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Advice on my rapidly deteriorating DX-100b audio?




 
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Author Topic: Advice on my rapidly deteriorating DX-100b audio?  (Read 22158 times)
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kf6pqt
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« Reply #25 on: June 03, 2007, 06:59:51 PM »

Quote
The "stock" mod section uses a helluva lot less components.

Lordy, you ain't kiddin.

Since I'm only looking at the "non-B" version schematic from Bama, could someone tell me if the section between the driver xformer secondary and the mod xformer primary caontains more than:

2 1625's
2 1k resistors (unknown wattage)
1 0.1 mf 600v cap
1 0.1 ohm resistor... that bigassed ceramic thing?

Thats it?
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W6IEE, formerly KF6PQT
The Slab Bacon
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« Reply #26 on: June 03, 2007, 07:12:17 PM »

Be careful with the low level end as thats how my dx100 blew up. a ultrasonic feedback built up and I was not around to shut the rig off. It melted everything including the LV transformer. That's how I met the Slab so many years ago.

Ah yes, the crapout / flameout of the original Derb 100!! If it wasent for that I prolly would never been lisenced! As I was contacted by its new owner to resurect it! That story is way too long to type here, but I have told it on the air many times. It has also brought some great long term friends and friendships!!


As far as mod tubes for 100w table top boatanchors, a pair of 6146s will work as well as just about any other pair of tubes as long as the associated circutry is properly designed. a pair of 6146Bs will easily make 120W+ of audio in class AB1 without any need for a strapping driver circuit as they dont need to see any grid current. You can feed them with a well designed fuzz inverter!

Just pick a plan for the modders and build a WELL DESIGNED modulator circuit. In that rig 6146s, 807/1625s, 6550s, and just about any other tube that can tollerate 750 - 800v on the plates will work just fine. Just build the rest of the speech amp/modulator to be compatable with them.

                                                                                 The Slab Bacon
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The Slab Bacon
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« Reply #27 on: June 03, 2007, 07:17:07 PM »

the .1 ohm resistor (that big assed ceramic hing) is prolly in the cathode circuit of the modders as a meter shunt for sampling the modulator current.
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kf6pqt
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« Reply #28 on: June 03, 2007, 07:39:30 PM »

Correctamundo, goes between cathodes, meter, and high-current supply center tap. That settles it then, this thing will be a few pounds lighter, having gone back to 1625's.


Anyway, I'm back from poking around her nether regions again... NO FUSES. I've found other amusing things, more when the pix are done copying over from the camera.
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W6IEE, formerly KF6PQT
kf6pqt
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« Reply #29 on: June 03, 2007, 07:56:05 PM »

Its just one of the 6146's (mod tube) superfluous cathode bypasses, but the damn thing still isn't soldered!


* notsoldered800.jpg (103.13 KB, 800x793 - viewed 342 times.)
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W6IEE, formerly KF6PQT
The Slab Bacon
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« Reply #30 on: June 03, 2007, 08:01:44 PM »

welcome to the world of quality repaired vintage gear!! Grin Grin Grin Grin
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W1GFH
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« Reply #31 on: June 03, 2007, 08:19:49 PM »

Its just one of the 6146's (mod tube) superfluous cathode bypasses, but the damn thing still isn't soldered!

Quote
NO FUSES. I've found other amusing things

AAaaaghhh! The humanity!!!  Tongue

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kf6pqt
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« Reply #32 on: June 03, 2007, 08:44:15 PM »

yeah, totally...

Ok, just noticed that one of my supposedly two 5r4gy rectifiers is a 5u4... bad stuff, right?

5U4-GB:
Vh    Ih    VaMax    IkMax    Notes
5    3.0    PIV=1550V    1000    Tube drop = 50V @ 275mA DC

5R4-GY:
Vh    Ih    VaMax    IkMax    Notes
5    2.0    PIV=2800V    650    Tube drop = 67V @ 250mA DC


 Undecided ?



