Heater battery connection

[cpaul]

Well now I'm feeling a bit of a dimwit, but the manual that came with my recent quickie shows the negative pole of the D-cell going to tube pins 1,7 and the positive from the power switch to tag strip 1 and then to pin 5.  I wired it as the manual instructed figuring that the manual would have been updated by now.  But when I re-read an earlier post, PJ said to make sure to wire the NEG pole to pin 5, with positive presumably to pins 1,7 in order to maintain the correct operating point.

I think I read more about this in other threads, but can't find them now.  Can someone please clarify for me the correct wiring and what happens when the orientation of the heater wires is backwards?  It's odd to me that the orientation on a floating heater circuit would have any impact, but I've never used DHTs before.

BTW, I'm still impressed by the sound quality of the quickie thus far.

Thanks,
Carl

 

[Grainger49]

I can't tell you the official orientation.  But can tell you that the answer was just to reverse the battery.

If the heater is not attached to the high voltage, plate voltage anywhere I do not see a difference.  

 

[cpaul]

Thanks, Grainger.  It isn't attached to the plate voltage, but it IS the same as the cathode, and sets the cathode operating point (since it's directly heated).  If the batteries are backwards, I'd guess that means the cathode voltage is negative, and I would think more negative than the grid, hence you'd get grid current (?) and make a mess of the bias/operating point.  But I really don't understand this situation much and it's hard to wrap my head around it.

It's probably easy enough for me to switch the D cells to test how it works, but I'm really looking for the proper wiring here.  In short, I assume the manual was never changed?  And if not, was there a reason (e.g. there isn't a problem either way - and if so, why not?)?

Thanks again.

 

[Paul Joppa]

I can't recall if the manual was changed yet or not. Doc is a little overloaded this week and next, but I hope he will answer this eventually!

I do recall my post, which is still correct - I tried to describe the orientation independent of the manual description.

The heater/filament is the cathode, and there is a bias resistor from one end of the filament (pin 5) to ground which drops about 2.0 volts with fresh batteries. Pin 5 should be the negative end of the D-cell, according to the data sheet. So the cathode potential varies from +2v to +3.5v along the filament, while the grid is grounded. This gives a grid bias that is the reverse. If the D-cell is reversed, then the bias is 0.5v to 2.0v along the filament, leading to greater plate current and shorter life for the 9-v batteries.

In practice, this has not been a huge difference and the preamp seems to work OK either way - but what I describe is how it was designed to work, and how the data sheet specifies the connections.

I do not know why the specifications make the distinction but I presume there was a reason back in the day, so they should probably be followed.

 

[cpaul]

OK, more dimwit here, but if I want to re-wire instead of flipping the batteries (I'm in mid stream right now), in order to keep the RC below the cathode also tied to the negative pole, the best bet would be to wire the negative (black) to the switch and the positive lead to pins 1,7.  If all else stays the same, that should work, right?

 

[cpaul]

Oh, and on another note, I was going to experiment with soft-start and soft turnoff, and was reviewing PJ's suggestions of caps for this.  For turnoff, PJ suggests a 1000uF/50-60vcap from the B+/high voltage to ground with neg end to ground.  I thought I'd solder + to the out lug of the switch and - to T3 (though that's getting crowded with the PJCCS installed), correct?

And for the turn-on, he suggested 1k-5kuF across either the 4k resistor on the CCS (both channels) or across both the resistor AND diode (adding a bleeder resistor, which would seem to provide a current path across the resistor/diode combination - hmmmm...).  When I look at the PCB, I now notice on my old version PCB (see post in PJCCS thread) that the B+ seems to go directly to the diode and not the 4k resistor first, as the schematic shows.  Could this be a difference in the old vs new PCB?  Note that I wired according the instructions for the current board, so diode went into D1 position.  It's that position that has a trace from anode (non-banded end of diode) to the I terminal (B+).  Or is the schematic in the manual incorrect, and the B+ should go through the diode, then into the 4k resistor, then to the Base pin and 120k resistor (or perhaps it doesn't matter which is first, diode or 4k resistor)?  The far end of the 4k resistor on my board is tied to both the 120k resistor and the Base pin  Aaaaacccckkkk.  I'm SO confused! 

If there were a schematic/diagram for the old PCB, that would probably help me out.  Maybe it's silly, but I was hoping to use the old PCB so Doc and the Queen wouldn't have to ship out another.  Seems like I learn a lot more that way too.

It's late so perhaps I'll wait for some answers before going on tomorrow.

 

[JONO]

Hi Carl

I had the same questions with my Quickie. I posted in Quickie satisfied costumer http://www.bottlehead.com/smf/index.php/topic,594.0.html my findings. I estimate my first battery "pack" live duration a little over 200 H in this configuration. Sounds great!

Jono

 

[cpaul]

Jono, thanks for the link and estimated time running.  I've fixed the filament wiring per PJ's posts but haven't yet tested voltages.  All works beautifully now, and while I thought at first I heard some negatives on the PJCCS (mostly great, but a little dry), I'm now starting to revise my thinking.  I'm enjoying it more and more, and all it's strengths are just getting stronger.  Component burn in?  Ear burn-in (I'm getting used to it)?  Something else?  Who cares.  This has got to be the best $100 ($135 with PJCCS) investment in audio...period.  Certainly is for me, and I'm a dyed-in-the-wool from scratch DIYer. 

Carl