Help Needed BEE PRE

[cjk5933]

I just completed the build of the BeePre Amplifier and could use some help.

I'm getting odd voltage readings on terminal 5 and terminal 20.  Per the Manual I should see 0 volts.  But I'm seeing around 7.7 M Ohms at both 5 and 20.  All of the diodes on the circuit board are lighting up.  And all four tubes are warm to the touch.  The smaller 9 pin tubes glow a bit, but the 300B tubes do not glow at all.

Terminal 4 and terminal 19 read correctly at about 147 V

Any suggestions would be welcome.

 

[Doc B]

Per the Manual I should see 0 volts.  But I'm seeing around 7.7 M Ohms at both 5 and 20.

Does not compute - different units. Are you measuring resistance or voltage?

 

[cjk5933]

Sorry for serious confusion.  I had to run to work.  Multitasking never works.

I spent several hours this morning carefully measuring the resistance and voltage values.

I have 2 bad resistance values.
A1 and B4 should read 'start high, drops to 4 ohm'.
But I measure both slowly climbing to 1 kohm at each. 
All other resistance values are good.

I have 12 bad voltage values:
Terminal  Measured  Should be value
5 7.7 mV 0
7    cycles from +40 to -40 mV 0
12  cycles from +20 to -20 mV 0
20 7.8 mV 0
23 -6.3 mV 0
24 -6.3 mV 0
28 -47 mV 0
37 40.4 mV 0
41 -10.3 mV 0
42 -10.5 mV 0
C2 -6 mV 0
D2 -10 mV 0
All other voltages are good.  I measured the voltage with all tubes hot to the touch.  The 4 LED lights on both circuit boards light up

 

[Paul Birkeland]

There's a big capacitor in the path of getting a good resistance measurement for those terminals, so some variation is acceptable.  Since you did your voltage checks and passed, I'd give it a listen.

-PB

 

[cjk5933]

Thank you for the help.
So those voltage values I listed above are close enough to 0?


I see some other threads with resistance issues at A1/A4 and B1/B4

So here are the resistance measurements with and without the 300 Tubes

With 300 tubes inserted
A1 5.2 ohm
A2 9 Mohm
A3 13.5 kohm
A4 4.0 ohm

B1 4.7 ohm
B2 2.3 Mohm
B3 12.6 kohm
B4 5.9 ohm

Without 300 tubes
A1 1000 ohms
A2 7 Mohm
A3 13 kohm
A4 4.2 ohm

B1 4.7 ohm
B2 9 Mohm
B3 12.6 kohm
B4 1000 ohms

 

[Paul Birkeland]

With 300 tubes inserted
A1 5.2 ohm
A4 4.0 ohm

B1 4.7 ohm
B4 5.9 ohm

Without 300 tubes
A1 1000 ohms
A4 4.2 ohm

B1 4.7 ohm
B4 1000 ohms

I'd move on to voltages.

-PB

 

[cjk5933]

SUCCESS!!!!

I hooked up the BeePre to my system.  Sounds wonderful!

All input channels are working.  Balance and Volume copacetic.

My ambition was to introduce a tube preamp to soften the harshness of my system.  I can hear the improvement.  I'm playing Saint-Saens Piano Trio.  The violins sound sweet without the harsh overtones that were chronic in my system.

The BeePre will replace a NAD integrated amp that I was using as the preamp

My system:
BPT Power Regenerator
First Watt J2 Amp
Yamaha CD-C600
Bottlehead BeePre
HornShoppe Horn

 

[cjk5933]

I purchased the kit in Sept but didn't start work until Dec.

Between work and other obligations I averaged about 1 hour a day so I'd say this was 50 - 60 hours for me.  Your mileage may be different.

The instructions are outstanding.  Every solder joint, every component is detailed and illustrated.  Outstanding!

Only a few hick-ups:
The sent the wrong circuit boards for the filament so I got those replaced

They also sent MJE5731A transistors with too short leads.  This was the most serious issue.  I thoughtlessly installed them on the head sink without even considering the implications. Then, stupidly, I tried to bridge the gap to the circuit board by soldering short pieces of wire from the transistor lead to the holes in the circuit board.  A disaster.  I spent a few hours sucking the solder out off of the circuit board with a cheap barely functional solder sucker and some used solder wick.  They sent a set of replacement MJE5731A transistors with longer leads and I got it together. 

I can't think of any other issues.  I worked slowly and double and triple checked the instructions.  Biggest gotcha with the instructions -- sometimes it states 'attach and solder', sometimes just 'attach'.  Pay close attention to this.

I used a Hakko Fx-888D solder station.  I experimented with different solder tips.  For me, the sweet spot was 12mm chisel head.

I used AlphaFay rosin core solder .032 diameter.  But on some of the ground lugs with multiple wires I used the thicker AlphaFay 31605.  It worked to get all the wires into the solder joint but i end up with solder joints the size of a pea.

As was suggested, I printed a hard copy of the manual in black and white but kept the electronic copy available on a computer because seeing the illustrations in color can provide clearer details and context.

There were many moments when I was mentally calculating the cost of sending a failed kit assembly to Bottlehead for completion. 

By the way, the MJE5731A comes in two packages -- a long and short lead package.  You need the long lead package.

Some of my solder joints look like giant tumors but they work.

If I had to do it again, I think I would invest in a solder/rework station with a good solder sucking function.  Using spring loaded solder suckers and Solder braid is slow and awkward.