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W6IEE, formerly KF6PQT
kf6pqt
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« Reply #33 on: June 03, 2007, 09:11:10 PM »

I think what I've just done is commonly referred to as "give up in disgust," in terms of my circuit tracing.  Theres stuff that goes between the modulator section and speech amp, (outside of the usual path, the driver xformer) and some of this strange stuff goes right through the burned section. Also looks as if whoever did this also bundled some of their wiring into the  stock wiring harness, to make it look stoc- er, to burn some of the other wires.

Regardless.. It doesnt work good the way it is. It aint rocket science, its basically an audio amplifier, why make it more complicated than it needs to be?

I'm gonna cut this crap outta here, and redo the modulator section as stock.

I would like a copy of the 100b schematic, if anybody has one in electronic form, as well as any hookup details for the mod xformer... as in, secondaries are this color, etc.

I'm going to carefully pull out the speech amp as a single unit to have a better look... its been "partially" recapped, but I think I better check it out... also need the skizmatic for that, as the non-b doesnt have my front-panel audio knob/pot.

Thanks,
Jason kf6pqt
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kf6pqt
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« Reply #34 on: June 03, 2007, 09:41:25 PM »

K, I just checked, I'll probably be ok for 1625's... Worse comes to worst, I can dig into my ARC-5 collection, too...


 Wink


* 1625s_800.JPG (137.29 KB, 800x600 - viewed 334 times.)
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W6IEE, formerly KF6PQT
W1GFH
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« Reply #35 on: June 03, 2007, 10:01:50 PM »

Quote
need the skizmatic for that, as the non-b doesnt have my front-panel audio knob/pot.

I dunno what all the diffs are between the 100 and the 100b, but the 100 skizmatic clearly shows the vol. pot wiper off of pin 2 of the 12AX7.

Quote
I would like a copy of the 100b schematic, if anybody has one in electronic form, as well as any hookup details for the mod xformer... as in, secondaries are this color, etc.

If the 100 is the same as the 100b, get the assembly manual from BAMA. It will tell you the lead colors of the mod tranny (which are standardized).

Inspect the rig for non-soldered terminals, any new parts, or sections that "look" monkeyed with. The previous owner was not the sharpest knife in the drawer, so you will have to undo his fu*kups.

Definitely add a chassis mount fuseholder and fuse.

(PS: I have nicknamed yer rig "The Hindenburg".  Wink )


* dx100.jpg (242.99 KB, 827x674 - viewed 347 times.)
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #36 on: June 04, 2007, 01:01:05 PM »

notwitstanding any of the excellent advice proffered so far, the place to start is with that mod iron! I'd pull the mod iron and determine the status before doing anything else. Depending on what you find, and if it is toasted, what mod iron you get to replace it will make the biggest difference in terms of what tubes are best/correct to use with the mod iron. Why? Because the power transferred to the final depends mostly on the impedance match of the tubes - mod iron - load combination, not one tube being "better" than another on paper.

For example, if you find an Apache iron to put in, then the 1625s are probably not the best choice, whereas with the stock DX-100 iron the 1625s might match better.

Again, fyi, for extreme closeups on a digital camera place a magnifying glass over the lens and move the camera to create focus... ur closeups are all blurry and seeing what is going on is difficult, fyi...

             _-_-bear

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_-_- bear WB2GCR                   http://www.bearlabs.com
kf6pqt
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« Reply #37 on: June 04, 2007, 02:21:11 PM »

Yeah, its definitely coming out...

Sorry about the pics, the lighting is bad, and I have to rely on the flash. Once I have it busted up into manageable chunks, I'll carry the bits outside into the sun and photograph them with Natural Lite(tm).
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W6IEE, formerly KF6PQT
N3DRB The Derb
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« Reply #38 on: June 04, 2007, 11:55:07 PM »

the panasonic lumix LS70 has a freaking awesome macro mode. it's my wifes camera - does not work with macs. I can get a sharp focus on a point 1" away.

my nikon coolpix L11 is good bu the macro on it sux.
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kf6pqt
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« Reply #39 on: June 05, 2007, 12:35:14 AM »

Mine's the Lumix FX-07, with a Leica lens, the LS-70 probably has the same. I just need a little more practice with the macro mode. Works with my mac just fine, Just treats it as a thumbdrive on the end of a cable, just the way I want it to!
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W6IEE, formerly KF6PQT
Todd, KA1KAQ
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« Reply #40 on: June 05, 2007, 09:30:26 AM »

Look at it this way, Jason: if you 'rip and strip' and return the thing back to something near stock, sure - you'll have a fair amount of work involved. Best of all, once you get it working right, you'll have a known-quantity to move forward with should you decide to improve upon the design yourself.

 
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kf6pqt
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« Reply #41 on: June 05, 2007, 10:52:45 AM »

Thats the plan! Besides, its useless as it is, (unless I do some serious cw practice) we're not allowed to transmit out here unless the audio is perfect, and the carrier is strong enough to quiet down 12 kc's of receiver bandwidth.

 Wink
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W6IEE, formerly KF6PQT
John K5PRO
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« Reply #42 on: June 05, 2007, 10:59:05 AM »

You don't have to PULL the mod iron, just disconnect the leads and measure! I see a lot of comments say rip out the homemade stuff and put it back to stock, then mod as you please. If you have lots of time on your hands, by all means, go for it. If it were me, I would (and have) just trace out the wiring on a pad, and compare to the 100B or 100 on BAMA, very similar designs, and then decide what to rip out and change. There is absolutely nothing wrong with 6146 modulators, Johnson used them in Valiants. Or 6550, 6CA7, EL34, sweep tubes, you name it. Just get a tube in there that can idle with sufficient current to keep the distortion down and handle 100% at full carrier. Personally I spent a lot of time removing and replacing the 1625s in mine, because I could not find good matched tubes, since the 1625 is such an old bottle. Whereas the other tubes are still commonly available.

Those unsoldered connections and tube substitutes (like the 5U4 in place of 5R4) are signs of sloppy workmanship on the part of some previous owner/user, and can really cause you grief. Glad to hear you are finding them and eliminating those blunders.

Good Luck!
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W2VW
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« Reply #43 on: June 05, 2007, 12:14:49 PM »

6146's are a lousy choice for linear amplification unless inverse feedback is added. The feedback is likely to make the stock DX-100 iron unable to match the modulator's output impedance and still deliver enough power to fully fill out the carrier. That iron has a high ratio to begin with.

Here is some interesting stuff on various toobs in R.F. linear service. Audio and R.F. linear service are very similar.

http://www.qsl.net/n6ev/SwpTube.txt

The 6146 will however make an excellent mudulator tube when used with a good feedback loop.

Be glad that your rig was hacked. It will take a little shoehorning to make clean audio.

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W1GFH
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« Reply #44 on: June 05, 2007, 01:53:54 PM »

We're not allowed to transmit out here unless the audio is perfect, and the carrier is strong enough to quiet down 12 kc's of receiver bandwidth.

You think he's kidding, but in certain areas of 6-land, this is true!
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kf6pqt
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« Reply #45 on: June 05, 2007, 03:53:37 PM »

Nah, it just depends who all's in the QSO.  Wink

...And why I'm glad I have some VFO options in the works!

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W6IEE, formerly KF6PQT
W1GFH
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« Reply #46 on: June 05, 2007, 11:44:05 PM »

I'm listening to 3870 right now. 5 people in the roundtable, *all* using broadcast transmitters. I need to find a new ghetto...
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flintstone mop
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« Reply #47 on: June 10, 2007, 07:32:03 PM »

A modified plastic radio and a legal limit linear and no one would could tell the difference.
Fred
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Fred KC4MOP
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