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 Post subject: Ranger I - this time, mod bias
PostPosted: Jun Fri 17, 2022 7:39 pm 
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Testing the transmitter the other day and unkeyed -- and the mod current suddenly spiked. Angry buzzing, pilot lamps flashing, and then blown fuse.

Replaced fuse and tested. Passed the dim bulb test. And no blown fuse at full voltage with rectifiers in and mod tubes out.

R35 voltages (top and tap) are in spec.

With the mod tubes out, measured the center tap of the driver xfrmer secondary. I get between -8vdc and -10vdc negative bias voltage. It should be at least -28v. I assume this is why the mod current is spiking.

I dismantled the keyer/bias rectifier platform and checked out resistors, they are in spec. I replaced C90A/B with a new 47uf electrolytic, and replaced V14 with a new 6AL5. No luck.

Pulled the 6AL5 and measured 0 vac to ground at pins 5 and 1 tube socket. I am wondering if the power transformer tap that feeds the cathodes of the 6AL5 (marked Y Y on the schematic) has failed.


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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sat 18, 2022 1:31 am 
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Check the transformer with an ohm meter.

If you have all the other voltages I'd think its strange for both of those taps to be open, but one never knows.

If in fact they are open, you could use the circuit below to generate your voltages. My Ranger is a Very early edition, and the transformer doesn't have the bias taps. It was modified to include the bias and keyer circuits using resistive dividers off of the Low B+ windings. Here is the power supply circuit for the keyer and modulator bias voltages.

Image

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sat 18, 2022 3:54 am 
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Did you measure voltage from each cathode (pins 1 and 5) to ground and to each other? Modern DMMsoften don't do well with transformer resistances. The voltages will tell the truth.

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sat 18, 2022 1:30 pm 
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Not possible to get at the 6AL5 pins when the tube is in place due to the position of the keyer platform. (I suppose I need one of these: https://www.ebay.com/p/1434745751?iid=333598791646 . Argh)

But with the tube out, I get...

Pin 1 to 5 = 6VDC (and 0 VAC)
Pin 1 to GND = 6VDC (and 0 VAC)
Pin 5 to GND = 0 VDC (and 0 VAC)

I rechecked the power transformer voltages and I am getting 630 VDC at the HV filter cap, 329 VDC at the R22 center tap, 345 VDC at the LV filter cap, and about 7 V at the tube filaments. So it appears other taps on the power transformer are within spec.


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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sat 18, 2022 4:39 pm 
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Location: Edmonds, WA USA
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It does look like bad taps with 0 volts ac.. The resitive network mentioned earlier would be a good fix.

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sat 18, 2022 4:48 pm 
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Lolyn wrote:
It does look like bad taps with 0 volts ac..


I should check the two yellow tap wires from the xfrmer aren't damaged in some way. They are buried in a rats nest of wiring.

Question: if the bias rectifier is dead, why am I getting between -8vdc and -10vdc at the center tap of the driver xfrmer secondary?

Lolyn wrote:
The resitive network mentioned earlier would be a good fix.


Here is a circuit from AD5X which uses the taps, but adds an adjustable bias feature. Would love to use this kind of mod bias setup to get rid of R22, the big heat-generating resistor.


Attachments:
AD5X bias mod.jpg
AD5X bias mod.jpg [ 42.1 KiB | Viewed 925 times ]
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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sat 18, 2022 7:28 pm 
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Plunged into the rats next of wires and found the two rectifier tap Y Y leads from the transformer had been cut and badly spliced and soldered and scotch taped by previous owners. So I cut the leads at the splice and tested voltages there:

DC
Lead to lead: cycling between 1.5 and 2.5 VDC.
From each lead to ground: cycling between 1 and 1.5VDC

AC
Lead to lead: 313 VAC.
From each lead to ground: 140VAC.

So, what should the voltage at tap Y Y be at? All the manual says is "0.5 VAC open circuit".


