Drip Dual-STA 5167 Limiter

[Heikki]

I have some questions about this build. Gregory was being really good at getting back to me about getting back to me but never did...

Drip sells kits? Isn't the idea of buying a kit that you get support too.

 

[JMan]

Drip explicitly does NOT sell kits, they sell PCBs with accompanying build documents.  Gregory is notoriously inconsistent with communication, so sometimes you may get an answer from him, but much of the time you will get no reply.  I’ve personally emailed him on a few different occasions, and have literally never received one single reply even acknowledging my messages.

The projects themselves are awesome, but God (and GroupDIY) help you if you run into an issue that you can’t figure out yourself.  :

 

[FarisElek]

Drip explicitly does NOT sell kits, they sell PCBs with accompanying build documents.  Gregory is notoriously inconsistent with communication, so sometimes you may get an answer from him, but much of the time you will get no reply.  I’ve personally emailed him on a few different occasions, and have literally never received one single reply even acknowledging my messages.

The projects themselves are awesome, but God (and GroupDIY) help you if you run into an issue that you can’t figure out yourself.  :

I kinda of knew this was the case when I started.  But I was hoping that if I just follow the silk and BOM I could answer any questions myself. My only problem is know little to nothing about tube circuits. Also the lack of others peoples build experience makes it even more difficult. I'm like 50% sure there are 0 problems with my build so far. I'm just waiting on the output transformers and I'm done. But the scary thing is that this a a "corrected" board for the control, PSU, and Main board. So the eratta's don't necessarily apply since they have minor new layouts. Also the collective case holes for the mainboard are so confusing. They literally don't make any sense (presumably because of the PCB changes. One of the main Eratta info's was the avoid 6.3v to ground by clipping pin 15 on the control board, but apparently this was fixed. I'm getting 1.5ohms between 6.3v and ground which my meter just calls continuity. Besides that i've followed the silk/directions and have confidently chosen all of the parts. I just rather catch any problems before they become serious. Working with power like this is also iffy for me. If he's going to go through the trouble of correcting PCB's, he probably should at least make a new eratta for people with the new PCB just to say to follow the silk, or follow the previous eratta's despite the change in appearance. Or something?

 

[JMan]

Cheers to you for leading the charge here, though.  I’m with you, it’s frustrating that the Drip units don’t ever seem to have the lengthy build threads here to learn from that other projects do, but this is how they start!  Someone started a (currently rather stalled out) thread for the U73b as well.  I’m optimistic.  Someday down the road I’ll be contributing to this one as well — well, more likely I’ll be harassing the thread with questions.  For now, my Dual STA boards are sitting off to the side, neglected, while you forge on.  But I’m following the thread, as I am very interested in seeing what happens!

 

[FarisElek]

Okay! Here's the deal. 6.3v is separated from the ground by about 1.5ohms with the tubes installed. Without the tubes it's completely detached. This is normal. Only worry about continuity with tubes uninstalled. This is probably an obvious thing but I'm not an expert on this. Tubes are essentially diodes and push voltage into whatever direction you align them. So small resistance is normal although it seems insane. For instance, in the PSU there is 600v going to ground but it's not really because there is some resistance between them AND diodes in the way that push voltage the opposite direction. I'm sure this is an extremely crude and not 100% way to understand it but the she is.

I've attached a picture of the build so far. I haven't finished wiring the meter or the IEC socket yet. I'm also waiting on the input transformers. It's definitely on the messy side and I was troubleshooting things I thought were strange as I'd rather find out now before I plugged it in down the line. I also decided to go with the SS PSU circuit for now as I still haven't got any answers about using the tube circuit.



Ryan

 

[scott2000]

I guess another helpful thing would be to follow the original Sta level schematic and basically trace through the boards to get a feel for what is going on. 

 

[FarisElek]

I guess another helpful thing would be to follow the original Sta level schematic and basically trace through the boards to get a feel for what is going on.

For sure. The thing is that the PSU is of his own design and there was the previous Eratta had a section about the control board causing 6.3v to be grounded. That apparently wasn’t the case on my “corrected board”, but i didn’t know what else was causing my meter to go off. My problems were mostly worry as it seems everything is good.

I’ll keep y’all up to date on my process. I want to go back and clean the PCB now that I’m done fluxing everything up.

If anyone gets into this project, the pcb holes on the bottom from collective cases seem completely arbitrary. I have no idea why. I’d maybe map out where you need them and ask Dan to do it. He’s super nice and helpful. I didn’t realize this was going to be a problem so ended up making Swiss cheese out of the bottom because I don’t have a drill press  :-\

 

[Bowie]

I have some questions about this build. Gregory was being really good at getting back to me about getting back to me but never did so I'm going to attempt to find out some of these questions here as he seems really busy.

1) The XLR PCB  has holes for underneath the relays for Diodes. I believe they all say "D9". Are these alternatives to the Relays? I ask because there is no mention of them in the build information and they weren't any extra diodes in the BOM. They're also not labeled as to which diodes they were referring to. Since I'm pretty sure these are universal XLR PCB's, i'm thinking it's for a different build and that I just use relays in this one. I may be very wrong as I'm pretty sure I've used relays along with diodes in other builds.

