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 1 
 on: Today at 04:21:45 PM 
Started by KD1SH - Last post by KD1SH
Good idea - I've seen K3MSB's site, and he sure seems to know the rig.  Pretty sure I checked that resistor, but I'll take another look.


I have a 5100B and have not experienced these issues. However, if you haven't talked to Marc Bell, K3MSB, you may want to give it a try. He is very experienced with this rig.

One more note- there is a filament dropping resistor on the 6u8 audio amp, I believe it is R415 and 4.7 ohms. This resistor takes a beating and it's value should be checked if you have not already done so.

ka8gef

 2 
 on: Today at 04:19:14 PM 
Started by KD1SH - Last post by KD1SH



The Audio modules between his two rigs were wired differently at the plug. Caused lotsa smoke!


  I'm quickly discovering that this is the curse of many boat anchors: they were made in many iterations, with the differences being poorly documented, if at all.


I just looked at the schematic from BAMA, and boy that schematic is busy, and the connectors sure clutter things up. Noticed R23 on the 6146 PA grid bias...22K. That means with 5ma grid drive, this resistor adds -110v grid leak bias on top of the fixed bias from the big tapped power resistor. What if this resistor has drifted up in value?? Does varying the grid drive have an effect on the modulated positive peaks?


  I think you're looking at a schematic for the 5100, non-"B".  In the "B", that resistor is R318 and it's 3.3K.  The "B" doesn't have that big tapped power resistor.
  Grid drive changes don't seem to have any effect on the modulation.


Would be nice to have a scope, and a 100X compensated probe (~$20 on Ebay). Need to determine if the peak modulation is limited to audio power, or the RF side where the 6146's are limited for some reason.


  Yes - having a 100X probe would be fantastic!  Was out running errands earlier today and thinking that I wish I could put the scope on the modulated B+.  Thought of kluging up some sort of resistive divider, but the additional load might have a Heisenberg effect.


 3 
 on: Today at 02:19:55 PM 
Started by KD1SH - Last post by ka8gef
I have a 5100B and have not experienced these issues. However, if you haven't talked to Marc Bell, K3MSB, you may want to give it a try. He is very experienced with this rig.

One more note- there is a filament dropping resistor on the 6u8 audio amp, I believe it is R415 and 4.7 ohms. This resistor takes a beating and it's value should be checked if you have not already done so.

ka8gef

 4 
 on: Today at 12:32:39 PM 
Started by KD1SH - Last post by WD5JKO


I have no direct experience with the BW5100.

A good friend had two of them, and he discovered a few things.

On 40m with the internal VFO, these things FM...badly. There was evidence from prior owners to better shield the VFO cover. Using a direct crystal (7160) eliminates the issue.

The Audio modules between his two rigs were wired differently at the plug. Caused lotsa smoke!

The audio modulation was never right on either rig. Had to drive it hard to get the average up, and when doing so, was pretty wide. Most likely he was over modulating on the negative side like yours.

I just looked at the schematic from BAMA, and boy that schematic is busy, and the connectors sure clutter things up. Noticed R23 on the 6146 PA grid bias...22K. That means with 5ma grid drive, this resistor adds -110v grid leak bias on top of the fixed bias from the big tapped power resistor. What if this resistor has drifted up in value?? Does varying the grid drive have an effect on the modulated positive peaks?

Would be nice to have a scope, and a 100X compensated probe (~$20 on Ebay). Need to determine if the peak modulation is limited to audio power, or the RF side where the 6146's are limited for some reason.

Jim
Wd5JKO

 5 
 on: Today at 12:27:05 PM 
Started by KU8L - Last post by Tom WA3KLR
Something that irks me about the HQ-129 and HQ-120 designs is that the audio output transformer is next to the power transformer where magnetic coupling from the power transformer to the output transformer can result in hum.  The output transformerís core in my HQ-120X is oriented 90 degrees from the power transformer. This may be deliberate.  It looks like the audio transformer in the -145 is underneath the chassis and is a ways from the power transformer.  Some receivers and hi-fi audio gear put the transformers in opposite corners of the chassis, not necessarily required, but was guaranteed to eliminate the magnetic coupling.

