Official 251 point to point on Acrylic build and support thread

[cornell9]

I am getting no sound on my 251 point to point build.  The universal PSU voltages are all correct.  I measure 6.30v inside the microphone.  Tapping the microphone or switching to the other patterns also produces no sound or relay clicking.

I read the full 251 and C12 build threads and am wondering if anyone knows the steps I should take to isolate the issue.  I posted a while ago in the other 251 thread but no one replied.

Can anyone please help with troubleshooting steps?

 

[Timjag]

Make sure the cathode is grounded - it's a classic for me. Thought I'd grounded it then realise nope, no cathode to ground = no sound..make sure you have dc to the back plate, you won't be able to meter it after the high meg resistors so measure before hand and then test for the high meg resistors to the backplate with the continuity tester.

6.3 volts is only for the heater as long as that goes to the heater and returns to ground it should work. You should be seeing 120v on the anode(plate) and 60v to the backplate after the voltage divider.

 

[Potato Cakes]

Did you follow the diagram exactly that is at the beginning of this post? If so, and if the voltages are correct from the PSU, then you should be up and running. If you are following someone else's build guide, then posting here won't do you much good. I built a 251 using this exact layout (no relays) and it worked and sounded beautifully right out of the gate (with Tim Campbell's capsule).

Don't know if that helps. At the very least, I hope it doesn't hurt.

Thanks!

Paul

 

[cornell9]

Thanks Tim and Paul - there was a loud hum before that was all but covering up the sound, but I forgot to put the mic back in the entire metal enclosure - not just the headbasket.  Now the hum is gone and all is well!

I had to adjust the Universal Passive Tube PSU to use it with the 251 - here's what it looks like, for those who are using the Universal PSU with their 251.  I connected the center pin of the 3 position switch to P8 Heater, and connected the pin going to omni directly to the 7 pin xlr receptacle's omni wire, and the corresponding pins with the Figure 8.  The relays click and work well for all patterns.

 

[freshtapescent]

Anyone happen to have this thread saved with all the pictures? Internet archive doesn’t have it, and there seems to be a wellspring of build information that we’re missing. I’m particularly curious in his layout and how he does the patterns for my own 251 build. Thx!

 

[rock soderstrom]

Anyone happen to have this thread saved with all the pictures? Internet archive doesn’t have it, and there seems to be a wellspring of build information that we’re missing. I’m particularly curious in his layout and how he does the patterns for my own 251 build. Thx!

+1

I came across this interesting thread through this thread.

Does anyone still have the photos and the other missing info?

 

[thomasdf]

251 point to point boards for Apex 460 Alctron HT-11A, ShuaiYin,SYT-1200 !!
​

Maybe OP has them ?
@OPR

 

[freshtapescent]

Maybe OP has them ?
@OPR

If I had to guess…now that OPR is selling his 251 mics, they’re not as interested in remaking this information available. And it’s not any sort of slight, it’s 100% understandable. I wish the wayback machine had archived this site!

 

[kingkorg]

There are tons of images of the original. Why go after the replica images? This is a very simple p2p build with few components.

 

[thomasdf]

There’s still the relays for polar pattern that needs to be addressed. But I’ll probably go ptp when I get the time to dig into it.