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Old 2nd Nov 2013, 12:29 pm   #1
Restoration73
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Default Masteradio D517/VHF Skymaster

I've recently acquired this. Externally it looks like the Masteradio D517 aka GEC G817, but the printed front dial has the FM section missing and
a printed tuning scale 108-136 MHz is attached to the plate behind thetuning pointer. The circuitry is otherwise unmodified.
There is a front stuck on label "VHF Skymaster" covering up Masteradio. The original set is from about 1967, but this version seems to have later
dates on some parts, despite being an elderly germanium design for the early 1970's. Does anyone know how the airband version originated,
i.e. is it a GEC special or were a batch of sets purchased, modified, and supplied to airband enthusiasts ? Answers appreciated.
It is quite a rugged design.
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Old 2nd Nov 2013, 4:50 pm   #2
dave walsh
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Default Re: Masteradio D517/VHF Skymaster

Transistor radios aren't usually my thing but I thought [at first] that you might have the same model as myself [a Shorrock]. I was intrigued to find such an early set with airband some time ago and started a thread which I've now managed to find .. "First Air Band Set 2/9/09". Paul RK and Howard seemed to be founts of knowledge! Hope it may help in some way.
Dave W

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Old 2nd Nov 2013, 6:41 pm   #3
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Default Re: Masteradio D517/VHF Skymaster

Thanks for that - I am aware of larger portable sets with airband that were probably for those working in aviation and specifically design to cover airband.
Apart from a good clean and audio distortion which I cleared by replacing an AC127, this works quite well, with intermittent signals caused by a dry joint on the band switch board. All the AF116s seem ok. As it actually demodulates AM sigs, I am assuming the ratio detector has been set for this. I can hear a local FM on 107.8 by slope detection.
Tony
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Old 14th Feb 2015, 12:48 pm   #4
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Default Re: Masteradio D517/VHF Skymaster

Hi, I googled VHF Skymaster, and found this thread, leading me to join the forum.
I've owned one of these radios since new, in the mid 60s. In its day, it was probably the best airband radio you could buy.
Sadly, mine stopped working a long time ago, and is looking rather sorry for itself [see pic attached]. It's like an old friend, though, and I'd love to get it working again.

Any advice on repairing it would be much appreciated.

Cheers,
Steve
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Old 15th May 2021, 1:19 pm   #5
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Default VHF Skymaster/Masteradio D517

Hi, I posted here previously, regarding my VHF Skymaster.

I never did get round to checking if the AF116 transistors were the problem. Life got in the way etc.

Well, I now have three of these radios. A friend donated his non-working example to me for spares, and I've just bought another in very good cosmetic condition, although also non-working.

The AF116s seem like a good place to start. Substitution with an item that doesn't suffer from the tin whiskers problem seems like the best long term option.

I've seen here... https://www.electronica-pt.com/engli...ence?ref=af116 that GT322V is suitable, but can find no reference to it on this forum. Russian made, apparently.
GT322V datasheet: https://alltransistors.com/transisto...ansistor=36088

I'm a relative novice at this, although I've repaired a couple of LCD monitors with bad caps.

Thanks for any advice.

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Old 15th May 2021, 1:32 pm   #6
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Default Re: Masteradio D517/VHF Skymaster

Mine continues to work. You may find the push button switch contacts need a clean.
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Old 15th May 2021, 2:03 pm   #7
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Default Re: Masteradio D517/VHF Skymaster

That's good to hear. I'll check those, too.

If I remember correctly, with my original radio, VHF packed up, but I was still listening to MW for some time. Eventually, MW died as well, but that was probably 30 years ago.
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Old 15th May 2021, 4:50 pm   #8
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Default Re: Masteradio D517/VHF Skymaster

Well, I've spent the last few hours dismantling #1 [original] and #2 [donor] Skymasters. First I tried the tapping test on the AF116s [TR4, TR5], but with little success - although I did think I heard a slight crackle once or twice. However, tapping the AC127 [TR7] in both cases has started to get things working again.

So far, MW and LW seem to be working sporadically on both. Nothing on VHF, though. I'll check the solder joints on the AC127s tomorrow. Channel changing doesn't seem too good, either. What's the best method of cleaning this component? It looks like it could be rather fiddly...

Thanks
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Old 15th May 2021, 7:23 pm   #9
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Default Re: Masteradio D517/VHF Skymaster

Seems it's a conversion performed and marketed by Volstatic of Acton:

https://www.airband-radio.co.uk/volstatic/

Paul

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Old 15th May 2021, 8:22 pm   #10
blackaddler
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Default Re: Masteradio D517/VHF Skymaster

Volstatic certainly provided service/repairs for the Skymaster, and another pocket sized airband radio I have. I remember visiting their workshop in Acton, a couple of times back in the late 60s, early 70s for aerial replacements. If I get these working, I could certainly do with a couple of new aerials. Lord knows where I might find them.
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Old 16th May 2021, 1:33 pm   #11
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Default Re: Masteradio D517/VHF Skymaster

Quote:
Originally Posted by Restoration73 View Post
Mine continues to work. You may find the push button switch contacts need a clean.
Did you clean with compressed air, and then lubricate with something like Servisol Super 10?

I've just had a look in the garage, and I have some GT85, and Tetrosyl Double TT, both of which contain a PTFE lubricant.

