C9-10 Question

I am about to try out the k40ys in my vta70 board, along with a few riken resistors. I was checking the install manual on this site and noticed that the parts list says not used for c9-10 (47 uf-50v).
Has the board changed?
If not should these be pulled?
Also can I get away with soldering the k40s from the bottom?
Great forum, Richard

Hi Richard,
the circuit is the same for 20 years now, however, the PCB has had a few minor changes over the past couple years to make room for larger capacitors, etc.
C9 & C10 are commonly used in this type of circuit to increase the gain by bypassing the cathode resistor on the first gain stage. However, due to feedback from customers and from additional research on circuit design, C0 & C10 are not actually needed. By removing them, there is a slight benefit in reduced distortion as well as very slightly reduced gain. It's a small difference.
As for the PIO output coupling caps, follow Bob's instructions, and let me add - be careful that the capacitor body does not touch anything else, such as the PCB traces, or the octal sockets/test points on the front of the amplifier.
Roy

Thanks Roy,Bob, appreciate the help.

Richard

I finished the install late last night. Took a bit of rearranging, but otherwise went well. I put two bands of sorbothane around each cap to try and keep them up off the board, and they should help dampen any vibrations.
About 11 hours of break in and these pios sound great. Previously had sonicaps gen 1 and wasn't satisfied. The gen 2 are much better imho. Both sonicaps require at least 100 hours of play.
Almost put in the Audiocap thetas-ppt. These are my favorite reasonably priced cap, but for now I'm extremely happy with the k40y-9s.
I had JJ kt77s in this before and they do sound excellent, but 3 out of the six I bought do not hold a bias worth a damn! Recently bought a quad of Tung Sol reissue EL34bs and they sound at least as good as the JJs. Excellent bass, midrange, high end. Deep and wide sound stage, nice air with good recordings, esp. hdcds.
Richard

Forgot, posted pics in the Your Dynaco System. Richard

Roy wrote:

"C9 & C10 are commonly used in this type of circuit to increase the gain by bypassing the cathode resistor on the first gain stage. However, due to feedback from customers and from additional research on circuit design, C0 & C10 are not actually needed. By removing them, there is a slight benefit in reduced distortion as well as very slightly reduced gain. It's a small difference."

Damn, am I glad to read this. I was just pricing Black Gates or giant Russian caps to use for C9 & C10. Instead, I'll just remove the Panasonic FM's I have in there and be done with it.

I'm going to like this forum!

Hi, if I wanted to reinstall c9-10 for old times sake would a 35volt cap work okay? I have some around the house. Thanks

Thanks Bob. While we are on the subject of boards, I noticed that mine has a spot for some type of transistor in each channel. What was this used for originally?

Sure, see it by VR5 and 6. The board traces make it look like a transistor. It's clearly on my board with traces going to it. I figured it may be for some type of Constant Current Source that got abandoned sometime in the past.

There's also a spot for another component to the side of it by C13 and 14 labeled RC.