Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1] 2 3 4 Next   Go Down
  Print  
Author Topic: All-American Five  (Read 7907 times)
KB1WSY
Member

Posts: 1282




Ignore
« on: September 12, 2017, 12:10:46 PM »

I picked up this little "All-American Five" at a neighbor's yard sale. It is an Admiral Model 7T10E-N with the 5K1 chassis.





This is the classic design used in millions of postwar radios regardless of manufacturer. This one is the "octal tube" version and probably dates from the late 1940s or early 1950s. To save money, there is no power transformer. The B+ is rectified directly from the AC power supply. The filaments are connected in series across the AC supply, which explains the strange heater voltages of the last two tubes (as denoted in the first two digits of the tube name): 12SA7 pentagrid RF/oscillator/mixer, 12SK7 pentode IF amplifier, 12SQ7 double diode/triode detector and first AF amplifier, 50L6 tetrode final AF amplifier, 35Z5 rectifier.

I changed the power cord, making sure that the wider "neutral" pin went to the chassis side. I replaced all the "waxy capacitors" and the filter caps. A 1K resistor had gone high (reading slightly more than 2K) so I replaced that, too.





Powered up the radio: zilch. The tubes lit up (so at least all the filaments are good) but no sound. Touching the wiper lug of the volume control with a screwdriver did not produce any sound. Feeding an audio signal to the grids of the AF stages using an AF frequency generator had no result either.

First possible culprit: the speaker. Feeding a brief 1.5V pulse to the speaker with a small battery produced a crackling sound. So the speaker is OK. Next: measure the resistances of the AF output transformer. Aha.... the primary is open-circuit. Next: connected a pair of high-impedance headphones across the primary and turned the radio on. After about 30 seconds, there is a reassuring "woosh" in the headphones.

Turned off the set and unplugged from AC, then temporarily replaced the dead output transformer with a tiny spare transformer with a rating of 150mW (which is under-powered for this radio and earmarked for another project, but good enough for a brief test). Powered up the radio and it works! I am only running it for a few minutes at a time, to avoid blowing the tiny transformer and have ordered a proper replacement. There is also a missing power/volume knob so I need to find a replacement.

First impressions: surprisingly good, in particular the sensitivity (better than most of the other BC AM radios in the house, whether tube or solid-state), and this is just with the wire-loop antenna that is built into the back of the set. Pleasing sound quality, within the limitations of a small set with a narrow AF bandwidth. Am amazed that such a bare-bones radio, clearly produced to the lowest possible cost and of fairly dubious build quality, works so well. No wonder they built them by the millions, well into the 1960s.

Those reading this post probably know this already: these radios are also "death traps" (another term was "widow makers"). Even when they are switched off, the chassis can be live. Fortunately this little Admiral set is about as well insulated as these things ever were. There are only a couple of metal screws that can be touched from the outside of the cabinet, and the bracket that they screw into is insulated from the chassis with a thin strip of bakelite. Still, the idea that people had things like this in their kitchens (and who knows, maybe even in their bathrooms) makes me shudder. Similar circuits were used by European manufacturers with 220-240VAC supplies. Yeech.

So far, this has nothing to do with ham radio, but maybe I'll built a small converter to put in front of the set to see if I can pull in 40m. (I guess I could also build a small BFO to feed to the IF stage, but it would have to be loosely coupled rather than directly connected.)

73 de Martin, KB1WSY
« Last Edit: September 12, 2017, 12:31:50 PM by KB1WSY » Logged
KB2WVO
Member

Posts: 382




Ignore
« Reply #1 on: September 12, 2017, 12:41:15 PM »

pix no show....
Logged
KB1WSY
Member

Posts: 1282




Ignore
« Reply #2 on: September 12, 2017, 12:49:43 PM »

Sorry about that. I posted the photos to Google Photos then posted them to this forum. When I then "shared" them so everyone could see them, the links changed so the original links no longer worked. Silly me. Here they are (too late to edit the original post):









73 de Martin, KB1WSY

« Last Edit: September 12, 2017, 12:57:31 PM by KB1WSY » Logged
KB2WVO
Member

Posts: 382




Ignore
« Reply #3 on: September 12, 2017, 01:40:44 PM »

cool radio.. love the sound of old stuff
Logged
AC5UP
Member

Posts: 4413




Ignore
« Reply #4 on: September 12, 2017, 04:28:54 PM »

If you have a small-ish 6.3 vac filament transformer in the junque box you can use it to sub the AF output transformer.

Won't be a perfect match and certainly not Hi-Fi, but neither was the original.  The radio was designed for 20% tolerance parts so don't sweat the details........
Logged

KC4ZGP
Member

Posts: 1637




Ignore
« Reply #5 on: September 12, 2017, 06:25:35 PM »


Just one picture. Looks like capacitors and one resistor.

Kraus
Logged
K0OD
Member

Posts: 2954




Ignore
« Reply #6 on: September 12, 2017, 07:00:33 PM »

Is this it?

Logged
KB1WSY
Member

Posts: 1282




Ignore
« Reply #7 on: September 12, 2017, 07:11:11 PM »

OK let's have another go at sharing these photos. Several years ago I used Picasa and it always worked fine on eham. Then, Picasa was bought up by Google (and renamed as Google Photos). The interface changed completely and ever since, I have had a lot of trouble sharing my pics. All my fault no doubt.









Did that work? (I have no problem seeing these photos on eham but that is because I'm the one who posted them in the first place. The issue is with the sharing permissions.)

73 de Martin, KB1WSY
« Last Edit: September 12, 2017, 07:19:35 PM by KB1WSY » Logged
KB1WSY
Member

Posts: 1282




Ignore
« Reply #8 on: September 13, 2017, 01:52:53 PM »

The new audio output transformer has been installed. Everything working fine now.



73 de Martin, KB1WSY
Logged
AC2EU
Member

Posts: 1204


WWW

Ignore
« Reply #9 on: September 13, 2017, 06:56:31 PM »

Wow that was almost a total "re manufacture" of the radio !   Shocked
BTW, The pictures worked this time.
Logged

N8FVJ
Member

Posts: 354




Ignore
« Reply #10 on: September 14, 2017, 09:19:33 AM »

These old tube radios have a voice clarity missing from transistor radios. My GF (soon to be wife) listened to a cheap cube shaped transistor AM-FM radio. It sounded terrible. I replaced it with an early 1960s AM-FM tube type table radio. Even with a small 4 inch speaker the audio sound from the tube radio was far superior & enjoyable vs that terrible sounding transistor radio.
Logged
KB1WSY
Member

Posts: 1282




Ignore
« Reply #11 on: September 14, 2017, 06:53:06 PM »

Wow that was almost a total "re manufacture" of the radio !   Shocked

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. The AC cord on the original set was rotted down to bare wires, so no choice there, it had to be replaced. The open-circuit output transformer obviously had to be replaced (or rewound, but I don't have that expertise) -- unfortunately the new $20 transformer cost more than what I paid for the entire radio at the yard sale. Even with all of that, most of the parts are still original!

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.

Anyway, getting back to ham radio, I am still rather impressed by the economy/efficiency of the AA5 design and looking at it is giving me some ideas for receiver design. Perhaps I will use a pentagrid tube in the front end of my first homebrew superhet, when I get around to it!

73 de Martin, KB1WSY

« Last Edit: September 14, 2017, 06:56:13 PM by KB1WSY » Logged
VE3WGO
Member

Posts: 151




Ignore
« Reply #12 on: September 14, 2017, 06:56:29 PM »

looks like a nice restoration!  I like the sound of those radios.

And the hum your can hear in the few brief moments while it is warming up and the tube audio sound bring back fond old memories of childhood listening to the Hit Parade on the AM radio in the living room.

I guess those replacement electrolytics you used make it no longer completely "All American" anymore   Wink

Logged
N2DTS
Member

Posts: 732




Ignore
« Reply #13 on: September 15, 2017, 12:05:02 PM »

Simple is sometimes better then complex.
I have built my own ham receivers and used the AA5 detector/agc setup, as well as the single conversion and low plate voltage ideas.
Its very quiet and high fidelity.
For ham use I added a more stable seperate LO tube, a good filter, an S meter circuit, and a bfo.
I also used a freq counter with an offset to show the exact frequency.
Works great.
Logged
KD8IIC
Member

Posts: 648




Ignore
« Reply #14 on: September 15, 2017, 11:24:12 PM »

 Anymore I'm leaving working wax caps intact.
 The one's I have replaced gave very little, if any, improvement in performance.
Logged
Pages: [1] 2 3 4 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!