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Author Topic: DX-60A Bias issue?  (Read 54114 times)
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w2rik
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« Reply #25 on: August 23, 2016, 04:59:28 PM »

Very good!

I put in 6DE7 and when I tried to load the fuse blew. If you noticed, on my opening note I was getting 50v on pins 2 and 6.

Next step?
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w2rik
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« Reply #26 on: August 23, 2016, 05:02:49 PM »

I just tried to read the voltages on V4 and as soon as my probe touched pin 2, the fuse blew.
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KA2DZT
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« Reply #27 on: August 23, 2016, 05:27:00 PM »

Does this xmtr have caps on the incoming AC line??  If it does and they are original, remove them.  You don't need AC line caps.

Your DC probe should not be causing fuses to blow unless you shorted something when you use it.
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W1RKW
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« Reply #28 on: August 23, 2016, 05:37:13 PM »

If you'd like to save some fuses, build one of these. Comes in handy for a variety of things.

It's a fuse saver.  You'll need to select an incandescent bulb that won't draw more than an amp or more over the rated fuse in the rig. 

If all is good the bulb should be dim or dimmer than full voltage across the bulb when the rig is operating as it should.  If there's a short in the rig or abnormal current draw, the bulb will glow full brightness or very close to full brightness.  Select the appropriate wattage bulb.  I have a variety of bulbs on hand from 25w to 200w I use for testing.

It's a cheap and dirty variac and fuse saver.



* DSCN1610.jpg (153.42 KB, 800x600 - viewed 594 times.)

* tester.GIF (2.01 KB, 352x134 - viewed 524 times.)
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Bob
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w2rik
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« Reply #29 on: August 23, 2016, 06:22:25 PM »

Tnx Bob!

Fred, I will remove those caps, Tnx.

Ok, so I put the 6DE7 in my tube-tester and it is completely DEAD! I am hesitant to put another tube in there for fear of blowing it until I can figure out why the voltage was off.

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KD6VXI
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« Reply #30 on: August 23, 2016, 07:44:34 PM »

Just FYI.

Harbor freight fuses are garbage.   I was working on an amp that had blown a fuse I didn't have,  and harbor freight is the closest place with an asst. 

Got home,  two 20 amp fuses blew in a row.   Upon inspecting the HF fuses left,  one end was able to be pulled off the glass.   Caused a hot spot on the fuse there because they rely on friction to make electrical contact.

The 20 amp fuses blow apart at 10 to 12 amps.

Just in case you made the same mistake on a purchase of them as I did.....

--Shane
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w2rik
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« Reply #31 on: August 23, 2016, 08:05:55 PM »

I didn't know that Harbor Freight sold fuses. These are probably the same cheap Chinese crap, although packaged by Radio Shack.
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Pete, WA2CWA
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« Reply #32 on: August 23, 2016, 08:20:35 PM »

Tnx Bob!

Fred, I will remove those caps, Tnx.

Ok, so I put the 6DE7 in my tube-tester and it is completely DEAD! I am hesitant to put another tube in there for fear of blowing it until I can figure out why the voltage was off.


I would check the two caps and the two resistors coming off of Pin 9 and the resistor between Pin 1 and Pins 2 & 6 for starters. The 6DE7 is used as the modulator, so with it out, you should be to play and check operating voltages/characteristics on various bands with the transmitter in the CW mode.
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w2rik
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« Reply #33 on: August 23, 2016, 09:45:19 PM »

Pete,

Both pins 8 and 9 on V4 are grounded, it doesn't matter which leg of C35 or R26, they are both grounded.
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w2rik
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« Reply #34 on: August 23, 2016, 09:52:44 PM »

Looks like C35 shorted. I will put the original cap back in and see what happens.
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w2rik
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« Reply #35 on: August 23, 2016, 10:30:15 PM »

Well, I thought that I was on to something.  I'm surprised that the cap rated for 630v blew out.

The same problem is there, when I load up, the fuse blows.


* image.jpeg (1249.75 KB, 3264x2448 - viewed 645 times.)
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KA2DZT
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« Reply #36 on: August 23, 2016, 10:51:47 PM »

Maybe the coupling cap from the plate of the final and the Pi network is shorting under the load.  Did you replace that cap.
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DMOD
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« Reply #37 on: August 23, 2016, 10:54:34 PM »

Tnx Bob!

