avatars?

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
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philba
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avatars?

Post by philba » Mon Apr 10, 2006 2:31 pm

I tried to add an avatar but no joy. I was able to upload an image (jpg, 120x114, 4Kb) with no errors but nothing appeared to happen. any ideas?

hp
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Post by hp » Mon Apr 10, 2006 2:34 pm

Probably an incorrectly chmoded / chowned avatar directory on the servo website.

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Michael Kaudze
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Post by Michael Kaudze » Mon Apr 10, 2006 2:44 pm

We are actually fixing that - but we are updating the phpBB to 2.0.20- Should be fixed in the next 24 hours.

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philba
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Post by philba » Tue Apr 11, 2006 4:30 pm

thank you. it now works.

now, if I can just get my april issue...

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Edd
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Post by Edd » Wed Apr 12, 2006 3:30 am

Hmmm??? Philba, do I recognize your Image selection being the utilization of a 6A8 mixer along with a 75 in the back ground and being tuned with a post neanderthal / pre cro-magnon vintage tuning condenser....circa 30'ish ?

73's de Edd
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There's no such thing as a stupid question, but they are certainly the easiest to answer! Image

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philba
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Post by philba » Wed Apr 12, 2006 8:51 am

Its from an Atwater Kent model Model 427, circa 1932. Truely a golden age radio. The tube in the foreground is a 58 (RF tuning). The first two in the background - another 58 (detector, not quite visible) and a 56 (oscillator). Behind the second 58 is a 55 (IF) and a 2A5. The 3 section air variable is work of art. I'm restoring it but its a bit of a slough - all the caps are falling apart, insulation is dried out an cracking and so on. Worse yet, many of the wires are resistor wires so i need to match those. And my nightmare is this potted multicapacitor with non-standard values (like 2.8 nF, for example). Nothing that can't be overcome with a little sweat.

Image

I have to say the quality of engineering that went in this puppy is impressive. Like the speaker doesn't use a PM but rather an electro magnet. that same electro magnet is used as a ripple filter on the power supply. There is a no low pass filter built into it to reject the 120 hz hum - I think they induced an inversion of the hum back into the audio output to cancel it. They avoided large (and expensive for the time) filter caps and got double use of the component. Brilliant engineering. Sadly, the mass market killed AK in a foreshadowing of economics to come.

Kind of surprising for a microcontroller guy, huh?

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Post by dr_when » Thu Apr 13, 2006 5:42 am

I don't believe I have ever heard of resistor wires. So they used different metals/gauges/lengths of wire with set resistance (like ni-chrome)? Or was there just a resister in-line with a cloth covered wire. Never have noticed that in old equipment. EDD... do you have the history of this?
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philba
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Post by philba » Thu Apr 13, 2006 4:38 pm

it looks like plain wire. OK, it looks like 75 year old plain wire that's falling apart. The parts list calls out wires with an ohms value. it appears to be proportional to the length. I haven't done the obvious measurement/calcs. I have gotten advice to ignore the resistor wire and replace with normal hookup wire. frankly, I'm not sure the guy was right.

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Post by Robert Reed » Thu Apr 13, 2006 5:21 pm

D r When
a type of "resistance" wire has been used for years by the automotive industry. It is the ignition/spark plug wires and is of about 10K per run. Another type of this wire was used in coil/points ignition systems.It was run in parrellel with standard wire from the ignition switch. When ign. sw. was turned to start, the standard wire fed the coil for a good boost at full 12 volts. once started and the key released to run position, the coil was fed thru the resistance wire and ran at a lower current.However I guess the most common type of resistance wire would be of the special metal alloy type. The resistance can be all over the place as also the gauge of the wire, as witnessed by your toaster heating coils and "fusible" wire links.

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Edd
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Post by Edd » Sat Apr 15, 2006 1:24 am

I had assumed your initial photo to be from some clip art source, with you happily finding it to just fit within the cramped pixel/density limitations being allocated for a photo / logo placement. Little did I realize you actually having one of the old beasts in your possession.
BTW I tend to think that JPKNHTP......QRSTUVWXYZ has the best one, with his little rotating "K-Mart blue light special" thingy. I was even able to find a density compliant image to update from my dismal looking, lethargic little mouse to the now hyper-animated silly scope.

Viewing your initial photo and then the viewing of your massively larger second photo reveals that I am not in need of a recalibration
after all. I was merely up one "G envelope" generation in its tube complement, such as was then to be used in the very late '30's . Upon a further review, with its greater resolution, I can then better see the grid lead over to the tuning cap and its wickedly brittle condition.
Seems as if I also see the AC line cord coming into the set up behind the power xformer.
Like wise I see the (cringe) 3-4? "thermo plastic leads" at the front foreground, for your ground and antenna leads running downwards.
Topside front and center should be the speaker receiving its voice coil drive from the AF output xformer mounted atop it along with the energization for the speakers electromagnetic field coil / series B+ filter choke. Also take note of the miniscule capacitance values of 4 and 8 ufd WET electrolytic capacitors with their low Z. That, along with effective inductive filtering and slight hum bucking feedback kept the AC ripple component down quite well. Currently in common raw DC power supplies, it is not at all uncommon to see upwards of 330-820 ufd values of capacitance being utilized in DRY electrolytic filter capacitors.

