The AM Forum

THE AM BULLETIN BOARD => Technical Forum => Topic started by: w3jn on January 30, 2011, 08:30:31 PM



Title: Aitch-Tee 20 on the air
Post by: w3jn on January 30, 2011, 08:30:31 PM
I've had this HT-20 sitting around for several years and keep meaning to put it on the air.  Finally got to it this week, and the first QSOs were with Rich N2RY, Chuck W3FJJ, Ralph, W3GL, and Todd KA1KAQ checking in on slopbucket.

Yesterday I was about ready to pitch the damn thing out the window.  I kept having problems with the shaft coupler on the tuning control coming loose.  Of course getting to it entails removing dozens of screws, and even then, it's tricky getting to the coupler.  After the sixth time taking the thing out of the cabinet and the coupler almost immediately coming loose again, I carefulyl removed the set screws and installed new ones, that got a bit more "bite" on the Bristo wrench.  OK, worked for about 3 round trips on the tuning control and it came loose again.  This time I reefed down on those screws as hard as I could.  So far, it seems to be holding OK.

Also during the process it was obvious the final tune capacitor and roller inductor were making intermittent contact, so a light coat of de-oxit on a q-tip cleaned things right up.

Anyway, got decent reports with it.  It's a really cool xmitter and hope to use it more with the SX-88!


Title: Re: Aitch-Tee 20 on the air
Post by: K5UJ on January 30, 2011, 10:51:48 PM
I almost skipped over this thread not recognizing the subject.  thought it was some kind of heathkit at first  :)

todd, what are you doing on slopbucket  ;D just kidding.

JN, if you can pitch a HT20 out a window I hope I never get you mad at me.  So, I need to get a set of bristos. 

Is all you had to do was rework the shaft on the PA tune, and clean with de-oxit?  That's it?   No recapping?  What's the fan on the 4D32 like? 

Rob


Title: Re: Aitch-Tee 20 on the air
Post by: k4kyv on January 31, 2011, 01:12:39 AM
I almost skipped over this thread not recognizing the subject.  thought it was some kind of heathkit at first  :)

todd, what are you doing on slopbucket  ;D just kidding.

JN, if you can pitch a HT20 out a window I hope I never get you mad at me.  So, I need to get a set of bristos. 

Is all you had to do was rework the shaft on the PA tune, and clean with de-oxit?  That's it?   No recapping?  What's the fan on the 4D32 like? 

Rob

The HT-20 isn't a slopbucket rig.

http://www.radioing.com/museum/tx2.html

I have had the same problem with set screws, particularly if there was only one set screw instead of two on the shaft, located 90 apart.  It would seem to me that three set screws 120 apart would be even better, but I never have seen that used.

One way I  have cured the problem is to remove the knob (and if possible the shaft) and grind or file a flat spot on the shaft where the set screw goes, kind of like you sometimes see on BC radio volume control shafts.  Also, partially drilling into the shaft to leave a shallow hole to accommodate the tip of the set screw should work.

What really sucks is when the knob or other fitting rotates on the shaft and the set screw scores a groove in the metal, which can make the knob almost impossible to remove.  The main tuning knob on the early HRO receiver is bad about that. On later versions they went to dual set screws 90 apart.

I have seen set screws with a pointed tip instead of a flat end.  They work well to keep the knob from slipping, but they permanently damage the shaft making it nearly impossible to remove the knob once the screw has been tightened the first time.  Maybe the gouge left by the sharp set screw tip could be de-burred by hand using the tip of a small gauge drill bit.


Title: Re: Aitch-Tee 20 on the air
Post by: w3jn on January 31, 2011, 07:50:02 AM
Todd was on slopbucket, I was on AM using the HT-20.

The coupler in question has two setscrews but they're 180 degrees apart.   No way to get in there and grind a flat spot w/o removing the whole front panel and the cap/inductor assembly.  And Don, I've been there and done that with HRO and NC-100 knobs - the end mushrooms and they're almost impossible to remove.

I had done a recapping of it some years ago when I first got it - a few coupling caps and a few electrolytics as i recall.   The fan is pretty quiet but doesn't seem to do too good a job of keeping it cool - it gets uncomfortably warm just sitting there idling...


Title: Re: Aitch-Tee 20 on the air
Post by: K5UJ on January 31, 2011, 08:33:39 AM
Okay, well I have to remove the front panel of mine anyway because the paint is peeling so badly the front panel needs to be redone.  Bob W0YVA has a screen for the HT-20 f.p.  The bezel pot metal on mine is warped and cracked so I may just remove it and run the rig without it.   I wonder if running it with the covers off will aid in the cooling.   I've heard the fan was in there because the rig got hot due to all the TVI shielding. 

