[tomb]

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif so.. problem not solved... With the pot out, i get 70 plate, and then like 51, 56 on the 2 +40 check points..... No matter how much i turn the trimpot either way, neither of these values change The second I connect the pot.... I get plate voltage at +60 and both +40 voltages, or If I turn the pot all the way one way, I get plate voltage at one +40 and a lower voltage at the other.... Ended up breaking a RK27 pot trying to desolder it from my pimeta to try on the soha... GAH any ideas... With teh pot wiper all the way one way, I get a short between input left and ground... Confused.....

Evaluating test points without the pot in the circuit is a long-standing issue: it doesn't work. Same for the opamp: you cannot get intelligible measurements. If everything measures OK with the pot and the opamp in the circuit, then you're fine.

 

[matheprat]

I've rebuilt my SOHA and I'm having some more problems. All the voltages are fine with the tube out, but when it's in the heater voltage drops from 12.6 to 6.3 (despite being hooked up to pin 4 (5 is connected to ground). Also, the trimmer pots have very little effect on the voltage, it stays between about 55-65 for both. The +-12V for the Opamp are fine. I have the pot installed (47K).
Does anyone have any ideas? I have pins 1 and 6 connected to the JFETS, 8 and 3 connected to the trimmers, 2 and 7 for the input, 4 at the heater, 5 ground, and 9 not connected.
Many thanks.

 

[tomb]

Quote:

Originally Posted by matheprat /img/forum/go_quote.gif I've rebuilt my SOHA and I'm having some more problems. All the voltages are fine with the tube out, but when it's in the heater voltage drops from 12.6 to 6.3 (despite being hooked up to pin 4 (5 is connected to ground). Also, the trimmer pots have very little effect on the voltage, it stays between about 55-65 for both. The +-12V for the Opamp are fine. I have the pot installed (47K). Does anyone have any ideas? I have pins 1 and 6 connected to the JFETS, 8 and 3 connected to the trimmers, 2 and 7 for the input, 4 at the heater, 5 ground, and 9 not connected. Many thanks.

Sounds like a P2P version. Runeight is still supporting those if you post in the "SOHA Thread 2" thread stickied in the DIY section of Headwize.

 

[gates_2]

so.. with the rk27 correctly connected, it's still not working.

My plate voltage is reading +75 volts(at the +60 test point). Both +40 test points are reading the same plate voltage. Double/triple checked the CCS, tried several tubes...no change... Turning the trimpots doesn't change the +40 points. I can't seem to bias at all.. Tried taking out the trimpots... no change. Also, the +40 test point closest to the bottom of the board(closest to the heatsinked regulator in my pic) will read between like 62 and 75 depending on whether or not the pot is turned one way or the other.

 

[tomb]

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif so.. with the rk27 correctly connected, it's still not working. My plate voltage is reading +75 volts(at the +60 test point). Both +40 test points are reading the same plate voltage. Double/triple checked the CCS, tried several tubes...no change... Turning the trimpots doesn't change the +40 points. I can't seem to bias at all.. Tried taking out the trimpots... no change. Also, the +40 test point closest to the bottom of the board(closest to the heatsinked regulator in my pic) will read between like 62 and 75 depending on whether or not the pot is turned one way or the other.

Pics - top and bottom, please?

 

[headphonejunkie]

Check your r7,17,r8,18 and make sure they are connected properly. I had something similar to this happen to me except I did not have them in circuit.

 

[gates_2]

mm... checked all those R's... R 7,17 are 348 ohms and r8,18 are 1K ohms, checked for continuity under the board on both... they seem good



tons of pics..maybe this will help:
(note the scraping on the bottom was me making sure i didn't have any bridges... I inspected the board rather thoroughly, and didnt' find any before scraped it, but I just wanted to make sure.

 

[achina]

R3 looks like it is a 562Kohm instead of 562ohm. R13 is probably the same, hard to tell from the pics.

 

[tomb]

Quote:

Originally Posted by achina /img/forum/go_quote.gif R3 looks like it is a 562Kohm instead of 562ohm. R13 is probably the same, hard to tell from the pics.

Agreed. Since those are the cathode resistors, it pretty much means little to no current flowing and the trimmers would be useless.

Change those out and things should be a lot different.

 

[pddjsteve]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Agreed. Since those are the cathode resistors, it pretty much means little to no current flowing and the trimmers would be useless. Change those out and things should be a lot different.

Those are easy to get wrong, I actually ALMOST did this myself, but then double checked the part values before I soldered. I actually had bought the wrong one mistakenly (searching on mouser for 562 got me the 562k as well).

 

[tomb]

Quote:

Originally Posted by pddjsteve /img/forum/go_quote.gif Those are easy to get wrong, I actually ALMOST did this myself, but then double checked the part values before I soldered. I actually had bought the wrong one mistakenly (searching on mouser for 562 got me the 562k as well).

Hey! It must be a Mouser bug! I did the same thing, but like you - noticed it before I built one.

 

[gates_2]

ahh- works now- great

still messed up the rk27 pot... oh well

it kinda works....when it's turned up all the way i get balanced channels, other wise much more out of one

 

[gates_2]

one more thing... I can't seem to get the bias down on one channel below 44V. Is it just this tube or should I be concerned?

 

[sphinxllama]

Hello diyers,

so I almost finished my SOHA. Installed all parts and now...

The first time I applied power, the fuse in our house went out!!!

What happend??? Double checked the power cable wiring, like shown on mb3k.com homepage. Everything looked right to me. Do you have a clue what could be wrong??? I am from germany and used the 230V option shown on the homepage. Do I need to put the OPA in for testing? Do I need to connect the AudioIN and AudioOUT? Other than that everything is in place!

I know hard to do without pictures, but I forgot my camera! Tomorrow I am going to ask my neighbour but right now it is to late. But I would like to figure it out tonight.

EDIT: Maybe I found my mistake. Does the yellow lead go to ground? I understood it that black and red goes to ground but after reading ofer it several times I am not sure any more. Is it the mistake pleeease...

 

[headphonejunkie]

Check your transformer wiring. Something must be wrong.