internal and external), but nothing... I tested the relays and they work fine. Now I'm stuck !!

I tried to trace the signal with the same test tone on each bypassed/engaged channel with a DMM to compare them and found a strange behavior on B channel: The signal is getting very low at the input when I engage the B channel. Looks like a short somewhere in my circuit ?
When comparing I also found that for all tubes plates pins I had greatly lower voltages than the ones on A channel when the unit is engaged (like 230V vs. 150V).

If this symptoms tells you something, or if you can point me the right way to debug this channel, that would be wonderfull

Thx in advance.

Jerome

Sorry for your troubles, maybe these have find a positive ending?
Maybe just a Resistor value error? Or just a bad solder joint?
If you say the relay is acting fine, then this takes out the "errata" i made for this one, but double check if there is continuity on the repair,
never know.

Unfortunatly i'm just selling the PCB, and haven't build the thing, my partner Bernd has, but he is off the business now, i just continue
selling these and if there is interest (reorders only if interested).
WM helps this Forum as well, so .

Bernd took care of for the support thread, but he decided to leave it for a while.
We go by the principle that most of the obvious errors have been covered up, so we leave this to the generous help of the members who have run into same kind of troubles or else....
Most Troublshooting are anyway going around the same procedures of triple check etc... and distance and not beeing the guy who builded it, doesn't make things easier for helping.

Hope you'll get to the bottom of the problem

 

[petermontg]

Hello folks, I hope this message will find each of you in great shape ;-)

I need your lights please, my B channel won't pass audio when engaged...

Channel A seems working properly. Unit built with sowter xfmrs, 1,2mA meters (but I'm looking to get some nice 1mA). I made the tubes heaters wiring modification.

I already tried to swap one by one the tubes, the xfmrs, the cabling (internal and external), but nothing... I tested the relays and they work fine. Now I'm stuck !!

I tried to trace the signal with the same test tone on each bypassed/engaged channel with a DMM to compare them and found a strange behavior on B channel: The signal is getting very low at the input when I engage the B channel. Looks like a short somewhere in my circuit ?
When comparing I also found that for all tubes plates pins I had greatly lower voltages than the ones on A channel when the unit is engaged (like 230V vs. 150V).

If this symptoms tells you something, or if you can point me the right way to debug this channel, that would be wonderfull

Thx in advance.

Jerome

Hi Jerome

Whats your scenario around the Rtrim in the B+ line?
Your points that are marked on the PCB D,E,F etc etc?
Whats is your reading before the 10K resistor and across the CT

Best
peter

 

[Ayman59]

Hi Peter,

I replaced my meters with 1mA ones.

I left Rtrim empty and I get 330VDC on A point, 261 on B channel A, and 260 on B channel B.
Pretty high? I'm supposed to make the calculation to have Rtrim giving something like 245 on B+ ?

Other points readings, respectively on A and B channels, are as follow:
C 267,7 C 268,7
D 176,6 D 171,2
E 168,5 E 170
F 3,22 F 3,26
G 3,65 G 3,59
H 3,93 H 3,68
I 266,6 I 268
J 266,9 J 266,9

Looks like VR104 and VR103 tweaking have no impact on read values???

Thanks for your help ;-)

Regards,
Jerome

 

[petermontg]

Hi Peter,

I replaced my meters with 1mA ones.

I left Rtrim empty and I get 330VDC on A point, 261 on B channel A, and 260 on B channel B.
Pretty high? I'm supposed to make the calculation to have Rtrim giving something like 245 on B+ ?

Other points readings, respectively on A and B channels, are as follow:
C 267,7 C 268,7
D 176,6 D 171,2
E 168,5 E 170
F 3,22 F 3,26
G 3,65 G 3,59
H 3,93 H 3,68
I 266,6 I 268
J 266,9 J 266,9

Looks like VR104 and VR103 tweaking have no impact on read values???

Thanks for your help ;-)

Regards,
Jerome

You should have a small difference with left right matching as it stands probably 1/1.5db max. I increased R1 to bring my values down if I remember correctly. I ended up with something around 1K5 there. Brings it down to 230V after the 10K/6k8 and across the CT. You could try there to bring it down. Your B+ needs to be closer to 290V before the 10k resistor

If the volume is lower on input I would be looking at the replacing the relay also

Your VR points should be balancing as close as possible L/R I think A difference of +/-1volt is best. If you can get the overall B+ down they might move. If not they could do with replacing

 

[studiosus]

Hi all,

I´m slowly gathering all the parts I need to start building this nice unit.
What B+ Voltage should I aim for?
From the measurements from the protoype in this thread and most of your already built units, it´s somewhere close to 270VDC.
But if you read the comment in the bom about the trim resistor in the powersupply for b+, it looks like this would actually be designed for about 245VDC.

 

[grapyofire]

In BOM for PSU there are a few minor mistakes V+RLED 24V is 34.8K(4.8k), r6 24v is 3.6K. Mouser link are correct, but not everyone using them. May anyone explain hot to "tweak" rtrim to correct htrled on psu board?

