SP3a1 tube map.


Member Sponsor & WBF Technical Expert
Jun 23, 2010
Monument, CO
NP. I wish I had taken advantage of the upgrade program ARC did a few years ago, but it is not in my system now and has not been for a while, and I had modified it to use a DC source for filaments and to regulate the B+. ARC said it would have to be stock to do the upgrade even though they were replacing the old board so I passed.

Many years ago (late 70's/early 80's) I measured mine and distortion and noise was very, very low. It also had ridiculously high phono overload and line out capability. The only bad thing I found was that the zener bias string was not temp-compensated so bias varied for a while (tens of minutes) until it stabilized, and it had very large slow output ripples during the first minute or three. I built a timer circuit to delay powering on the amp for a minute after getting a SS amp; the tube amp I had with it (ARC D-79) took long enough to come up on its own that it wasn't an issue. I almost had a heart attack the first time I hooked up a sub (SS amp) and saw what the cone did in the first minute or two... I think the B and C versions corrected the start-up output (ground loop issue causing motorboating inside the preamp) and I made that mod to mine at some point (was a simple resistor fix but don't ask exactly what after all these years!)

My current SS setup is cleaner and far more powerful but I still miss that magical tube sound.

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. A place where audiophiles and audio companies discuss existing and new audio products, music servers, music streamers and computer audio, digital to audio convertors (DACS), turntables, phono stages, cartridges, reel to reel, speakers, headphones, tube amplifiers and solid state amplification. Founded in 2010 What's Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals we enjoy learning about new things and meeting new people and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing