Tube Crackle?

[BassmanPaul]

I'd go back to the 6L6GCs and see what that does for you. Your problem could be coming from the overstressed PT. If you want to stay with the 6550 type supply an additional 6.3V 10A transformer to handle the additional load of the heaters. 0.9A to 1.6A per tube is a significant increase.

 

[carbonfold]

If the PT was overworking for the current needed for the extra .7a per tube, would there be a sag in the heater voltage? Or really no way of knowing unless I had a spec sheet of the PT?

I'd go back to the 6L6GCs and see what that does for you. Your problem could be coming from the overstressed PT. If you want to stay with the 6550 type supply an additional 6.3V 10A transformer to handle the additional load of the heaters. 0.9A to 1.6A per tube is a significant increase.

 

[carbonfold]

Stuck the 6l6gc in and same problem. Crackling still occurred even before I got to bias them to mA value ( crackling even at low biasing or normal ).

I'd go back to the 6L6GCs and see what that does for you. Your problem could be coming from the overstressed PT. If you want to stay with the 6550 type supply an additional 6.3V 10A transformer to handle the additional load of the heaters. 0.9A to 1.6A per tube is a significant increase.

 

[carbonfold]

So after staring at the original wires on the input channels and wires to V1 and V2, I said what the heck.... I'll just re-wire them myself with new wire.

Before I got started, I noticed that when I tapped the pre-volume pot or wires to V2 I could hear the tapping bleeding into the speakers ( like a bad instrument cable sound when you jangle it one the floor).

I went ahead and re-wired it.
Unfortunately still get the crackling and tapping bleed through on wire from pre-Volume pot into V2. So, I went crazy rotating the this pot and it does seem to increase some of the crackling when it occurs during warm-up. I guess maybe a bad pot? I have never encountered a pot that mainly crackled during warm-up.

So that led me to checking all the preamp solders and EQ solders. Went ahead and reset the PTP solders and found two questionable PTP on a few EQ pots.

Now with that all said and done... Crackling has subsided approx 90%. So broke some ground ha...

 

[carbonfold]

I was looking at the specs of a Tung-Sol KT120. Wouldn't it make more sense just to run a pair of these? mA draw seems to be about the same and handle the voltage well.