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Author Topic: DX-60A Bias issue?  (Read 54105 times)
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DMOD
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« Reply #50 on: August 24, 2016, 10:36:45 PM »

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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).

Okay, in your original post you said DX-60 so that's why some of us are confused.

For C18 it would be preferable to use a 0.001 uF (1,000 pF) 2kV ceramic.

Phil - AC0OB
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w2rik
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« Reply #51 on: August 24, 2016, 10:37:29 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

V1 6CL6 Crystal Oscillator
V2 6CL6 Driver
V3 6146 Final Amp
V4 6DE7 Modulator
V5 12AX7 Speech Amplifier

I was on the radio in a QSO and the fuse blew mid-way. If you look back at my first post I did before the QSO, I was looking for assistance with wacky voltages. The fuse blowing came later and that's where I am now.

The 6146 does have 2.5 ma of drive and it's when I dip the plate and increase the Final Tuning in CW mode (per manual), the fuse blows.
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w2rik
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« Reply #52 on: August 24, 2016, 10:40:59 PM »

Quote
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).

Okay, in your original post you said DX-60 so that's why some of us are confused.

For C18 it would be preferable to use a 0.001 uF (1,000 pF) 2kV ceramic.

Phil - AC0OB

Oops! I corrected the Subject and text. Tnx Phil.
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« Reply #53 on: August 24, 2016, 10:46:16 PM »

Those yellow caps, like what you pictured, should not be used anywhere in the RF sections of the xmtr  You need ceramic disc caps in the RF sections.

C-21 in another cap that should have high voltage rating,  it is part of the plate tuning capacitor on the lower bands.

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w2rik
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« Reply #54 on: August 24, 2016, 10:56:50 PM »

Understood on the ceramic caps. Isn't C18 the Domino Mica cap? Do you think that needs to be changed?


* domino.jpg (2226.34 KB, 3264x2448 - viewed 538 times.)
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« Reply #55 on: August 25, 2016, 03:32:44 AM »

Those large postage stamp micas can be problematic especially the red ones.  Problem is finding the right cap to replace it with.

Searched on line for a manual for a DX-60.  Found one,  it showed a 3amp fuse in the parts list.  Wonder why Heath went to the circuit breaker in your rig.  Could the circuit breaker been rated a little higher than 3 amps?  Circuit breakers are slow to react to an overload.  At the least you need to try a 3amp slo blo fuse or try a slightly higher value fuse.

If you have a Variac, try running the rig on slightly lower line voltage (say 115 vac).  Right now, with everything you've done and posted, we don't know if there is something that is breaking down under load or the fuses you're using are not right.

If you had an accurate AC amp meter you could put that in line and measure the AC current.  Easy for me to say, i have a dozen lab type AC amp meters than can measure from millamps to 200 amps.

No amp meter,  if you have a 1ohm resistor at about 10-20watts,  put it in line with the power line cord (put it in line with the white neutral wire).  Use a DVM and measure the voltage drop across the 1ohm resistor.  1 volt ac equals 1 amp.  Of course you would use an external set up that you would plug in the rigs line cord to.

Again, at this stuff is easy for me,  I have a 300watt 1ohm resistor already made up for this purpose.

Fred

 
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w2rik
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« Reply #56 on: August 25, 2016, 11:59:10 AM »

I do have a variac and set it at 115 v. I also have a meter called a Kill-a-Watt (see image) on it and here are the readings:

Standby - .28 Amps
Tuning up, Key Down, CW - 1.19 Amps, then the fuse* blew.

*I put the stock circuit breaker back in line to save on fuses.



* 2016-08-25 11.47.54.jpg (1340.99 KB, 3264x2448 - viewed 607 times.)
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KA2DZT
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« Reply #57 on: August 25, 2016, 12:54:14 PM »

OK great,  does that Kill-a-Watt meter read amps or just wattage or both??  Two amps shouldn't be blowing fuses.  So, there must be something breaking down under load.  Not easy to find these type problem.

