Hum from new VTA120 newly built kit

I have recently built an ST120 purchased from tubes4hifi.com and am having a few issues upon initial start up.

ST120
Octal driver board w/ upgraded caps
Dual rectifier board
Tridode/pentode switch
Bias display ports

Tubes used for testing
2 JJ 5AR4/GZ34 Rectifiers
3 6SN7s
4 Soviet 6L6 (6P3S(6N3C))

With initial startup I have been using my variac to slowly increase voltage.  Everything seems ok, tube heaters come on, no red plating.  But I have no bias readings on the display ports.  Wanting to simplify, I replaced the display ports with the octal socket so I could read the bias with a multimeter.  All bias ports are still reading 0. I am getting 10 ohms on the bias ports when the amp is not on.

I have double and triple checked my wiring and everything looks correct.  

Is this an issue with the rectifier board?  Any help would be appreciated.

Chad

Did you ever get your bias voltage? I had similar issue and it was rectifier tube not seated issue. I see you have the DR so probably not the issue…

batman7349 wrote:Did you ever get your bias voltage? I had similar issue and it was rectifier tube not seated issue. I see you have the DR so probably not the issue…

I'm a friend of the OP. I've been with him throughout his entire journey of building his VTA-120. He did indeed get bias voltage, and the amp was fine. He's running the dual rectifier board and also the pentode/triode switches.  Was talking to him on the phone and he let me know after a day of listening to music, a slight hum started to come from one channel. I had him record the hum, and apparently now one of the rectifiers sparked and he's hearing the hum come FROM the amp itself. Not sure if it's coming from the PT, but it's rather loud. I had him turn off the amp for now for remove the compliment of tubes (2 Genalex Gold Lion GZ34/5AR4, Quad of Svetlana EL34s, 3 Vintage Tungsol 6SN7s). He will be posting some photos and his experience.  I'm posting the audio of what he recorded as well.....

The last time I heard this happen was when my Quad cap on my VTA-70 was going to hell in a hand basket. I was wondering what you guys think on if it is filter capacitors on the dual rectifier board.



This is a brand new kit and the amp was working fine. I've not much experience with the Dual Rectifier board, so if anyone else has any suggestions, please do let us know.

FG. (Jon)

Click on the image to see a larger version.

Yes as fedoragent said I was able to get rid of the bias issues. This seemed to be caused by a bad JJ GZ34 rectifier new out of the box. After changing the JJ rectifiers out for some old 5U4GB's I had this issues worked itself out and I was able to bias the tube and start listening to music.

After a short period of time another issue came about. I started hearing a hum coming from the right speaker. At first it was very slight but after a few hours of playing music the hum has become louder now to the point that I can hear it while playing music during quiet parts.

Trying to figure out the issue I first swapped my vintage RCA 6SN7's out for some chinese 6SN7s, no change. Next I tried swapping the power tubes, Svetlana EL34s, putting the ones in the left side on the right and right on left. My thought being if it were the power tubes the hum would switch from the right to the left side. Upon powering up I had the heater rectifier tube spark bright white. I quickly shut things down. At this point I swapped out the rectifier tubes, I had in Gold Lion GZ34's for the 5U4GB's I had been testing with. This time using my variac to slowly increase the voltage I got to about 65 volts and starting hearing a hum coming from the amp itself. I quickly shut things down, I did not leave the amp on long enough to see exactly where this hum was coming from but it seems like the power transformer

Adding a couple more images of the top of the dual rectifier board.

What did you use for solder - 60/40 or 63/37 tin/lead, or some of the newer lead free stuff (which is crap in my opinion)?  And for that matter, what kind of soldering iron?  A lot of the solder joints I see look to be on the cold side to me - they might not be making good contact.  Looking at the photo of the top of the dual rectifier board in your latest post, from that angle it appears the tube sockets are not soldered at all.  I know from the views of the underside that they are, but the joints look questionable.  When soldering plated through holes like those on these boards, I like to see a nice fillet of solder on the TOP side of the board as well as the bottom.  See the following photo of my M125 board:


In the earlier post showing the right end of the dual rectifier board with it tipped up (the one with the two diodes within the tube socket outline), pin 1 (directly above pin 8 ) definitely looks like it's a cold joint, as does pin 4 (just above the cathode of the horizontally mounted diode).  It's tough to tell for certain from the photos looking directly down on the chassis mounted tube socket terminals, but they look like they could use more solder as well.  (look at the Blu/Wht wires going to pin 4 on both of the output tubes on the left side - it appears that there's barely any solder on the connection.)  You want smooth, shiny fillets of solder there, too.  It's ok to tack them with a small bit of solder when in the build process if more wires are to be added to the terminal, but once everything is in place you should go back and add enough solder to get that nice fillet.

