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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 11th Dec 2010, 11:41 am   #1
Jooppg4i
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Default RACAL RA-17: taking out the first VFO?

Hello,

I own a RA-17 which was previously used in the Dutch army. This receiver has been suffering from a bad working first VFO. When I turn the megacycles knob, there are a lot of cracking noises from the speaker and it is hard to tune to a new band. It seems as though there is a bad contact somewhere.

So now I would like to take the first VFO out. I have remove three knobs from the front panel: the large megacycles knob, the antenna tune and range knobs. Als removed 2 10 cm long screws from the top of the VFO. So now I can move the chassis with the VFO freely, but it seems to be stuck somewhere.

Is there anyone who can tell me how to take the VFO out?

Thanks,
Joop
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Old 11th Dec 2010, 4:28 pm   #2
Nick G8GRA
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Default Re: RACAL RA-17: taking out the first VFO?

Joop - hi,

I have only done this on a RA117E but the chassis design is similar to the RA17. Others who may read this may have alternative methods, but this is the easiest although time-consuming:

1 Remove all knobs, then remove the front panel. This is necessary to get exposure to the mechanical bits such as the film-strip lock and the 2nd VFO chain for cleaning / lubrication, then,

2 Unplug and remove the 100kHz calibrator from the 2nd VFO – easy, just a knurled knob and a BNC connector.

3 Lock the VFO from the front panel-locking spigot. This moves some of the metalwork away from the 2nd VFO.

4 Remove the 2nd VFO. There are some bolts on the top of the chassis and one underneath. You will need to unsolder the heater and HT leads underneath located on a black tag strip. You will also need to unsolder the blue wire (on a RA117E) that connects to the Harmonic Mixer board at R18/L20, and the Orange and red wires that connect to the 40MHz band pass filter.

5 Now you have sight of the uncluttered 1st VFO.

6 Undo the bolts on the top; unsolder the HT, Heater and AGC screened cable from the bottom tag strip.

7 Unsolder the RF input co-ax from the attenuator.

8 Gently remove the first oscillator feeding the RF input co-ax through the chassis grommet.

9 Rebuilding is the reverse of the above.

10 Use some silicone grease to lubricate the grommet for the RF input co-axas it will be easier to pull through on re-installation.



It sounds daunting but its worth it. I use some screened microphone cable to connect the tag strip to the 1st VFO so it can be powered on the bench to fault-finding.

As you have gone to this trouble, its worth checking that the front-end gain is correct by injecting a known value into the front-end co-ax and measuring the output on Test Point 2 at the output of the 0-30MHz BPF.

Above all else, good luck with your project!

Regards,

Nick
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Old 11th Dec 2010, 6:32 pm   #3
radiotircoed
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Default Re: RACAL RA-17: taking out the first VFO?

Glad Nick could help. I've work on a million of these and can't remember at all. Senile dementia?

Bob W
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Old 12th Dec 2010, 7:11 pm   #4
Jooppg4i
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Default Re: RACAL RA-17: taking out the first VFO?

Hello Nick,

thanks a lot!

I will have a go at it later this week and let you know my results.

Regards,
Joop
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Old 14th Dec 2010, 5:45 pm   #5
amornummi
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Default Re: RACAL RA-17: taking out the first VFO?

If you remove the round "megacycles" white dial , and the RH side panel it is possible
to get the first vfo/mixer chassis out without disturbing the Kc/s VFO.
I usually replace the "Aerial" input cable with min ptfe coax.
Whilst you are in there replace the two grid bias 100k ht to gnd resistors.
G3TSA
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Old 17th Dec 2010, 10:36 am   #6
saxmaniac
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Default Re: RACAL RA-17: taking out the first VFO?

I have had this problem on mine & I think it is poor earth connection to the spindle of the tuning capacitor, probably dirty wiping leaf spring contact, I cured it without dismantling by getting loads of switch cleaner round the tuning capacitor shaft at the front and working it back & forth to clean the contact. Its worth a try to save having to dismantle
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Old 27th Dec 2010, 9:19 am   #7
Jooppg4i
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Default Re: RACAL RA-17: taking out the first VFO?

Thanks saxmaniac, sounds like it will be an easy repair

Still have to take the VFO out, Christmas holiday has been busy

Will keep you informed
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Old 29th Dec 2010, 1:26 pm   #8
Jooppg4i
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Default Re: RACAL RA-17: taking out the first VFO?

It worked!

I wanted to have a look at the capacitor anayway, so I decided to dismantle.

Took all the knobs off, then the side panel. Removing the white scale helps a lot, there will be more room when you do this (be sure to mark the position of the scale). After desoldering a couple of wires, I could take the VFO out sideways.

Will replace the coaxial cable, a thinner cable will have more room inside the switch cabinet.

Thanks to all that helped
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Old 30th Dec 2010, 3:13 pm   #9
amornummi
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Default Re: RACAL RA-17: taking out the first VFO?

IMPORTANT- switch cleaner can make nylon grow bigger!

The bandswitch rotor is nylon. You will not notice for a while ,however the slightly stiff rotation will cause the centre hole to become bigger.Then you will discover you have to turn the switch a little too far , then back. The only solution then is to replace the whole switch. (This also happens to the gears in the Drake T4/R4)
Over the years I have seen this in about 1 in ten sets.
When you have the unit out , replace the two 100k resistors r32/r32a. They are often high.(HT to ground ECC189 bias)
There is no need to replace any others unless they are more than 20% high.
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