Counterpoint 5.1- Beyond My Comprehension

I just experienced good news a moment ago- my Counterpoint 5.1 preamp is again operating properly. I had experienced greatly diminished volume in my system. This happened suddenly- when I powered everything up an placed an LP on the table, it was barley audible. All other selections were lower also.

To make a long story of tube swapping, amp swapping and speaker swapping short, I replaced the CA4 in the power supply and all is well. It appeared to have a smoky band around the center of the tube.

Does anyone know why this caused a reduction in volume instead of a total loss of volume?

Thanks in advance!
If I remember correctly, tubes do not stop working unless they are cracked/broken or somehow lose their vacuum. But the burnt band you described is going to cause diminished performance, thus your lowered, but not total, loss of sound.

I'm not 100 percent sure if I'm right, its been a while since I've messed around with tubes. But I hope I helped anyway,

Synesthesia Studios
If that tube is used as a voltage reference or as a voltage regulator and the voltage was low, that could potentially cause a loss in gain. I'm just guessing at this point. The dark band/ring around the center of the plate of the tube usually indicates the tube is worn out or damaged.
The 6CA4 inthe SA5.1 is the rectifier (note: not regulator) for the high voltage B+ of the SA5.1.
It converts AC to some 500V of DC that goes into the regulator.
If the B+ going into the regulator has low voltage, then obviously gain will be diminished.
Glad you didnt damage the regulator by replacing the 6CA4 quick.
Johnsonwu is correct. The Counterpoint regulators seem to be an issue now that the units are getting older. Either Johnson or myself can repair the Counterpoint units and we are both listed on the Alta Vista Website.

Happy Listening.
@ Johnsonwu & Bigkidz

Do either one of you do upgrades like Alta Vista used to do on SA 5.1s?

Thank you

I have done upgrades to SA1000, 2000, 3000, and limited stuff on the 5000 which is very hard to work on.
The SA5.1 schematic is floating around the Internet and the official one available from Catherine Weber per Altavista. Both Bigkidz and I have similar ideas of what Mike used to do with the mods (chokes, resistors, oil bypass, naked vishays, Non inductive WW plate resistors, etc.) It wont be 100% what the premium / gold level mods Mike used to offer but the ideas would be close.
Bringing a box to spec by replacing noisy resistors and old lytics is easy. Executing the mods take a lot of creative mounting work due to the 1U size of the SA5.1 vs the the HUGE size of the oil caps and the modern better sounding coupling caps (there is a reason why Mike sticks with Dynamicaps)

Same as what JWu said. One big improvement with the SA-5000 is the Direct In modification. I found that the sound stays close to what you hear now except the sound opens up and is clearer like using windex on your windows. It takes so much time to take apart an SA-5000 but worth the effort IMO if you choose to go down that path.
RE: Bigkidz & Johnson

Thanks for the reply! If either of you would be willing to tackle upgrades in the caps, I would love to talk with you further.


The 5.1 is good as it is as long as it's stable. I wouldnt sink money into it unless there is some sentimental value.
There's really nothing special to a dual 6922 grounded cathode parallel plate-drive line stage. An SA5000 with the followers pulled is essentially an SA5.1.
The Phono stage is a 2 stage 6922 with grounded cathode. Really nothing special.
The Power supply... The section after the 6CA4 rectifier could use a choke. The tube regulator section is in the main chassis I recall and without a service manual I wouldnt start working on it.
you can just do a signal path mod by changing out resistors and coupling caps (the output cap will be smaller, less bass, after the mod as I recall it uses a 10uF RelCap. Modern high end caps are 10x the size)
If you want to get it up and running either email JWu or myself from the Alta Vista website. JWu is in CA and I am in NJ.
You may also want to mod the power supply to a pure tube set-up.
Bigkidz the 5.1 is pure tube rectifier and regulator contrary to whats written on AltaVista. The 3.1 is solid state.
I think even the voltage reference uses a gas tube.
I am looking for some tube suggestions for the RIAA/ Line stage? Any ideas I would greatly appreciate.
With all the counterfeit 6922s floating around your money is better spent on caps and resistors.