Rob


Title: Re: Aitch-Tee 20 on the air
Post by: w3jn on January 31, 2011, 10:20:26 AM
There's a lot going on in that thing; it's well populated with iron!

Rob, go for it - it's a pretty nice sounding rig right out of the box, and (once I cleaned all the contacts on the caps and roller inductor) it tuned very nicely.  I did notice that max power didn't correspond with a dip in plate current.  Neutralization?  No neutralization cap I can see though....

I'm driving it with a HP 3325 sig gen.  1 volt to the VFO input jack works FB.


Title: Re: Aitch-Tee 20 on the air
Post by: K1JJ on January 31, 2011, 10:54:38 AM
"Todd KA1KAQ checking in on slopbucket."

With all those big AM rigs down there, it's come to this???   ;D


Johnny - I've always had trouble too with those Allen set screws on shaft couplers, especially with vacuum variables and turns counters. When one slips, all the preset numbers on the counter are lost.  Nowadays, I pull out those homo-Allen screws right away and replace them with manly 6-32, or whatever standard-head  screws that can be torqued down. I've even added some LockTight if I get really POed.


For how long are you back from SV-land?


T

 



Title: Re: Aitch-Tee 20 on the air
Post by: k4kyv on January 31, 2011, 11:47:14 AM
I did notice that max power didn't correspond with a dip in plate current.  Neutralization?  No neutralization cap I can see though....  

Is the plate tank tuned with a variable cap, or does it use a fixed cap tuned with the roller inductor?  With fixed capacitance/variable inductance tuning, there is a slight offset between the dip and resonance.  I once read an explanation somewhere, which was simple and made perfect sense at the time.  But I forget the exact reason, and have never been able to relocate that explanation although I know it is hidden somewhere in my radio library, and I have never taken the time to re-research it.  It must have something to do with the way reactance is introduced into the tuned circuit when the inductance is varied versus when the capacitance is varied. I seem to recall that the explanation included a vector diagram.  Maybe  someone reading this already knows the answer or can point me in the direction to relocate the textbook explanation.

With the Gates BC1-T, the  factory recommends dipping the final, and then rotating the tuning inductor until the plate current increases about 10%, while watching the rf current to make sure it increases, not decreases. If you tune off the dip the wrong way, you will tune away from resonance not towards it.

And Thom, I agree with you regarding the Allen screws.  Let the hex wrench slip one time and you have a nice pivot bearing assembly.  Bristo head screws are better, but never ever try to turn one with an allen wrench; you will strip the splines and turn it, too, into a pivot bearing assembly.  I seem to get the best results with a Torx drive.  Too bad you can't easily find the common sizes of  set screws with Torx heads. If they have their own disadvantage, I haven't discovered it.  I have found with automotive work, the screw (or the driver blade) will twist in two and break before the wrench will slip. I have had less spectacular success with plain slotted screws; the driver blade may slip and damage the slot, or half the head will break off at the slot. But if you use a regular screw as a set-screw, file the burrs off the end; otherwise it will gouge the shaft and make removal of the knob difficult or nearly impossible. Look at the tip of a factory made set screw and compare it to a regular run-of-the-mill screw.

Phillips screws have to be the worst of all possible worlds; those things come ready-made as pivot bearing assemblies from the outset because both screw and driver easily round out whenever enough torque is applied, and you have to apply downward force at the same time you apply the torque to get the driver to grip the screw.

One method I have used successfully to remove a stripped out Bristo screw (should work equally well with an Allen) was to take a left-handed drill bit that is just the right size to grab inside the stripped out hole, and turn the screw out in normal fashion.  Of course, an Ease-Out may work, but they only make those down to a certain size and I have never found one small enough to fit tiny screws like #4 and smaller. I used a #49 left-hand drill bit to remove the kilocycle dial from the tuning shaft of the 75A-4.  First, I determined the proper drill size via trial and error using regular right-hand drill bits, then ordered the same size left-handed bit from McMaster-Carr. But be careful; break off a drill bit or ease-out inside the screw hole, and you will never get the thing off.  I heated the screw in the 75A-4 using a tiny pencil type soldering iron with a blob of heat-sink compound on the tip, to soften up the green Locktite that Collins used, and it  came right out.  I made a heat shield out of cardboard and tin-foil to keep from melting the plastic kilocycle dial disc with the barrel of the soldering iron.


Title: Re: Aitch-Tee 20 on the air
Post by: WD8BIL on January 31, 2011, 12:01:22 PM
Quote
I did notice that max power didn't correspond with a dip in plate current.  Neutralization?  No neutralization cap I can see though....