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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sat 18, 2022 10:59 pm 
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Greetings to W1GFH and the Forum:

My copy of the manual states that the two bias tap leads are brown wires and the voltage between them should be 150 VAC Open circuit (i.e. not loaded).

I found this data on page 22 of my manual, which has a date entry (at least that is what I assume it is) in the lower left corner of "1/55".

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sun 19, 2022 2:16 am 
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Hi Joe,

Based on your measurements, and Jim's information it looks like your transformer taps are good. Just re-splice them and use some shrink sleeve to cover the splices, and verify you have the AC voltages at the rectifier's cathode pins. If they are there, make sure you have about 15KΩ to ground at the plate pins of the rectifier, re-install the rectifier, turn it on, and you should have your correct voltages.

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Sun 19, 2022 8:58 pm 
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Quote:
verify you have the AC voltages at the rectifier's cathode pins. If they are there, make sure you have about 15KΩ to ground at the plate pins of the rectifier, re-install the rectifier, turn it on, and you should have your correct voltages.


Yes the plate pins read 15K to ground, each. And I have verified I now have around 150 VAC at both cathode pins.

But with the 6AL5 installed I'm still only getting around -13VDC dropping to -8VDC on warmup at the driver transformer center tap.

I also checked at the junction of R52 and R53, and it's the same. I'm not getting the required -28VDC.

There is -140VDC on the 6AL5 plates. *** And -55VDC on the capacitor negative side of R54 (6.8K resistor). ***

I have tried two different tested good 6AL5s. Not sure what's going on.


Attachments:
biassupplysmall.jpg
biassupplysmall.jpg [ 33.56 KiB | Viewed 843 times ]


Last edited by W1GFH on Jun Mon 20, 2022 12:57 am, edited 1 time in total.
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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Mon 20, 2022 12:39 am 
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Greetings to W1GFH and the Forum:

Two suspects remain (aside from the driver transformer itself and we hope to not go there). C59B, the 15 uF electrolytic capacitor on the center tap of the transformer and one or both of the 1614 modulator tubes.

I'd start by pulling both 1614's and see what the bias is then. If it comes up to normal, install one of the 1614's and see if it remains OK. Then try the other one. Hopefully, it is a shorted tube rather than a problem with the driver transformer.

Good Luck,

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Mon 20, 2022 1:00 am 
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Jthorusen wrote:
Greetings to W1GFH and the Forum:

Two suspects remain (aside from the driver transformer itself and we hope to not go there). C59B, the 15 uF electrolytic capacitor on the center tap of the transformer and one or both of the 1614 modulator tubes.

I'd start by pulling both 1614's and see what the bias is then. If it comes up to normal, install one of the 1614's and see if it remains OK. Then try the other one. Hopefully, it is a shorted tube rather than a problem with the driver transformer.

Good Luck,


Both 1614's have been pulled due to mod current spiking and subsequent blown fuse. That's the only way I can take voltage readings while powered up. The problem is a lack of -28v bias at the driver xfrmer center tap. I’m going to take a closer look at the bias supply tomorrow, especially the two 4.7k resistors. They test good, but there may be some wiring error or short in that area.


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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Mon 20, 2022 2:03 am 
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Just disconnect one (either) end of C59B and see if you have the correct voltage. If not disconnect the center tap wire from the transformer. I think I'd put my money on a bad cap, but...

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Mon 20, 2022 3:44 pm 
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And the prize goes to Mike :D for winning diagnosis. I lifted C59B and got -33VDC at the driver xfrmer center tap. Replaced that capacitor and mod bias is back to normal.

However, now I have no grid drive and the audio stages don't seem to be working :( The initial "incident" that blew the fuse and prompted this whole thread may have taken something else out. I'll be checking various voltages. Here I go again... :!:


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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Mon 20, 2022 8:29 pm 
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Hey.... I want a share of that prize! I stated that C59B could be the problem in the post just before Mike's! :D

Just kidding.... glad you found it. Please keep us posted on what else you find. I've known Rangers to have strange and serial problems before, but I believe that yours is in the running for the most recalcitrant Ranger ever. Of course, by the time you finish up with it, it will be bullet-proof and the best Ranger out there. :!:

....So..... hang in there!

