voltage measurement problems after output upgrade BeePre 2

[denteom]

I finally finished the upgrade but ran into some problem. I noticed immediately the D tube is dim compared to the C tube. Do I need to plug the D tube deeper and not getting enough contact? (It's a daunting task plugging these small (6CM7), feels like it might break. The 300B glow looks equal.  When I measured the voltages at terminal 45 I get 6.5 vdc.  But terminal 60 voltage went up to 7.8 vdc.  The LED on the output upgrade PCB all lighted up bright and equal intensity.

Also not sure how to measure kREG voltage. Is the black lead still connected to 4u and use the red lead to measure kREG? positive or negative terminal. Or do I remove the black lead at terminal 4U then measure kREG (-) with black terminal and kREG (+) with red terminal?  Not to sure about this.

The voltage at Terminal 46 is 175 vdc while terminal 51 showed 225 vdc.

 

[Paul Birkeland]

To measure Kreg you use the red probe just like all the rest of the measurements.

I would list the OA, OB, KregA, and KregB voltages on the new boards.  The glow intensity of the 6CM7 can change substantially from tube to tube, so that's not necessarily indicative of a problem.

 

[denteom]

Thanks, what about the voltage imbalance between the two halves? it's kinda wide difference, need to troubleshoot anything?

 

[Paul Birkeland]

It would be good to know the IA, IB, OA, OB, KregA, and KregB voltages on that upgrade board before being concerned about the other voltage difference.

 

[denteom]

Found the problem it is the Kreg B.  But what should I do?

Measuring voltage at
Terminal 45- 6.4 VDC
Terminal 60 - 7.2 VDC
Terminal 46 -  175
Terminal 51- 210 VDC
IA 220 VDC
IB 230 VDC
OA 175 VDC
OB 220 VDC
KregA 8.2 VDC
KregB 200 VDC

 

[Paul Birkeland]

The KregB tells me that the 431 regulator on that side is deceased.  You also either have a massive miswire on that side of the PC board, or possibly that the resistor on pin 8 on that 6CM7 socket isn't well connected to ground.

 

[denteom]

Finally I got it right it was just the black solid wire connecting -reg to bB one end went loose
The new measurement are now spot on:
voltage at
Terminal 45- 6.4 VDC
Terminal 60 - 6.4 VDC
Terminal 46 - 175 VDC
Terminal 51- 175 VDC
IA 215 VDC
IB 215 VDC
OA 175 VDC
OB 175 VDC
KregA 8.2 VDC
KregB 8.2 VDC
I'll give it a listen in a while

 

[denteom]

Having problem with sound.  The volume became very soft and muffled with either using RCA or XLR.  Before I was already okay with the third coarse notch.  There is also an audible crackling sound.  It is the same using a power amp to speakers, or to a headphone amp. I thought my problems are over. How do I trouble shoot this?

 

[denteom]

The left channel sounds slightly softer.  It sounds like a bad sounding radio.  kinda lost it's life,
.

 

[Doc B]

Did your voltages change when you discovered this problem?

 

[denteom]

I did listening after the voltages were already correct. If you mean to check it again I have not taken it out from the audio chain. I will check it again later after work.  Just the voltage checks found on the output upgrade manual? No need for additional voltage checks?

 

[Paul Birkeland]

I would still measure OA and OB on the large C4S board installed with the attenuator upgrade.

 

[denteom]

I got almost the same values
Terminal 45- 6.2
Terminal 60- 6
Terminal 46 175
Terminal 51- 175
IA- 215
IB- 215
OA- 175
OB- 175
KregA- 8.2
KregB- 8

 

[Paul Birkeland]

Could you check OA and OB on the large C4S board with the heatsinks?

 

[denteom]

The  from the C4A board (BeeTwo Quiet)
OA 115
OB 115

 

[Paul Birkeland]

Well all your tubes are working properly.  When I have run into issues like this, usually it ends up being input/output wiring issues that are causing the problems. 

It may help to post some build photos and we could look at what you have built.

 

[denteom]

Nice to know the voltages are fine.  I don't think it is the input. Have checked that before during the initial build and the upgrade one, have already fixed the problem, already re-enforced, added additional solder to the inputs and was listening to the unit prior to the second upgrade and it was fine.  I think it is the output since we de-solder and resolder again with added xlr.  Hope these photos can tell what the problem is.

 

[Paul Birkeland]

With the preamp running, play a 60 Hz tone into it using an 1/8" TRS to RCA adapter and an old phone or a computer as a source with the volume control turned all the way up.  Turn the level controls to maximum, then set your meter for AC volts and measure the AC voltage at:

1.  Pin 3 on each 4 pin socket
2.  The center post of each 9 pin socket
3.  The center post of each output RCA jack

That will give a good idea of where the signal isn't getting through.

 

[denteom]

Does the trs in one end headphone and the other end in stereo that is 2 RCA or the more common, 2 ends in TRS which commonly used in battery powered portable speakers? Then I plug it in the inputs? Will the small TRS be easily be plugged to the line in (no need for adapters)? If  it ends in a single TRS where do I plug it on the red side or on the (white or black side of the line-in?)

 

[denteom]

Also can can the problem be also due to poor contact on the nine pin tubes? Not sure how hard should I push.  The pins are so tiny unlike the one on the 300B which is easier to push through the socket.  They should build sockets like the ones on PC computer, with zero insertion force. hahahah...