2) There is no information for set up once everything is wired. How do I calibrate all the voltages and trimmers correctly? Will that not work because I need the load? Which trimmers do what? Some of them are obvious but others I'm not exactly sure.

3) On some builds as well as the collective case panels there is an area for the meter zero adjust. There is no information of this on the build, how do I instal it? what kind of pot should I use?

4) Is there any affordable meters for this build that are shaped like the Simpson model 47 but not $200 a pop? I have some old vintage meters lying around I can use but I just noticed today that the lamp is potted in some clay and the bulbs are dead so I can't use the whole lamp mechanism without jerry-rigging some LED into it, on top of that the GR isn't right and I'd rather just get a new one.

5) The lamp/6.3v seems shorted to ground even on the SMA connector despite if I cut pin 15. What's that about? The main PCB itself seems to have shorted to ground somewhere. It seems like it's because the IDC header pins for ground and 6.3v are connected. But even if I cut pin 15 on the control board there is continuity. Is it because the electricity flows one way and I don't have to worry about continuity? Also, my high voltage 600v transformer wires have continuity with ground on the PSU pcb too. Is this another thing that's okay because the diodes move the current away despite being connected to ground?



I'm awaiting the output iron but besides that I'm completely that and what I mentioned above, I'm completely done. I'm really nervous about it because I've never built anything quite like this + the lack of build info.


Thank you,
Ryan

Just saw this thread. I would reference the older Drip build docs (I think I may have sent you one) as they should explain the two trimmers. One being the 6V6 balance pot and and the other being the meter adj.  Start w/ the 100r (6V6 pot) in the center and adj as needed to get the 6V6s to balance.

 

[FarisElek]

Thanks for the heads up! It totally says the 10k trimmer is the zero adjust. That's interesting because in the build pics he uses a variable resistor style trimmer, but in the Collective Case case there is a position for a potentiometer for adjusting the zero adjust. Does that mean it's same to assume I can use a 10k audio pot in place of the variable resistor and put that on the front panel in it's place?

The next pot I have no idea what it does is that there is a second 100r "balance" next to the 10k meter pot. I know it's not the 6v6 balance because there is another pot actually labeled "6v6 balance".

Any ideas?


Ryan

 

[FarisElek]

Off topic but I just accidentally stumbled upon Gregory of drips artwork and it’s amazing. 100% recommend.

 

[Bowie]

Thanks for the heads up! It totally says the 10k trimmer is the zero adjust. That's interesting because in the build pics he uses a variable resistor style trimmer, but in the Collective Case case there is a position for a potentiometer for adjusting the zero adjust. Does that mean it's same to assume I can use a 10k audio pot in place of the variable resistor and put that on the front panel in it's place?

The next pot I have no idea what it does is that there is a second 100r "balance" next to the 10k meter pot. I know it's not the 6v6 balance because there is another pot actually labeled "6v6 balance".

Any ideas?


Ryan

Yes, a pot works.  That's the more common method.

As far as the unknown pot, trace it back on the PCB to see where it connects. If I were to take a wild guess, it could possibly be to balance the two triodes of the vari-mu tube. But, that's just a random guess. Definitely follow the traces (verifying with a meter) to see where they lead.

 

[FarisElek]

Thanks Bowie. I’ll definitely follow the pot next time I open it up. Although I do believe it is 6386 balance as I’ve read it was included in later models.

A couple things I’d like to know if anyone has the answers:

1) What fuse should I use with this build? The original Gates had a .2amp slow blow but since it has double the tubes should it be a .4amp? It had a solid state psu though? How do I calculate what I need?

2) What are the steps for balancing the 6v6 and the 6386 cathode (assuming that’s what the other 100r pot is for) with the trimmer resistors? IE where are the test points? What voltage does it need to be etc?

3) should I test voltages without tubes in? I’m really nervous about the upcoming day when it’s ready to turn on and I have no idea what the calibration method is, what safety measures I should take, etc. I followed the silk and the eratta to the T. Even (at least temporarily) opting for the SS Psu. So I shouldn’t have any problems, but I don’t know?? I’m just assuming the heater voltage and the B+ will be within reason and I only need to make minor adjustments with the pots?

Ryan

 

[FarisElek]

Bump!

 

[Bowie]

Thanks Bowie. I’ll definitely follow the pot next time I open it up. Although I do believe it is 6386 balance as I’ve read it was included in later models.

A couple things I’d like to know if anyone has the answers:

1) What fuse should I use with this build? The original Gates had a .2amp slow blow but since it has double the tubes should it be a .4amp? It had a solid state psu though? How do I calculate what I need?

2) What are the steps for balancing the 6v6 and the 6386 cathode (assuming that’s what the other 100r pot is for) with the trimmer resistors? IE where are the test points? What voltage does it need to be etc?

3) should I test voltages without tubes in? I’m really nervous about the upcoming day when it’s ready to turn on and I have no idea what the calibration method is, what safety measures I should take, etc. I followed the silk and the eratta to the T. Even (at least temporarily) opting for the SS Psu. So I shouldn’t have any problems, but I don’t know?? I’m just assuming the heater voltage and the B+ will be within reason and I only need to make minor adjustments with the pots?