Hi Johnnie,
Same thing happens in the Viking Bud roller/cap setup. I just tune for best looking waveform at max power, check the 2nd harmonic and go for it. Been working HI HI FB so far.


Title: Re: Aitch-Tee 20 on the air
Post by: Todd, KA1KAQ on January 31, 2011, 12:37:08 PM
"Todd KA1KAQ checking in on slopbucket."

With all those big AM rigs down there, it's come to this???   ;D

Uh...pot, kettle, black, Mr. SSBDX?  ;)

Sure sure, pile on, guys. Ralphie got me good too when I first tried to break in, reminding me that they were using radios with carriers (wise-ass).  ;D

As things go here, everything is currently 'broken' or not-quite-working-right in the AM transmitter dept - again. Not counting the 450 rig that still needs reassembly. I suppose the positive side is, you can't break it if you don't use it, so at least I can say that in my defense (we'll ignore the obvious reciprocal statement 'you can't use it if you don't fix it' for now). And this particular SSB rig is going to FrostFest next week, so maybe it will find a new home and redeem my sullied name. So sullied!

There's a lot going on in that thing; it's well populated with iron!

Rob, go for it - it's a pretty nice sounding rig right out of the box, and (once I cleaned all the contacts on the caps and roller inductor) it tuned very nicely.

And I'll add, you sounded GREAT here on it, Johnny. I recall hearing you mention it when I first tuned in on the 75A-4, but between getting the SSB rig hooked up and switching between AM for listening & back to SSB to try to break in (forgot a few times and transmitted in the AM position, resulting in zilch), I forgot you were using it. It just sounds like you.

Signal was S9+10 here and aside from not quite having the same punch as the GPT-750, I really couldn't hear a difference. Maybe not as many lows, but as you know the 380 doesn't exactly have a Hi-Hi-Fi receiver either. So it does indeed sound good as-is. Recalling the one we hauled north to NEAR-Fest, it's amazing they had room in it for anything else with all the iron inside. And all those screws....must be at least as bad as trying to open a Johnson Flashbox *twitch*. 

Fire yours up, Rob!


Title: Re: Aitch-Tee 20 on the air
Post by: K5UJ on January 31, 2011, 06:45:55 PM
<<Fire yours up, Rob!>>

Well I feel like the pressure is on  :D to be honest Todd, all my stuff is busted here too, and my operating has been limited to an occasional check-in to a net on 20 meters running a plastic radio on USB  ???  May as well come clean.

Rob


Title: Re: Aitch-Tee 20 on the air
Post by: w3jn on January 31, 2011, 08:24:44 PM
Quote
For how long are you back from SV-land?

Going back Feb 15.  I'm in training this week, gonna head to FrostFest this weekend and see part of the MSDS crew  ;D

Quote
Is the plate tank tuned with a variable cap, or does it use a fixed cap tuned with the roller inductor?

Don, it's a ganged variable cap/roller inductor a la the Viking I or II.  Good points on the set screws, I oughta replace the damn things with regular flatheads that I can get a bit more leverage on.  They're Bristo spline set screws but quite small so you can reef on the spline wrench only so much before it starts twisting.

Quote
And I'll add, you sounded GREAT here on it, Johnny. I recall hearing you mention it when I first tuned in on the 75A-4, but between getting the SSB rig hooked up and switching between AM for listening & back to SSB to try to break in (forgot a few times and transmitted in the AM position, resulting in zilch), I forgot you were using it. It just sounds like you.

Signal was S9+10 here and aside from not quite having the same punch as the GPT-750, I really couldn't hear a difference. Maybe not as many lows,

Yeah, I didn't have the processor/limiter in line so I had to watch the baseline, and that DAP stuff really fills out the audio.  I noticed the same thing in.re. lack of lows when I was listening to it on the SX-88 - sounded kind of tinny compared to the GPT-750, but I'm glad it wasn't earbleed quality!

And Bud, thanks for that.  The HT-20 has a staunch output filter and the output waveform looked nice and sine-waveylike so I'll just run ;er as is.



Title: Re: Aitch-Tee 20 on the air
Post by: K5UJ on January 31, 2011, 10:01:11 PM
After work tonight I went over to the local Sears hardware store and asked for "Bristo" wrenches.  Three guys gawked and made me feel like I was snipe hunting.  In a way I was, but not due to anything deliberate  ;)  It turns out the name of the company is Bristol with an L on the end.  And they're expensive.   I'm merely mentioning this so other noobs like me don't go making the same mistake.   Forget about Sears, Ace hardware etc.  Maybe Berland's House of Tools has them but Max Gain sells them however they're the kind of thing you don't want to buy until you know exactly which one you need, otherwise you'll be blowing a lot of ca$h.   They make a regular hex type and a spline type.  I figure the spline type is the one you all like.   Each one is around 15 bucks.