Fred, I will remove those caps, Tnx.

Ok, so I put the 6DE7 in my tube-tester and it is completely DEAD! I am hesitant to put another tube in there for fear of blowing it until I can figure out why the voltage was off.



What do you mean, "dead?"

No filament or shorted elements?

This tube is a "dissimilar" dual triode with each separate triode having different gains and power handling capabilities.

Phil - AC0OB
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w2rik
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« Reply #38 on: August 23, 2016, 10:55:40 PM »

The filaments lit up but no movement on the meter scale.
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DMOD
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« Reply #39 on: August 23, 2016, 10:56:56 PM »

I just tried to read the voltages on V4 and as soon as my probe touched pin 2, the fuse blew.

You most likely touched pin 2 and 1. Pin 1 has 700 volts on it.

Do that and the Final's screen voltage goes very high making the Final conduct a lot of current probably contributing to blown fuses.
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« Reply #40 on: August 23, 2016, 11:02:45 PM »

Looks like C35 shorted. I will put the original cap back in and see what happens.

C34 (DX-60 schematic) or C35 (DX-60B schematic) are 100 pF 500V units.

Which schematic are you looking at?

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w2rik
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« Reply #41 on: August 23, 2016, 11:06:17 PM »

Maybe the coupling cap from the plate of the final and the Pi network is shorting under the load.  Did you replace that cap.

No, I didn't replace C18.
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w2rik
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« Reply #42 on: August 23, 2016, 11:10:30 PM »

Looks like C35 shorted. I will put the original cap back in and see what happens.

C34 (DX-60 schematic) or C35 (DX-60B schematic) are 100 pF 500V units.

Which schematic are you looking at?

DX-60B


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w2rik
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« Reply #43 on: August 24, 2016, 10:17:45 AM »

Does anyone have the DX-60A manual in PDF?
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w1vtp
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« Reply #44 on: August 24, 2016, 01:44:04 PM »

If you'd like to save some fuses, build one of these. Comes in handy for a variety of things.

It's a fuse saver.  You'll need to select an incandescent bulb that won't draw more than an amp or more over the rated fuse in the rig.  

If all is good the bulb should be dim or dimmer than full voltage across the bulb when the rig is operating as it should.  If there's a short in the rig or abnormal current draw, the bulb will glow full brightness or very close to full brightness.  Select the appropriate wattage bulb.  I have a variety of bulbs on hand from 25w to 200w I use for testing.

It's a cheap and dirty variac and fuse saver.



This is what I used to check my Ameritron HV transformer when it was blowing fuses.  Not as fancy as yours but it worked.  Worked pretty slick.  As soon as an internal arc occurred, the bulb (a 60 watter) would flash brighter thus limiting the primary current.

Al


* AL-82 Transformer test (comp).jpg (446.83 KB, 2500x1656 - viewed 648 times.)
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w2rik
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« Reply #45 on: August 24, 2016, 07:32:54 PM »

Folks,

Here is an update. I returned to PS section back to its original configuration with three capacitors, not four as I previously had.

I removed all the tubes and added them one at a time. The radio tripped when I switched to CW and tried to load up with only V1, V2 and V3 installed.

The readings using an 80m crystal on V1 looked good, however V2 not so much.

XTAL V2 Pin 6 = 322v           REF V2 Pin 6 = 340v
XTAL V2 Pin 8 = 6.5v           REF V2 Pin 8 = 12v
XTAL V2 Pin 9 = -37v           REF V2 Pin 9 = -115v

The 1Mh choke on Pin 9 is reading 30 ohms... Isn't that extremely high?

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DMOD
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« Reply #46 on: August 24, 2016, 09:54:12 PM »

Folks,

Here is an update. I returned to PS section back to its original configuration with three capacitors, not four as I previously had.

I removed all the tubes and added them one at a time. The radio tripped when I switched to CW and tried to load up with only V1, V2 and V3 installed.

The readings using an 80m crystal on V1 looked good, however V2 not so much.

