Hacker Mayflower II - crackling sound

[hamid_1]

I have one of these lovely VHF/FM radios with a slightly annoying fault.

For the first few minutes after switch-on, crackling / rustling sounds are heard from the speaker as well as the sound of the radio station playing. The crackling noises gradually disappear, after about 20 minutes the sound is fine.

So far, all I've done is replaced the two ECL86 grid coupling capacitors C31 and C32 on the manufacturer's service manual (obtainable here) - the ones I took out were found to be very leaky - but the set still crackles.

Before I do a mass capacitor-change, what should I look for as the cause of the crackling fault that clears up when warm?

[Geordie McBoyne]

Hi Hamid, Does the crackling disappear when the volume control is turned down minimum?
At least this action would isolate the amplifier from the earlier stages. Those anode load resistors of the triode sections of the ECL86s could be suspect, high value carbon resistors can go noisy.

Geordie McBoyne.

[boater sam]

Try cooling the resistors when it is not crackling, freeze spray is good. But mind the valves!

[spot-wobble]

Hamid,

I had a problem with a radio a while back (can't remember make and model) was AM/FM though.
The problem was crackling, after much investigation it turned out to be the paxolin on wave change switch inner contacts. It had gone conductive. No sign of burning etc.
Adjacent contacts were audio switching and HT. HT was tracking to the audio circuit through the paxolin and causing the crackling. I could actually measure a small positive voltage on the audio circuit.

I had to remove the wave change switch and change the inner rotating paxlin contact holder. Fortunately I had a similar spare switch that I could canibalise!
Maybe you have a faulty paxolin tag holder etc in your Radio?  I am guessing that the Mayflower is VHF only so no fiddly wave change switch to deal with.


Good luck

Andy

[hamid_1]

Thanks for your suggestions. I spent a whole frustrating evening on it yesterday.

First of all, the 220K anode feed resistors. I took the chassis out of the cabinet (the resistors are underneath the chassis and otherwise inaccessible), turned it upside down to reveal the component side, then reconnected the speaker and aerial. I powered up the chassis in this position, but to my surprise the cracking noise did not appear, even when I sprayed the 220K resistors with freeze-it. So I put the radio back together and guess what, it started crackling again.

This time I tried to narrow the fault down to the tuner or the amplifier section. This radio has a phono socket for connection to a tape recorder. While the radio was crackling away, I plugged the tape output into an external amplifier and listened - no crackles! In other words, an amplifier fault.

Removed the chassis again. The next suggestion -  the paxolin tagstrip. Looking at the strip with the aforementioned 220K resistors connected to the output valves, nothing seemed obviously burnt. Again, with the chassis upside down there was no crackling, but when I tapped some of the components on the strip with a screwdriver handle, I heard a brief crack from the speaker. Could it be a dry joint?

There didn't appear to be any obvious dry joints, but I decided to re-solder the whole tagstrip anyway. While doing this, I noticed a few of the tags were screwed to the chassis. This completes the connection from component to earth and HT negative. I unscrewed these tags, cleaned them and tightened the screws. Now when tapping the tagstrip there was no cracking noise, and after reassembling the radio, the crackling had stopped.

Finally I thought I had fixed it, but shortly after putting everything back together, the tuning cord snapped  

That's as far as I've got now. I guess the crackling problem was most likely due to poor earth connection of the relevant tags on the strip. I'm rather surprised that Hacker simply used ordinary self-tapping screws without any "star" or shakeproof washers to connect the solder tags to chassis. Eventually they must have come loose causing crackling noises, but I suppose they held for over 50 years ...

Now I need to replace the tuning cord. Where to get it from, and what is it called? It's been years since I've replaced one (luckily!)

[boater sam]

Fishing line, bead thread as used for making necklaces, I even had one recently that had been redone with string!
I buy necklace cord from China, very cheap, doesn't stretch and available in many colours. Works well.

[Crackle]

Hi Hamid
I use waxed whipping twine, you can buy it online in various colours and thickness. http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR3.TRC1.A0.H0.Xwhipping+twine.TRS0&_nkw=whipping+twine&_sacat=0

It works very well, I have found that monofilament fishing twine does not grip the spindle very well and is very stretchy.

Mike