As far as loading goes you should terminate the input transformer with a matching load. In the case of the 1569 the 200k pot + 100K R1 gives you 75K loading. Am extra resistor should be added to get you closer to 15K to avoid ringing.
Also the input side of the amplifier looks like most tube amplifiers. Some may have a stopper at the input tube. The fun part of the 200K pot is you have an effective stopper as long as the pot is not above 80% or so. I have seen a 1570 oscillate once the pot is turned fully up. This was with an input transformer and it also might have been caused by a loading mismatch.
Also the input side of the amplifier looks like most tube amplifiers. Some may have a stopper at the input tube. The fun part of the 200K pot is you have an effective stopper as long as the pot is not above 80% or so. I have seen a 1570 oscillate once the pot is turned fully up. This was with an input transformer and it also might have been caused by a loading mismatch.
Another note about Altec amplifier loading. Some installations would Strap maybe four amplifiers together and use one input transformer for all of them. You would strap terminals 1 together along with terminal 2 together. Set the transformer in one amplifier and loading would be fairly close.
Thanks for notes. Yeah it’s odd, can’t really even begin to find the actual issue. It’ll be on idling fine with 100mvac on the input grid, then wall current will spike like it does from typical inrush but when it’s been on and fine.
all tubes have been rolled and rolled. It sounds like the typical switching on of a HT standby, inrush, but the amp has been operating and idling fine at the the time it does.
all tubes have been rolled and rolled. It sounds like the typical switching on of a HT standby, inrush, but the amp has been operating and idling fine at the the time it does.
My best guess is to measure the output and gently increase signal to the threshold and see if it really looks like oscillation. It could be more like shoot-through you see with a push pull amplifier is it is a phase splitter problem. The other thing would be to measure the output stage control grids with a dual trace scope and make sure the control grids are really out of phase.
Also make sure C5 in series with R8 is within tolerance or also works with higher voltages across it.
Also make sure C5 in series with R8 is within tolerance or also works with higher voltages across it.
I'd anticipate that orange plating causes additional plate and glass out-gassing in a tube, which then takes time for the gas level to subside from getter action (assuming there is still sufficient active getter/life in the tube).
Goldstache, how are you measuring each output stage valve's idle current?
The 811a needs some plate color in order to activate the getter. Letting the tubes run too cold can cause some gas problems.
My dad used to call it "care and feeding" of transmitting tubes which was sometimes different from audio tubes.
My dad used to call it "care and feeding" of transmitting tubes which was sometimes different from audio tubes.