Ryan

Check the schematic, it shows the pins on the 6V6 (8) that the pot leads to and conveniently tells you what voltages they should be. In fact, there's a wealth of information on voltages in the original schematics.

Couple things I'll caution you about with Drip;
-In some BOMs he lists a 47uf cap instead of 20 (22) for C12A. Don't do this.
-He lists the C13 as "optional". For me, "optional" meant, "doesn't work correctly without it".

Test it without the tubes but know the voltages in some sections will be WAY off. You can at least check your filaments (which should be in the ballpark), your B+ before and after the choke. see if voltage is getting to the tubes. But, to actually see if it's correct and within the 12% or so that you want to shoot for, you need the tubes to be in there so the transformer is under load. Refer to the schematic to make sure you don't have 300V going to the wrong places, etc. If something says 137v but reads higher without tubes, that's normal.

 

[FarisElek]

I appreciate the tips. This schematic doesn’t match the PSU at all as he created a universal PSU for all of his builds. There isn’t any 47uf in the PSU. The only 47uf are the two electrolytics after the regulators on the main PSU which he says can optionally be 100uf. There is however a 10uf in the PSU that the silk had changed to a 22uf. So I put that in instead of the 10uf in the original BOM. Hopefully that’s okay....

Now that I know I can test without tubes, I feel a little better. I know that without a load voltages won’t be quite right, but hopefully I can get the B+ and Heater voltages about right and everything will go smooth.

 

[mikeij]

I just started this build.  I've got the new PSU PCB as well which caught me by surprise.  The majority of the changes seem to be silk screen and layout, but a couple components were added - fuse holders on the 2 legs of the 600VAC rail and an "unregulated dropping resistor."

Was there anything useful in the old build docs?  If so, would you mind forwarding it?  Looking forward, I'm probably going to have a lot of the same questions you're asking, so if you can share any of your learnings, it would be appreciated.

Were you able to find a good source for knobs?

 

[FarisElek]

I just started this build.  I've got the new PSU PCB as well which caught me by surprise.  The majority of the changes seem to be silk screen and layout, but a couple components were added - fuse holders on the 2 legs of the 600VAC rail and an "unregulated dropping resistor."

Was there anything useful in the old build docs?  If so, would you mind forwarding it?  Looking forward, I'm probably going to have a lot of the same questions you're asking, so if you can share any of your learnings, it would be appreciated.

Were you able to find a good source for knobs?

i followed the eratta for now + choke. i installed tube socket as i THINK all you have to do is cut the diodes and use the tube but i’m not going to take any risks yet. knobs i used rca style knobs from tube depot as you can get all your sockets there too. my output transformers will be here by monday and i’ll probably wire it up and get the thing running by then. if all goes well i’ll try to write out all my revelations and i’ll 100% be available for questions. good luck,

 

[mikeij]

i followed the eratta for now + choke. i installed tube socket as i THINK all you have to do is cut the diodes and use the tube but i’m not going to take any risks yet. knobs i used rca style knobs from tube depot as you can get all your sockets there too. my output transformers will be here by monday and i’ll probably wire it up and get the thing running by then. if all goes well i’ll try to write out all my revelations and i’ll 100% be available for questions. good luck,

Yeah, the diodes are in parallel with the tube.  If you use the tube, don't use the diodes, use the 5VAC from the power transformer, and populate the regulators.  I'm going the diode route, so I didn't populate the rectifier socket, won't connect the 5VAC, and I need to populate the "unregulated dropping resistor".  All the talk of heat and smoke kinda got me nervous.  Unfortunately, I bought all the components for the tube rectifier, including the 272 transformer and opened it.  I'll be getting the 270 in the next parts order. 

I'll probably get knobs from donaudio when I get the meters.  I'm still waiting for the case and sowter transformers, which might take a while. 

Were you able to figure out what to use for the meter zero pots and how to use them?  I think I found the make/model of pot with recessed shaft and lock nut, but I'm not sure about the value or how they're used yet.  That's hopefully the last component I need to source.

 

[FarisElek]

Wow, totally didn't catch that i didn't need to use 5v for the diodes. Thank you for saying that  . I bought Simpson 27 model 200ma meters for $20 a pop. I photoshopped the sta level meter onto a scan of the 200ma meter and made sure that the farthest left and right of the scale matched. Happy to send you the pdf. It should print out exactly the right size. Then you can print it out onto a sticker, exacto knife it out, and stick it on. Unless you're okay with spending $400 on meters. If you can afford it will definitely look nicer but oy vey they're more than the transformers!

 

[mikeij]

Yeah the 5VAC is just for the rectifier filament. 

Looking at the pic on the donaudio site, it looks like the meters are 200 DCuA, not 200mA.  According to the data sheet, 2 meters fit this, the model 27 #03880 or a special order model 47.  Donaudio states theirs is a model 47 which may mean they special order it with the STA-level panel. 

But re-labeling the meter is a great idea.

I think I'm going to grab RV4L103C-ND pots from digikey for the meters.