Please Help for my Seduction problem.

[jamestw]

Hey Guys,

I'm a newbie and this is my first time post here. I have my first time to build a kit - the Seduction just completed this Tuesday.
It's my first DIY project, so I did it very carefully followed the kit building guide and the WWA website - thanks for these two very detailed instructions, It was a lot fun during the building.

After built, I got some problems and have back to check 4~5 times these days, but still can not figure out what caused the problem ! I'm hitched here, hope if anyone could guide me to solve these problems...
Sorry for my English language ability is not so good (I'm in Taiwan), I try to express these issues as detailed as I can :


(1)
I've done the resistance checks, I got figures from terminals, as follow :
- All 0 ohm and "*" terminals are same as kit manual suggested.
- Terminal 17, 19, 22, 24 are not in the ranges (lower) the kit manual suggested.
- I can not get the figures from A3,B3 and A8,B8 ,my DVM only can test voltage below 2Meg ohm, these four terminals shown far higher resistances than my DVM can read.

Terminal / Resistance
input jacks / 47.7K (R & L)
17 / 160.4
19 / 170.5
22 / 151.3
24 / 161.2
26 / 995K
36 / 997K~1001K
A2,B2 / 1002K,1000K
A3,B3 / out of reading.
A7,B7 / 47.9K,48K
A8,B8 / out of reading.
output jacks / 476K (R & L, the L were reading 0 ohm at first time, has corrected later.)

(2)
The voltage checks from terminals, as follow :
* My country main power supply is 110V/60hz, I got a stable power 113V from wall. Not sure if this will be a factor, the power transformer come with kit is PT-1.

- The 0VDC terminals are same as kit manual suggested.
- I got far lower voltages from T12, T15, T25, T34, T44.
- Unbalanced voltages on T27,T37 & T29,T39 & T30,T40 & A1,B1 & A6,B6

Terminal / Voltage
6 / 6.0 vdc
9 / 5.3 vdc
12 / 89.2 vdc
15 / 116 vdc
25 / 143.5 vdc
27,37 / 65.2, 87.6 vdc
29,39 / 61.1, 82.2 vdc
30,40 / 60.7, 81.4 vdc
34,44 / 89.2, 89.1 vdc
A1,B1 / 63.7, 85.6 vdc
A3,B3 / 1.5, 1.5 vdc
A5,B5 / 5.3, 5.3 vdc
A6,B6 / 64.6 85.5 vdc
A8,B8 / 1.5, 1.5 vdc

(3)
I built the Seduction directly with C4S upgraded (skipped the original four 18K plate load resistors) and changed 4 caps to M-cap SIO, two for 0.1uf interstage caps, two for 0.47uf output caps, these M-caps all are 1200vdc as I can buy conveniently from local.

When the first time I powered up my Seduction - I still remember how I was so exciting at that time - two 6922EH tubes slowly glow up, then all leds lighted (yes, 8 leds lighted !). However, after about 1 minute or so, a led died.
Then I noticed , on C4S board, two leds have weaker light then the other one.
But, the 4 leds on two tube sockets look all are normal.

(4)
After that, I checked again all the terminals and found the L output jack was shorted by extra solder !
I fixed the L oupt jack, and powered up Seduction again, all leds started to light... then, again, the same one led on C4S board, died again (and it never back again). There remained total 7 leds kept lighting.

(5)
Next day I checked again all the components, connections, and done the resistance, voltages checks, I can not find where's wrong, the figures from checking are same as before (except the L output jack, now it's fixed.).
Powered it up again, this time the second led one C4S board died, now I got two leds no light, the are two closed to 2N2907 and MJE350 transistors on C4S.
I connected Seduction with turntable and preamp, there is only R channel sounded, the L channel does no any sound.


I kept check the constructing and want to figure out, till now, the problem still there.
I'm thinking, maybe I should go back to original Seduction constructing, disassemble the C4S and put four 18K plate load resistors on ? But before do this, I really want to know where is the problem now in my Seduction.

