Seduction complete - a few voltage questions/concerns

[Laudanum]

I finally completed Seduction with C4S board last night.  Resistance measurments checked out fine and voltage measurements for the most part as well with a couple of questions/concerns.  BTW, line voltage at time of measurments was 120 VAC.  And, I measured using the included EH 6922 tubes.

Im listing voltages as Expected / Measured on the few I have questions/concerns about.

Terminal 6 - 6.5vdc / 6.42vdc
Terminal 9 - 6.0vdc / 5.6vdc
Tube Pins A5 and B5 - 6.0vdc / 5.6vdc
With only being less than .1vdc low at terminal 6, i didnt expect the .4 volts drop at terminal 9. And, if Im correct, the 5.6vdc measured there corresponds directly with the 5.6vdc at the both tube pins 5 which I think is maybe a little too low, atleast not optimal anyway, right?  If I remember right, the 6922's nominal heater voltage is 6.3 volts but Seduction was designed for 6 volts to extend tube life???  There wasnt much tech. detail supplied with the C4S upgrade so Im not sure whether that voltage is supposed to be a bit below 6.0vdc with the C4S upgrade installed.  I have a feeling that advice will be that 5.6 volts is a little low and I should increase it but I'll wait on experts for details and advice.

Also ...

Terminal 12 - 135vdc / 120vdc
Terminal 34 + 44 - 135vdc / 120vdc
Terminal 15 - 148vdc / 137 vdc
Terminals 12 as well as 34 and 44 are only a little over 10% low so it's fine according to the 10 - 15%  variation listed in the manual as acceptable/normal.  But I was wondering what would cause them to be a little low.  My line voltage at the time of measurements was 120vAC.  Terminal 15 is under 10% low so even less variation.  But again Im just curious for info here.

So, does it seem ok?  ... should I drop the value of the 1.2 ohm 3 watt wirewound resistor?  If so, I dont know the math ... maybe a 1 ohm?  Or is it fine at 5.6 volts.  If it's borederline, I'd rather raise it to as close to optimal as possible.

Thanks

[Grainger49]

Desmond,

All voltages are less than 15% off, go listen to music!

Individual component variances can cause voltages to be something other than expected.  The test unit might have had a few out of tolerance circuit elements in it.   

Terminal 12 is just an intermediate stage in the power supply filter.  The end of the filter, terminal 15 is closer to target.  See how things even out?  If you had a bad problem with T 15 then you would really care what is on T 12.

Now go listen to some vinyl!

[Laudanum]

I figured those voltages were fine being with 15%.

My main question was with the 5.6 volts on terminal 9 and on pin 5 of both tubes.  Isnt 5.6 volts a little on the low side for the filament voltage?

Thanks Grainger

 

[Grainger49]

Desmond,

Pin 5 to circuit common/ground should read the same 135V that you get on T12 because of the biasing circuit.

Measuring from pin 5 to pin 4 should give the 6.3V for the heater.  If that is where you get the 5.6V then check the voltage dropped across the 1.2 ohm resistor between T6 and T9.  Nope, I don't have a voltage for T6.  But measure the resistance of that resistor.  It can be trimmed by paralleling a resistor.  Post how much voltage is dropped across it and we can guess at a parallel resistance to bring the voltage back in line.

[Laudanum]

Hey, atleast I understand what we are looking for here ... 

I posted the voltage dropped in the first post.  Terminal 6 should measure 6.5vdc, I measure 6.42vdc.  T9 should measure 6.0vdc, I measure 5.6vdc.  So it's dropping about 0.8 volts.  And that is the same voltage I measure at pin 5 ...  5.6vdc.     I just dont know the math to figure it, I should but I dont.  But I think that you need to know the current to figure it, right?  Where does the current figure come from, tube specs?

Thanks Grainger

[Grainger49]

Did you measure the resistance? 

It looks like you have a good voltage coming out of the rectifiers, assuming your meter measures RMS voltage.  I have one that does and one that doesn't it makes a difference when looking at this voltage.

So, the drop through the resistor is too much, lowering it will require a resistor in parallel.  The trick here is that as the voltage across the heaters changes the current through the heaters changes non-linearly.  So it is a kind of guess.  To get there I need to know the resistance you measure.  If your meter has scales to select it would probably be the lowest. 

[Laudanum]

It's a 1.2 ohm 1% resistor but it actually measures 1.3 ohms (on two meters).  Unfortunately, my true RMS meter died years ago and neither of two meters I have now are true RMS.