My suggestion would be to start by getting your hands on a good soldering iron and some good 60/40 or 63/37 solder like Kester or Multicore (not something sketchy from the bay of evil - buy once, cry once), then go around and reflow all the connections, getting both the pin and the land (for the boards) and the terminal and the wire (for the chassis mount tube sockets and can cap) hot enough for solder to melt on them, and add solder as needed to get nice fillets and smooth shiny joints.  I would bet that this will go a long way towards solving the issues you're having with the amplifier.  For an excellent series of videos showing good soldering practices, go on youtube and search for "Pace soldering videos" - they're old, but still relevant, and show excellent techniques.  Here's a link to the first one:


Good luck!

-Pat

I’m using 63/37 solder and a Hakko soldering iron. Admittedly I don’t do a lot of soldering of resistors and such on boards. The majority of my experience is soldering wire onto pads and wire to wire. While I might not have enough solder on every spot for the solder to flow through to the opposite side I can say for certain that every solder point on the opposite side of the board is solid.

All that said, if this is a real issue that needs to be addressed I certainly will do so, but I’m doubting this is the overall issue.

Humor me and try reflowing/adding solder to get better looking, more solid connections. It should be relatively easy to do, and will eliminate the possibility of intermittent connections causing you grief that is very difficult to track down. It is not 100% guaranteed to fix the issue, but it certainly won't hurt.

-Pat

NewToTubes210 wrote:I’m using 63/37 solder and a Hakko soldering iron. Admittedly I don’t do a lot of soldering of resistors and such on boards.

What Hakko?
What tip?

Looking at the photos, I'd say your iron is under temperature and/or the tip is incorrect and/or technique needs work.

Keep the tip clean and use a metal scrubber to remove flux build up.

Apply a very little solder to the tip, place on pad and only add solder wire to the point when the pad solder has melted.

NewToTubes210 wrote:Yes as fedoragent said I was able to get rid of the bias issues. This seemed to be caused by a bad JJ GZ34 rectifier new out of the box.  After changing the JJ rectifiers out for some old 5U4GB's I had this issues worked itself out and I was able to bias the tube and start listening to music.

After a short period of time another issue came about.  I started hearing a hum coming from the right speaker.  At first it was very slight but after a few hours of playing music the hum has become louder now to the point that I can hear it while playing music during quiet parts.

Trying to figure out the issue I first swapped my vintage RCA 6SN7's out for some chinese 6SN7s, no change.  Next I tried swapping the power tubes, Svetlana EL34s, putting the ones in the left side on the right and right on left.  My thought being if it were the power tubes the hum would switch from the right to the left side.  Upon powering up I had the heater rectifier tube spark bright white.  I quickly shut things down.  At this point I swapped out the rectifier tubes, I had in Gold Lion GZ34's for the 5U4GB's I had been testing with.  This time using my variac to slowly increase the voltage I got to about 65 volts and starting hearing a hum coming from the amp itself.  I quickly shut things down, I did not leave the amp on long enough to see exactly where this hum was coming from but it seems like the power transformer

Of note, I do not recommend using dual 5U4 rectifiers with the dual rectifier board as the heater current requirement is over the rating of the 5VAC on the power transformer. Dual 5AR4 are within the current rating of the of the 5VAC on the power transformer.

Did you get your issue resolved? As some others have mentioned, there are some solder joints that do not appear to have enough solder flowed through them.

I have completely torn down the amp in order to go over every solder joint making certain that the solder has flown completely through all the joints on both the dual rectifier board and TVA board.

This evening I finished getting most everything soldered and back into it’s place. Unfortunately, sometime during this rebuild process I somehow broke one of the triode/pentode switches. I have ordered another replacement from tubes4hifi but am at a stand still until this coming in.

Once I receive the new switch I simply need to quickly solder it into place and I can look at starting the testing process again. Hopefully this next time I will have better luck.

Chad

I've been considering adding the dual rectifier to my VTA ST-70 myself. I built it about 11 years ago.
But my concern is the current rating for the 5v heater winding. Isn't it rated for 3 amps?
Wouldn't using two 5AR4's be pulling very close to 4 amps?
I tried a 5V3A that pulls right at 3 amps and the transformer got noticeably hotter.
Thanks.

lavane wrote:I've been considering adding the dual rectifier to my VTA ST-70 myself. I built it about 11 years ago.
But my concern is the current rating for the 5v heater winding. Isn't it rated for 3 amps?
Wouldn't using two 5AR4's be pulling very close to 4 amps?
I tried a 5V3A that pulls right at 3 amps and the transformer got noticeably hotter.
Thanks.

VTA ST-70 power transformer is rated at 4 amps on the 5VAC winding.
VTA ST-120 and M125 power transformers are rated at 5 amps on the 5VAC winding.

Thanks