The AM Forum

As I write tonight, the band is Loooooong, and AM broadcash stations are flooding in... the weather in Kentucky is good... Boston leads 8-1, tomorrow's game should be awesome... I'm a Yankee fan, but in a toss up between Baston and Kleveland, it's gotta come down for Boston... sorry 8-landers!

Well anyhow, the local NE AMers know that I bought a pretty clean Apache at Nearfeast from Harry, KA1DOP it had been on the air with rather ratty audio.

Being the geenus I am, I decided to not just troubleshoot it, but since it was stock, beef up the coupling caps, and a few other minor things with the stock speech amp... needless to say it wasn't about to be that easy. I won't bore you with the excrutiating details of woe in a circuit that is about as simple as they get, and where nothing much should go wrong... but apparently does.

Bottom line is that it did not want to work right and since I have a no-so-clean Apache on hand that is "all there" that I decided that it would be a very good idea to fire up the low voltage supply on it and see how the stock speech amp's voltages are (should be like the manual says) and what the bloody stock waveforms look like between each stage. The modded one looks like hell, and it looked like hell before I changed much. But onwards...

Obviously the first step is to fire up the LV in the parts mule Apache without the rectifiers and make sure it does the AC voltage thang. Well, that didn't go well... it looks like it's drawing too way too much juice (variac & ammeter dudes)... so after dorking about for a while and testing and retesting stuff, I decided to pull the xfrmr out. No prob.

Pulled it out. Tested it on the bench. All ok.  :o :o

Ummm... <scratches head>?? ??? ???

Ya know what?
That's wierd.

Maybe tomorrow I will put it back in the rig, and wire the connections one pair at a time while firing it up and try to see if it will do that juice sucking act again.

If it does... that will point right at the problem... maybe a big ass carbon track in the ceramic rectifier socket? <--- prime suspect now.

IF all else fails, I'm gonna cleep leed the filaments and the B+ from the good rig over to the bloody parts mule rig and TEST THE DARN STOCK SPEECH AMP!!

This whole business ought to have taken an hour or two, not several elapsed days over several weekends. It's a stupid speech amp!! Geez... >:(

I swear it's haunted, possessed or maybe cursed.

The ghost of the great indian chief??

                  _-_-bear

PS. oh, working or not that low B+ tranny is getting paint tomorrow before it goes back in!

It's karma for not attacking that SX-28  ;D

Wow! Pulling the LVPS xformer right off the bat is pretty radical. Of all the transmitters I had the privelege of working on, the Apache is probably the least complicated and easiest to follow circuit diagram. Not only that, unless the previous owner took to it with a hack saw, mods can usually be replaced to stock rather easily. Having opined like that, I would have disconnected the LVPS line and reconnected one circuit at a time. Does it draw too much LVPS I when in CW? I once found a problem with my DX-100 (which is even simpler) blowing fuses. Long story short, the puny drive xformer was shorted. Also, a real ball buster on a Ranger was the spaghetti used on the pins of the accessory socket had dry rotted allowing a pin (LV B+) to short to ground. As much as you hate to do it, that type of systematical troubleshooting will point you in the right direction fairly quickly.
Good Luck

THATZ RIGHT!! You have to shake off the bad Juju!! You must run around the block 6 times in a clockwise direction, then 4 times in the CCW direction, and then offer up "burnt offerings" to the SX-28 gods for offending them. They are telling you they want an apache for the needed sacrifice!!

The SX-28 and the Beastely 610 twins??   Way to much dark energy.
Burning some chicken  bones over a candle on his stoop may help;
I fear for his safety....  ..    klc

Indeed... bad juju...?   ???

Pulling the LV power iron wasn't too much... everything else was disconnected. No rectifiers, only fils going to the little toobes in the speech amp and NO TUBES!! Nothing else there. I fully expected to find that the thing drew like a shorted turn primary or secondary when I pulled it out. WHY it doesn't is friggin baffling to me. It should.

So, now I will get to spray paint it (done) so it looks sweet, and then put it back in one stupid wire at a time - this time a little neater than the original (remember this is the lesser of the two units...) - and then find out that it works absolutely fine!

