Revisiting voltage (and sound) issues

[smithanh]

Been a busy summer and fall and I'm finally getting back to sorting out problems with my Seduction. I'm still getting bad voltage readings (see below) after taking to a local tech who redid all the solder joints. I've gone back through my construction and did replace all the diodes in the Schottky bridge (had one in the wrong direction and it smoked). Also got a new tube, but that didn't fix the problems. I'd appreciate any insight or direction of things to check/replace. I'm just an amateur, but would like to fix it myself.

Here are the voltages that are off the specs ...

Terminal    Spec     Reading
7                  0          1.6
26,36            0        1.8, 1.5
27,37           70        74, 62
28,38            0         .4, .2
29,39           70        74, 62
30,40           70        74, 62
35,36            0          .2, .2
A1,B1           70        75, 61
A2,B2            0        2.6, 2.0
A4,A5            0        3.4, 5.4
A6,B6           70        72, 61

Some of the discrepancies seem to be from a tube as when I swapped them, the readings swapped as well (such as 29,39 and A1,B1). And it seems that there is still a ground plate issue, despite the local tech resoldering all the joints.  i should add that i have the C4S upgrade. I don't know how to go about testing for specific problems with individual components. Any suggestions for what to attack first? Also, the sound is still really dark and muddy.
Thanks,
Andy Smith

[Paul Joppa]

The plate voltages (nominally 70v) are close enough, indicating that things are working more or less OK The differences are due to tube variation and are not important - anything from 50v to 90v is OK, as long as the four LEDs at the tube sockets are glowing.

I suspect the small voltages that should be zero are millivolts (mV on the meter) not volts. This is a very easy mis-reading to make on an autoranging meter! So most of them may well be close enough to zero. The only one that bothers me is A5, but I think you probably meant B4. Check those readings first.

If the above is right, then the tubes are operating OK and we just have to track down the dark sound. That would most likely be an error in the RIAA equalization network. I'd first check the resistance between 29 and 30, and between 39 and 40. It should be 9.64K (9640 ohms) within a percent or two, it's just the resistor there. If the resistance is much smaller, it could pull the treble down more than 12dB. Another error that would have the same effect would be exchanging some of the three capacitors - 0.010uF and 0.0012uF from 29 to ground (and 39 to ground) and the 0.033uF from 30 to ground (and from 40 to ground). It's so symmetrical that it's easy to make the identical mistake on both channels

[smithanh]

Thanks Paul, I'll check those measurements first. No problem that the differences between the tubes is that large? Also, those were milivolts at the terminals that should read "0", I was concerned that they are consistently there at several points, and wondered if there may be another issue with the ground plate.

[Grainger49]

Andy,

The instructions typically say not to worry about variations of plus or minus 15%  On all readings, that are not 0V, you are very close to the targets.  

I guess the quandary is what is +/- 15% from zero volts?  

If Paul's guess above is correct, and that is very likely, you are spot on.  If you are reading whole volts (except 28/38 and 35/36 they are OK) you have a grounding problem that allows these points to be above ground.  Typically you wold read 0.1V maybe 0.2V and consider that zero.

[smithanh]

The resistance between 29 and 30 (and 39 and 40) is 1026F, I can barely read the number on the resistor because of how it is soldered, but it looks like "0902". Did I put the wrong resistors in there?

[smithanh]

Too early in the day to be philosophical, especially if one is not getting paid for it! Thanks for the editing tips (my last post magically disappeared!), any idea about this resistor?

[Grainger49]

Ok, that resistor should be 9.31k ohms.  It is part of the passive RIAA equalization.  I don't see why you couldn't measure the resistances directly, there is not a capacitor in parallel with them.

Did you verify that the voltages that were not zero were reading in millivolts?

[Paul Joppa]

1026F is a very high temperature, but not a resistance. If it's around 10K ohms (i.e. the "F" is a digit rather than a misprint) then it's probably right and the meter might be off a bit. If it's around 1K then it's way to low and probably the wrong value. In that case, unsolder one end and measure, to be sure it's not anything else but the resistor.

[smithanh]

My degrees are in political science, not REAL science!

After reading the instructions on my multi-meter and re measuring, the resistance is 9.31k ohms between 29 & 30 (and 39&40). I poked around and measured the other resistors and they're reading correct. The capacitors from 30&40 appear to be correct too (they are printed 122K and 104Krespectively).

[Paul Joppa]

Bingo! You got the wrong part, contact Eileen tomorrow. 104K is 0.10uF, it should be 0.010uF. That's costing you 20dB off the treble, no wonder it sounds dark!

[smithanh]

Thanks! I'll let you know how it goes.

[Grainger49]

Andy,

Packing errors at Bottlehead happen very seldom.  Knowing that they batch kit packing it appears they only put out the bins that will be used for the kit they are packing. 

I'm just saying that in 12 years of my being around this is the second instance.  Keep the faith.  It is more often that a new builder swaps parts in a kit. 

[smithanh]

No problem, all of the parts look about the same to me!

[Paul Birkeland]

Hey Andy,

Eileen is shooting those parts out to you today.

Can you be sure that you have 0.1uF coupling caps in there?  If the 0.01uf caps got put in there, you'd have dark treble and absent deep bass.  These go between 26/29 and 36/39, it'd be a good idea to check that just in case.

-PB

[smithanh]

Paul, PB, Paul & Queen Eileen,
Mae maxima culpa!

PB, I DID have the two caps swapped in both channels. Paul, you're back to only one occasion when the wrong part was sent. And Eileen, I'm glad I had a chance to talk with you yesterday, but I hope that you haven't sent those other caps yet.

I understand that you're updating the manual for the Seduction and I recommend that you either take photos of the individual components or print the numbers that are printed on the individual caps (etc.) on the parts list or in the instructions. This would be very helpful for amateurs like me who don't know a cap from a resistor.

But thanks for all of your help and patience in getting me through this.  It sounds beautiful!
Andy