Solved - Paramount - Low Volume very muffled

[Horatio]

Hi, just finished my Paramount kit build and am having a few challenges... The some of the voltage / resistance checks don't look right and the upshot is that while the Paramounts turn on, both tubes light up, the sound that comes out of my Orca speaker is of a very low volume, very muffled and somewhat distorted (this is regardless of whether driven by my BeePre (just built and not 100% confirmed working yet) or my DAC directly connected to them)... I have my suspicions around the power board but before I de-solder it from the transformer I thought I should get a second opinion:

Line Voltage measured by a power socket adapter that the Paramount is plugged into : 243.7 volts

Tube: EH 300b

Resistance         
         
Terminal   Manual   Paramount 1   Paramount 2
         
1   *   Infinity   Infinity
2   No Connection   No connection   No connection
3   No Connection   No Connection   No connection
4   No Connection   No Connection   No connection
5   1K   1K   1k
6   1118   1118   1118
7   249k   248K   248k
8   No Connection   No connection   No connection
9   124k *   *   *
10   0   0   0
11   3.0M   879k   889k
12   5.6M   1860k   1825k
13   0   0   0
14   9.2M   Infinity   Infinity
15   15M   Infinity   Infinity
16   *   *   *
17   0   0   0
18   0   0   0
19   128k   176.5k Measured on the 200k setting   177.7 Measured on the 200k setting
20   249k   2.47k on 20k setting   2.47k on 20k setting
         
Four Pin Socket   Manual   Paramount 1   Paramount 2
         
A1   1027   1015   1023
A2   *   Infinity   Infinity
A3   249K   249k   248k
A4   1028   1021   1016
         
Nine Pin Socket   Manual   Paramount 1   Paramount 2
         
B1   0   0   0
B2   8.2k   11.72k   14.96k
B3   249k   2.71k on 20k setting   2.71k on 20k setting
B4   130k *   176.5k *   177.5k
B5   0   0   0
B6   177k *   *   364 measured on 2000k setting
B7   220   244   228
B8   *   infinity   Infinity
B9   *   0   0

Terminal   Manual   Paramount 1   Paramount 2
         
1   440   441   440
5   71   73   74
9   175   142   148
10   0   0   0
         
16   457   466   465
17   0   0   0
18   0   0   0
19   175   142   148
         
Four Pin Socket   Manual   Paramount 1   Paramount 2
         
A1   74.1   76   77
A2   440   441   440
A3   Close to 0   0.05 measured on 20v setting   6 measured on 2000m setting
A4   69.2   71   72.8
         
Power Supply Board      Manual Paramount 1 Paramount 2   
         
6V-Red Wire   3.1VAC   0   0
6V-Black Wire   3.1VAC   0   0
         
C4S/soft Start Board      Manual Paramount 1 Paramount 2   
         
Kreg (A Side)   4.1   1.88 measured on 20v setting   1.87 measured on 20v setting
Kreg (B Side)   6.3   3.96 measured on 20v setting   4.79 measured on 20v setting
OA   300   146   149.5
OB   175   143.4   147.8
         
Trimmer Screw Adj.      Paramount 1   Paramount 2
         
300k Resistor OB end      143.4   147.8
         
The power supply board values are making me suspect that something has gone wrong in that area however T11, T12, T19, T20, B3, B6 all see a little off.

Voltage wise the Power Supply Board is clearly not right and the Soft Start Board is low across the board...

Any help would be much appreciated - given the consistency across the two units it feels like I have made a schoolboy error in the same place on both of them!

Thanks,

Bill

[Paul Joppa]

The only power supply voltage you quote is the 6.3v winding, which must be measured on the AC volts scale, not DC volts. Since the tube lights up, it is getting the desired voltage.

The low voltage on the driver board are confusing me - would you first make sure you have identified the measurements with the correct (A or B) side, and if so re-check that the A and B sides are wired correctly, both on the board and from board to circuit?

The reason for the above is that the low kreg voltage would make more sense to me if it were on the other side.

[Horatio]

Thanks Paul, all help much appreciated...

1) Schoolboy error on the measurement of the AC volts - proper measurements below.

