Quickie + PJCCS voltages?

[paulw]

Finally installed the PJCCS board into my quickie and re-wired as per diagram.  So now 'D' cell positive, goes through on/off switch to A/B 1&7 tube socket pins & 'D' cell negative to T2/4L and out to A/B5, tube socket pins.

After install, checked voltages again and as to be expected A/B 1&7 are now (due to re-wiring) showing 3.2v and A/B5 is as per the PJCCS manual at approx 2v.  However, tube socket pins A/B6 are at 26v (in line with Quickie manual) but PJCCS manual states 19-20v.

Don't seem to be having any problems except I find the treble a bit 'hard' or 'glassy' compared to the non-PJCCS'd Quickie.  Bass seems more natural & I am getting better imaging, but not really liking the top end of the register too much as it stands.

Paul

 

[Dr. Toobz]

Try rolling the tubes. I had a similar first impression of the PJCSS w/ the supplied GE tubes, but a change to some Amprex Bugle Boys from the 1960's seemed to do the trick.

FWIW, I do feel that current sources are a bit harsher sounding than plate chokes or resistors, but chokes are somewhat non-linear and introduce hum into the circuit, and resistors aren't very good at optimizing gain. So, it's a trade-off either way. Bass definitely benefits from either type of loading vs. a simple resistor. With the S.E.X. amp and Quickie as described, as well as a passthrough/monitor switch I wired into the Quickie, I can't A/B the Quickie with the knob set to unity. That's with the PJCSS....

 

[paulw]

More concerned with clarifying the voltages at the moment.

Of course tube rolling is an option for the treble, but it would have to be something from my stock as I've probably got a lifetimes supply of 3S4's and wouldn't really be looking to get any more.  ;

 

[basb]

Hi All,

Finished my quickie with PJCCS upgrade and although the voltage readings are ok by the PJCCS manual, other voltages are off according to the quickie manual (and these are not covered in the PJCCS manual):

A/B 1&7: 0.5v (quickie manual: 1.2-1.5v)
A/B 2: 19.6/17.1v (quickie manual: 23-25v)

All other voltages are as described in the manual.
Tried different tubes and readings are the same. Is it the PJCCS upgrade, or is there something wrong?

Please help, many thanks!

Bas

 

[Paul Joppa]

My guess is that the D cells are wired in reverse. This is an error in the manual; there are threads about it but I can't find one right now. It really ought to be a sticky.

There are two ways to fix this. I'll give the one that matches the circuit diagram first:

In the manual, where it says on p.21 to connect the black wire from the D cell holder to tube pins 1 and 7, that should be to tube pin 5. On p.24, T2L should be connected to tube pins 1 and 7; same for T4L.

The lazy fix is to put the D cells in backwards.  :^)

The preamp will work either way, it just draws less current when done as intended, giving a longer battery life for the 9-v batteries. I don't recall anyone having a strong preference for the sound one way or the other, but it's certainly an easy experiment to try for yourself!

(The second way to fix it is to connect the red wire from the battery holder to tube pins 1 and 7, and the black wire to the switch. I don't recommend this, only because it is then inconsistent with the circuit diagram in two places.)

 

[basb]

Thanks, the D cell was indeed wired in reverse. Now, almost a year later (!), I made the change and the A5 voltage is now 2V as it should.

However, these voltages are off when using the quicky/pjccs manuals as reference:

A/B 2,4,6: 26.5v (PJCCS manual: 19-21v)
A/B 1,7: 3.3v (Quicky manual: 1.2-1.5v)
T2, T4: 1.9v (Quicky manual: 2.5-3v)

In another thread I found this comment:
"When the battery is fresh, the B+ is 36 volts and the plate voltage is about 28 volts, bias voltage 2 volts at 2mA plate current. That leaves 8 volts compliance for the plate to swing  positive and negative."

If I'm not mistaken A/B 2,4,6 is the plate voltage and T2, T4 are the bias voltage, so are my readings correct after all? I tried with fresh batteries and different tubes, more or less the same results. My PJCSS uses the MJE350.

Best regards,
Bas

 

[Paul Joppa]

I believe both manuals were measured with the reversed 1.5v battery orientation. Once I get a Quickie into my lab, I'll do a more complete set of measurements, and post them in a sticky as soon as possible. We are going to revise the manuals, too. The posted numbers you quoted are from a theoretical analysis, assuming the correct battery orientation.  :^)