The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    Quad cap "pin-outs"

    Share

    Clik2media

    Posts : 40
    Join date : 2009-01-18

    Quad cap "pin-outs"

    Post by Clik2media on Tue Mar 03, 2009 1:59 am

    Probably old hat for the pros' but can anyone tell me the "code" for determining the voltage at each section of a quad cap. The triangle, the square, the oval and the blank, on the quad caps. I am trying to track a glowing EL34 tube plate and making sure I oriented my cap the right way. thanks a million

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Quad cap "pin-outs"

    Post by Bob Latino on Tue Mar 03, 2009 9:45 am

    Clik2media wrote:Probably old hat for the pros' but can anyone tell me the "code" for determining the voltage at each section of a quad cap. The triangle, the square, the oval and the blank, on the quad caps. I am trying to track a glowing EL34 tube plate and making sure I oriented my cap the right way. thanks a million

    Hi,

    You didn't say which Dynaco amp. With your mention of the EL34, I am assuming it is an ST-70. On the original ST-70 quad cap the quad cap DC voltages should as below.

    HALF CIRCLE - About 435 volts DC - This section should face the bias potentiometers and have one choke lead and a wire from pin 8 of the rectifier tube.

    NO SYMBOL - About 415 volts DC - This section should face the rear of the amp and have one choke lead, the two red leads from each output transformer and one end of 6800 ohm resistor.

    TRIANGLE SYMBOL - About 375 volts DC - This section should face the right side of the amp and have the other end of the 6800 ohm resistor, one end of a 22000 ohm resistor and a wire going to eyelet 20 on the driver board.

    SQUARE Symbol - About 315 volts DC - This section should face the front of the amp, have the other end of the 22000 ohm resistor and a wire going to eyelet 19 on the driver board.

    I don't think that your problem is related to an issue on the quad cap. From your glowing plate symptom you have either a bad tube or a bad bias on that tube socket. Move the tube with the glowing plate to a new location and see if it does the same thing. If the same tube glows in another socket then that tube is bad and just replace the tube. If any of your other tubes will show glowing plates in that tube socket then first check out the tube socket. Pull the tube and clean the tube socket pins (especially pins 5 and 6) with a Q-tip with most of the cotton removed.

    A glowing tube is a sign of "runaway bias" in which there is a problem with the bias system. Check the 1000 ohm resistor between pins 5 and 6 on that tube socket and also try replacing the main coupling cap for that tube. Check also the 270K resistor for that tube. The four 270K resistors (one for each tube) are the four resistors (two on each side) at the very side of the driver board. Check that you get near 270 K on the resistor that feeds that tube.

    Bob

    Clik2media

    Posts : 40
    Join date : 2009-01-18

    Re: Quad cap "pin-outs"

    Post by Clik2media on Wed Mar 04, 2009 12:15 am

    Hi,

    You didn't say which Dynaco amp. With your mention of the EL34, I am assuming it is an ST-70. On the original ST-70 quad cap the quad cap DC voltages should as below.

    HALF CIRCLE - About 435 volts DC - This section should face the bias potentiometers and have one choke lead and a wire from pin 8 of the rectifier tube.

    NO SYMBOL - About 415 volts DC - This section should face the rear of the amp and have one choke lead, the two red leads from each output transformer and one end of 6800 ohm resistor.

    TRIANGLE SYMBOL - About 375 volts DC - This section should face the right side of the amp and have the other end of the 6800 ohm resistor, one end of a 22000 ohm resistor and a wire going to eyelet 20 on the driver board.

    SQUARE Symbol - About 315 volts DC - This section should face the front of the amp, have the other end of the 22000 ohm resistor and a wire going to eyelet 19 on the driver board.

    I don't think that your problem is related to an issue on the quad cap. From your glowing plate symptom you have either a bad tube or a bad bias on that tube socket. Move the tube with the glowing plate to a new location and see if it does the same thing. If the same tube glows in another socket then that tube is bad and just replace the tube. If any of your other tubes will show glowing plates in that tube socket then first check out the tube socket. Pull the tube and clean the tube socket pins (especially pins 5 and 6) with a Q-tip with most of the cotton removed.

