Uber Tuber Issue

[chongmagic]

Hello I have been working on the Uber Tuber for a few days now and finished a majority of the board. I tested it out before boxing it, I don't have the input and output jacks wired in yet but I tested the voltages at TP1, TP2, TP3, and TP4. At TP1, TP2, and TP4 I am getting right at 18.00 volts. I was able to dial in TP3 to 11.5 per the instructions. I notice that the tube or 39R resistor are not getting hot at all. The LEDs on the board all light up. I checked all my components and reflowed the joints to make sure. I am guessing if test points 1, 2, and 4 are at 18v then the tube is possibly dead. I also measured across 39R and it is 18v on both sides which I would think would heat it up pretty good. I am at a loss at what else to troubleshoot at this point. I purchased the tube at smallbear, just as an FYI.

Any help would be greatly appreciated.

[thomasha]

Check if the tube heater is still good, there should be a small resistance between the pins.

If the heater is good, the tube should at least heat up, unless there is a bad solder somewhere. I guess the 39R goes in series with the tube, to drop the voltage to 6v, so it should be droping 12v at 300mA I guess. If it's not getting hot there is a short somewhere, or there is a bad connection/solder joint.

If the tube took 18v on it's filament it could burn the filament, but I guess there is either a short before the heater or no connection at all. Since you sad you're measuring 18v on both sides of the resistor, there is only a small current flowing to the other side of the resistor, which means that there must by a bad connection or burned filament somewhere.

Check if one of the h terminals is grounded and the other has continuity to the 39R resistor

[chongmagic]

I test continuity between the 39R and one side of the heater and it is connected. However the other side of the heater shows continuity to the positive lead.

I know this is a noob question but could it be because I don't have the input or output jacks connected causing a grounding issue.

I have my multimeter connected to the negative lead since it isn't boxed yet.

Sent from the unknown

[chongmagic]

Measuring directly at both heater points I am getting 18v. And still getting 18v at both ends of the 39R. Still no heat coming from the resistor or tube. Could 39R just be defective?

Sent from the unknown

[thomasha]

Well, if at both sides of the heater you have 18v you found the problem!
One of the sides of the heater should be grounded. There is no current flowing, so there is no voltage drop.

Check the second pin from the right, shown at the first picture. It should be connected to the ground plane. Check continuity between this pin and ground. And check the resistance between this pin and the other heater, should read something like 20R to 10R.

[chongmagic]

I do know that the heater pin on the left is connected to 39R.

But you are saying that the right heater pin should show continuity with the ground pad on the PCB correct? And that the resistance between both heater pins should show a resistance of 20R or less? Just making sure I understand.

I did check the resistance yesterday between the two heater pins and if I recall correctly it showed a fluctuating resistance up to 220k. But I will check again when I get home.

If I do find that there is no continuity to ground on the right heater pin, could that indicate that the tube is bad? I mean after reflowing and checking it from the schematic it should be a straight shot to ground. I don't believe any other components are in that path. I am not the best at reading schematics yet so I definitely could be wrong.

I did test all other components before I populated the board, which has become common practice for me. All of the readings were within tolerance.

Thank you for your help!

[thomasha]

220k is way off, are you sure that you measured between heaters?
If it's really 220k the tube is bad, or the pins are oxidated, which gives a bad contact with your meter and even with the solder.

Some tubes are old and have an oxide layer which makes it difficult to solder to.
I like to sand old components that have this oxidation, so that the solder sticks better to them. Some dirty pots have the same behaviour. Check that connection to ground from the tube pin, not the solder, it should be a short.

[chongmagic]

Yes, I measured between the heaters. I had my probe on each H of the main board. I cannot get a consistent reading however, I just tried again and initially it was 1M then it went down to 1k, and keeps rising and falling.

I did measure the right H pad and it is in continuity with ground, with the left H being in continuity with the 39R.

I bought this 6111 tube new from small bear so it had no oxidation. If the tube is indeed bad I will have to figure out how to get it unsoldered from the daughter card. I guess I should have measured the resistance before I soldered it in. But this is my first tube build, and these things are expensive in comparison with other components so it sucks that it could be bad.

[thomasha]

I would definetely sand the pins a little bit. This tubes are not in production anymore, even an unused tube must be NOS from the 60's or 70's.

I also saw that you cut the pins really short. Sometimes there is some coating at the base of the pins.



see here how the base of the pins of the first tube is a little darker. That would definetely be a problem when soldering.

The fact that you can't make a reliable measurent means there is something there.

[chongmagic]

I see what you mean, but I am not sure I can salvage the tube since I did cut the leads so close.

I have ordered another tube, is there a way to test it before I mount it so that I don't waste time and money?

[hasanova]

You could breadboard just the input stage to test tubes. If one triode works chances are the second one does, too. You will need to hook up the heaters though so you would need to be very careful about touching the 5W resistor (let it cool down after powering off).

[chongmagic]

Do you think it will be possible to salvage the daughter card? I have a desoldering iron I was going to use to try and remove the tube. But I am not sure how well the pads will hold up.

[madbean]

I can send another. Wait just a bit before doing anything. Can't type more right now.

[chongmagic]

Will do, thank you for your help!

[chongmagic]

I got a new tube today but I am a little hesitant to try and desolder the daughter card and then waste a new tube. Any suggestions?

Sent from the unknown