Latino VTA ST-70 kit problem/challenge

No I didn't have any problems with the tracings. HOWEVER those eyelets and tracing were quite small. I did your a mag lamp when I was soldering it up. These old eye don't see so good anymore.

Don't worry we'll get your amp working again. Once you do you will be VERY happy. I've been using mine for several years and I gave up amp hunting.
I really appreciate all the help I’m getting! Ironically, I’ve been listening to it (quite critically) most of the day and if I didn’t know about the messed up tube with 0v bias in triode mode I wouldn’t know anything was wrong. This brings up the philosophical question- if you can’t tell anything is wrong is something wrong?
Seriously, I think my next test is likely to come when my replacement tube comes, I rebias everything and see if all of my checking and resoldering has accomplished anything.
 
Here's what I'd do to diagnose your amp. Take the power tubes out, set them aside. Using alligator clips, clip the pos volt meter probe on the plate pin and the negative volt meter probe to ground. Power on the amp. Take a pair of insulated needle nose pliers and with one hand only (leaving the other hand in your pocket) grab the insulated part of the wire near the tube socket pin with the tip of the pliers and tug that wire around a bit. Watch the meter and see if the voltage fluctuates. It should be rock steady no matter how you tug the plate lead wire.

Do the same with the screen pin wire.

Do the same with the grid #1 pin wire.

Check the solder connections on the traces of the junction of the red arrow location. Check that 270K resistor to see if it sometimes reads as an open circuit. Check the 1K resistor to its right on the schematic also for same condition.

View attachment 1444103


Check the other three output tube sockets the same way.

If all the above checks out, check tube socket connections to tube pins. Tighten tube socket pins if necessary.
Very helpful! Thanks for going to the trouble to post the schematic.
 
Check and make sure non of the solder joints are touching. Both on the sockets and board. Make sure there are no long tails from components that could be hitting the chassis or another part.

What I did before I "fired" up my VTA was go through the instruction manual step by step. Make sure EVERY step was connected correctly. It only takes about an hour but it would eliminate an crossed wire on some contact. Make sure when you check that you orient the tube numbers lug, lugs, switch leads and other parts correctly.

Post your results
 
I got my replacement tube and I still have two issues:

1. When in pentode mode the left channel pops during loud passages
2. When in triode mode, the amp sounds great, but the bias on one of the left channel tubes is 0v and can't be adjusted

Note that I have no trouble adjusting bias on all tubes in pentode mode, but in triode mode the bias on that one tube goes to 0, but the amp works well, and the popping stops.

Does this narrow things down?
 
re check all the wiring to the tube sockets and your Pentode/Triode switches, also double and triple check all the soldering on the tube sockets and switches. What gauge wire did you use to wire to the P/T switches.
Also make sure that the pins in your power tube sockets are still nice and tight, swapping tubes a lot will loosen them!
 
Again! go over the manual and check EVERY!!! step as if you were building it again. It should only take about an hour. Even check that you put the correct parts in the correct orientation on the PCB board. You clearly have a miss wiring problem.
 
Fixed! As suggested it was a wiring mistake on the socket that was demonstrating the problem. I’m trying not to let the mistake damage my self esteem, but mostly I’m glad to have it resolved. Thanks to everybody for your help!
 
Fixed! As suggested it was a wiring mistake on the socket that was demonstrating the problem. I’m trying not to let the mistake damage my self esteem, but mostly I’m glad to have it resolved. Thanks to everybody for your help!
Hey be proud that you worked the problem and fixed it yourself. Congratulations, now get to listening to that thing and give us YOUR review.

With the Gold lion KT-66's - It's my favorite amp!!!!

Enjoy
 
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