VTA-120 Possible Pentode/Triode Switch Problems

I was not getting sound from the Right channel, and when I switched into Triode mode the sound came on but very faint and crackly. I turned off the amp.

Might it be as simple as the Pentode/Triode switch?


A few years ago the amp had sparks, and subsequently literally partly melted this switch (since replaced), so I'm really paranoid of turning it on again. I will be re examining the solder points...

Any thoughts?

Could be the LM334 on the weak side of the VTA board. When my ST-120 had low volume and "rustling leaves" on one side, it turned out to be this. I followed Bob's suggestions. Do a search on the forum, it's in there.

I did not have an issue related to the switch. Could that be coincidental?

Thank you, I'll check that out. A search for LM334 did not turn up any posts with input from Bob. What is the weak side of the board?

look in here:

https://dynacotubeaudio.forumotion.com/t4926-vta-st120-lost-right-channel-help-needed?highlight=low+volume+on+one+channel

weak side= the channel w/ low volume /noise on the VTA board

Just saw your location-

I got serious road rash on the alpine slide summer of '94.
Also visit N Adams every once in a while.

As to your previous problem with the switch. Flipping the switch on the fly may have caused arcing and it's probably good practice to power off before flicking the switch.

Thanks for the link. I'll try it before I start any part replacement. I'll report back what I find. Again, thanks for the replies.

I'm pretty sure the switch took the hit from my shorting debacle. Here's the link to the story. Some pics are no longer accessible. https://dynacotubeaudio.forumotion.com/t4151-beautiful-sound-of-my-vta-st120drt1-part-2

These pictures should be visible- https://photos.app.goo.gl/QNwFYshyzzmwaY2W9

So, I don't usually switch between modes while the amp is on. Just when it was silent on the right channel. I learned that lesson the hard way.

I swapped the inputs and got sound from both channels. Thank you all for the information. I'm glad the amp is OK. Whew.