No Sound from Right Channel

[ScottAstroNut]

I have checked the tube socket, and it is oriented correctly. I also checked my wiring and didn't see any miswires. I resoldered all the connections around the 4 pin socket, the entire C4S board, all the connections around the power transformer under the filament board, as well as a couple of suspect joints on the filament board itself.

Put everything back together. Applied power. No changes. Terminal 2 still reads close to zero, and terminal 6 reads high. LED's on A side of the C4S board on the R channel still don't light.

I am enclosing pictures for you to help me spot any problems. Perhaps I have just looked at the same circuit too many times to see my faults.

Thanks!

[ScottAstroNut]

More pictures.

[ScottAstroNut]

Still more pictures.

[Paul Birkeland]

Could I get the IA, IB, and OB voltages of the high current C4S board on the side that's not working?

After that, can you repeat those measurements with no 300B in the socket on that side?

[ScottAstroNut]

Hi Paul,

Here you go...

With 300B Tube:

IA = 189V
IB = 186V
OB = -0.4V

With 300B Tube Removed:

IA = 192V
IB = 189V
OB = -0.5V

Thanks!

[Paul Birkeland]

You can try swapping the high current C4S boards.  If the bad voltages follow a board, then we can focus on that.  If they stay on that side of the amp, then you know the board is OK at least.

[ScottAstroNut]

I swapped the C4S boards. An immediate change I noticed was that now all the LED's were lighting up. However, I also noticed that whereas the R channel C4S previously had been cooler than the L, now it was the other way around. The same "cool" board stayed cool.

Checking voltages, the bad voltages migrated with the change in position of the boards. Terminals 2 and 6, which had previously read as 1.7V and 187V, now read 90V and 146V, just as they should. However, now terminal 11 reads 185V and terminal 17 reads 0.1V.

So the problem is with the C4S board?

[ScottAstroNut]

As a further note, I had previously resoldered the entire "bad" (previously R channel side) C4S board, bur resoldered a couple of connections again anyway. I also double-checked that all the components were in the correct locations and in the correct orientations. I couldn't find a problem. I reconnected and retested the board, but with no change. As far as I can tell it's not a bad solder joint.

[ScottAstroNut]

I should say, in that last comment, that I reconnected power to the board, not the board itself. I didn't remove and resolder it a second time.

[Deke609]

Terminal 1 at close to zero volts (1.7V)
Terminal 6 at 187V
...

Terminals 2 and 6, which had previously read as 1.7V and 187V, now read 90V and 146V ...

Ah ... so terminal "1" in your earlier post was a typo?  That's what prompted the recommendation to check and resolder the filament wiring.

[ScottAstroNut]

Hi Derek,

Yes, a typo!!! My apologies! I can see how that would have sent you down an entirely different path!!!

You know, I must be getting a bit dull in my "old age." Not only am I making typos, but I am making wiring mistakes, too. This BeePre is my seventh Bottlehead kit, and it's the first one that didn't work right the first time I plugged it in. Usually I am very good at following directions and wiring. In this kit I have found two significant mistakes in my wiring, both simple mistakes that I should have caught if I had been more careful.

I have to say, though, that even though I am having a bit of trouble with this BeePre, overall the Bottlehead kits have been amazing. My undergraduate education is in electrical engineering, but I actually did relatively little with analog circuits and nothing at all with vacuum tubes in my college education. I was mostly into microprocessors and digital logic, so all solid state and mostly IC's. Lots of prototyping with wire-wrapped sockets on perfboards and lots of assembler language programming. Getting to play with tubes has been great fun and very educational.  I just wished I had gotten into it years ago.

I really appreciate how helpful the people on these forums are, including yourself! It's a great community.

[Deke609]

My undergraduate education is in electrical engineering, but ... all solid state and mostly IC's.

I'm jealous.  No EE education here, and I really struggle to grasp the basics. I am particularly envious of your solid state background.  Although BH is known as a tube amp company, I think of BH amps as hybrid amps: tubes "do" the amplifying, but solid state devices (alone or in conjunction with a tube -- e.g., tube shunt regulator) are used to tightly control the amplifying tubes' operating conditions.  I think BH's approach of combining the best of tube and solid state is one of the things that sets their amps apart.  And, yeah, the community is really great.  Which also sets BH apart.

Good luck with the troubleshooting. It looks like you've narrowed down the issue to the board.

cheers, Derek

[Paul Birkeland]

Well that's good, you have the issue isolated down to the board itself.  You can post more photos of that board top and bottom, and maybe we can see what went wrong.  I don't suppose this kit sat around unbuilt for a long period of time? 

[ScottAstroNut]

Hi Paul,

Here are some pictures of the suspect C4S PCB. I hope that you can spot something, because I have checked this board repeatedly and can find nothing wrong. Every solder joint has been reflowed at least twice at this point. I have also checked that I didn't reverse the resistors on R1 on the A and B sides. You can't tell this from the pictures, though, as I foolishly didn't think to put the resistance values "up" so that they can be seen when mounted to the PCB.

Scott

[ScottAstroNut]

More pictures...