I assumed it had something to do with that but, we are getting above my head. Any suggestions for 4uf caps? Have been doing some reading on those also and trying not to overdo it. The recommend caps are in the sub 1.0uf values or stuck in a supply chain. Thinking of starting with some Solens and see what happens. I saw some Panasonic MPP but would be a coin toss.
Wanted to give an update on my progress to let you know that without your help I wouldn’t be this far. New ‘partner’ is up and running. My first concern is whether my operating voltage are within tolerance before I start tidying up and ordering new tubes.
I have run the amps for about 30 mins with no overheating, but wanted to check in.
First impression is impressive low volume bass with some sparkle at the top through my Forte II’s. This is certainly better than my diytube stereo 35 (PP el84). It sounds quite nice without any hints of strawberry superlatives 🙂 .
My B+ to the 5881’s is 388 to the plate (pin 3) and 395 to the grid (pin 4). From looking at the W3 manual that seems okay. The cathode (pin 8) is around 41v.
The B+ to the splitter and driver is 355v. V2 (12ax7) has 100K anode load which brings the plate to 250-ish so that seems to be within range. Cathode is at 22v.
I am wondering about V1&3 (12au7) cathode followers which have 356 on the plate. Ignorantly looking at the spec sheet says 300 max which is my concern. Cathode is reading 19-20v
As mentioned from the start, this is my first amp without a known design so I am in above my head. I am reading about load lines and to “broaden my horizons”. But wanted to ask for a quick check on wether it is safe to run.
I have run the amps for about 30 mins with no overheating, but wanted to check in.
First impression is impressive low volume bass with some sparkle at the top through my Forte II’s. This is certainly better than my diytube stereo 35 (PP el84). It sounds quite nice without any hints of strawberry superlatives 🙂 .
My B+ to the 5881’s is 388 to the plate (pin 3) and 395 to the grid (pin 4). From looking at the W3 manual that seems okay. The cathode (pin 8) is around 41v.
The B+ to the splitter and driver is 355v. V2 (12ax7) has 100K anode load which brings the plate to 250-ish so that seems to be within range. Cathode is at 22v.
I am wondering about V1&3 (12au7) cathode followers which have 356 on the plate. Ignorantly looking at the spec sheet says 300 max which is my concern. Cathode is reading 19-20v
As mentioned from the start, this is my first amp without a known design so I am in above my head. I am reading about load lines and to “broaden my horizons”. But wanted to ask for a quick check on wether it is safe to run.
Attachments
First of all, congrats on getting the mate up and running. Unfortunately I am not familiar enough with the Van Skoyoc to really help determine the proper voltages. The output stage seems fine. Looking at the original schematic, it's strikes me that, normally, a cathode follower would have a sizeable load on the cathode, like 47K, rather than the 4.7K used here. It's possible that your B+ to the preamp stages is too high. Hopefully someone with more experience can chime in. It sounds like a matter of tweaking, though.
Interesting read about cross coupled phase inverter circuits.
https://tubecad.com/2009/07/blog0166.htm
https://tubecad.com/2009/07/blog0166.htm
Thanks @nerdorama, will give it a read. I found this article this morning, https://next-tube.com/articles/cci/cci_EN.pdf
which looks almost exactly like my setup. It is calling for 300V for B+ with a target of Vk of 20V in the driver. I currently measure 20V on the driver but will try and drop my B+ from 350 ish and see what happens. Hopefully I have something in the parts box.
which looks almost exactly like my setup. It is calling for 300V for B+ with a target of Vk of 20V in the driver. I currently measure 20V on the driver but will try and drop my B+ from 350 ish and see what happens. Hopefully I have something in the parts box.