Resistance check beepre A4/A1 B4/B1 question [resolved]

[quad]

Hi

I am building a BeePre preamplifier and I am verifying the resistance checks before I put in tubes and plug it in..

I am using the Oct 22, 2014 manual

My question is thus:
on page 60 I see these resistance checks, and these specific ones (from the manual):
A1 starts high, drops to 4R
A2 greater than 1 00KR (OL)
A3 varies with volume/balance settings, could be 0R to 50KR
A4 5-6R with 300B in socket
B1 5-6R with 300B in socket
B2 greater than 1 00KR (OL)
B3 varies with volume/balance settings, could be 0R to 50KR
B4 starts high, drops to 4R

I See this
A1 no 300B in socket, various resistance readings
A2 greater than 1 00KR (OL)
A3 varies with volume/balance settings, could be 0R to 50KR
A4 4 ohms
B1 4 ohms
B2 greater than 1 00KR (OL)
B3 varies with volume/balance settings, could be 0R to 50KR
B4 no 300B, various resistance readings

Checking the manual it looks like A4, B1 are connected to 2 parallel 8 ohm resistors that then connect to a capacitor that is hooked to ground?

What do you think?

Tx for your time.

Carl

 

[Doc B]

Your post is somewhat confusing because it doesn't say whether or not you ever put a 300B in the socket where that is called out, nor whether the various resistance readings at A1,B4 showed a trend of starting very high and getting lower, i.e. heading towards 4 ohms. Assuming the above it looks like everything is working the way it is supposed to.

 

[quad]

With 300B tubes in the circuit I see:
A4 4 ohms (no delay)
A1 5+ohms
B1 4 ohms (no delay)
B4 5+ ohms

 

[Paul Joppa]

That looks right. The two 300Bs have opposite-polarity filaments so you can swap tubes every year or two, extending the cathode lifetime somewhat. I doubt it's a big deal, but for the OCD among us it might reduce stress.  :^)

 

[quad]

Ah didnt see your comment Paul, very interesting, tx!! You mean swap the 300B from one channel to the other?


Am I beating a dead horse? My original question was something like this: let me jump right to my confusion on these specific resistance checks, I will paste directly from my manual to here.

In my manual I see this (I am pasting directly from the manual, as I am trying to understand it and determine if I made a wiring error, or the manual has something transposed)

Resistance checks, p 59-60:
Terminal Resistance
1 starts high, eventually drops to 4R
...
A1 starts high, drops to 4R
A2 greater than 1 00KR (OL)
A3 varies with volume/balance settings, could be 0R to 50KR
A4 5-6R with 300B in socket
...

But on page 52 I see this:
Cut a 2" (50mm) piece of black solid core wire. Strip both ends
¼" (7mm). Attach and solder one end to A4. Attach and solder the
other end to 1 L.

It seems from this information from the manual on page 52 that the resistance at 1L should be the same as A4, since this above step appears to connect 1L with a wire to A4.

Thus I would expect the resistance check for A4 to be the same as for 1, but that is not the case.

In any case I just want to construct a fine working BeePre to replace my aging, but fine in its day, foreplay preamp and am eager to do so!


Tx!

 

[Paul Birkeland]

You haven't ever mentioned what resistance you get at terminal 1, but you've said it's different than A4.  What do you measure there?

Your measurements with 300B's installed are what they are supposed to be, so you should proceed to the voltage checks.

-PB

 

[quad]

I will proceed then. Tx!

I measure 4 ohms at terminal 1 (started higher the first time I measured it and then settled down to 4).

Carl

 

[Paul Birkeland]

Yeah, you're good to go.

-PB

 

[quad]

The new preamp lives and breathes!

Her sound is quite sublime.

Carl