RESOLVED - original Dyna / VTA ST-70- One Output Tubes Doesn't Light

knotscott wrote:My Dynakit ST-70 with a VTA PCB has been working nicely for over two months and has about 30 hours on it.  It played beautifully last night.  Today I went to fire it up, and the front output tube on the right side didn't light, and had 0 bias voltage.  The rear tube on the same channel lit up and had normal bias.  The left channel was fine.  It also appeared that the middle and right side driver tubes weren't lit.  I switched out several tubes to eliminate them as possibilities.

It's got a new VTA driver board, new quad cap, and new tubes.  What can cause this?

Bob Latino wrote:

knotscott wrote:My Dynakit ST-70 with a VTA PCB has been working nicely for over two months and has about 30 hours on it.  It played beautifully last night.  Today I went to fire it up, and the front output tube on the right side didn't light, and had 0 bias voltage.  The rear tube on the same channel lit up and had normal bias.  The left channel was fine.  It also appeared that the middle and right side driver tubes weren't lit.  I switched out several tubes to eliminate them as possibilities.

It's got a new VTA driver board, new quad cap, and new tubes.  What can cause this?

The most likely cause is that the 6.3 volt AC filament line that goes between the rear output tube pins 2 and 7 to the front output tube's pins 2 and 7 has a bad solder connection on the front output tube. Resolder pins 2 and 7 on the front right output tube socket.

Bob