A lot appreciate, any suggestion could guide me fix the problem.
Please help, thank you guys.

james

[Grainger49]

Ok, you should post the expected voltage or resistance reading next to the actual reading.  There is no need to post anything that is 15% high/low as that is the tolerance expected with varying input voltages.  With yours expect slightly low readings.  But the +/- 15% still applies.

Since you have sound from the right channel you only need to post the left channel readings that are out of the expected range.

The immediate thing I see is you put in the C4S and you will not get the proper resistance readings through the dead (no voltage on them) boards.  So A & B 1 & 3 can not be measured for resistance.

Don't disassemble it till you make a few checks first.

[jamestw]

Thanks, Grainger,

So now only the left channel I have voltage readings that out of +/- 15% ranges as follow :

T37 / 70 vdc ... I got 87.6 vdc
T39 / 70 vdc ... I got 82.2 vdc
T40 / 70 vdc ... I got 81.4 vdc
B1  / 70 vdc ... I got 85.6 vdc
B6 /  70 vdc ... I got 85.5 vdc

Though the right channel does sound, but the T12/135vdc that I got only 89vdc that is far lower, is it OK ?

I'll back to do more checking.

james.

[jamestw]

... also attached a photo.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.bikedomeworks.tw%2Febay%2520images%2F2.jpg&hash=2c1d4488110a1cadb9143f7480707d66b4ca12ad)

james

[Grainger49]

Ok, if T12 is good and every thing attached to the left channel plates (T37, T39, T40, B1 & B9) is high what reading are you getting at B3 & B8?  You had posted 1.5V DC.  Is this still right?  Do the LEDs on those terminals light up?

Everything you listed is the left channel after the plate load C4S circuits.  Are the LEDs on the C4S board on the left channel out? 

[Doc B.]

Hi James,

It is possible that one or two of the 2N2907 transistor metal cans are touching a PC board trace. You might check for that and if it looks like the problem, try reheating the solder pads that the transistor is soldered to and lifting it up from the PC board a tiny bit. That PC board is one of our very early designs (we have been selling that kit for something like 10 or 11 years now!) and that has been an occasional problem.

[jamestw]

... from another view.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.bikedomeworks.tw%2Febay%2520images%2F3.jpg&hash=a3fb912b8d8e8bdb24b9f2a89e1d8ac6723ff2fd)

james

[Grainger49]

That is nice and very neat work.

[jamestw]

Thanks, Grainger,

Are these two died leds on C4S at photo that indicate the left channel ?
I was try to see the underside of C4S board, but can not for sure, unless I disassemble the board.

james

[jamestw]

Thanks, Dan,

I'll do these to lift 2N2907 transistors up a little bit.
I did a similar thing as you suggestion but I focused on two died leds that I though they might have their tiny silver plates underside are shorting two trace holes, as two holes for led's leads are so closed.
So I've lifted two leds up a little, though, the problem are not on leds obviously.

james

[Grainger49]

James,

There are two LEDs on the C4S board for the left channel and two on the tube socket for the left channel.  Your pictures don't show but 2 of the 4 LEDs on the C4S board lighted.  I expect those would be for the working right channel.  In the first picture I think can see all four LEDs on the tube sockets lighted.  

If you have 1.5V on both tube socket's pins 3 and both tube socket's pins 8 then the problem is most likely on the C4S board.  That board must be passing some current for the left channel's tube socket LEDs to be lighted.  But the problem is on the board.  

[Doc B.]

Actually it appears that one LED is out in each channel. I think you have two different problems - one is that the LEDs aren't lighting which means the C4S loads are not working right - the other is that there is some problem in the left channel around the RCA jacks or left channel tube socket that is blocking the signal.

For the LED problem, start by unplugging the preamp from AC mains and lifting up the C4S PC board from its nylon standoffs and rotate the PC board so that you can use your ohm meter to test resistance between each pair of the three solder pads that each transistor is soldered into. There should be no readings lower than about 1000 ohms. If you find any reading under 100 ohms that transistor may be blown. Sometimes the 2N2907 can blow if it touches that copper trace under it.

