[CatalinM]

Have a look at the schematic. You have a power supply that should give you 24V. Start measuring from the power supply input and follow the path to your filaments. C5 should measure 24V. The output of the U3 regulator should measure 3.3V (C10 as well).

Let us know what you find.

 

[gdogpwns]

Have a look at the schematic. You have a power supply that should give you 24V. Start measuring from the power supply input and follow the path to your filaments. C5 should measure 24V. The output of the U3 regulator should measure 3.3V (C10 as well).

Let us know what you find.

I am still trying to make mine work, sadly. I think it's just bad solder from Lowe's that oxidized and my Lowe's soldering iron that was falling apart also didn't help. Probably goofed up a lot of my motherboard. I actually melted a pad and I am not sure if it is a problem since I do not see any trace on the PCB. I highlighted the pin I am talking about below.

I probably messed up some trace with how bad that soldering iron was. I have access to a good one now, so I may just start placing wires at the bottom of the board. The filaments like to glow after I resolder those points, then they usually sound very crackly then one (or both) filaments power off with a loud pop in my headphones. I also noticed in the documentation that there should be a 10 second mute when I turn it on that I am not experiencing. Could this be related?

 

[silverfishla]

I am still trying to make mine work, sadly. I think it's just bad solder from Lowe's that oxidized and my Lowe's soldering iron that was falling apart also didn't help. Probably goofed up a lot of my motherboard. I actually melted a pad and I am not sure if it is a problem since I do not see any trace on the PCB. I highlighted the pin I am talking about below.

I probably messed up some trace with how bad that soldering iron was. I have access to a good one now, so I may just start placing wires at the bottom of the board. The filaments like to glow after I resolder those points, then they usually sound very crackly then one (or both) filaments power off with a loud pop in my headphones. I also noticed in the documentation that there should be a 10 second mute when I turn it on that I am not experiencing. Could this be related?

Why don't you post a picture of both sides of your board and see if anyone here can do some visual diagnosis of what you have going on....

 

[gdogpwns]

Why don't you post a picture of both sides of your board and see if anyone here can do some visual diagnosis of what you have going on....

Here ya go!

 

[silverfishla]

Here ya go!

Hmm. My first inclination would be to recheck my solder joints. I would get a magnifying glass and wiggle each component from the opposite side and see if I could see any movement from the solder side, or crack. I might just retouch any that I might have doubts about with new solder. That's what I would do first. You've got a lot of flux on your board, I might clean that off first with some alcohol.

 

[gdogpwns]

I got the amp working for about ten minutes until it broke again. Here's what I'm noticing:

1. The pins on both filaments are taking in the exact same amount of volts.
2. The output of the left filament (the non-working one) is significantly lower than the right filament .

It seems to only work sometimes after I solder. I'm assuming that I either got a broken Nutube (unlikely) or I broke it myself (extremely likely) and heating it gets it going for a short amount of time. Should I just suck it up and buy another Nutube if these are my symptoms?

 

[CatalinM]

If the input is fine, you might have a bad tube (or a solder connection is still bad).

On a separate issue, I enjoyed Pete's suggestion to increase R8/R9 and now I'm thinking about taking it a step further. I'd install a rotary switch that would allow me to route the signal through various resistors (1, 22, 47, 80, 100) so I can adjust it anytime for the cans I'm using. What do you guys think?

 

[gdogpwns]

Decided to suck it up and buy mostly all new parts (saved the case, opamps, and power supply) and rebuild it from scratch. The amp working fine now. Sounds absolutely incredible. I'm so glad to finally hear my HD-6XXs at their full potential. Thanks, Pete!

Edit: I have gotten some listening in now and the device isn't as microphonic as some people are describing. I guess it's dependent on the particular Nutube. In the few moments where my broken Nutube was working, it was definitely microphonic as hell. This one sounds incredible. I can't compare this to any other tube amps since this is my first, but it sounds very rich.

 

[SchwarzeWolke]

Just ordered one a week ago and thought I bought a cheap TKD 2CP601 via Ebay. It turned out that I bought a 1kOhm one and not 10kOhm... Tried to find it on the schematics but didn't find it. Am I right that 1kOhm is just to low and would not work?

 

[pmillett]

Just ordered one a week ago and thought I bought a cheap TKD 2CP601 via Ebay. It turned out that I bought a 1kOhm one and not 10kOhm... Tried to find it on the schematics but didn't find it. Am I right that 1kOhm is just to low and would not work?

The amp is fine with 1k, but the source that you're using it might not like it. It will present a 1k load to the source. Some sources are fine with 1k, others might distort a little more with a 1k load than a 10k load. And tube sources may not work well at all.

I am guessing that phones should be fine with it. If you're using a DAC, check to see if they specify a minimum load impedance...

Pete

 

[SchwarzeWolke]

Thx Pete!
I got some problems with the availabilty of two components and maybe some more might have this problem:
Two components from KEMET are at least here in Germany not available.

• EC2-24NJ
  
  
• SU9V-05020

For the low signal relay I've found some alternative from Omrom and Panasonic. They're much more expensive but I don't want to wait until next year...
For the common mode filter chokes, I just found alternatives with a little higher inductance. Sorry for asking but I don't have experience with such stuff and don't know if I can replace them.

 

[pmillett]

Thx Pete!
I got some problems with the availabilty of two components and maybe some more might have this problem:
Two components from KEMET are at least here in Germany not available.

• EC2-24NJ
  
  
• SU9V-05020

For the low signal relay I've found some alternative from Omrom and Panasonic. They're much more expensive but I don't want to wait until next year...
For the common mode filter chokes, I just found alternatives with a little higher inductance. Sorry for asking but I don't have experience with such stuff and don't know if I can replace them.

Yeah, that relay seems to be perpetually out of stock. I know that the TE V23079A1005B301 works fine, and as it is a common footprintt I'm sure there are others.

Nothing critical about the common mode choke, anything that fits in the holes will work. Higher impedance is actually better.

Pete

 

[MrKazador]

Its been a few years since I built my o2 and wanted something new/different. I don't know if I have bad hearing but its not that microphonic. When you first turn it on there is a high pitch ring but it goes away after about 10 seconds. I have to tap on the case real hard to get it to ring, with normal usage I don't hear anything.

 

[ilikepooters]

Ordered the PCB and NuTube and also the parts from Mouser.

The power adaptor says unavailable in my country (guess it's because it's US version) will the following be ok that i found on ebay?
https://www.ebay.co.uk/itm/Mean-Wel...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

This is my first DIY project, wish me luck!

 

[pmillett]

Yup, that should work.

Pete