Regards,

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Mon 20, 2022 8:39 pm 
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Quote:
I've known Rangers to have strange and serial problems before, but I believe that yours is in the running for the most recalcitrant Ranger ever.
:x I'm almost ready to call Chuck, K1TLI.


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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Tue 21, 2022 11:29 am 
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I agree with Jim, he mentioned the suspect C59 cap first, I just said disconnect it, so he should get the credit, and I get the "also ran" mention.

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Tue 21, 2022 5:40 pm 
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Location: Located in 9 land since 1992.
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I've held off commenting until now, but it seems like the time has come to step back and assess.

You've put in a lot of time and energy on the Ranger. As we age, we become more aware of time we can never get back.

If, IF you get it going, what will you have. A 40 w. AM and CW rig. 40 w. CW is okay but AM? Operating enjoyment entirely dependent on band condx and your antenna. I hope you have a really good antenna. But you also will have basically a Novice CW rig with a VFO and modulator smashed into a too small cabinet. And when fired up, for troubleshooting, the killer B+ is on all the time because everything is on one transformer. Personally, I think a rig like that is more dangerous than a broadcast rig running 3 KV or more. You already know how much fun it is to work on it, with everything smashed into a tiny cabinet and impossible to get to rotary switches. Do you want to pour more time into this loser or hand it off and find something else?


Me, I had a Ranger like yours and I ditched it like a bad date and went back to 100 w. and larger rigs with external VFOs. Maybe my standards are different, but I do know that I don't know how much time I have left in this life to waste.


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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Tue 21, 2022 11:18 pm 
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40 Watts is only down about 4dB, or a little over half an "S" unit from a 100 Watts, not that big a deal.

I like more Watts too, like using the Ranger to drive my thunderbolt or Clipperton-L. Of course using higher power transmitters such as a Valiant, a Johnson 500, or an Invader 2000, can be a lot of fun, but a Ranger is a lot of fun too, just like any number of other old low power transmitters.

Some days its pretty impressive how many miles per Watt you can get, regardless what you're talking on.

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 Post subject: Re: Ranger I - this time, mod bias
PostPosted: Jun Wed 22, 2022 1:09 am 
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Greetings, All!

A Ranger was my first transmitter... I used one as a novice back in 1962-63. And yes, it had some idiosyncrasies.... one of which was due, I believe, to a gassy 6146. When I stopped transmitting (switched from "CW" to "STBY"), I would have an S-9+ white noise level on the band (40 meters). I had to take the transmitter down to "TUNE" and back to standby in order to get rid of it.

All in all, it worked for me and it has a certain nostalgic appeal, which is why I acquired another one some years ago. I have used it on the "Novice Rig Roundup" once or twice and it works just fine as a CW rig. To tell the truth, I don't even know if it works on AM. I don't much care, either, although I suppose I should check it out. It would be worth more when my wife goes to liquidate my stuff upon my demise if the whole transmitter works as designed.

Here's my novice station reproduced for the "Novice Rig roundup". This is pretty much what I had in 1962-63 except that I didn't have the keyer (so I had no side tone) and I didn't have the antenna relay. Going from transmit to receive back then required throwing a DPDT knife switch and manipulating the Ranger "OPERATE" switch. I had to be a bit careful because the HQ-129 B+ was also on that knife switch as I recall... that was the receiver "mute" function.

The key you see in the photo is the very same key I had in 1962. That and my actual paper novice license are all that remain of the original station.

Attachment:
Novice Rig Roundup Station R.JPG
Novice Rig Roundup Station R.JPG [ 289.47 KiB | Viewed 700 times ]


Regards,

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KB6GM
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