GROUP BUY: Universal Audio 176 - a 100% faithful recreation of a legend! CLOSED!

[kosi]

Hi everyone, i also started mine and it all comes together pretty nice.
But I run into a few small problems.
First: How do I get the cables from the Sowter to the front of the lower PCB ? In the pics of the originals, there's a pretty big hole, where the cables come thru, but in Martins pcb there's only one small hole.
Are we supposed to drill this up ? Or do I miss something  ?
I thought, I ask, before I bring out the 7mm drill

 

[kosi]

Second:
When I rechecked my solder joints on the pcbs, I found a few contacts, which weren't connected !
But I thought, my solder points were good. I found, that the little vias sometimes make no contact to the trace and you have to make sure, that the solder flows to the trace underneath. This took me by surprise and I resoldered both pcbs completely.
attached are pics of 2 points, where I thought, I'm good, but I wasn't.

 

[jslstudio]

Original has bigger hole drilled in middle of pcb. Then contacts to another small pcb.
Martin did not include in kit. I made mine.
And yes. The solder joints are crucial on both sides of pcb. The metal material on traces is not like
gold traces. And takes a good amount of heat to solder the contacts.......
This kit is not for the faint hearted......A reason of detail was a lot of SMALL wire 24 and 28 gauge wire.
As measured in my original.  These original units where made with a very high quality of detail and lace wiring
to keep everything neat a tidy........
Also the plate/cathode pots and meter. Are suppose to be wire wound pots.
Along with the vernier pots.
John

 

[Potato Cakes]

In the manual it mentions that since the turrets are pressed on, you should solder them to the board to ensure contact to the traces. The same would apply to the rivets as well making sure solder goes fully around the outside of them.

Have you worked out the output transformer mounting? I have the same transformers on the way and am curious if I need to make any alterations.

Thanks!

Paul

 

[kosi]

Sowter fits perfect

 

[kosi]

backside

 

[moltenwok]

Surely you mean trace from R15 to pin 2 of 12ax7?

 

[moltenwok]

On my pcbs pin 7 has a complete track to r17, as does pin 2 go via to r15, sorry if I've missed something. Happy to hear you've built one~congratulations

 

[kosi]

Few Points,
I have mine up and running sounds great and just like my original.....

The trace to pin 7 on the 12AX7 is missing from from R15. It can be jumpered or use a small pice of resistor lead
and solder to the above hole on pin 7 of the 12AX7...On the original this is left open and has a direct trace.
I think even in the original schematics this trace is not shown...Probably how it was missed....

Also being these boards are longer then the original and thinner gauge. They flex. They should not. On the original they are 1/8"
thick and also shorter and do not flex.

Flex is not good because when you change tubes it stresses the traces on the tube sockets. I actually had a trace lift when I was changing a 12ax7....Be careful and hold the pub when changing tubes.
Thought I would post this to save people some trouble....And make sure all contacts tested after soldering of course....

Other then that its pretty great..But would like to see thicker  pcb boards 1/8" thick like the originals....
John

Sounds like your original ! That's what I wanted to hear Congratulations !
Also thanks for the tip with the flexable pcbs ! 
I checked mine and I have a perfect connection from R15 to pin 2 and from R17 to pin 7, like moltenwok mentioned. Maybe you just need to resolder the via ?

 

[jslstudio]

Surely you mean trace from R15 to pin 2 of 12ax7?

Let me double check..The pin 2  that has the open trace to the top is not used..Only for test points I believe.
Yeah maybe my socket came lose from trace...But I will look at the pcb again.
There is a trace but it goes above the socket....on backside..I could be mistaken...will re check....
Im pretty detailed but will check......If you have connection via the 20K ohm to pin 2/7
then you are good.
( not pin 7 ) Removed previous post. Do not want to confuse people.....
John

 

[jslstudio]

Other notes:
OB2 tube is suppose to have pin 2  to to ground per schematics.
Also the Poles to the compression ratio switch are suppose to be to C 8 "A" goes to the compression RATIO board.
He has this going to the wrong spot on diagram.

C6 and C7 go to the left and right side ratio taps.  Per the schematic.

John

 

[Potato Cakes]

Hi, John,

Do you have any notes for the calibration process for this build?

Thanks!