Fred
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w2rik
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« Reply #58 on: August 25, 2016, 01:10:57 PM »

OK great,  does that Kill-a-Watt meter read amps or just wattage or both??  Two amps shouldn't be blowing fuses.  So, there must be something breaking down under load.  Not easy to find these type problem.

Fred

It will display Volts, Amps, Watts, Hz, VA.

Is it possible that the .005 caps on the 6146 are failing?
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« Reply #59 on: August 25, 2016, 02:02:26 PM »

OK great,  does that Kill-a-Watt meter read amps or just wattage or both??  Two amps shouldn't be blowing fuses.  So, there must be something breaking down under load.  Not easy to find these type problem.

Fred

It will display Volts, Amps, Watts, Hz, VA.

Is it possible that the .005 caps on the 6146 are failing?

I've been working with electronics over 55 yrs,  I don't think I've ever seen more than 5 or 6 bad ceramic caps.  If the .005ufd caps are ceramics it's unlikely they're bad.

Looked at the schematic,  C-18 would be the more likely cap to be bad.

What are you using for a dummy load or antenna??  Reason I ask is that if C-18 was maybe breaking down inside your HV will short through the pie network through the dummy load to ground.  That will blow the fuse every time.  If your antenna is a dipole,  a short circuit through the antenna wouldn't occur.

I see that xmtr has some added low pass filtering after the pie network,  have to take a closer look at that for any possible problems.

Fred
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w2rik
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« Reply #60 on: August 25, 2016, 02:32:07 PM »

OK great,  does that Kill-a-Watt meter read amps or just wattage or both??  Two amps shouldn't be blowing fuses.  So, there must be something breaking down under load.  Not easy to find these type problem.

Fred

It will display Volts, Amps, Watts, Hz, VA.


Is it possible that the .005 caps on the 6146 are failing?

I've been working with electronics over 55 yrs,  I don't think I've ever seen more than 5 or 6 bad ceramic caps.  If the .005ufd caps are ceramics it's unlikely they're bad.

Looked at the schematic,  C-18 would be the more likely cap to be bad.

What are you using for a dummy load or antenna??  Reason I ask is that if C-18 was maybe breaking down inside your HV will short through the pie network through the dummy load to ground.  That will blow the fuse every time.  If your antenna is a dipole,  a short circuit through the antenna wouldn't occur.

I see that xmtr has some added low pass filtering after the pie network,  have to take a closer look at that for any possible problems.

Fred

When the issue of the fuse blowing first occurred, I was in QSO and using an Alpha-Delta LB-DX+. For a dummy, I have been using a light bulb and it's the same one that I have been using all along.

I can't seem to find a .001 in 4Kv.

The only change I made in the filter cage was changing the RCA phono plug to an SO-239, see attached.


* image.jpeg (283.11 KB, 2048x1536 - viewed 540 times.)
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« Reply #61 on: August 25, 2016, 04:13:20 PM »

A 3amp fuse popping at 1.2amps?Huh   Sure it's a 3amp fuse?
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« Reply #62 on: August 25, 2016, 04:51:11 PM »

A 3amp fuse popping at 1.2amps?Huh   Sure it's a 3amp fuse?

Yes, but I reinstalled the stock circuit breaker and when I say the fuse blew, it's the circuit breaker that resets itself in about 7 seconds.
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« Reply #63 on: August 25, 2016, 05:28:29 PM »

Not sure what the Alpha Delta antenna is but it may be a DC grounded antenna.  You can put an ohmmeter on the coax end to see if it is.

The plate coupling cap (C-18) can be a pain to find a replacement.  In my HB 6146 rig I used an old TV door knob cap.  Most are 500pfd at 20KV,  works FB.  In my HB 813 rig I used two 680pfd at 18KV, both door knob type caps.