2) Re-soldered all main joints, took off the driver board and re-attached...

3) I believe I have the correct A and B side - slightly different figures this time for Kreg A

Updated measurements:

Resistance      
      
Terminal   Manual   Paramount 1
      
1   *   *
2   No Connection   No connection
3   No Connection   No Connection
4   No Connection   No Connection
5   1K   1K
6   1118   1118
7   249k   248K
8   No Connection   No connection
9   124k *   *
10   0   0
11   3.0M   Infinity
12   5.6M   Infinity
13   0   0
14   9.2M   Infinity
15   15M   Infinity
16   *   *
17   0   0
18   0   0
19   128k   177k Measured on the 20k setting
20   249k   2.47k on 20k setting
      
Four Pin Socket   Manual   Paramount 1
      
A1   1027   1029
A2   *   Infinity
A3   249K   248k
A4   1028   1030
      
Nine Pin Socket   Manual   Paramount 1
      
B1   0   0
B2   8.2k   14.9k
B3   249k   2.71k on 20k setting
B4   130k *   268k
B5   0   0
B6   177k *   363 measured on 2000k setting
B7   220   236
B8   *   infinity
B9   *   0

Voltage 240V 300B      
      
Line Voltage   243.7   
      
      
Terminal   Manual   Paramount 1
      
1   440   446
5   71   74
9   175   145.8
10   0   0
      
16   457   472
17   0   0
18   0   0
19   175   145
      
Four Pin Socket   Manual   Paramount 1
      
A1   74.1   78
A2   440   441
A3   Close to 0   2.9 measured on 20v setting
A4   69.2   73
      
Power Supply Board   

Terminal Manual Paramount 1   
      
6V-Red Wire   3.1VAC   2.8VAC
6V-Black Wire   3.1VAC   2.8VAC
      
C4S/soft Start Board   

Terminal Manual Paramount 1   
      
Kreg (A Side)   4.1   4.76 on 20v setting
Kreg (B Side)   6.3   1.86 on 20v setting
OA   300   150
OB   175   146
      
Trimmer Screw Adj.      
      
300k Resistor OB end      143.4
      
Tube   EH 300b   

I have attached pictures of the driver board and the 9 pin socket underneath. For reference I am measuring kregB from the kreg label in the bottom left of image 'Driver Board 1' and kregA to the immediate right of the heatsink in the top right of the image.

kregB connecting to B8

OB connecting to B4

-kreg (A side) connecting to T17U

IA connecting to T16U

Kreg (A side) to B2

OA to B6
 


Many thanks,

Bill

[Paul Birkeland]

For the sake of completeness, I'd swap 5670's to be sure that the weird voltages don't follow a tube.

[Paul Joppa]

Nice, careful documentation - it's a big help, thanks!

Assuming that swapping the 5670 made no difference, here's what I see so far:

The low voltage at OA indicates the regulator output is far too low, and the low voltage at kreg on the B side indicates that's because the 431 is saturated.

I can't get a good look at the B side 431 and its associated R3 (2.49K). From the back side I can't see that there is anything in the 431 holes at all, but it may be just a trick of the light. Anyhow that 431 and associated 2.49K R3 are the places I'd look first. If the R3 is not connected, or the wrong value. If you put the 4.99K resistor in there (instead of in the A side R3, where it belongs) you would get a regulated voltage of 150v, which is what you have - but I'm not ruling out coincidence yet!

[Horatio]

Paul, thanks for the help... I think the resistors are in the correct holes... I have attached a few more pictures to show those areas of the board more clearly. I will re-do the solder joints in the morning (taking snaps of the front and back) and will check the 5670 at the same time. I am currently waiting on more solder being delivered - what a time to run out!!!

Thanks,

Bill

[Horatio]

Ok, solder arrived so I have taken off the driver board, heated every solder point on the back, touched up any on the top that looked like it could do with some more contact. Reattached and got exactly the same readings as before.

Assume this rules out any issue with a specific 5670 as the same issue is showing on both...

I hooked up my second Paramount and it is giving essentially the same readings... Readings listed again for completeness... Along with some more pics of the driver board prior to me reattaching it...

