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THE AM BULLETIN BOARD => Technical Forum => Topic started by: Opcom on November 23, 2023, 11:48:02 AM



Title: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: Opcom on November 23, 2023, 11:48:02 AM
I wonder if this is a kit or a commercial product. If it's home brew, the quality is excellent. Has anyione seen a unit like this? There's no name on it.

The handset TS-9-AP is similar to that from EE-8 military field telephone. It looks like there are separate audio input and output transformers. The round one in the top corner and the square black one below it which looks very telephone-ish. The handset is probably carbon mike and a 200-600 Ohm receiver.

The three tubes are all 3A3 dual triodes designed for RF amplifier use, with plate dissipation of 2 Watts and 'ample' cathode current reserve for high peak class-C use according to the data sheet. Here they are used for audio and RF. One is the push-pull modulator for this AM set.

Batteries are six "D" cells in series, providing +1.5, -1.5, -4.5, -9V. The plate voltage is provided by an inverter using Germanium transistors. The single crystal is on 27.005 Mhz.

No more investigation has been made. It's not clear about the receiver, but it looks like a regenerative or TRF, rather than superheterodyne as there are apparently no I.F. transformers. to find out more, almost everything will have to be removed, but it seems possible since it's all put together with screws. The antenna whip is missing but I believe it fits into the white post at one end of the top. There are no labels on the switches or tuning control so it's a mystery at this point.


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: Tom WA3KLR on November 23, 2023, 01:46:33 PM
That's cool. I think it is a prototype from the early days of C.B. Is the fiber board wired point-to-point or is it printed circuit? Kinda looks like swaged in posts though. It might borrow from the BC-611 w..t. schematic.


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: Opcom on November 26, 2023, 11:54:18 PM
The board looks like point to point with a few terminals - no printed circuits. It doesn't seem to have to much in common with the -611. Its TX/RX switching isn't nearly as complex as that of the BC-611. I may have to disassemble it and draw out the schematic.

I checked out the BC-611/SCR-536 and it's very interesting for a minimalistic rig with a short entenna. Alas it's a superhet with all screen grid tubes and two crystals so the schematic will be something else. The 611 is interesting in that it's choke modulated. I don't yet know the modulation scheme on the Portable. It's literally too hard to see back in there to count the wires on the large 'modulation' transformer


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: KD6VXI on November 27, 2023, 06:22:01 AM
That's cool. I think it is a prototype from the early days of C.B. Is the fiber board wired point-to-point or is it printed circuit? Kinda looks like swaged in posts though. It might borrow from the BC-611 w..t. schematic.

Early days of cb....


CB started in 1958.  Wouldn't that predate the TO3 transistors on the side?

Regardless, cool piece, nice construction and a killer treasure hunt to find out what it is now.

Incidentally, one xtal is odd for cb rigs.  Usually they will have two, separated by the If freq.  Most xtals for cb where 455 KC separated due to the cheap 455 kHz murata filters available.  Of course, this rig predates those, too.

27.005 is cb channel 4.  Not a real popular channel ever that I remember.

--Shane
WP2ASS / ex KD6VXI


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: Tom W2ILA on November 27, 2023, 07:37:39 AM
Early inexpesive CB HTís used one crystal for TX and the receivers were so broad (regens?) you could hear a significant part of the band.


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: KA3EKH on November 27, 2023, 09:36:44 AM
Pure speculation but think that may be a Ham transceiver from back in the dinosaur days of 11 meters being a Ham band 27.005 would put it between 49/58 before Citizen Band was established. Going to base this on that only a holder of a second class or above license was allowed to work on CB junk and the CB operators were not permitted to operate transmitters that were not type accepted by the FCC or allowed to do anything that affected the transmitters output, so donít think much CB junk was home built and by my limited understanding would be illegal.
The switching power supply would place it past 1950 so it would fit right about in with that mid-fifties time frame. Thought it may be a six-meter transceiver but the second harmonic falls just outside the six-meter band.



Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: Jim, W5JO on November 27, 2023, 10:31:03 AM
Keep in mind the CB band was, originally, conceived to be a business band and a lot of the early equipment was for that purpose.  This may be a set designed for an on-site communication purpose.


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: KA3EKH on November 27, 2023, 11:29:17 AM
About the oldest thing I can think of is the Johnson Viking Messenger and they were all type accepted, canít think of any kit except the Heath CB-1  Lunch Box, no home built CB stuff beyond the almost endless string of non-accepted linear amplifiers. If it was originally intended as a home-built CB it may be one of the few that ever existed.
Looking at the radio in the picture its clear to see that it would not do beyond a couple hundred mW so maybe thatís an exempt radio being under 125 mW and was a project back in the old days in Radio & Electronics magazine?
Class D operators were never allowed to build or adjust any of the parts of the transmitter, the Heatkit CB-1 Lunch Box in 1959 had the warning that you had to hold a first- or second-class license to build it, or maybe you would take it to a 2-way shop and have it checked out before you use it? I donít know.



Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: WD5JKO on November 28, 2023, 03:35:27 PM
27.005 is cb channel 4.  Not a real popular channel ever that I remember.
--Shane
WP2ASS / ex KD6VXI

I have one of those crystals that I use in my Central Electronics 20a to replace the OEM "drifty" 9.000Mhz rock.
27.005/3=9.00166 Mhz.
Most of those CB crystals are third overtone.

Jim Wd5JKO


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: Opcom on November 28, 2023, 04:14:39 PM
The possible timeframe is appropriate for early Germanium TO-3 transistors in an inverter power supply, in combination with low-power tubes. It may have saved weight, space, or cost over a B battery and replacements but D cells were the best energy for the dollar. Might still be.

Most of what's in there looks like it comes out as assembly (no connectors) and should all come out once every screw is removed. The HV supply, the battery holder, and 'the guts' with the switches and dangly bits like the handset transformers, etc.

The 3A5 was released in 1942 and should have been inexpensive in the 1950s. Maybe there will be a date code on a part in there, if date codes were commonly used back then.

TO-3:
https://www.semiconductormuseum.com/Transistors/LectureHall/JoeKnight/JoeKnight_EarlyPowerTransistorHistory_CBS_Index.htm

https://www.semiconductormuseum.com/Transistors/LectureHall/JoeKnight/JoeKnight_EarlyPowerTransistorHistory_Motorola_Page2.htm

https://en.wikipedia.org/wiki/TO-3


Title: Re: Interesting portable tube type AM transceiver found - kit or home brew?
Post by: WA5VGO on November 29, 2023, 10:58:52 AM
In the early days of Criminal Band radio, homebrewing was allowed. Check out the March 1959 issue of Radio & TV News magazine. Donald Stoner has an article for constructing one. Also notice his design was stolen by Heathkit almost part for part for their Lunch Box transceivers.
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands