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Author Topic: All-American Five  (Read 23277 times)
KM1H
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Posts: 5247




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« Reply #15 on: September 16, 2017, 05:17:23 PM »

Quote
Re-capping the radio was optional, but I had the parts in the junk box so why not. The one resistor that I changed was way out of range.

Nope, it is mandatory if you intend to use it regularly. All the caps will have high leakage simply due to the technology used and the AA5 throwaways used the cheapest parts available. Sometimes a way out of tolerance resistor appears to have no effect but one common result is the AVC is shot; the converter and/or the IF amp gain is down and eventually the volume control needs to be full on. One real fun cap isolates the chassis from the AC line since the line cord can be plugged in either way; many have been introduced to their first electrical shock that way.
As leakage increases so does current and eventually the 35Z5 will let go as well as the audio transformer. In AC sets the power transformers are added to the trash.

The more complicated radios have their own ways of reacting from defective components.

The various tube radios here run from 4 to 20+ tubes. Some I have fully restored and use, others are display shelf queens.

Carl
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N8FVJ
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Posts: 883




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« Reply #16 on: September 17, 2017, 07:02:15 AM »


Even with a small 4 inch speaker the audio sound from the tube radio was far superior & enjoyable vs that terrible sounding transistor radio.

I know what you mean but, at that (very crude) quality level I don't think it's a tube-vs-transistor issue per se. I have several transistor radios built in the 1950s with point-to-point wiring and two-transistor push-pull output stages with an output transformer, relatively large speakers and sturdy cabinets. They sound very similar to the contemporaneous tube radios. Even when the solid-state radios transitioned to "transformerless" AF output stages, miniaturized PC designs and smaller speakers, they didn't necessarily sound any worse, or better, than tube radios. When I was at school in the UK in the 1960s and 70s many people had sturdy "Roberts" solid-state AM/FM radios (almost as large and heavy as my AA5) that sounded great (but, for that matter, so did the earlier Roberts tube radios).

At a much higher level (hi-fi) it gets much more controversial. I personally like the "tube" sound, but there is quite a lot of evidence that this effect can be attributed to "pleasing" harmonic distortion, that "warm tube sound." Likewise, I often prefer the sound of an LP to the "antiseptic" CD/digital sound but am totally prepared to admit that the CD sound is probably closer to the original.

I hear a distinct difference of tube vs SS even if SS uses discrete components vs the modern OP-Amps. I can hear a cheap tube radio in another room and always correctly identify it. And, when moving into high-end tube audio the difference is more apparent. I ship custom high-end tube electronics around the planet.
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W3RSW
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Posts: 606




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« Reply #17 on: September 17, 2017, 08:09:15 AM »

As you may know, "Working" is relative.   The approx. .01 cap from the plate of the first triode AF amp, (12SQ7) to the grid of the AF output tube (50L6 or equivalent. ) may be working but have just enough DC leakage to upset the grid bias in the 50L6.  If you have a bit of audio distortion, replacing that cap may cure it.  Also the cathode bias resistor on the 50L6 is notorious for being underrated and baking to different value over time.  This resistor is usually around 220 ohms, possibly 1 watt. Should be 2 watts to help heat aging.

Also be sure to replace the dial lamp if installed.  It is needed to keep the filament string in current balance.  The 35z5 rectifier tube filament is tapped for best current distribution using the lamp bulb for balance.
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Rick, W3RSW
VE3WGO
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Posts: 445




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« Reply #18 on: September 17, 2017, 10:26:42 AM »

I suppose the "tube sound" of those older AA5 (1940s - 1960s) AM table radios was due mainly to the fact that their cabinets were fairly large, perhaps 1/2 the size of a cinder block, for heat management and tube height as much as anything.  They usually had fairly common 4-inch paper cone speakers, and most of them had almost identical circuits.  With their steel chassis, output transformers, and either solid bakelite/plastic or even wood cabinets, they were on the solid weighty side too.  So the sound was pretty good.

I'm what you'd probably call an audiophile, ... however... while the AA5 radios I have collected and semi-restored almost all sound similar with that kind of recognizable "woody-sounding" 250 to 2500 Hz audio response, I don't mind it at all.  Not much high frequency response to speak of, just enough low-end (with some kind of bump due to the cabinet in the 300-400 Hz range) to not sound too crappy, the distortion is acceptable (most probably because of the high frequency rolloff), and tuning is easy.  At 110 VDC on the plate, a 50C5 is capable of putting out almost 2 watts, so that's a pretty healthy audio level.  50L6 is over 2 Watts, but interestingly the 35L6 in some radios is a little less capable, spec'd at only 1.5 watts. I do like the sound, but these days most AM stations are just talk shows so the music station pickings are getting slimmer.