A good possible pseudo archival grade of replacement for the wire on the 58 RF tube cap (as well as the others ..and even the wire going down into the 1st IF’s transformer) might be to pull out some original Belden black test prod wire and use it. (Well tinned however, as it is usually a bit sluggish on taking a good tin without a liberal fluxing).

A comparison of the two photos also reveals the utilization of a 3 section tuning capacitor , relevant of having the incorporation of a tuned RF stage. That could not even be noticed in the very small thumbnail photo. The only final possible enhancement of a chassis /set of that vintage would been to its having also incorporated 2 IF tubes in its strip and push pull output tubes feeding a big speaker downside, along with a frontal display of a green "magic eye tuning tube".

That sets tuning capacitor with its quasi-rectangular rotor plates configuration looks to be of a manufacturing / design engineers aberration, rather than an RF design engineer’s optimal selection. Delving into LC resonance characteristics will reveal a crunched logarithmical response across a tuning band …eg…on the all popular AM broadcast band .Certainly the customer would be more desirous of his dial scale being evenly spread across in a linear fashion, rather than the progressive cramping across the dial scale of a log plotting. By an examination, you can see the initial quantum leap in attaining that condition on your /others tuning capacitors by merely incorporating an off center positioning of the rotational axis of the caps rotor plates. That along with a proportional arcing of the outer profile of the blades…….(not so optimal in your tuning plates outer plate profile)….. so that they deviate away from a common semicircle, and further enhances the log-linear transition.

Back in the 60’s I completely built up a Ham band only receiver 160-80-40-20 meters with its tuning cap being hand made, and about 1 1/3 the physical size of yours. Initially the outer periphery of a single plate was painstakingly trimmed down to the proper arc for the most linear freq tracking in a test bed oscillator circuit while being frequency plotted and then mechanically replicated en masse to build up the multiple plates required. The alum was 27 mil temp aircraft sheet aluminum with all the 3/8 in holes punch pressed and THEN the first master plate cut to optimum tuning profile with all other plates overcut and then brought down to profile by being all clamped together and ground down to duplicate that master profile with a fine belt sander. The condensers ½ inch….. ball bearing supported….. front shafts end had a 6 in dia tune pulley which fed to a tandem cantilevered pulley arrangement giving a 2x multiplying effect. The dial cord stringing was done with microfine aircraft cable and produced a total dial pointer tranverse width across an 18 inch horizontal dial scale……that being on a 24 in wide radio case.
That unit served me as a criterion of performance on up until the concept of frequency synthesis and digital tuning.

As per your AK model 427 (there is also a D and Q version) here is an online accessible Ryders of it just in case you don’t have it.


(THIS SPECIAL URL IS NOT ALL HOT....U HAVE TO CUT AND PASTE)

http://www.nostalgiaair.org/Resources/v ... 001362.pdf


Yes, your set is certainly incorporating the forerunner of the modern PM speaker. Consulting the schemas right side you will see the Af output transformer coupling to the voice coil of the speaker . If you will track down to the power supply center you will see the the field coil for the speaker wired so that is both serving as a series inductive filter choke coil along with its design into the speaker acting as the magnetic field source of the speaker. Also at the same time notice the wee winding shown feeding up a series connected signal with the voice call secondary to further null out any power supply induced hum….chum.
I didn’t thoroughly go through all schematic notes in fine detail , but one point that I did see was the first det ckt having a fil ckt mod where some “resistive wireâ€

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dr_when
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Post by dr_when » Sat Apr 15, 2006 7:04 am

Edd, thanks for the lowdown on the resistor wire. Fascinating info also on Philba's radio!!

Au Le Docteur When?:

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Actually the avatar and name (obvious to those watchers of BBC) are a tongue in cheek play on DR. WHO, the longest running TV series ever. The outhouse/police-call-box is the infamous Tardis with some cheap self embellishments.
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philba
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Post by philba » Sat Apr 15, 2006 10:42 am

Yeah, I was wrong on the multicap value but there are a number of nonstandard values in it. Here's a couple of pix of the multicapacitor beast.
Image
Image

rodent tracks? I don't think so. Looking closer at the stain, it looks more like the remains of a sticker, probably some adhesive. I don't see any evidence of wire gnawing, either.

Here's a picture of the wire deterioration:
Image

I bought it last year for less than $100. The cabinet looks pretty good.
Image

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Post by ecerfoglio » Mon Apr 17, 2006 7:35 am

[quote] EDD posted:
As per the “resistance wireâ€
E. Cerfoglio
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Argentina

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Edd
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Post by Edd » Thu Apr 20, 2006 2:27 am

I can only say that the persons advice given to you as per the utilization of common hook up wire for the direct replacement of the designated “flexible resistorsâ€

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philba
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Post by philba » Thu Apr 20, 2006 3:59 pm

thanks edd. the cabinet is very clean. It's part of the reason i was able to get a high WAF on the purchase. I have no idea how the unit was stored so it's any one's guess.

Several of the ohmic wires have deteriorated so I'll need to replace. I think the solution is to build a wire with an inline resistor and use shrink tubing. I have to make sure the wattage ratings though. especially on the low ohm ones.

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