Here's a test you can do.  Remove the 6146,  power up the rig,  carefully measure the HV at the top of the final plate RFC.  You should see the 5-600 volts from the PS.  Now check for any leaking DC voltage on the other side of the plate coupling cap (C-18),  the end connected to the plate tuning cap.  If you are seeing any amount of DC voltage on that end, for sure the cap is NG.  By this time, 50 plus years,  most of those type micas are bad.  I have boxes of them but wouldn't think of using them.

Make sure to remove the 6146 from the socket.  Reason is the screen will draw heavy current with the plate voltage absent, which can quickly damage the tube.

Also disconnect any antenna or dummy load while doing the test.

Fred.
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w2rik
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« Reply #64 on: August 25, 2016, 05:48:18 PM »

Not sure what the Alpha Delta antenna is but it may be a DC grounded antenna.  You can put an ohmmeter on the coax end to see if it is.

The plate coupling cap (C-18) can be a pain to find a replacement.  In my HB 6146 rig I used an old TV door knob cap.  Most are 500pfd at 20KV,  works FB.  In my HB 813 rig I used two 680pfd at 18KV, both door knob type caps.

Here's a test you can do.  Remove the 6146,  power up the rig,  carefully measure the HV at the top of the final plate RFC.  You should see the 5-600 volts from the PS.  Now check for any leaking DC voltage on the other side of the plate coupling cap (C-18),  the end connected to the plate tuning cap.  If you are seeing any amount of DC voltage on that end, for sure the cap is NG.  By this time, 50 plus years,  most of those type micas are bad.  I have boxes of them but wouldn't think of using them.

Make sure to remove the 6146 from the socket.  Reason is the screen will draw heavy current with the plate voltage absent, which can quickly damage the tube.

Also disconnect any antenna or dummy load while doing the test.

Fred.

Fred, the Alpha Delta antenna is good from 160-10m (see image).

I did the test and get 720 v on top of the RFC and an up/down from 0 to .600 mv on the other side of the cap.


* image.jpeg (21.37 KB, 580x118 - viewed 522 times.)
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« Reply #65 on: August 25, 2016, 06:46:46 PM »

OK on the antenna.  Only a few millivolts is better than I thought you would see.  Doesn't seem like it's leaky, so, less likely it might be the cause of the fuse blowing.  For now leave it in there and look elsewhere for the problem.  I'm not sure where to look next.

Have you tried any transmitting with the circuit breaker in line.  Might be the next step,  see what happens.  The circuit breaker is slower to react to an overload.  While transmitting keep an eye the plate current.  You may see it shoot up or even pin the meter before the circuit breaker reacts.  You need something to point you in the right direction.  You may even keep an eye on the Kill a Watt meter using the current mode.

It would take a heavy load on the HV line or the low voltage (300V) line to blow the fuse.  Other areas of the circuitry might get a short but the current would be limited by any resistors in the circuit.  Example, say the screen bypass cap shorts,  normally this would not blow a fuse, instead you would see the screen resistor smoke.  A short on the filament line would probably blow the fuse.

Fred
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« Reply #66 on: August 25, 2016, 07:26:40 PM »

Parasitic or other type oscillation?

I'm not sure the time constant of the kill a Watt.....   But is it fast enough to show?

A thought.

--Shane
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w2rik
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« Reply #67 on: August 25, 2016, 08:34:15 PM »

What I did notice tonight is that on pin 6 of V3, 6146 gives me a dead short to ground. Shorted C14 capacitor? See close up of this area attached.


* image.jpeg (1761.74 KB, 3264x2448 - viewed 574 times.)
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w2rik
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« Reply #68 on: August 25, 2016, 11:05:36 PM »

Parasitic or other type oscillation?

I'm not sure the time constant of the kill a Watt.....   But is it fast enough to show?

A thought.

--Shane
KD6VXI

I'm not sure if it is parasitic or other. It changed so rapidly, you'd miss it if you blinked. How can I tell the difference?