Would they be suitable? If not, I'll order some Super 10.
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Old 16th May 2021, 3:53 pm   #12
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Default Re: Masteradio D517/VHF Skymaster

Hi

If you want to clean and lubricate contacts, I strongly recommend a properly formulated contact cleaner. Things like WD40 or PTFE lubricants are to be avoided.

I remember plenty of Multi-band VHF transistor sets in the 60's and 70's from the far east. Most of them simply used the broadcast FM detector, as USA based 2-way radio used FM. In the UK, 2-way radio used both AM and FM, but aircraft comms worldwide used (and still do) exclusively AM. The performance on air band must have been rather compromised, with a need to tune off centre to hear anything.

To avoid difficult VHF switching, these sets often simply used separate front ends with a common IF strip.

I guess the conversions being discussed did a rather better job of the detector, and possibly added AGC.
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Old 16th May 2021, 4:27 pm   #13
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Default Re: Masteradio D517/VHF Skymaster

Thanks, I'd read about WD40, and wasn't going to use that, but wasn't sure about the PTFE lubricant.

Airband comms are VHF [civil] and UHF [military].

Here's a pic of my most recent acquisition.
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Old 17th May 2021, 7:32 am   #14
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Default Re: Masteradio D517/VHF Skymaster

Hi blackaddler

When I mentioned AM and FM, I was referring to the modulation method rather than the frequency band.

Radios (especially for the US market) often use "AM" as a shorthand for "Medium Wave broadcast band, AM modulation", and "FM" as shorthand for "VHF broadcast band, FM modulation"
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Old 17th May 2021, 7:54 am   #15
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Default Re: Masteradio D517/VHF Skymaster

Yes, I realise that, but airband comms are FM not AM as you suggested. A typo, perhaps?
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Old 17th May 2021, 8:07 am   #16
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Default Re: Masteradio D517/VHF Skymaster

Definitely AM. Wikipedia isn't the ideal authority, but currently seems mostly sensible on this subject:

"Aircraft communications radio operations worldwide use amplitude modulation, predominantly A3E double sideband with full carrier on VHF and UHF, and J3E single sideband with suppressed carrier on HF. Besides being simple, power-efficient and compatible with legacy equipment, AM and SSB permit stronger stations to override weaker or interfering stations. Additionally, this method does not suffer from the capture effect found in FM. Even if a pilot is transmitting, a control tower can "talk over" that transmission and other aircraft will hear a somewhat garbled mixture of both transmissions, rather than just one or the other. Even if both transmissions are received with identical signal strength, a heterodyne will be heard where no such indication of blockage would be evident in an FM system." ( https://en.wikipedia.org/wiki/Airband )

Paul
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Old 17th May 2021, 8:16 am   #17
blackaddler
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Default Re: Masteradio D517/VHF Skymaster

Thanks for that. I stand corrected.

You learn something every day.
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Old 17th May 2021, 10:17 am   #18
Mr 1936
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Default Re: Masteradio D517/VHF Skymaster

Hi

A bit more background. Ground to air comms in the UK switched from HF to VHF during WW2. AM was used at VHF as it was simple and proven. In later years the use of AM continued, and I suspect that by the time FM came to the fore (especially in the USA) there was so much installed hardware worldwide that changeover (even if there was an advantage) would have been too costly.

At some point, a system was developed using multiple ground transmitters to cover a wide geographic area. All the transmitters carried the same modulation (presumably via GPO lines) but they were slightly spaced in frequency by (from memory) -5, 0 or +5 kHz. The aircraft receivers were wide enough to receive 2 or 3 ground transmitters simultaneously, and the 5 kHz heterodynes from the multiple carriers were above the audio band so the whistles could be filtered off after the AM detector. This cunning scheme only works with AM. I don't know if the same system is used today.
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Old 24th May 2021, 10:49 am   #19
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Default Re: Masteradio D517/VHF Skymaster

At the weekend, I picked up yet another Skymaster from a another mate, so I have four here at the moment. I had a quick look at it yesterday, and it wasn't difficult to diagnose one problem. A totally destroyed Callins 400uf 10v cap.

Interestingly, this radio has 4 of these Callins caps [marked SPA 14], while the rest were built with TCC Elkomold B1 caps. I was wondering if this was an earlier or later build, but the sticker with the serial number is missing from this radio, so I can't tell.

All the caps are axials, even though 3 out of 4 caps are mounted vertically on the board. I might as well replace them all while I'm about it, and shall probably order some Panasonic FM 470uf 25v radial caps. From what I've read, they seem to be good quality, a reasonable price and much more readily available. The legs might be a tad short to mount in the horizontal cap position, which appears to have a spacing of about 40mm between holes.

I'm still undecided with what to do about the AF116s, and the AF115 on the VHF side. I'm leaning towards replacement. The AF115 looks very difficult to get at Maybe I can cut it off at the legs and solder a replacement to those.

I'm thinking about the GT332B as replacements, but it seems that they're only available from Russia or Ukraine, so may have a bit of a wait if I chose those.
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Old 24th May 2021, 11:42 am   #20
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Default Re: Masteradio D517/VHF Skymaster

I forgot to mention the AC127.

Again, the GT332 seems to be an option, but would I need to replace the AC128 as well?
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