Viking Mobile - audio

[VK3SL]

Greetings,

I am fairly new to AM and have been  really enjoying a Viking Mobile rig which was superbly restored by a fellow VK ham. I just wonder if anyone with experience with this set can comment on optomising audio quality and gain? I presently use a CB style mike with reasonable punchy audio on the low impedance setting. Alas I do have to speak quite loudly and very close in order to achieve decent modulation with the mike gain on full. I don't have a crystal mike, nor have tried the high impedance setting, yet I wonder if anyone has experienced a particular mic 'synergy' with this diminutive Viking set? I suppose I'm just interested in peoples experiences / observations before I begin experimenting further. There seems to be very little written about the Viking mobile online.

At some point I would also be keen to source a VFO for this set - I wonder about the weight and shipping expenses to VK, but they do look quite small.  Alas, I suppose this is a query for the wanted forum..?

Thanks for any thoughts re audio and this fascinating little set.

Cheers,

Stephen VK3VSL

[WQ9E]

Stephen,

Welcome to the forum!

For the Viking Mobile, unless your unit has been modified, there is no setting for low/high impedance mics.  It is switchable to use either a carbon mic which is placed in the cathode of the first audio stage or a dynamic mic which is fed to the first audio grid.  I wonder if you have your mobile set to the carbon mic setting?  Try the other setting.  It has a lot of audio gain and I have never had to run the audio anywhere near full with the various dynamic mics I have used.

The Viking Mobile is for some reason fairly collectable over here leading to fairly high prices and the matching VFO is less common than the transmitter leading to high prices for it.  Any good vintage VFO will drive the Viking Mobile, I finally found a reasonably priced matching VFO for mine but prior to that I used a KnightKit VFO which worked fine and has its own power supply.  The fairly common Johnson VFO-122 that was typically used with the Viking I and II will work well with the Mobile.

[VK3SL]

Thanks so much Rodger,

I will investigate the situation and see where it leads. The carbon mic setting may well be the problem as the gain is indeed low.

I also appreciate your advice re the VFO - it seems like the Johnson VFO-122 may be a worthwhile consideration and would perhaps be an easy  'plug-in and play' solution. I think I actually have an old Geloso VFO module in the shed too but this would require a rebuild and maybe a dedicated PSU. Of course there are DDS options too but that may be sacrilegious!

Thanks again for your thoughts,

Kind regards,

Stephen VK3VSL

[WQ9E]

You are very welcome Stephen.

I assume you have the schematic for your Viking Mobile and if so the footnotes on it show the three connections that have to be changed in order to use a dynamic microphone.  The default setup is for a carbon mic so if it is original or restored to original then it will be set up for the carbon microphone.

Your Mobile may also have the PTT relay added, if not it is a fairly simple addition if you want to use PTT.

The Geloso VFOs are very nice assemblies.  I have a Geloso AM/CW transmitter receiver pair along with two iterations of their SSB oriented transmitters and receivers and a homebrew CW transmitter that someone built around a Geloso VFO.  The stability seems quite good with the Geloso VFO.

There probably aren't many Viking Mobile owners in Australia so you are in an elite group   For several years one kept showing up at local hamfests wrapped in plastic wrap and priced at $400.  I waited until I found a much better price on one.