I don't know about the Kill-A-Watt either.
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« Reply #69 on: August 26, 2016, 09:34:31 AM »

What I did notice tonight is that on pin 6 of V3, 6146 gives me a dead short to ground. Shorted C14 capacitor? See close up of this area attached.

Pins 1,4 and 6 are all connected together internally in the 6146.  Pull out the 6146 and measure each socket terminal.  These three terminals also may be tied together at the socket.  You should be seeing about 8 ohms on one of them unless they're all tied together at the socket.  Check the meter switch, move it to grid and back to plate.  Check the wires going to the switch,  there may be something shorting along the wiring.

Even if there is a dead short on any of those pins it would not cause the fuse to blow.  In fact the only thing that would happen is the plate current meter wouldn't indicate any current. The xmtr would still continue to operate.  OTOH if you find a shorted wire somewhere,  you might find other bad wires at the same location that could blow fuses.

Fred
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« Reply #70 on: August 26, 2016, 10:25:39 AM »

I took another look at the schematic,  If there was a short on the meter-switch wires that go to the grid circuit that would cause the fuse to blow.  A short there would short the bias supply and the 6146 would lose grid bias.  The tube would draw heavy current along with the shorted bias supply would blow the fuse.  Check the slide switch, it's rare, but it may be shorting to the frame.

Fred
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« Reply #71 on: August 26, 2016, 01:49:20 PM »

If you suspect C18 or are having problems finding 2kV/3kV replacements for the plate coupling capacitor I highly recommend the Cera-Mite series from Vishay/Mouser such as:

http://www.mouser.com/ProductDetail/Vishay-Cera-Mite/564R75GAD10/?qs=IJbG%2FWJQIdLNaDusJv1gGw%3D%3D

Assuming no leaky capacitors in the power supply, what Fred said AND take another look at the Final's screen voltage in CW and AM mode.

I use up to three volt meters to check voltages in real time.

As far as the grid voltage on pin 2 of the 6DE7, I have seen anywhere from 30 to 50 V.

The important thing is how much voltage is being seen on Pin 3 of the Final. This static voltage in AM mode will vary between 55V and 85 volts, depending on the gain of the 6DE7.

The Final's screen voltage in CW mode should be kept below 180V, and preferably 170V. I routinely replace R18 with a 15k 2W.

Do we know if the Circuit Breaker is functioning properly. If the unit has been abused the CB may be faulty.


Like Fred, I am a big fan of SGM transmitters. Cheesy

Hang in there, you'll get it working.  Cool

Phil - AC0OB



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« Reply #72 on: August 26, 2016, 02:44:31 PM »

Inspect the switch wafers for any carbon tracking.  Any contact cleaner that leaves a residue on the wafers has a potential to carbon track especially any contact that has HV on it.  
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Bob
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« Reply #73 on: August 26, 2016, 04:09:22 PM »

That's a good point Fred. The original fuse was a neon bulb that blew out years ago. At that time I drilled a hole in the chassis and installed a fuse holder. When I google searched at that time, the most popular answer was just a 3 amp and no mention of a slo-blow.

Maybe Phil can comment on what he uses.

But my concern is now the fuse is blowing out on load up, it didn't do that before and as stated, I was in a QSO when it happens tonight.

As shown in the Modified Power supply, I use a 3A FB for testing and a 3A SB for operation.

I calculated the VA at 230VA so 230VA/120V = 1.9 amps operational and ~2.8 Amps surge.

Phil - AC0OB

* DX-60 6CL6 PS for Rik.pdf (39.46 KB - downloaded 256 times.)
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« Reply #74 on: August 29, 2016, 05:04:26 PM »

Folks, I stepped away from this for a few days being my daughter went back to school yesterday.

OK, I replaced the Grid/Plate switch and all .005uF caps on V3 (6146). There is no change.

Tomorrow I am going to pick up some 3A slo-blows and see if in fact the circuit breaker is faulty and I may have already corrected this problem.
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