CSS Chip blown up???

[Bola]

My first time here and my first tube amp (tubelab SE)...

After issues with the PSU (B+ seems to high (450V) as well as B- (290V), no power tube), I tried to get the 150V on the 5842. I have no reading (or very little, 5V or so) for both channels. Before I order new chips, I wanted to consult you folks who clearly have a better understanding of that circuit compare to me!

Could it be possible that both chips failed at the same time? One of the two seems to get very hot. I tried reading on R16 & R27 - nothing.

Any one can track me toward possible solutions???

Many thanks in advance!

[Jpeg]

It doesn't sound like you have anything too far out of the ordinary with your voltages. I had over -200 volts on mine, and there is a recent thread about it here:

Tubelab SE checkout shows -300V Bias voltage?

Your B+ will also sag quite a bit when you actully have tubes in them. I assume you are setting your's up for 300b with something like a 660 volt transformer?

I had a heck of a time setting the voltage on the input tubes, going off the coupling cap and ground, I could not get a reading at all. I can't tell you why. I ended up pulling the tube about 1/3rd of the way out of the socket and using those spring clip test leads to grab the appropriate pins on the tube and setting it that way. No matter how you test it be extremely careful, those are lethal voltages

I can't say for sure that your chips aren't blown, but like you said it seems pretty unlikly that they would both go at the same time. Hope this helps.

[rknize]

You have 5V at the plate of the 5842? That does not sound right. What do you measure on the other side of the R16/R27?

[Bola]

Originally Posted by Jpeg

It doesn't sound like you have anything too far out of the ordinary with your voltages. I had over -200 volts on mine, and there is a recent thread about it here:

Tubelab SE checkout shows -300V Bias voltage?

Your B+ will also sag quite a bit when you actully have tubes in them. I assume you are setting your's up for 300b with something like a 660 volt transformer?

I had a heck of a time setting the voltage on the input tubes, going off the coupling cap and ground, I could not get a reading at all. I can't tell you why. I ended up pulling the tube about 1/3rd of the way out of the socket and using those spring clip test leads to grab the appropriate pins on the tube and setting it that way. No matter how you test it be extremely careful, those are lethal voltages

I can't say for sure that your chips aren't blown, but like you said it seems pretty unlikly that they would both go at the same time. Hope this helps.

Thanks Jpeg. You are correct: 300B with 660V transfo. I will investigate a little more tonight based on your comments.

Your comments were helpful

[Bola]

Originally Posted by rknize

You have 5V at the plate of the 5842? That does not sound right. What do you measure on the other side of the R16/R27?

Rknize,

Direct mesurement on R16/R27 (clips on both sides of each resistors, not R16/R27 to ground), shows between 0 to 5V. When playing with R12/R23, I see a voltage fluctuation (0 to 15v) for half a second or so.

The situation seems to show that there is almost no current across the input stage (5842). I see only two possibilies: bad contact like Jpeg suggested, or blown up CCS on both channel

[rknize]

5V / 330 ohms = 15mA. That sounds correct. What voltage were you expecting? What voltage are you getting at the 5842 plates (with respect to ground)? How about across R10/R21?

[Bola]

Originally Posted by rknize

5V / 330 ohms = 15mA. That sounds correct. What voltage were you expecting? What voltage are you getting at the 5842 plates (with respect to ground)? How about across R10/R21?

Russ,

I am currently at work. I will measure tonight R10/21 but if I remember my measure from last night it was around zero.

I am aiming to get 150V at the plate as per instructions from TUBELAB. I only have around 5 volts.... Something is definitly wrong.

Alain

[rknize]

I'm confused. Are you saying that you have 5V at the plate or that you have 5V across R16/R27? 5V at the plate (relative to ground) is wrong. That should be 170V or whatever. 5V across the resistor is about right.

If the answer yes to both, then it sounds like you have a short across the tube. Either the tube plate is shorted to the cathode or you have a solder short under the socket.

[Bola]

Originally Posted by rknize

I'm confused. Are you saying that you have 5V at the plate or that you have 5V across R16/R27? 5V at the plate (relative to ground) is wrong. That should be 170V or whatever. 5V across the resistor is about right.

If the answer yes to both, then it sounds like you have a short across the tube. Either the tube plate is shorted to the cathode or you have a solder short under the socket.

Russ,

I have 5V on plate to ground (fluctuating, it starts at 15v when I am powering up and falls down between 0 to 5 volts). Both tube comes from ebays - might be the cause...

I will investigate.

Many thanks Russ - I really appreciate your support.

Alain

[rknize]

What type of 5842 are you using? It's not the Russian one, is it? Those have a different pin-out.