Title: Re: Aitch-Tee 20 on the air
Post by: WBear2GCR on January 31, 2011, 11:06:36 PM

a set of Bristol wrenches on ebay for knobbers and things like that is not expensive on epay last time I looked - there are other sources that are not too expensive, search the 'net - I found a few likely candy dates last time I was looking...


Title: Re: Aitch-Tee 20 on the air
Post by: K5UJ on February 01, 2011, 09:55:26 AM

a set of Bristol wrenches on ebay for knobbers and things like that is not expensive on epay last time I looked - there are other sources that are not too expensive, search the 'net - I found a few likely candy dates last time I was looking...

Bear you are correct. I never thought about eBay.  How about this: 

http://cgi.ebay.com/SS-508-Bristol-Spline-Wrench-Set-Collins-Hallicrafters-/360273140402

rob


Title: Re: Aitch-Tee 20 on the air
Post by: Todd, KA1KAQ on February 01, 2011, 10:50:55 AM
After work tonight I went over to the local Sears hardware store and asked for "Bristo" wrenches.  Three guys gawked and made me feel like I was snipe hunting.  In a way I was, but not due to anything deliberate  ;)  It turns out the name of the company is Bristol with an L on the end. 

True Rob, though it still tends to confuse many people. The manufacturer is indeed Bristol, but the original wrench design really was/is Bristo.

http://www.datamp.org/patents/displayPatent.php?id=42304&pn=1,075,710

Description:
The patent covers the "dovetail" grooves in the recessed central socket of the set screw, and the corresponding splines on the wrench.

Produced as the BRISTO screw and matching wrenches. Contemporary ads note the screws could also be turned by a screwdriver with appropriate blade width.


This has been an ongoing debate for years with some insisting 'Bristo' was really just a typo in a Collins manual from decades ago that got carried forward (since they were such a prolific user of this hardware and name). Turns out the NAE were again wrong. Big surprise. Calling it a Bristol wrench is the equivalent of asking someone to hand you a Snap-On or Craftsman wrench.

BTW, Xcelite makes a nice set of these wrenches, can't remember the precise number but 99SP or such comes to mind. You can often find them on ebay and I saw someone carrying a handful at the last NEAR-Fest. The L type that Jon sells online are good wrenches, but the Xcelite version will give you more purchase on those stubborn, stuck screws. They're also long enough that you can grind the tips down clean when they get worn and still have plenty of wrench left.

There is also a fellow in VA who makes reproductions of the large aluminum L Bristo wrench found on the back of original R-390s (not the later, cost-reduced A models). Though it's only one size, it should fit a lot of the knob screws out there. Excellent quality, I think he gets around $9 for one. I'm going to order a couple more from him as soon as I track down his info again.





Title: Re: Aitch-Tee 20 on the air
Post by: Steve - K4HX on February 01, 2011, 11:09:29 AM
Bristo, Bristol. Either way, they suck.


Title: Re: Aitch-Tee 20 on the air
Post by: K1JJ on February 01, 2011, 12:15:54 PM
Bristo, Bristol. Either way, they suck.

How do you think the Dovells got the name to their song?

Stomp those Bristols into the ground.

http://www.youtube.com/watch?v=APR1ekM8AZ8


Title: Re: Aitch-Tee 20 on the air
Post by: k4kyv on February 01, 2011, 01:32:40 PM
Bristo, Bristol. Either way, they suck.

Not as much as Phillips heads.  Bristo screws work better than Allens as long as you don't break off the splines inside the holes, most  commonly done by trying to use an Allen driver to turn a bristo screw.  What sucks about bristo is finding the drivers.  I lucked out back in the early 80s and picked up a set of Xcelites at the local TV repair/electronics store, plus I have a bunch of the little L-shaped ones.  I would be very reluctant to use a flat blade screwdriver to try to turn a bristo screw, because you are exerting all the torque onto just one pair of the 6 splines, thus running a great risk of breaking them off.

Somebody finally got it right with Torx, but those are rarely seen in electronics equipment.  I suspect that most of our stuff was built long before Torx srcews and wrenches were even thought of.


Title: Re: Aitch-Tee 20 on the air
Post by: K5UJ on February 01, 2011, 02:08:48 PM
Bristo, Bristol. Either way, they suck.
Okay what doesn't suck--my tastes are simple--I'm easily satisfied with the best  :D

This Torx thing?  what is it?  

p.s. tnx for bristo bristol history Todd.