I have a couple of mono AM-FM wood cabinet table tube radios, equipped with a couple more tubes for the FM path so they have unusual series string heater voltages and solid state rectifiers, but the sound is better on FM..... still kind of "woody" but with brighter treble.  Of course these are not AA5, more like "AA7" if such a label exists.

The solid state table radios seem to have only had solid wood cabinets for a while, and I guess the designers soon took advantage of their lower heat and smaller size with smaller and plastic cabinets that usually called for smaller speakers too.  So the sound changed.  I have a couple of those, but I'm not too fond of them.

73, Ed VE3WGO
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VE3CUI
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Posts: 15




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« Reply #19 on: September 17, 2017, 02:14:32 PM »

Hi Guys,

For what it's worth --- in case nobody mentioned here (I didn't see any reference to it, anyway), the "Beginner & Novice" section of QST in the early 70's, I believe, featured a piece entitled, "New Life For The All-American 5."

It was a nice little treatise on converting one of these little classics into a working Ham bands receiver…

~73!~ de Eddy VE3CUI - VE3XZ
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KC4ZGP
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Posts: 1961




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« Reply #20 on: September 18, 2017, 11:09:17 AM »



I am turned on.

Kraus
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KA4LFP
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Posts: 273




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« Reply #21 on: September 18, 2017, 11:53:02 AM »

Anymore I'm leaving working wax caps intact.
 The one's I have replaced gave very little, if any, improvement in performance.

Replacing the caps isn't about performance increase, usually. Sometimes hum goes away, sometimes not.

It's ALWAYS about avoiding that old was cap from shorting through and taking the unobtainium main transformer or an unobtainium IF can with it.

I've seen half a dozen "grandpa's old radio from the basement storage " turned on proudly at the yard sale only to turn the transformer into slag and the radio into a parts donor.

I'm not a huge believer in the value of "re-forming" old caps at the price of new ones either....
although, starting up a newly obtained radio with a dim-bulb tester or variac is always good.

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KB1WSY
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Posts: 1309




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« Reply #22 on: September 18, 2017, 01:50:59 PM »

It's ALWAYS about avoiding that old was cap from shorting through and taking the unobtainium main transformer or an unobtainium IF can with it.

At this point I have done a lot of restorations of 1950s-era tube equipment. In most cases, I replaced all of the paper tubular caps (whether "waxy" or similar) with modern tubular film types, often with somewhat higher voltage ratings. Sometimes I replaced the power-supply filter caps, sometimes not. In a couple of cases, I later regretted not replacing the filter caps because the old ones failed a few hours after power-up and ended up having to be replaced anyway.

It seems there are several philosophies, all of them valid I guess. (a) Change as little as possible, just fix what needs to be fixed to get the set working. (b) My system, which is described above. (c) Change all the caps (apart from the micas) and a lot of other stuff, in some cases stripping the chassis down, deep-cleaning/replating it, and rebuilding the whole set from scratch.

To each, his/her way. They each have their own advantages and drawbacks. For sure, (a) is the *cheapest* route but only if it does not cause something expensive or unobtainium to fail later!

I had a lot of fun restoring this rack of test gear, and it's been become a great set of tools in further restoration work:



The 'scope has not been restored yet. That will be quite a challenge because it looks like a previous owner has messed with the EHT section.

Missing from the photo: an Eico grid-dip meter and several other items of restored equipment.

73 de Martin, KB1WSY
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AC5UP
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Posts: 4546




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« Reply #23 on: September 18, 2017, 03:33:09 PM »

The 'scope has not been restored yet. That will be quite a challenge because it looks like a previous owner has messed with the EHT section.

It's possible what you're seeing is a flat line zero signal trace with a buttload of AC power supply hum.  The thickness of the trace might be a clue-by-four something is superimposed on the vertical amplifier and 60 or 120 cps ripple would be my first suspect.  This is easily confirmed with your DMM........  Measure the B+ as DC volts and AC volts. 

If DC volts are near the schematic value and AC volts are near zero you're golden.  Otherwise, it's time to swap out the electrolytic(s).
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KB1WSY
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Posts: 1309




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« Reply #24 on: September 18, 2017, 07:12:12 PM »

It's possible what you're seeing is a flat line zero signal trace with a buttload of AC power supply hum.

The horizontal sweep control is set to 60 Hz. On that setting there is no problem getting a clean sine wave, (presumably the vertical signal is just noise, given that I have not even input an external signal). The bluriness is fixable with the focus control. So overall I think there isn't too much wrong with this 'scope (but see below).

This is easily confirmed with your DMM........  Measure the B+ as DC volts and AC volts.  

If DC volts are near the schematic value and AC volts are near zero you're golden.  Otherwise, it's time to swap out the electrolytic(s).

The problem, from what I remember (and it has been a year or two since I looked at it) is that the EHT circuit has been considerably altered from what is in the schematic. Perhaps there was a good reason, perhaps not. This kinda stopped me in my tracks because of the high voltages involved -- I am rather interested in stayin' alive. I will get round to it eventually.

There is also a large capacitor close to (or in) the EHT circuit that has dripped molten wax over the bottom of the cabinet. So definitely something to work on! When I get around to it I will start a new Boat Anchor thread about this 'scope.

It is an Eico 460, really crude by comparison to everything that followed, but this would have presumably have been a prized possession for a 1950s ham. I also have an Eico dual-trace "electronic switch" which is shown on the shelf above the 'scope in the photo I posted.

Edited to add: I also have a second Eico 460, in less good order, to cannibalize for parts, if needed. I also have the Heathkit EF-2 educational "How to Understand and Use Your Oscilloscope" kit and its textbook, to learn more about my 'scope once it is fixed.

73 de Martin, KB1WSY
« Last Edit: September 18, 2017, 07:24:37 PM by KB1WSY » Logged
AC5UP
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Posts: 4546




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« Reply #25 on: September 18, 2017, 07:45:23 PM »

The horizontal sweep control is set to 60 Hz. On that setting there is no problem getting a clean sine wave, (presumably the vertical signal is just noise, given that I have not even input an external signal). The bluriness is fixable with the focus control. So overall I think there isn't too much wrong with this 'scope (but see below).

Me Thinks it's time to review how an oscilloscope operates.........

When you select 60 cps horizontal line sweep it should do exactly that, sweep the beam horizontally at the rate of 60 passes per second.  If there is no vertical input signal to encourage vertical deflection there will be no sine wave or anything other than a horizontal line.  Maybe a little noise from the vertical amplifier, but aside from that, a flat horizontal line swept at the AC line frequency.  'Cuz that's the only signal the 'scope has to work with............  On a typical recurrent sweep 'scope like the EICO the Q&D vertical amplifier test is to touch a finger to the vertical input.  The flat line should become a distorted vertical pattern much like an audio amplifier will buzz when the input jack is touched.

What I suspect you have is a vertical amplifier being modulated by ripple on the B+ power supply.  With no vertical input there should be no vertical deflection.
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N2EY
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« Reply #26 on: September 19, 2017, 05:59:35 AM »

As you may know, "Working" is relative.   The approx. .01 cap from the plate of the first triode AF amp, (12SQ7) to the grid of the AF output tube (50L6 or equivalent. ) may be working but have just enough DC leakage to upset the grid bias in the 50L6.  If you have a bit of audio distortion, replacing that cap may cure it. 

And there's more!

As you say, if that coupling cap between the 12SQ7 plate and 50L6 grid is even slightly leaky - tens of megohms - it will upset the bias and cause the 50L6 to draw excessive plate current. The set will still work - but, over time, the high plate current can/will fry various components, such as the 50L6 cathode resistor, the 35Z5 rectifier, the 50L6 itself, etc. Worst of all, the most likely candidate for destruction is the audio output transformer.

A shorted 50L6 cathode bypass electrolytic can have similar results.

73 de Jim, N2EY
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KB1WSY
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Posts: 1309




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« Reply #27 on: September 19, 2017, 08:34:02 AM »

As you say, if that coupling cap between the 12SQ7 plate and 50L6 grid is even slightly leaky - tens of megohms - it will upset the bias and cause the 50L6 to draw excessive plate current. The set will still work - but, over time, the high plate current can/will fry various components, such as the 50L6 cathode resistor, the 35Z5 rectifier, the 50L6 itself, etc. Worst of all, the most likely candidate for destruction is the audio output transformer.

I replaced two .01uF paper "waxies" during the restoration. I still have the removed caps, but of course have no way to tell which was the AF coupling cap since they look identical. On my VTVM, one of them is more than 60 megs, but the other one zooms down to 7 megs before drifting back higher as it charges.

So Jim-san and W3RSW seem to have found the most likely culprit in the destruction of the original output transformer. Changing the cap prior to installing the new transformer made sense!


... the Q&D vertical amplifier test is to touch a finger to the vertical input.  The flat line should become a distorted vertical pattern much like an audio amplifier will buzz when the input jack is touched.

What I suspect you have is a vertical amplifier being modulated by ripple on the B+ power supply.  With no vertical input there should be no vertical deflection.

Thanks, that advice will be very useful when I start on the restoration!

73 de Martin, KB1WSY
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KC2QYM
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« Reply #28 on: September 19, 2017, 09:26:24 AM »

We have to admire the ingenuity of previous generations of radio engineers and technicians that led the way in the last century to the proliferation of radio products.  Every time I see an old radio I can certainly relate to them because of my age and being lucky to have owned them and still be part of the radio hobbyist community. 
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N2EY
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Posts: 5079




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« Reply #29 on: September 19, 2017, 12:36:54 PM »

Couple of things:

 1) It is a common meme today to point out unsafe practices of the past and then say "so why are we all here?" or "we survived!" or similar.....implying that the modern push for safety is overblown.

 BUT....those who didn't survive aren't around to speak up and remind us of what happened to them, because they're dead. Often they are forgotten. This distorts the perception of the actual danger. (Just look at motor vehicle deaths and rates before and after seatbelts):

https://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_in_U.S._by_year

 And all it takes to become a statistic is ONE mistake. Just ONE.

 2) AC/DC "transformerless" radios were usually housed in cabinets made of wood or plastic, with plastic knobs having no setscrews, with back panels of nonconductive material and with no exposed conductive hardware. No shock hazard as long as you didn't poke around inside, and the cabinet, knobs, etc. are intact. But if you are restoring/repairing/aligning such a set, you probably have the cabinet off.....

 3) In many - but by no means all, or even most - AC/DC "transformerless" designs, the chassis is NOT, repeat NOT, tied to one side of the power line. The chassis is isolated for power by a capacitor, so that if you touch the chassis or a control shaft, you won't get full line voltage if the plug is in the socket "the wrong way". In most of these designs, the short-circuit current through the capacitor is very low - IF the capacitor is in good condition.

 For example, suppose the coupling capacitor is 0.05 uF. Such a capacitor has a reactance of about 53,000 ohms at 60 Hz, and at 120 volts, only about 2.2 mA will flow. If you were in series with such a capacitor and the AC line, you'd get even less unless you were well grounded and soaking wet. 2.2 mA of shock current is no joke but it's not the same as getting yourself directly across the 120 volt line.

 HOWEVER - in old radios, the capacitor(s) mentioned above may be leaky or even shorted. In every "isolated" design I have seen, the capacitors mentioned above can fail and the set will still work perfectly - but the isolation the capacitor provided is GONE.

 So the risk of decades ago, when a set was relatively new, is very different from today. And the "isolation" of the design can actually be a trap, because the set can work perfectly with the isolation failed.

 4) Transformerless radios were made for three reasons:

 First, they cost less - even a small power transformer cost several dollars back then, which was a sizable part of the cost of the radio. So the parts used were often not top-of-the-line.

 Second, not having a power transformer made the set smaller and lighter.

 Third, such sets could be used in 60 Hz, 50 Hz, 25 Hz and DC territories with no changes at all. (Fun fact: There were parts of Boston that had DC power at least into the 1960s, and parts of Buffalo NY that had 25 Hz at least into the 1980s)

 All big concerns in the past....not so much today.

 5) (The big one) - No matter what the original design was and no matter what the schematic says, you must NEVER assume ANYTHING about a transformerless AC/DC set until you personally check it out. Bypass capacitors fail shorted or leaky. Insulating hardware dries out, cracks, and fails. Schematics contain mistakes. Most of all, there may be undocumented repairs, modifications, substitutions and other hazards which can only be found by actual test and examination.

 Be safe - it only takes ONE mistake.

 73 de Jim, N2EY
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