To find the problem with the left channel, start with the easy things. First swap the tubes between the sockets and see if the problem follows a tube. If the tubes are OK (I think they are OK, because your voltage readings are not perfect, but they do show that the tubes are drawing current and lighting the LEDs on the tube sockets), then with the Seduction switched off and unplugged from AC mains take your ohm meter and measure the resistance between the center pin of each RCA jack and the outer shell of the same RCA jack. The output jacks should read about 470K ohms and the input jacks should read about 47K ohms. If any read around 0 ohms there is another shorted jack like the one you already found, that needs to be fixed. If the RCA jacks are all OK, then carefully check the wiring of the resistor and capacitors on the terminal strips to make sure they are all on the correct terminal and no solder joints were missed.

[Paul Joppa]

I agree with the value of swapping tubes to see if the problem moves, which would confirm my theory:

I think the main problem is the low power line voltage, and consequently the low heater voltage. See if you can find a low value resistor, in the range 0.39 to 0.68 ohms and rated 1 watt; place that resistor in parallel with the 1.2 ohm resistor in the power supply (T6 to T9). This should raise the heater voltage (T9, A5, B5) into the range 5.7vDC to 6.0vDC. You can adjust the value of this resistor if it seems to be too large or too small.

The low heater voltage makes the cathode too cold and unable to produce enough electrons, so the plate voltage rises. The plate voltage is the same as the power supply voltage (around 89v) on two triodes, so the C4S does not have enough compliance and that extinguishes the LEDs. The power supply voltage is high enough at first, before the tubes begin to conduct, but then the tube current pulls the power supply voltage down.

Another problem is that the power supply voltage drops too much between terminals 25 and 15. There should be a 1000 ohm resistor between those two points. Either that resistor is too big it should be easy to measure), or something is shunting extra current to ground at T15. There is a resistor of 270K in parallel with a capacitor of 220uF, both from T15 to ground (T14). Make sure the capacitor is oriented correctly (negative terminal with the stripe on the side goes to T14) first. If that is correct, then see if the resistor is 270K ohms. You may be able to measure the resistance T15 to ground if you leave the meter connected for a long enough time; you may have to measure it in both directions (the diodes can cause a false reading), or you may have to disconnect the resistor at one end to get an accurate measurement.

[jamestw]

Yes Grainger,
Four leds on two tube sockets are lighted, and A3, B3, A8, B8 voltage readings all are 1.5v.
Looks I have to lift C4S board and check it...

Thanks Dan,
I'll go for C4S board checking first.
Switching tubes on both sockets that I've done few days ago, but it not make difference that still only right channel sounded, left channel keep quiet. I did not measure voltages after tubes switched, I'll do it again and check the readings.
Both input RCA jack resistance readings are 47.7K, and both output jack readings are 476K. They are OK.

Yes Paul,
Both power supply voltages really bother me, they are low and I don't know how to do them...
Thanks for the tips, I'll check and try to fix them.


Thank you guys, if without you I don't know how to start to do with these problems
I'm going to do these ways, will report the results later :-)


james

[jamestw]

Another problem is that the power supply voltage drops too much between terminals 25 and 15. There should be a 1000 ohm resistor between those two points. Either that resistor is too big it should be easy to measure), or something is shunting extra current to ground at T15.
There is a resistor of 270K in parallel with a capacitor of 220uF, both from T15 to ground (T14). Make sure the capacitor is oriented correctly (negative terminal with the stripe on the side goes to T14) first. If that is correct, then see if the resistor is 270K ohms. You may be able to measure the resistance T15 to ground if you leave the meter connected for a long enough time; you may have to measure it in both directions (the diodes can cause a false reading), or you may have to disconnect the resistor at one end to get an accurate measurement.

Okay, Paul,
T25 & T15, and T12 & T15, both have a 1001 ohm resistor reading I just measured there.
The 220uf cap orientation is correct on T14 & T15 with " - " connect on T14.
I clipped " - " of meter to chassis ground post and "+" on T15 of 270K resistor it parallel with 220uf cap, the reading started from about -360K, to -100K, to 0 K, resistance getting rise and slower and slower, took about 18 minutes the reading stopped and stayed on 278K.
I guess it's OK :-)

I'm going to inspect the next...

james