Resistance         
         
Terminal   Manual   Paramount 1    Paramount 2
         
1   *   *   Infinity
2   No Connection   No connection   No connection
3   No Connection   No Connection   No connection
4   No Connection   No Connection   No connection
5   1K   1K   1k
6   1118   1118   1118
7   249k   248K   248
8   No Connection   No connection   No connection
9   124k *   *   *
10   0   0   0
11   3.0M   Infinity   889k
12   5.6M   Infinity   1825k
13   0   0   0
14   9.2M   Infinity   Infinity
15   15M   Infinity   Infinity
16   *   *   *
17   0   0   0
18   0   0   0
19   128k   177k Measured on the 20k setting   177.7 Measured on the 200k setting
20   249k   2.47k on 20k setting   2.47k on 20k setting
         
Four Pin Socket   Manual   Paramount 1   Paramount 2
         
A1   1027   1029   1023
A2   *   Infinity   Infinity
A3   249K   248k   248k
A4   1028   1030   1016
         
Nine Pin Socket   Manual   Paramount 1   Paramount 2
         
B1   0   0   0
B2   8.2k   14.9k   14.96k
B3   249k   2.71k on 20k setting   2.71k on 20k setting
B4   130k *   268k   130k
B5   0   0   0
B6   177k *   363 measured on 2000k setting   364 measured on 2000k setting
B7   220   236   228
B8   *   infinity   Infinity
B9   *   0   0

Voltage 240V 300B         
         
Line Voltage   246.3      
         
         
Terminal   Manual   Paramount 1   Paramount 2
         
1   440   446   440
5   71   74   74
9   175   145.8   148
10   0   0   0
         
16   457   472   465
17   0   0   0
18   0   0   0
19   175   145   148
         
Four Pin Socket   Manual   Paramount 1   Paramount 2
         
A1   74.1   78   77
A2   440   441   440
A3   Close to 0   2.9 measured on 20v setting   6 measured on 2000m setting
A4   69.2   73   72.8
         
Power Supply Board         
         
6V-Red Wire   3.1VAC   2.8   2.7
6V-Black Wire   3.1VAC   2.8   2.7
         
C4S/soft Start Board         
         
Kreg (A Side)   4.1   4.81 on 20v setting   3.98 measured on 20v setting
Kreg (B Side)   6.3   1.85 on 20v setting   1.84 measured on 20v setting
OA   300   148.3   142.5
OB   175   146   144.2
         
Trimmer Screw Adj.         
         
300k Resistor OB end      143.4   142.5
         
Tube   EH 300b      

[Paul Birkeland]

I see 249K resistors on the board where 2.49K resistors should be.  Check your color codes and parts between amps. 

-PB

[Horatio]

Ah ha! I think that may well be it - soldering iron is warming up as I type!!!

Fingers crossed...

Thanks,

Bill

[Horatio]

PB, I think you nailed it... Fixed one Paramount and readings are now spot on... Doing the second while the first sits for 20 mins before trying with music... Fingers crossed!!!

[Horatio]

PB - you were bang on with your prognosis... Resistors swapped and Paramounts starting to sing! Cant believe I didn't notice it - especially looking back on the resistance check...

Thanks again - very much appreciated, as was the help from Paul!!!

Bill

[Paul Joppa]

That was exactly the reason I kept asking for pictures that showed that resistor and the associated 431.

So, the 431 was saturated and the 150 volts being half of the target 300 volts was just a coincidence.

Re "... I think the resistors are in the correct holes..." - yeah we've all been there; I get reflexively suspicious whenever I hear myself saying that. Which I do, all too often! When in doubt, check. Still in doubt, check again. Absolutely certain, get someone else to check for you.

[Horatio]

I think I was thrown by how much it looked like the part in the photograph in the manual when I should really have been trusting the meter / re-reading the text and thinking about the words...

Thanks again for all your help - the end result is nothing short of spectacular!!!

[wullymc]

Congratulations!

I too have messed up on the resistors on the pcb....you're not alone!  I hopefully will be fixing them this week.

Enjoy your sweet music.  Anxiously waiting to hear mine!...