Kriesler 11-77/78
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Location: Umina Beach, NSW
Member since 9 April 2020
Member #: 2410
Postcount: 33
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Okay so I found those c16 and 17 mica caps off the 12ax7. one grounds to the chassis off pin 1 and the other grounds to the on off tone pot. so I guess the question here is can I test these with a standard multimeter? just to let you guys know I am confident on what I'm doing its just I'm not sure how to do it. ive got to start some where.
And here is one for the books. here is exactly what I did. so I went in and removed chassis again and removed 1 tube so it wouldnt rest on it.Then I had a squizz at the underside of chassis poked and prodded a bit just looking for anything out of the ordinary. I rotated the volume pot a bit just to check as I had sprayed wd40 into it the other day and then put chassis back in and put tube back in. I then started it up but this time in low volume and just had it playing to where the noise starts to come in and no noise. I then increased the volume no noise. So its now played 21/2 records no noise. It just has not returned. Ive just shot back down to shed as Ive had it playing at volume just below max and it seems fine. Just I cant even get the noise to come back.Haha. I mean what is with that?
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Location: Toongabbie, NSW
Member since 19 November 2015
Member #: 1828
Postcount: 1313
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May have been a valve pin contact noise.
Valve sockets on old sets will be corroded along with the pins!
A squirt of CLEANER, not !#$$$ WD40 on the pins and into the sockets and a couple of in and outs of the valves can do wonders!
Good work so far keep going!
Fred.
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2476
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Re the micas, yes, they can do that if you prod them. They can be very long term intermittent. Might not come back for years!
No you can't test them with a multimeter, Silver migration breakdown happens at high voltages. Best way is unplug the 12AX7, fire up the chassis and put a scope, AC coupled, onto the cap. The scope will show up breakdown in its very early stages that you probably won't even hear. That is how I found a very long term intermittent mica in an HMV TV horizontal AFC circuit.
Another way, when the fault comes back (and it will) is use the 0.1μF cap with clip leads while the radio is running. If the noise goes away with the 0.1μF in place and comes back when removed, you have nailed it.
For intermittent faults, you'll do well to disturb as little as possible otherwise they can fix themselves and you've lost your opportunity for now.
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Location: Albury, NSW
Member since 1 May 2016
Member #: 1919
Postcount: 2048
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Shane when you get it fixed,
And you start to look at the cartridge and needle it may have a Garrard cartage.
It's shaped like 2 carriages stuck together at a 45 degree . Their hopeless!
Problematic!
The chassis is set up for crystal cartridges and so if you use a ceramic the volume will be very low , often 2 caps need to be charged.
But if you want a crystal that works ,let me know and I'll send you the link where to buy it.
Pete
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Location: Umina Beach, NSW
Member since 9 April 2020
Member #: 2410
Postcount: 33
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Ian noise is back. pfft haha it played janis joplin pearl 3 times then I put on wish you were here and it played up.
peter its got a bsr in it mate. looks like its been retro fitted which I dont mind.
fred. ive got some cleaner which I might spray and see if it cleans it.
thanks guys.
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Location: Umina Beach, NSW
Member since 9 April 2020
Member #: 2410
Postcount: 33
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Peter sound is awsome mate its just the noise which has crept back in...
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2476
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No sorry that's not a noisy contact.
Remember what I said. You have to catch it in the act.....
If you pull the 12AX7 out while it's running and it gets worse, it's a mica for sure.
If it goes away and comes back when the 12AX7 is plugged back in, it'll be a resistor.
It is just in one channel, isn't it??
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Location: Melbourne, VIC
Member since 11 July 2012
Member #: 1179
Postcount: 56
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It could be the 6V4 starting to arc inside. You probably don't have a spare good one? If you had some 1N4007 diodes you could put one in series with each 6V4 anode, but that is a little technical.
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Location: Albury, NSW
Member since 1 May 2016
Member #: 1919
Postcount: 2048
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Ian , That's a good trick about pulling the 12ax7 out !
I will have to remember that trick .
Pete
I'm taking bets it's a mica !
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Location: Werribee South, VIC
Member since 30 September 2016
Member #: 1981
Postcount: 485
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Get a can of Deoxit (available from Mektronics).
WD40 is way to oily for electronic use and will attract dirt and make matters worse in the long run.
It's not cheap but a can lasts for ages.
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Location: Sydney, NSW
Member since 28 January 2011
Member #: 823
Postcount: 6761
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Deoxit (available from Mektronics).
and Altronics: https://www.altronics.com.au/p/t3063-deoxit-d5-spray-142g/
and Jaycar used to stock it as cat #NS-1434 but not sure of that status now.
Jaycar also has a cheaper, non-spray version which I haven't tried: https://www.jaycar.com.au/deoxit-contact-cleaner-rejuvenator-solution-kit/p/NS1436
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2476
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Doesn't sound like dirty contacts behaviour to me.
Easy check - thump the chassis with a screwdriver handle and see if that makes it crackle. Or wiggle the valves of course.
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Location: Hobart, TAS
Member since 31 July 2016
Member #: 1959
Postcount: 563
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Ian, all these little tips show very much that your an experienced field and workshop tech.
No technical commentary needed.
Things like drawing an arc off top cap of a damper diode, horizontal output or EHT rectifier top cap.
All indicating exactly the state of health of the section under test, in a matter of seconds, to the experienced tech.
Another of the many tips that I did not realise I used was holding the top of a valve with one finger and and flicking the valve with your finger nail on the next finger. With the right technique one quickly established a problematic valve instead of a problematic valve base.
Its hard to relay all these tips, as in the Kriesler noise problem, Ian.
A problem that should be diagnosed and remedied very quickly.
Its the faults that disappear as soon as you approach the unit that are difficult.
Keep up the good work.
JJ
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Location: Albury, NSW
Member since 1 May 2016
Member #: 1919
Postcount: 2048
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Drawing an Arc of a Diode Cap ,
The first time I did that I aged about 10 years !
Yes your Tips are wonderful Ian and I try to remember them .I for one appreciate them .
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Location: Sydney, NSW
Member since 28 January 2011
Member #: 823
Postcount: 6761
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drawing an arc off ... EHT rectifier top cap.
I did that once and I quickly learned the breakdown voltage of the screwdriver's handle.
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