[Maxx134]

if possible take some close up pictures of the resistor in question that is burning I like to know what is the exact location of this resistor so I can know which anode resistor, and also the surrounding socket and connections.

In order for that resister to be burning, there has to be an incorrect connection, excess solder connection, or other variables like if you using tube adapter sockets.

The fact that your measurements are similar only shows that the PSU is feeding the resistors.
You need measure the Anode(plates) from chassis ground to each anode which ia the other end of the resistors.
Did you measure with tubes in place?
The burning resistor must be having a problem from the Anode connection or the bias for that specific triode section, or a wrong connection by that specific triode cathode connection.
We talking only three points for that specific triode (anode-grid-cathode)section of the circuit and socket area.
Coin is right an incorrect bias is a possibility meaning a wrong connection on its grid.
all other sections are fine don't start looking at the unit as a whole board with 4 powrtube sections , as you only have to focus in that one specific tube section.

 

[coinmaster]

Burning resistors mean too much current, an incorrect bias voltage is the only thing that would push the tube to draw more current unless your cathode/anode voltages are way off. Check both grids of each tube in the faulty channel and let us know the voltages.

 

[nuport]

Since this is a balanced amp,
You should use the balanced output to gain the benefits of full power and zero hum.

If you have hum on balanced oit Itwould be surprised.

Sometimes my single ended output is nice and quiet and sometimes it has a very low level hum.
It depends o. How solid the board to ground I Assuming.

The balanced output was always quiet.
Right now it's dead quite at full volume.

 

After speaking to the ebay seller I have decided to return the amp. I will be purchasing a new one but I guess I have to wait now for delivery. 

 

[baronbeehive]

if possible take some close up pictures of the resistor in question that is burning I like to know what is the exact location of this resistor so I can know which anode resistor, and also the surrounding socket and connections.

In order for that resister to be burning, there has to be an incorrect connection, excess solder connection, or other variables like if you using tube adapter sockets.

The fact that your measurements are similar only shows that the PSU is feeding the resistors.
You need measure the Anode(plates) from chassis ground to each anode which ia the other end of the resistors.
Did you measure with tubes in place?
The burning resistor must be having a problem from the Anode connection or the bias for that specific triode section, or a wrong connection by that specific triode cathode connection.
We talking only three points for that specific triode (anode-grid-cathode)section of the circuit and socket area.
Coin is right an incorrect bias is a possibility meaning a wrong connection on its grid.
all other sections are fine don't start looking at the unit as a whole board with 4 powrtube sections , as you only have to focus in that one specific tube section.

 
I'll take some pics tomorrow. I'm not using adapter sockets, and I don't think there is an incorrect connection, I've looked everywhere, including pics of the reverse of the board, and as you know I've been pretty sparing with the solder!
 
Yes I measured with tubes in place.
 
Just after I took the last lot of voltages the heat melted the solder and a wire from the Mcap came off and shorted to the chassis ground via one of the screws. I'll have to solder that on again first.
 
Does it matter which end of the resistor to measure when measuring from it to ground?
 

  Burning resistors mean too much current, an incorrect bias voltage is the only thing that would push the tube to draw more current unless your cathode/anode voltages are way off. Check both grids of each tube in the faulty channel and let us know the voltages.

 
I'll check the 2 grid pins, pins 1 and 4, for each of the 2 tubes, tomorrow, its getting late here.

 

[baronbeehive]

  After speaking to the ebay seller I have decided to return the amp. I will be purchasing a new one but I guess I have to wait now for delivery. 

 
That's a good move. I don't know if they still do the modded version with Mundorf coupling caps and silver wiring but the wiring would save you some work!

 

[baronbeehive]

Here's the  pics:
 

 
Shows the burnt resistor. The yellow wire coming in from the left is connected to the Mcap and came off after I took the voltage measurements when the solder melted with the heat and shorted through the screw. I've got to reconnect it.
 

 
 

 
The black and red wires go to the WCF cap. The 2 black wires to the right of the red wire go to the coupling cap and bottom Ecap respectively.
 

 
The 3 wires going to the cathode bypass cap joint are connected to the RIFA for that circuit, the bottom Ecap and the Mcap.
 

 
A pic of the reverse of the board when I finished it, there look to be no problems from the pic. (I put in new heater wires).
 
Readings to follow.

 

[Mogos]

........
This weekend I will compare my settings with SonicTrance to decide on settings..
The consensus is that lowering theses values placed the tube in a more linear part of its bias curve,
And the impact on sound was rather HUGE(!)...

