Have any one experience with Eico 753?

[6AL5W-Martin]

hello friends,

I am searching for any informations, Tips and experience reports about the use and knowledge of problems of the Eico TRX Type 753
I have one in restoration.

known: the transistor VFO is drifting. (the rest of the radio is glowing)
the manual is at BAMA.

greetings
Martin

[G6Tanuki]

I think you'll need to contact some of the US boatanchor-sites for the lowdown on that particular radio - unless it was sold here in Europe under a different name/model-number?

[6AL5W-Martin]

it was sold here also. I found adress from Eico Sales Co germany. They made that like Heathkit, complete, or as a self building set. But only for 110 volts, so a transformer is required to use it here.
I am collecting all informations I can get.
1) the VFO is swimming (info from USA)
2) "not true AM" (only one side band given to AM? Info from germany)
3) there was a version with glowing VFO and one with transistor VFO (Info from germany), I have the transistor VFO. The rest is complete warm.
4) the manual is at BAMA
this restoration is a kind of adventure. But I want to finish that Oldie as a useful glowing TRX.

greetings
Martin

[FrankB]

Boy this takes me back to the early 70's.
The 7Drifty3.
IIRC, there were some articles either in QST, 73, Ham Radio, Electronics Illustrated, or another ham magazine that addressed that exact problem. VR tubes solved it I think it was. I think you could use Zeners to regulate now much easier. Have to try to remember back 45 years or so, & the memory is kinda fuzzy.
If I had my library reassembled, I could likely find the article.
You might use the Readers Guide to Periodical Literature at the library to find the articles(s) on this. HTH

[G6Tanuki]

Not saying this *necessarily* relates to the *specific* Eico radio you have, or its manufacturer, but as an example of the pitfalls of equipment designers this narrative from a seriously-well-respected US radio/electronics-author is as follows:

"In one column I passed along a request for information from an amateur working in the jungles of central america; he had a low-cost transceiver that made a brief splash on the amateur market. His problem was that it drifted badly, and in fact had always drifted even when new.
My request was answered by an engineer at Stoner Communications who passed along the information that the rig had been designed by a consulting engineer whose reputation is spotless.

His name is well-known to technically-oriented amateurs but I suspect he prefers privacy.

Contacting the designer I found that the original prototypes and first-production had a specified drift-tolerance of 100Hz in the first 15 minutes, and 50Hz/hour thereafter. Not terriffic but good for a cheap rig. Furthermore, those early rigs actually met the specification.

So what happened?

The designer told me that the original design used Litz wire in the VFO inductor and a special low-TC fiberglass form. The VFO also used DM-25 silver-mica capacitors except for a couple of ceramics used for temperature-compensation.

The inexperienced manufacturer used a 'kid technician' to redesign the rig to make it cheaper to produce; the technician replaced the Litz wire with enameled wire, the coil-form with an off-the-shelf ceramic type and the DM-25 SM capacitors with generic NP0 disk ceramics.

The result was a disaster".

[6AL5W-Martin]

http://bama.edebris.com/manuals/eico/751/Eico751.pdf this is the PSU part shematic
http://bama.edebris.com/download/eico/753/Eico753.pdf this is the TRX part shematic

there was an early model using a glowing VFO, and a later where the VFO is made with transistors. I have the later one, compatible to that shematic on BAMA.

About this VFO: there is a zener, 20V, I will replace that with a series of 4x 5,1V so there will not be any temperatur drifting in the voltage for the VFO.
Other changes there, we will see and use some test equipments ...
If all will fail there is to insert a HuffPuff stabilizer to make that working.

At begin is the restoration, means washing, recapping something and run the receiver.
Recapping the PSU also.

At last I will look for that VFO

greetings
Martin

[6AL5W-Martin]

continue.

In the PSU I will remove the electrolytics downside,
they are out of time.

the styropor block you see here is made from the pre owner, may be a temperature stabilizer thing... there is the problems area.
PSU: the loudspeaker I have removed for washing that all there, it will go back in the place later.

greetings
Martin