Question regarding Midland 77-800

hi all can anyone help me I have a midland 77-800m portable cb radio which which works on a 5 din pin speaker mic would a midland 77-805 portapack cb speaker mic work on a midland 77-800m portable cb radio

Hi Paul I moved your topic to it’s own thread, as it was posted in someone else’s thread

Nice job Paddy, the question could have been so easily missed otherwise.


Paul,

According to the schematic for the 77-800, (link below) :-

https://www.qsl.net/iz8hhq/cte77-800/index.html


The wiring looks the same as the 77-805 so hopefully yes.

Hope that helps.


All the best,
Victor

As best I recall, and it's been a long time since, I seem to remember that the portapak (which wasn't a bad lil Beastie as far as compact mini-manpack portable CB went and one of very few we got in the UK) was a modified 77-800 mobile or something similar compact mobile wise and just about all with the 5-pin din shared the arrangement of pin out.

But it's easy to verify with a multimeter and a bit of scrap wire to determine what PTT and subsequent wiring arrangement is needed, by the rig, and with a multimeter or a basic continuity test to be able to work out whether the RX audio needs to be shorted to GND to get receive audio and if the mic side wiring does so.

But classically, the older (and yet still more radio world common) convention of Rx audio being internally muted on Tx but live otherwise and only Mic and PTT lines grounded during TX (ie three pins wired only on a regular mic) means you only need to establish mic, PTT & GND pins and wire any dynamic or self-powered condenser mic to be hitting the ground running.

If you unplug the mic, and lose Rx audio, then it's a four pin setup (not counting any CHNL or suchlike mic side functions) where on Rx you need the Rx audio pin shorted to GND, Tx audio not grounded, and PTT not grounded. So with no mic, you use a dummy plug with an Rx audio pin ->>Gnd wire strap. On Tx, the Tx and Rx wiring states reverse, so Rx isn't grounded, Tx is and PTT is grounded.

Most 5 pin din sockets radios back in the day used a common or maybe two pins swapped breakout. Most 4 pin'ers where virtually mirrors pinout wise between Cybernet based chassis types and Uniden chassis types.

On a 5 pin, if any normally unused pins carry functions, they are usually either a phantom low voltage to drive condenser mics or a logic state for a function that's simply a connection to GND to implement.

That's why I loved the old three wire sets, you only needed a breakout lead to jacks, and you could quickly use almost any dynamic or self-powered mini-jack mic on the mic in connection breakout, and a simple momentary or locking simple switch to trigger PTT, making testing mic insert donors rapidly tested - and you could roll up a remote mic, mic/speaker remote and even have a separated remote PTT as easily as gutting a good vocal mic and a guitar compressor to make a punchy base mic re-cased into something worth pride of place in your shack.

Worst case, just try the potential substitute, the worst that can happen isn't going to damage the rig.

It appears that that the radio you've got and the portapak were essentially the same radio based on a mobile, where one's an AM set vs FM in the portapak, so given the core mobile donors and typically manufacturer in-brand common wiring, shouldn't be any problem I can think of. But where one may (again probably maybe the portapak FM unit, but recollection is grey) have had a condenser mic not a dynamic, then if the other set doesn't provide a phantom DC and desired mic needs it for electret/condensor driver, you may have to find DC to suit (an AA battery is sufficient), but most CB's were still using dynamic inserts on mics, and speaker mics either shared a single dynamic for speaker and mic functions or had a large and small insert pair respectively.

I should be able to recall, as I had the portapak mic apart various times when I tested different inserts, but I ditched my notes ages ago when the PP went to a new home.