Brand new preamp tubes seem to be bad ?

[gtrplayr1976]

1002620 - YouTube
1002621 - YouTube

[g1]

There have been a few discussions here recently involving the high rate of returns for tubes "bad out of the box", so three hummy JJ's doesn't really surprise me.
There doesn't seem to be much QC going on by the tube makers or their distributors.
The fact that the end user has to pay the return shipping means a lot of them will just get thrown out rather than returned, so there is no incentive for anyone to improve the QC.

[gtrplayr1976]

This is the first time I've had issues with JJs ,but I normally get them from Eurotubes ,or somewhere else where they are tested.

[Randall]

Please don't take this the wrong way, but why do you flip the switches in slo-mo?

[gtrplayr1976]

Please don't take this the wrong way, but why do you flip the switches in slo-mo?

Is that what I did ? I think I'm just a little jumpy these days.

[km6xz]

That is strange but is it possible they were mislabeled? There are a lot of tubes sold as 12AX7s which are dual triodes but with parallel heaters for 6.3volts AC but the pin 9 that is the center tap pin of the 12AX7, is used as an internal shield. That was a common tube in Central and Eastern Europe. For example the 6н2п (6N2P in Latin characters). Depending on how your circuit is wired, it would cause loud hum.

[gtrplayr1976]

That is strange but is it possible they were mislabeled? There are a lot of tubes sold as 12AX7s which are dual triodes but with parallel heaters for 6.3volts AC but the pin 9 that is the center tap pin of the 12AX7, is used as an internal shield. That was a common tube in Central and Eastern Europe. For example the 6н2п (6N2P in Latin characters). Depending on how your circuit is wired, it would cause loud hum.

Thanks for the info. I have tried various 12AX7s even have a matched set ,and a balanced phase inverter. There IS another issue(s). My voltage has dropped on some of the pins, and the volume I now have is very low especially on the Vibrato channel. I seemed to have had the amp working one night ,and the next night I changed the bias resistor to a higher value ,put the new preamp tubes in it ,and that's when the issues started. I checked the solder joints ,and all seems good. I've attached some voltage readings from when it was working to after the resistor change,and without tubes. I also have a high pitched noise on the normal channel until I get the tone control above 2. I had one voltage fluctuating ,but traced that to the speed control . When I disconnected the wire to the control the fluctuation stopped. The tube reading that's by itself in the middle of the page is from the rectifier tube.

Thanks a heap !

[gtrplayr1976]

Ok, so I solved the issue here mostly. There was a bad .0047 cap off V3 pin 1. Got all my volume back, all the preamp tubes seem to work now also. I still have some lingering issues. I have tremolo on the vibrato channel even with the controls at 0. Only slight ,but it's there ,and the foot switch seems to do absolutely nothing.