    A glowing tube is a sign of "runaway bias" in which there is a problem with the bias system. Check the 1000 ohm resistor between pins 5 and 6 on that tube socket and also try replacing the main coupling cap for that tube. Check also the 270K resistor for that tube. The four 270K resistors (one for each tube) are the four resistors (two on each side) at the very side of the driver board. Check that you get near 270 K on the resistor that feeds that tube.

    Bob
    [/quote]

    Bob much appreciated. I checked the resistors they all look good.
    Here is my "upgrade. The new quad cap is 80-40-30-20 the instructions where to orient the "square" towards to closest bias potentemeter. Could that be my issue? With your explanation above that is the lowest voltage section.

    On my setup One choke wire is on that pin, the other choke wire is on the half circle. the triangle goes to #20 on the pcb and the blank goes to 19 on the pcb, both output transformers go to half circle. How do I look?

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Quad cap "pin-outs"

    Post by Bob Latino on Wed Mar 04, 2009 8:09 am

    Hi,

    I am assuming you have the CE distribution 80, 40, 30, 20 cap. On that quad cap you want the square symbol side of this cap (40 Mfd) facing the potentiometers. The 80 mfd section then faces the back of the amp. The blank terminal (20 mfd) faces to the right and the triangle terminal (30 mfd) faces the front of the amp.

    You have the orientation correct. The 6800 ohm goes between the half-circle and blank and the 22000 ohm resistor goes between blank and triangle.

    The thing that doesn't jibe with what you have said is the wires that go to eyelets 19 and 20 on the driver board. The wire from the blank terminal should go to eyelet #20 and the wire from the triangle terminal should go to eyelet #19.

    Bob

    Clik2media

    Posts : 40
    Join date : 2009-01-18

    Re: Quad cap "pin-outs"

    Post by Clik2media on Wed Mar 04, 2009 7:42 pm

    Bob, did all that, and double checked. Now the plate glow moved from the back tube on the right to the front tube on the right. seems to be a stronger plate glow. btw yes it is a ST-70

    I am going to triple check everything again.

    Mike

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Quad cap "pin-outs"

    Post by Bob Latino on Wed Mar 04, 2009 8:01 pm

    Mike,

    Check the values of the two 10K resistors between lugs 1 through 2 and lugs 3 and 4 on the 7 lug terminal strip. Try replacing the two 50 Mfd 100 volt capacitors between lugs 1 and 3 and lugs 1 and 4. When you do make sure that the positive side of each 50 Mfd capacitor is connected to lug # 1.

    You should also replace the selenium rectifier (if you haven't already done so) with a 1N4007 or 1N4004 diode (Radio Shack has them). Those old selenium rectifiers were unreliable and are not as good as a diode.

    Again, old tube sockets that make intermittent contact especially on pins 5, 6 and 8 can cause this. I would replace the tube sockets.

    Glowing plates are almost always a sign that the tube is drawing too much current. The bias system sets the idle current. If you lose the bias system the tube will draw too much current and the plates will start to glow.

    Bob

    Clik2media

    Posts : 40
    Join date : 2009-01-18

    Re: Quad cap "pin-outs"

    Post by Clik2media on Thu Mar 05, 2009 3:25 pm

    Bob according to this set up should the recitfier wire still go to the 80-mfd half circle?
    thnx

    mike

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Quad cap "pin-outs"

    Post by Bob Latino on Thu Mar 05, 2009 3:49 pm

    Clik2media wrote:Bob according to this set up should the recitfier wire still go to the 80-mfd half circle?
    thnx

    mike

    Mike,

    No - On the CE Distribution 80, 40, 30 20 cap. The wire from pin 8 of the rectifier tube should go to the 40 Mfd (square symbol) terminal. When set up this way the 80 Mfd (half circle) is set to the REAR of the amp. This is the proper way to set up that cap on an ST-70.

    Bob

    Sponsored content

    Re: Quad cap "pin-outs"

    Post by Sponsored content Today at 8:15 am


      Current date/time is Mon Sep 26, 2016 8:15 am