cs4 voltage problem

[John]

Many Thanks Paul,  No problem on the delay as you are helping me.   I found no shorts  between C1, C2 and C6, C7.  I next removed the C4S boards and triple checked the Terminal strip wiring, and rewet all C4S solder joints.  When unit was reassembled still had same problem of low OA voltage.  I next removed tube A,B, and C and voltage raised to around 136 volts.  I think my next step may be to remove and test transistors on C4S board although that will have to wait till Monday.

Tons of thanks for your help
Charette

[John]

Here is a picture with C4S's  boards removed.  All sockets where tested for tubes A,B, and C.

Thanks Again.
Charette

[Paul Joppa]

Bingo!

If the voltage at the plate terminal (2, 7) rises to 136 volts with the 6922 removed, then the current through the 47K resistor to ground is 2.88mA - which should be the value on the OTHER SIDE of the PC board. Check the R1 which should be 113 ohms on the A side, and 301 ohms on the B side. I think you have 301 on the A side, but check both. You must have built both boards the same way.

[2wo]

That gets my vote for "Deerstalker" award for this week...John

[John]

Many Thanks go out to Paul.  I did reverse the 113 and 301 ohm resistors....bad me.  Unit fired up and passed signal,  however one last problem.  Gain mismatch with -30db input @ 1100 hertz signal on both channels I get output reading of 13.66 db on the left and 20.25 db on the right.  This ratio stays consistent across the full frequency spectrum of frequencies.  6 db is a great number in balanced audio as pin 2 or 3 could be dropped but I am at a loss for this problem.  I have change positions of the pentodes and tried a new dual triode to no avail.  All DC voltage look equal except for the usual variations in Kreg which measure around 1.7 volts.  Oh boy.  Any ideas.

Many thanks
You guys have been the best
Charette

[Doc B.]

Did you also maybe swap a 47K input resistor for a 470K output resistor on one channel?

[John]

nope  47k ohms on input  470k ohms on output.

[John]

wow measuring 55 ohms across input RCA with 47k ohm and red wire disconnected form tag board to ground.  Does nylon washers go to junction of heater noise caps?

[John]

My nylon washers are on the audio ground and not on the heater noise caps.

[Paul Joppa]

Post is unclear - do you mean the RCA jack measures 55 ohms all by itself? In that case you probably have a solder blob or wire whisker partially shorting the jack.

[Grainger49]

John,

All 4 RCA Jacks have nylon washers that "Float" the outer conductor, signal common, from the chassis.  The signal common and shield are taken to ground elsewhere.

I hope this is what your question was about.

[John]

Hi all,
Here are the results so far.  The amp has no intermittancies when I tap on the circuit boards or sockets.  However the gain at 1000 hz is Left chan 42.85 db and Right chan. 49.33 db.  What components set the gain for the circuit.  Any suggestions greatly appreicated.

Many thank again
Charette

[Paul Birkeland]

A good idea would be to swap EF86's to see if it follows a tube.  6922's can also account for some imbalance, but 7dB is pretty large.


In the Eros, the 75K plate load resistors are (in my opinion), most responsible for gain.  Next up would be the EQ (if you have a connection issue within the EQ, it can present as gain imbalance), and lastly the tubes themselves. 

-PB