Paul

 

[rainton]

Wow you guys you've been busy over here!
Sorry for not chiming in earlier!

First of all - I'm putting together all infos on the calibration procedure  as per the service manual as we speak and will share it with all group buy members on the weekend.

John's indeed right regarding the grounding of the OB2 - I missed to add that ground wire in my wiring layout. Will correct that asap.
As for C8A, as well as C6 & C7 I don't quite get the point - the schematic shows all 3 are connected to one of the 3 poles of the ratio switch each as per the schematic.
And if I'm not mistaken that's how I drew it on the wiring layout...

 

[jslstudio]

Yes you have going to poles! But C 8  ( A )  goes to the Ratio board!
On the Diagram..not schematic you don't have the pole of meter ratio board going to the
Cap C 8 A......... On the diagram. You have C 8 going to one side of the taps.
Unless I am reading your pole designation wrong......)
I have mine working anyway......Just trying to help with any frustration.....

Thanks!
John

 

[kosi]

I'm using the newer switches which don't have the screws in the back to mount the ratio board, so I used some JB Weld to fasten some #4-40 threaded L-brackets to the side of the switch.

What switch do you use here ?  I found out today, that I somehow forgot to order the ratio switch ...

 

[kosi]

The BOM is wrong, for the ratio switch we need a 3P4T switch and the BOM says 4P3T ...

 

[jslstudio]

Second:
When I rechecked my solder joints on the pcbs, I found a few contacts, which weren't connected !
But I thought, my solder points were good. I found, that the little vias sometimes make no contact to the trace and you have to make sure, that the solder flows to the trace underneath. This took me by surprise and I resoldered both pcbs completely.
attached are pics of 2 points, where I thought, I'm good, but I wasn't.

Yes,
This is a major deal...The traces are not high quality silver traces.....They do not solder that great. I have soldered ALOT in my life.
And the metals/traces on these boards need to be tested at every solder joint! Every one!
The metals are very strange the way they resist solder.... I know exactly what you mean.....
I think the older lead solder may work better on these.....
John

 

[kosi]

That's my status, about one day work from finish, but I have to wait for the new ratio switch. Also ordered a new jewel lamp, my first one was too big...
I'm using the API meter and kind of improvised the mounting, if anybody has a proper idea, let me know !

 

[Potato Cakes]

Just got mine wired up with no smoke on first power up. However I don't have the correct fuses for the size fuse holder I am using (6.3x32mm) so it doesn't stay powered on too long before the 250mA fuses I do have blow. But it's encouraging that there was no violent reaction to me throwing the power switch.

I had started this with the original wiring diagram and I believe my OB2 is missing the ground connection per the new layout. I also need to go back over the correct wiring diagram and make sure I'm good.

For my build, I am only using the GR function for the meter so I am omitting the metering controls as once I have this racked up and am using it, I won't be flipping the front panel down to change the meter setting. Per the schematic, the GR function has the + side of the meter connected to the wiper of the GR Zero potentiometer and the - side to ground. Am I missing anything? I noticed the meter did not make any movement towards the 0 position but I'm certain that has to do with the fact that OB2 is missing the ground and the unit won't stay powered up long enough for the other tube's voltages to come up to nominal operation. If I am mistaken someone please let me know. I did go back over all the stakes and rivets with solder to ensure connection to the traces.

Also, could someone like jslstudio or anyone else that has theirs up and running share how they set the cathode and plate adjustments? And does any peoples know a place in town that consistently has 32mm fuses? I think Ace Hardware does but they are 2A. I'll try them in the morning as I would like to know that this unit works so I can proceed with the second one I have to build.

Thanks!

Paul

 

[Potato Cakes]

All righty!

I took the spring out of the other fuse holder so I could make a 5x20mm fuse with the correct value work and I'm able to start testing. Also added the missing ground connection on OB2 tube. Voltages seem  good on the PSU and I am passing signal and am able to get what seems to be appropriate gain reduction when switching through ratios, although I am not getting any change at 2:1. This may be due to the current plate and cathode settings. Or, which is more likely, a bad solder connection.

However I am not getting voltage to the meter. I have confirmed that it does work when applying signal directly to the meter. So I've got some more digging as to why this is. But the unit does seem to be working as far as the compression circuit which I'm pretty happy about.

Thanks!

Paul