........

Guys I am also very interested in the outcome of your findings.
Did you manage to discuss the optimal values of the resistors?
Is there any mathematical or good practice rule connecting the values of the cathode and anode resistors?

 

[baronbeehive]

  baronbeehive did you change the PSU transistors or you are using the stock ones?

 
You changed yours when you had your problems didn't you? I don't know whether to change them, they are not on the list of mods on page 1 yet.

 

[Mogos]

Yes I have changed them. But in my case and also Sonic Trance the resistors and diodes in the PSU section get burnt and our meters did not move on.

 

[baronbeehive]

I think these are better pics:
 

 
1 - Circuit with burnt resistor
 

 
2 - Circuit with burnt resistor
 

 
3 - Circuit with burnt resistor
 

 
4 - Circuit with burnt resistor
 

 
1 - The other right hand side circuit next to it
 

 
2 - The other right hand side circuit next to it
 

 
3 -   The other right hand side circuit next to it
 

 
4  - The other right hand side circuit next to it
 
I tried to get readings today but some were all over the place and then I noticed the burnt resistor leg had come out of hole so I'll have to put it back in and try to get the readings again.

 

[Maxx134]

I am not understanding why the components are coming out of your board...

what type of solder low flash point cheap ***** solder you use?

another problem is shorting out that Cap 2 chasis..
hopefully you didn't exceed you power transistors rating, but if you get the same normal readings on other tubes you should be fine.

PSU feeds all tubes the same time.

As coinmaster stated, check the grid area of circuit, as it should be reasons why your tube is behaving to burn your anode resistor.

 

[baronbeehive]

I am not understanding why the components are coming out of your board...

what type of solder low flash point cheap ***** solder you use?

another problem is shorting out that Cap 2 chasis..
hopefully you didn't exceed you power transistors rating, but if you get the same normal readings on other tubes you should be fine.

PSU feeds all tubes the same time.

As coinmaster stated, check the grid area of circuit, as it should be reasons why your tube is behaving to burn your anode resistor.

It was the burnt resistor that melted the solder on the leg causing the (temporary) lead to come off. I think I made a mistake soldering the resistor in too far with one leg and not far enough with the other one (which came out). I checked pretty thoroughly all other joints to be satisfied they were ok but not this one because I was in a hurry to get the readings. All my solder joints have to pass the "tug test" before I'm satisfied, a good joint will not come out.
 
The solder is good - cardas solder so no problems there. The readings I managed to get before I noticed the resistor leg had come out looked good so hopefully no damage done

. I'll try again tomorrow.

 

[Maxx134]

Although you said you replaced heater wiring,
I like to know if this was the side of resistor burn.
It is super easy to make a mistake soldering back heater wires to wrong pin!

 

[MrCurwen]

PCBs and tube amps: not a good combination in my experience. P2P all the way.

 

[baronbeehive]

Although you said you replaced heater wiring,
I like to know if this was the side of resistor burn.
It is super easy to make a mistake soldering back heater wires to wrong pin!

 
I was wondering this too. The engineer said that one of the heater wires I replaced was too close to the resistor and burned when he tested it and he said he moved it. I don't know the answer to your question without contacting him or getting the board out again and I will probably have to get him to do that because the board is screwed in so tight. I did wonder if what he said had burned was the resistor or the heater wire, if it was the resistor then it was a preexisting problem, if it was the heater wire then as you said it could be this put in wrongly.
 
Anyway I have the readings from left good side to right bad side:
 
1 - Grid pin 1 to ground -20.2, Grid pin 4 to ground -106.3
     Grid pin 1 to ground -18.7, Grid pin 4 to ground -105.9
     Grid pin 1 to ground -0.6,   Grid pin 4 to ground -104.8
     Grid pin 1 to ground -17.4, Grid pin 4 to ground -105.3
 
2 - Cathode -88.3
     Cathode -87.5
     Cathode -86.3
     Cathode -86.4
 
3 - Anode 72.1
     Anode 70.9
     Anode 44.3
     Anode 69.8
 
The 4 cathode 330ohm resistors are the ones in the cathode bypass joints on the component side I believe.
The 4 anode 330ohm resistors are the ones in the reverse side I believe.
I'm  assuming it doesn't matter which leg of the resistor I measure to?
 
BTW Maxx the problem resistor is overheating so much that the solder is melting again so it isn't my soldering that's the problem!