EDIT ...  It's 1.2 ohms, my leads added .1 ohm.  I dug out the old true RMS meter which did work, to my surprise.  Anyway, Voltages are the same as measured with that meter.  At 121 volts AC line voltage there is 6.42 volts into that resistor and 5.6 volts out.  At 114 volts line voltage, there is 6 volts into that resistor and 5.2 volts out.  So, it's pretty darn sensitive to voltage fluctuations.  My gear is plugged into a power conditioner with voltage regulation that kicks in when the line voltage drops to around 113 volts. 

Thanks

[Grainger49]

After several calculations I get that you need to parallel a 1.7 ohm resistor with your existing 1.3 ohm resistor.  This is still going to be a little off since the current relationship is not linear. 

I calculated that you have 0.6833A, with a drop of 0.82V drop.  The resistance I calculated that you needed was 0.7317 ohms.  That is quite a way off of the 1.2 that is in the kit.  So I'm wondering if I got it right.

[Laudanum]

I posted an edit while you were posting. 

But I'll just clip the reistor in and see what happens before soldering.   I dont know how much the tubes come into play but I read they have an effect.  I wont be using the EH's.  Im going to plug in some 6H23EV's that I have and I'll re-measure.  I wonder if I should be shooting for a little higher voltage since it seems pretty sensitive to the line voltage.  The drop is consistently about .8 volts but it drops down to 5.2 volts at the tube when the line voltage drops to 114 volts.  I read that 5.7 volts to 6 volts is ok for the Seduction.  Maybe I should shoot for a little higher voltage when line is at 120 so that Im not too low when it's at 114 or so.  Or maybe Im just overthinking it ....

Thanks kindly Grainger.

[Paul Joppa]

First, see if you can confirm that all four Schottky diodes are working and soldered in correctly and tightly. The somewhat heavy leads on them can take longer to heat with the soldering iron sometimes, leading to unexpected cold solder joints. If there is a problem of this sort, it would explain the lower HV measurements as well.

The resistor does not behave as you'd expect because it is in a mix of AC and DC currents. A change of 0.1 ohms will change the voltage about 0.1 volt - i.e. as if you were drawing 1.0 amp instead of 0.62 amp (the 6922 nominal draw).

[Laudanum]

Hi Paul.

I replaced the EH 6922's with the 6N23EV's which are the tubes I planned on using.  The other voltages that I mentioned are still about the same, 10% low or so but the tube heater voltages came up.  Checking with the line voltage at 116 volts I had right at 6.5vdc at T6 and 5.86 at T9.

I checked the Schottky's and they are oriented properly and solder joints looked fine but I re-wet anyway.

Whatcha think ... just component tolerances with the 10% low higher voltage readings or something to worry about? 
Are the tube heater voltages ok at 5.8 - 5.9 vdc or should they come up a hair?  Im betting that they are at 6 volts or a hair above when the line voltage jumps up to 120V (or when it drops and my AVR corrects it up to 120 volts).

Thanks


PS.  Seduction sounds great by the way.  I've only been able to spend a half hour or so listening but she's quiet, no noise at all that I could hear, and she sings.
I need to get Foreplay built so I can quit the cable plugging and unplugging to switch sources.

[Paul Joppa]

Looks like one or both of the EHs are drawing more than the spec 300mA or 310mA.

The design target was 6.0 volts, +/- 0.3 volts. Most tubes are made to be OK with -10%, or 5.7v, minimum.

If the voltage goes too high, the cathode material is more easily deposited on the grid wires, increasing grid leakage current and creating some noise. The target was intended to be sure that does not happen. (High voltage also shortens the life of the heater, of course!)

If the voltage goes low, the grid emission is reduced. This is most important when the plate current is near the maximum rating, because the space charge can be depleted, allowing ions to bombard the cathode and poison it. A high plate voltage makes this worse by increasing the velocity of any ions. In Seduction they are drawing a bit less than 4mA, and the spec maximum is 20mA, so maintaining full cathode temperature is not as critical. I calculated approximately a minimum heater voltage of 5.4 volts for full performance at 4mA; the calculation is crude so I settled on 5.7 as a reasonable minimum.

[Laudanum]

Thanks for the explanation Paul.  Looks like Im ok with the 6N23's as far as heater voltage goes.  The 120 volts at T12, 34 and 44 is just over 10% low and Seduction sounds great .  Maybe just tolerances of the Schottky diodes ? ...  Unless you, Paul, or one of the smart ones thinks I should be concerned about it,  I guess Im good to go.

Thanks