As far as putting the speech amp back to stock - sure, but that's not the point! The one giving the problem is clearly possessed! So changing it back would have nil effect!! The logic is inescapable!

Besides it should have taken about 10 mins to check the PS in the lesser one, and test the stock speech amp - not several hours.

Anyhow, perhaps I will sacrifice some mice tonight, maybe that will suffice?

Imagine the insanity inside that SX-28!!!
Who knows what karma was attached to that radio??
Who knows what juju Harry, KA1DOP, has/had and stashed inside that big green Apache cabinet??

I am burning incense.

                 _-_-bear

Yes Mack, it is true.  :(

Unexplicable events. Shades of Roswell?  :o
Or, maybe it was that bad mojo I had in '72??

             _-_-bear

This is why I get the really big bux$$!!

The "problem" appears to be a silicon diode, one of the ones used in place of the 6AL5 toobe for the biass supply. I swear I checked it and it measured good with the diode check, but... operator error is the statistically the number one cause of failures.  :o :o

Working in stuff when I am bushed appears to not always yield the best results... but otoh the transformer looks very nice with fresh paint.  ;D

Perhaps later I will test the "stock" speech amp and see how good it works...

Ah well...

                _-_-WBear2GCR

Bear,
  I will speak an incantation over SX-28 I have been looking at for 2 years and see if that helps.
 

Bill KA8WTK

Bill, be cautious!

That incantation over an SX-28 could have unforseen consequences!!
Who knows where it will strike!!!

(better open it up and replace the caps... it is a darn good reciever)

But, the PS in the #2 'Patchie is all good now... maybe tomorrow I'll 'scope it out. Today I did troubleshooting on an old Spellman HV module, found the problem. No bad juju today.

Maybe it was a good nights sleep... ::) ::)

                  _-_-bear

Oh gee... working for a bit on the #2 'pache this afternoon.

It is definitely pose S'd!!

The secondary voltage when rectified on the low B+ is only 100vdc too high.

There is probably a good reason, and it will likely turn out to be a miswire on the primary side, where there appears to be an extra 6.3v winding... maybe. I'm surprised, but didn't have time to get to the bottom of it.

Likely "operator error" still the primary culprit.

But the stock speech amp seems to work pretty much as advertised. Soooo... after the   PS problem gets "cured" it's back to the modified one... and get it straightened out.

            _-_-bear

bear,
       dont forget that if you have everything else disconnected from the lv B+ string, it will read high. Pretty much all of the factory built table top transmiters use the class A draw from all of the low level audio and rf stages (which are on even when in standby) for the bleeder load on the lv supply. This is done to improve regulation.

                                                 The Slab Bacon

Yeah... but the other one is not THAT high...

I'll look deeper... deeper... deeper

                     _-_-bear

Damn, you beat me to it Johnny. Was thinking the very same thing!

Don't be messin' with the Radio Gods....  ;D

In my youtt when I worked as a repair tech for Heathkit in Manhattan, one quickly learned the order of preceedence for equipment failures:
- operator error
- solder connections
- capacitors
- transistors
- resistors
- everything else

Caps and transistors ran neck and neck.

So what was the problem with the wierd too high voltage reading??
Was it real?
Yep.
So what then?
Bad winding?
Nope.
It was operator error (mine) due to the #2 problem, a solder connection!!

Heh.  ;D

The solder connection was PERFECT to look at! Problem was that while it looked perfect and was in the right place it was between two wires and NOT the ground lug or the other wires on the ground lug!! Ah geez.

Darn thing sat there and looked daggum perfect!  :o
All ok now...

My excuses:
- I can't see as well as I once could by a long shot (anyone see those strong glasses?)
- the number two bench really isn't lit as well as the #1 position
- I was tired
- It looked good
- I never make a bad solder joint
- It is in a tight spot on the chassis
- I'm an imbecile

(gitcher own excuses OM!!  ;) )

Ok?  :o :o :o

                   _-_-bear