6146B in Globe Scout, etc.

[AF9J]

Hi Everybody,

Lately, I'm having an issue with my Globe Scout 680, that seems to be getting out of control.  Trying to tune up for this morning's Midwest Classic Net, has brought it to a head.  Well, actually I have 2 issues:

1.  Lately, powerup is  very slow.  Considering that the main HV capacitor for the power supply is the original paper cap (I saw this when I pulled the enclosure off, and discovered that the rectifier tube was smashed during shipping), I suspect that it's drying or dried out.   So I'll have to replace it (hello Mouser!).

2.  The last couple of weeks, the 6146 final has been very unstable during tuneup.  It is difficult to even get a dip, or set the Load for its typical carrier output of 25W or so.  If I do manage to get it set, checking a few minutes later, things have changed radically (the Plate current is off the scale [pegged at 150 mA plus]), and I have to retune the final (the driver/grid current is typically OK).  I suspect that the 6146 is toast.

I don't have any 6146s or 6146As laying around here.  But, I do have a couple of Chinese 6146Ws, that I bought as replacements for the 6146Bs that were bad in my Kenwood TS-820 (Kenwood hybrids don't like Chinese tubes [they run about 800 plus volts on the plates, which causes the Chinese tubes to arc out - I had to put in a set of NOS Phillips to make my TS-820 happy). They are just collecting dust.  Now as many (if not most) of you know, today's 6146W is pretty much like a 6146B.  Also, using the 6146B in rigs designed around the 6146 or 6146A, can be a use at your own risk affair. 

RCA originally claimed that the 6146B was a direct replacement for the 6146 & 6146A (which of course really isn't true; the internal structure is different), and recommended using the 6146B to replace worn out 6146s & 6146As.  It wasn't until reports were received about rigs like Heathkits, and Collins not being able to neutralize, or suffering runaway parasitics that nuked them out, that RCA decided to recommend against using the 6146B as a replacement for the 6146 or 6146A. 

BUT, I also remember reading that not all 6146 & 6146A rigs had problems using the 6146B.  The only problem, is that I don't have any info on whether or not Globes (especially rigs like my Scout) had issues with the 6146B.  Does anybody have any info on this?  I'd sure hate to find out the hard way (by trying to neutralize a 6146W in my Scout 680, and cooking it out in the process), that Globes don't like 6146B & W tubes.

73,
Ellen - AF9J

[The Slab Bacon]

6146, 6146A, and 6146W should be totally interchangable in just about any rig specing a 6146. the "A" is a slightly improved version with a better heater / filament, the "W" is a mil spec "ruggedized" version. But the "B" is a horse of another color!

The 6146B has a slightly higher dissipation rating and a little different grid structure. It was actually designed for class AB1 grid driven SSB linear service.

The plain 6146, and the A &W variants are totally interchangable, but the "B" is not. It will work in some rigs and not in others. some people have swapped them with no problems and others have had problems. It is totally rig specific.

I dont think it would make a big difference in your 680, as they run a pretty low B+ and low power, but you will have to try it and see. I have a 680 on the shelf, but it has been a long time since I have looked at it. If the rig has a biass adjustment, just set the final biass up high enough that it cant take off and work backwards from there.

                                                                                    The Slab Bacon

And besides, 6146s look pretty cool when they fry out.............. Inside the bottle first the plate will glow bright red, then everything starts the blue glow, and then the lightning bolts fly around inside the bottle!!   But I dont think the 680 power supply is strapping enough for that kind of failure.

[AF9J]

Thanks Frank,

Nope, I think the Scout only does about 700V on the plate.  As for the W in the 6146 - all the W means, is that' it's a militarized/ruggedized version of the 6146. When RCA discontinued the 6146A, all 6146Ws were basically made as variants of the 6146B.  They do put out a little less than a 6146B though.  My Kenwood TS-820 will do about 10W more with the B, than the W version.  In some cases though, the Ws were nothing more than handpicked 6146Bs that passed vibration testing.  How do I know?, the Phillips 6146Bs I put in my Kenwood are listed as JAN/Milspec 6146Ws by RF Parts (whom I bought them from).  A friend of mine who has a TS-820S, talked with one of the RF Parts guys at Dayton in 2006, and was told by him that the data they have on their Phillips Jan/Milspec 6146Ws, basically shows them to be renamed 6146Bs that were rugged enough for military use.

I may give things a try this afternoon.  I think there's an internal short or break in the 6146 final in my Scout.  As soon as I hit a dip, the plate current pegs back up to 150mA, and RF output goes down to zero.


BTW,  here's the HTML version of the info I just mentioned:

http://64.233.167.104/search?q=cache:iTNXtBe55UgJ:www.n6wk.com/kenwood/The_6146_Family_of_Tubes-

 

73,
Ellen - AF9J

[The Slab Bacon]

Ellen,
         I dont think the HV in the 680 is anywhere near 700v (I have been wrong before)
But, IIRC it is somewhere around 450-500v. It sounds like your 6146 may be gassy.

There have been discussions here before on this same topic several times. Many hams that dont know better usually opt for the "B" figuring that it is the upgraded better choice,
little do they know.

I believe that the "B" was originally designed to be a "drop in" replacement with the standard screen voltage and control grid biass left the same as the original, or you could readjust the grid voltages accordingly to take full advantage of the higher gain of the
new variant tube. Unfortunately it didnt work out that way. One of he reasons that they go parasitic is that you have to increase the control grid biass to keep them tamed down.

The B versions do work pretty well in AB1 service. (which they were designed for) In my valiant, I have 6146As for the class C finals, and 6146Bs for the AB1 modulators, and they work flawlessly and have for years. Also keep in mind that some transmitters
 (like Apaches) have pretty crappy neutralization scheems. Like I said before interchangability is definately application specific.

                                                                                    the Slab Bacon

[AF9J]

Hmmmm,

I'll give it a try, but watch things closely.  Thanks for your input Frank.

73,
Ellen - AF9J

[AF9J]

Hi Everybody,

Well, I did the dirty deed tonight - I put in one of my spare 6146Bs in my Globe Scout 680.  I'll have to keep an eye on it.  There is NO neutralizing capacitor in my Scout.  While I was at it, I sprayed the tube socket pins with DeOxit.  Also, I replaced the metal 6V6 that is used for the crystal oscillator, with a glass 6V6G, that saw some light use in a guitar amp I had about 17 years ago.  Everything loaded up.  The plate dip point on 75m is still razor sharp (if I overshoot it, and max out the plate current meter, I hear what sounds like some arcing).  So far, it seems stable plate current-wise, and I'm getting about 25W of carrier, with decent modulation, at about 110-115mA of plate current. Strangely enough, I seem to have lost the meter shunt for reading grid current (In spite of the fact that I am getting full power [about 40W on CW, and 25W-27W of AM carrier).  Tomrrow morning, I'll give it the acid test on the Midwest Classic Net.  I'm beat. Good night.

73,
Ellen - AF9J