Another source of hum in the speaker is a ground loop in the ground side of the output transformer secondary to the speaker.  It looks like the output transformer in the -145 is close to the rear and the secondary wire to ground might be connected directly to the speaker jack ground; this is the best connection as it eliminates a ground loop with the filament currents.

If either of the two above hum coupling modes exist, they can be listened for by pulling out the HV rectifier and turning on the radio and listening in the speaker for hum.  Ideally there should be no hum in this test.

 6 
 on: Today at 11:49:25 AM 
Started by ka1tdq - Last post by ka1tdq
I'm building my knowledge too. To be honest, I was relying on Phil's schematic for those components. I'm not sure what changing their values would have on the circuit.

Jon

 7 
 on: Today at 10:03:51 AM 
Started by KU8L - Last post by KU8L
Thanks Dmod.

Yep, brand new can.  It was one of Hayseeds'  65mf on output, 45 on input so I added another 60 on the input.   Only minor difference.  This is the A version with SS rectifier.  

I think I have a solution now.   I am going to put a 10W resistor between the rectifiers and the filter input.  This should knock it down some.  Also, without the feedback modification, the hum is now tolerable.  I would say it is somewhat better than stock.  THe resistor will reduce the plate and screen voltages on the 6AQ5 which is OK because the thing has pleanty of output.

ALL of the audio examples I can find take feedback from the out of phase side of the output trans secondary back to the cathode of the driver.  OR, as the Wireless Girl site mentions from plate back to plate.  THese are correct negative feedback--as is the original Hammarlund setup for auto-response.

But it really doesn't matter in this case because ANY small amount of ripple that shows up on the plate of the output tube is going to couple back to the input and show up amplified.

So I will be adding negative FB from the secondary of the output trans, back to the input of the driver or the cathode of the driver to see if it is any better, if not, I'll leave the autoresponse FB net in place but apply it so the FB is there all the time, not just at lower levels.

THe  129x got it right by using two PS chokes!

Curt

 8 
 on: Today at 09:06:54 AM 
Started by KD1SH - Last post by KD1SH
  BTW: I also tried swapping the leads of the D104 crystal head - no significant difference.  Tried injecting a clean sine into the mic jack, and it's still asymmetrical, so it's not my voice (which probably is somewhat asymmetrical) or the microphone.  Also tried using my IHY box, which gives me positive asymmetry with the Ranger, and that made it just a tad better, but still strongly favoring the negative.

 9 
 on: Today at 08:51:29 AM 
Started by KD1SH - Last post by KD1SH
  That was the first thing I tried, being the easiest. Swapped the plate leads, then the tubes.  Today I'll try a pair of new (NOS) 6146's.
   The 5100B's modular construction is very nice, but in this situation it's a bit of a pain, since I can't probe into the modulator without removing it from the chassis.
   I've already gone through the modulator in my recap process: replaced the electrolytics, and both of the screen resistors in the RF deck, one of which had drifted up to 174 ohms from the original 100.  Everything else looked nice in there, but I'm going to go back into it today.
   I'm also going to get my LCR meter on that 20H screen choke; shorted windings in there would certainly banjack the modulation.  I'll check the screen bypasses on the final PA 6146's, too.
   Many other hands have been into this rig before I got it - I've already set right a couple of wiring errors, - one of which had shorted out the filter choke in the pi-section bias supply filter - so maybe there's something like that going on that I missed.

Might be a weak modulator tube. Try swapping the modulator plate cap leads.

 10 
 on: Today at 08:39:01 AM 
Started by ka1tdq - Last post by K8DI
Yes, and actually I had to make a few resistor changes in the original provided schematic since my lower B+ is 375 vdc and not 350. I hand drew a complete schematic yesterday. The oscillator supply is from the 375 vdc center tap and uses a series dropping resistor.

Jon
Hi Jon,
I am reading your schematic over coffee this morning, and I have a couple questions.

First, why no audio bypass caps for the last audio stage cathodes (and maybe why such a small bypass on the first stage)?

Second, the word around here seems to be that the screen bypass on finals should be smaller, like 0.001uF, to avoid bypassing the higher audio frequencies along with the RF. Iím not sure what the reactance target is supposed to be or how to determine the AC impedance at the screen so that one could choose the bypass to be small at RF but big at AF compared to the screenís reactance in a given circuit, though.

Iím building my knowledge here....not questioning your decisions. Please explain so I can learn.

Ed

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