 

[HerbertR]

Hi, I am also in for this build. Very exciting...
What is the better choise for the Output TX :
-Sowter 1232 (23k/150or600 Ohm) like Holger or Drip used .....or the
-Sowter 8650 (15k/185 Ohm) like mentioned in the BOM...
?
What is the better choise? Price is nearly the same.... I ve already ordered a pair of 1232 today because Holger also used them and they are advertised as Altec 436 replacements on the Sowter site....but I think there is more than enough time to change the order from Sowter I think at least three months....

As for InputTX I will try as big Lundahl fan the LL1540.
For the Meters I found on Ebay nice originally looking smaller 1mA Honeywell MM1's. They should fit better for this build on a 3HE 19" frontpanel than the bigger original MM2's on the Altec 436. And I love the powder green coated frontpanels from Altec ...

 

[camshash]

Forgive me if I didn't read the thread thoroughly enough, are PCBs for this build still available?

 

[Rob Flinn]

Forgive me if I didn't read the thread thoroughly enough, are PCBs for this build still available?

Look in the white market.

 

[petermontg]

There's a bunch of 3575's on eBay at the moment if anybody is going the sowter route on input.

I picked up a couple of pairs.

Best
Peter

 

[HerbertR]

I have also finished my build. I ve used LL1540s the Sowter 1232 for my build. I could grab a pair of small 1mA Honeywell MM1 Meters on Ebay for about 65 Euro. I also tried to buy directly from Jewell Company NOS MM2 Meters. But their behavoir was so rude - neeeevvvveerr again. So a snooty, disgusting company. Bäaah...
The Compressor is in my opinion super clean, really fast, it has a very expensive sounding texture. Its difficult to get this piece really dirty sounding, hard to get it pumpin'. Like SSL on Tubes.... Wow....

Nothing to mention, no real problems with the build. It works excellent.
My Power TX is a customer made TX, with 0.2A 215V secondary, 4A 8V secondary and 1A 12V secondary from Audiophonics France. I have 315V DC after the B+ Bridge and about 15V Voltage Drop over R1. As for B+ Rtrim I ve used 1K -> total 48K for R3+Rtrim to get about 260V. That works super and the Components like the heatsink and resistors only gets slighly warm within the B+ PSU circuit. The heater PSU Circuit also works perfectly. My secondary shows 8.3V AC. The Input Voltage before of the TL338 regulator shows no necissitiy to tweak the Voltage down. The heatsink gets not really hot.
As for the meters I also think you will really need a 1mA DC Meter or they will not get adjusted within the range. The Meter adjustments also affect the other calibration adjustments. So it required more calibration cycles. I used a 1kHz Signal with +5dBu on the input and adjusted a 5dB Compression / Voltage Drop to 0dBu on the Output with the compressor. After that I adjusted the Meter Zero with the Multiturn Potentiometer and tried different Resistor in parallel to get the 5dB GR on the Scale and Zero in Bypass. It ended with 100 Ohms parallel between the Meter. Its a funny work. I also "slowed down" the meterspeed with a 10uF Capacitor parallel to the meter. Okay, you should not expect a high precission device. But it works pretty well. Only on high Compression Values bigger 15dB my two Channels show a difference of about 1.5 dB and more due my 6BZ7 Tubes are not really matched and should be replaced as last part. Changing of the 6BZ7 Tubes between the two channels clearly showed the difference.
Thanks to Bernbrue and Zyance - you are amazing!

 

[zayance]

Nice Build Herbert, thanks again for the nice comments and words.

 

[sbranco]

I am a complete amateur but have managed to build a couple Seventh Circle N72's, a couple API 312's using rob higgins pcbs from years ago and four of mitsos John Hardy style M1 preamps.

I think I have enough preamps though never got around to doing a tube preamp.

Instead, I was thinking of building a tube compressor and this seems like a good candidate.

Bernd recommended using parts available and I was wondering if the transformers I have on hand would work or why they would not.

I have Jensen JE-8251 , 1to1 transformers which worked well as output transformers in the John Hardy M1 preamps. I also have Altran C-3402-2 1:8 mic input transformers also used in the John Hardy M1s.

Also, I got overzealous and got some tubes thinking of doing a tube preamp and never used them. I have 6AK5, 6072A, E80F, 6AU6 and 6AU6A tubes in my closet.

The transformers seem like they might work well. Would the Altran's fit the pcb?

Read through this thread a couple times and have gleaned a lot. You guys sure do some nice work.
This project would be a stretch but I feel a lot better working with the voltages having a pcb to help keep things straight. Test voltage spots and tips should help too.

 

[Rob Flinn]

The jensen would possibly work as an input transformer if it's 10k:10k & has a centre tapped secondary. The Altran is not right for this project either as an input or output transformer. If you look at the Sowter website or UTM industries websites where they sell transformers that are suitable. Or you could just read the information on this thread to give you an idea of the specs of the transformers & what people are using.