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 AWA B15 woes
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 Return to top of page · Post #: 1 · Written at 4:26:25 PM on 24 September 2015.
Simplex's Gravatar
 Location: Bathurst, NSW
 Member since 7 August 2008
 Member #: 336
 Postcount: 398

Dug out one of my B15's which has been recapped throughout about a year ago and gave it a bit of a run.

Works well with good reception and audio except every so often there is a bit of a faint splat and the audio level drops markedly.

Quickly switch off and on, usually this restores full volume.

One of my new capacitors leaky or a resistor somewhere that may need changing ?

Its been a while that I have looked at the underside and don't think I bothered to replace all resistors.

Some guidance as to where to start would be appreciated.

Thanks


 
 Return to top of page · Post #: 2 · Written at 7:25:14 PM on 24 September 2015.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 2116

One thing you could try is finding where the "splat" is coming from. Open up the radio, and remove the dial lamp(s). Turn on the radio and turn off all the lights, so you're in the dark. Give about 10 minutes for your eyes to adjust. When the "splat" happens, you might be lucky enough to see it.

This isn't so reliable, but it did work twice. First time it was a resistor with internal sparking, 2nd time it was a flashover on the output valve's socket. This one was cured by replacing the cap that connects to the anode.


 
 Return to top of page · Post #: 3 · Written at 9:18:42 PM on 24 September 2015.
TheDanger's avatar
 Location: Devonport, TAS
 Member since 26 March 2015
 Member #: 1718
 Postcount: 22

Ha what are the chances having some other problems with my B15 at the moment!

https://youtu.be/7b6u9j7wH8k

Could this be a tube heater problem? As the heater coil warms up it shorts out causing the splat then cooling down it recommences operation?


 
 Return to top of page · Post #: 4 · Written at 11:39:25 PM on 24 September 2015.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 2116

That youtube link takes me to the crackly radio featured in another thread.


 
 Return to top of page · Post #: 5 · Written at 11:53:29 PM on 24 September 2015.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6802

Seems its the season for B15 blues.


 
 Return to top of page · Post #: 6 · Written at 6:21:51 AM on 25 September 2015.
Simplex's Gravatar
 Location: Bathurst, NSW
 Member since 7 August 2008
 Member #: 336
 Postcount: 398

Thanks for all of the comments, the condition is not consistent unfortunately.

Sometimes there is a soft "splat" , other times the volume level just goes soft.

I have seen the condition discussed before as is not uncommon but for the life of me can't remember the thread now.

It is not the problem that is occurring with the B15 in the video.


 
 Return to top of page · Post #: 7 · Written at 10:03:52 AM on 25 September 2015.
MonochromeTV's avatar
 Location: Melbourne, VIC
 Member since 20 September 2011
 Member #: 1009
 Postcount: 1221

Having two AWA B15 queries on the same day I had a bit of trouble deciding which thread to include these in.

AWA B15 Mantel Radio
AWA B15 Mantel Radio


My mums Astor BPJ presents the same symptoms as the B15 in this thread. I cant remember if I changed the micas but I did suspect the micas inside the IF cans could've been faulty. I would change the mica caps that Marcc suggests on the other thread and see if this solves the problem.


 
 Return to top of page · Post #: 8 · Written at 11:52:34 AM on 25 September 2015.
Garyoz's avatar
 Location: Perth, WA
 Member since 19 November 2008
 Member #: 381
 Postcount: 240

If you read Silicon Chip July 2013, page 93, they mention a modification to prevent IF being radiated and feeding back into the front end which can cause instability.

They suggest adding two 47pF caps. One between the junction of R6 & R8 and deck & the other from pin 1 (or 7) of the 6AQ5 to deck. This will drop the unwanted IF by 20 to 30dB.
They go on to suggest that this mod will benefit most domestic valve AM radio receivers.


 
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