XTAL V2 Pin 6 = 322v           REF V2 Pin 6 = 340v
XTAL V2 Pin 8 = 6.5v           REF V2 Pin 8 = 12v
XTAL V2 Pin 9 = -37v           REF V2 Pin 9 = -115v

The 1Mh choke on Pin 9 is reading 30 ohms... Isn't that extremely high?

The choke reading is normal. You need to read the DC voltages at the bottom of V2's grid choke and the bottom of R8.

What was the voltage at V4 pin 3 screen grid when it blew another fuse?

Check your 6146 again and make sure you didn't blow it when you shorted pins on V4.

Quote
Here is an update. I returned to PS section back to its original configuration with three capacitors, not four as I previously had.


Both versions of the DX-60 series have four - 40 uF electrolytics in the power supply.

Have you replaced C18/C21?

Here is the DX-60B schematic.


Phil - AC0OB




I have the DX-60 Manual as well so PM me if you need it. Can't upload it here.

* DX-60B-sch.pdf (1187.84 KB - downloaded 270 times.)
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KA2DZT
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« Reply #47 on: August 24, 2016, 10:16:55 PM »

I mH RFC could read 30 ohms.  What are tubes V1 V2 V3  I don't have a drawing.  What final plate current are you seeing.   Before you switch to transmit you need to tune the driver stages to be sure you have enough drive to the final stage.  A 6146 should have 2.5 to 3 ma of drive.  Once you're sure you have drive, switch the meter to read plate current.  Switch into transmit with key UP.  Nothing should happen.  No fuses should blow.  Key down, quickly look at the plate current and dip the final.  If the plate current is not too high to begin with (say 150 ma)  no fuses should blow.  Dip the final, load up to about 110 ma.  No fuses should blow.

Of course use a dummy load or an antenna for the load.  If you can't get past these basic steps, which apply to any xmtr,  you need to start back at the beginning and check all wiring and components.

OTH if you can get past these steps and you have power output (say 50 watts) and as you may be transmitting some CW, the fuse blows,  you need a little bit heavier fuse (say 4 amps).  IMO I think a 3amp fuse is a little light for that xmtr.

Fred
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w2rik
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« Reply #48 on: August 24, 2016, 10:27:27 PM »

Folks,

Here is an update. I returned to PS section back to its original configuration with three capacitors, not four as I previously had.

I removed all the tubes and added them one at a time. The radio tripped when I switched to CW and tried to load up with only V1, V2 and V3 installed.

The readings using an 80m crystal on V1 looked good, however V2 not so much.

XTAL V2 Pin 6 = 322v           REF V2 Pin 6 = 340v
XTAL V2 Pin 8 = 6.5v           REF V2 Pin 8 = 12v
XTAL V2 Pin 9 = -37v           REF V2 Pin 9 = -115v

The 1Mh choke on Pin 9 is reading 30 ohms... Isn't that extremely high?

The choke reading is normal. You need to read the DC voltages at the bottom of V2's grid choke and the bottom of R8.

What was the voltage at V4 pin 3 screen grid when it blew another fuse?

Check your 6146 again and make sure you didn't blow it when you shorted pins on V4.

Quote
Here is an update. I returned to PS section back to its original configuration with three capacitors, not four as I previously had.


Both versions of the DX-60 series have four - 40 uF electrolytics in the power supply.

Have you replaced C18/C21?

Here is the DX-60B schematic.


Phil - AC0OB




I have the DX-60 Manual as well so PM me if you need it. Can't upload it here.

Yes, The DX-60 and DX-60B use 4 caps. I have the DX-60A and attached the schematic. The difference between the A & B is in the extra cap and a 7w resistor. Also R36 and R37 are wired differently.

I didn't replace C18 or C21. I couldn't find C21 in it's value and will this work for C18? (See attached).

I tested the tube and it was OKAY, same reading as last time.

* DX-60A.pdf (190.51 KB - downloaded 279 times.)

* 2016-08-24 22.18.57.jpg (1534.3 KB, 3264x2448 - viewed 593 times.)
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KA2DZT
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« Reply #49 on: August 24, 2016, 10:33:30 PM »

That cap you pictured will not work for C-18,  You need a door knob cap or a ceramic cap and the voltage rating should be at least 5KV.

Fred
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