Title: Re: Aitch-Tee 20 on the air
Post by: k4kyv on February 01, 2011, 03:05:55 PM

Okay what doesn't suck--my tastes are simple--I'm easily satisfied with the best  :D
Gravity doesn't exist.  The world sucks.   :)


Quote
This Torx thing?  what is it?

http://en.wikipedia.org/wiki/Torx

Interesting, but here is exactly what sucks about Phillips screws:

By design, Torx head screws resist cam-out better than Phillips head or slot head screws. Where Phillips heads were designed to cause the driver to cam out, to prevent over-tightening, Torx heads were designed to prevent cam-out. The reason for this was the development of better torque-limiting automatic screwdrivers for use in factories. Rather than rely on the tool slipping out of the screw head when a torque level is reached, thereby risking damage to the driver tip, screw head and workpiece, the driver design achieves a desired torque consistently. The manufacturer claims this can increase tool bit life by ten times or more.

I nearly always damage the driver and/or the screw head from the driver slipping out of the Phillips head, long before any danger of stripping the threads or breaking off the screw.


Title: Re: Aitch-Tee 20 on the air
Post by: K5UJ on February 02, 2011, 09:58:13 AM
Don, thanks, but it looks like the torx are not used for knob shaft set screws.   Or are hex replacements available?  Yes, the philips are a pita. 

Rob


Title: Re: Aitch-Tee 20 on the air
Post by: Todd, KA1KAQ on February 02, 2011, 11:26:13 AM
That's the thing - you get to choose Allen head, Flat blade screw head, or Bristo head for set screws. I've found that Bristos work the best IF treated properly from Day 1 and not mangled up by someone trying to use an Allen wrench or beat-to-snot Bristo wrench. Those little slots really work well for adding positive grip. The problem is, the first time it gets over-tightened, rusted in place after decades, or the wrench slips and damages the walls, it's all downhill from there. But the same is true of the other two types, with less grip to start with. Any way you look at it, if you play with this old stuff long enough, at some point you'll be breaking things and swearing a blue streak.

And John's problem with the ever-loosening shaft coupling on his HT-20 is just another example of the FUN to be had.

Now, if we all used plastic radios with those push-on, slip-off Fisher-Price knobs, well.....life would be so much....simpler.  :)


Title: Re: Aitch-Tee 20 on the air
Post by: Steve - K4HX on February 02, 2011, 11:49:42 AM
It's also a matter of making things more complicated than they need to be. Proper design would ensure that a human could torque down a single-slotted set screw (or set screws) with a flat blade screw driver and the shaft would turn without slipping.


Title: Re: Aitch-Tee 20 on the air
Post by: W2VW on February 02, 2011, 12:20:19 PM
The first guy you meet in hell is Allen.



Title: Re: Aitch-Tee 20 on the air
Post by: k4kyv on February 02, 2011, 04:56:07 PM
It's also a matter of making things more complicated than they need to be. Proper design would ensure that a human could torque down a single-slotted set screw (or set screws) with a flat blade screw driver and the shaft would turn without slipping.

The first step in the proper direction would be to use a fine thread on an adequately sized set screw.  6-40 or 8-40 maybe on larger knobs. A torx head would work great.  They don't self-destruct with excessive torque the way allens and bristos do. I have never busted one trying to turn it, but I did break a driver once.  The splines remained intact, but the shank at the end of the driver couldn't take the torque and literally shattered to bits.  When a screw is stuck, I have found PB Blaster to be a big help.  Works much better than WD-40 or Liquid Wrench, but stinks like hell.

Another thing that sucks about allens and bristos is that the driver blade is sometimes left with a permanent twist after you try to turn a stuck screw. I've had that to happen to both the short L-shaped drivers and good quality Xcelite drivers with a plastic handle.


Title: Re: Aitch-Tee 20 on the air
Post by: KM1H on February 02, 2011, 09:17:21 PM
With 2 set screws on that HT-20 Id suspect its time to measure the torque on the Cardwell (Im guessing but its Cardwell in the HT-90) cap.

And if you get tired of tightening drive it up here some Nearfest.


Title: Re: Aitch-Tee 20 on the air
Post by: w3jn on February 03, 2011, 06:38:03 AM
The tuning knob drives a gear assembly that turns the tuning dial, a roller inductor, and variable cap all in tandem.  I did lubricate the shaft bearings on everything the best I could and it's much better, but I have my fingers crossed that the setscrews will stay put this time.


Title: Re: Aitch-Tee 20 on the air
Post by: W3DBB on February 03, 2011, 09:08:16 AM
.
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands