[R-390] R-390A blown fuse, now distorted line and local audio

[Tom M.]

 Thanks Jordan.  I found a pair of 12AU7s in my box that tested so I'll try them later today.

    On Wednesday, April 10, 2024 at 07:01:25 AM CDT, Jordan Arndt <outposter30 at shaw.ca> wrote:  
 
 In the interim, you might try pulling one or both of the 5814 tubes from the 
calibrator circuit and swap them into your AF deck to see if that corrects 
the problem or not...

73...Jordan VE6ZT



----- Original Message ----- 
From: "Tom M. via R-390" <r-390 at mailman.qth.net>
To: <r-390 at mailman.qth.net>; "Jacques Fortin" <jacques.f at videotron.ca>
Sent: Wednesday, April 10, 2024 4:56 AM
Subject: Re: [R-390] R-390A blown fuse, now distorted line and local audio


> Very good advice. Thanks for your prompt response. I did not have any new 
> 5814 on hand so I ordered one and will pop that in and give it a try.If 
> that's all it is, that would be great.
> ThanksTom
>
>    On Tuesday, April 9, 2024 at 07:46:15 PM CDT, Jacques Fortin 
> <jacques.f at videotron.ca> wrote:
>
> Hi Tom,
>
> My guess is that V601B filament gave up.
> So you have the 1st audio stage working, most probably, but the cathode 
> follower stage that follows is inactive.
> Quick fix: change V601 and check if the audio returns to normal.
>
> If not, more investigation in the AF chassis is due.
> That could be also the V602 that developed a gas leak....
> Let us know what you found, anyways.
>
> 73, Jacques, VE2JFE in Montreal
>
> -----Message d'origine-----
> De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la 
> part de Tom M. via R-390
> Envoyé : 9 avril 2024 19:38
> À : r-390 at mailman.qth.net
> Objet : [R-390] R-390A blown fuse, now distorted line and local audio
>
> Hello all,
>
> looking for advice to help fix this problem.
> I was operating my radio today when it exhibited some funny business, 
> flickering dial lamps and then sudden OFF.Found 3A fuse was blown (but B+ 
> fuse OK).
> Not knowing what else to do I replaced the fuse and supervised the power 
> on. It powered on normally with no other fuse blowing or flickering, but I 
> have low and somewhat distorted audio on both the LINE and LOCAL audio 
> circuits.
> Initially thought the AGC was out so I switched IF decks; same issue.
> I checked the audio at the DIODE LOAD through an amp and it is 
> lovely/normal.
> So Q: where should I start looking to repair this audio problem?I don't 
> know if the blown fuse was a red herring or not but it sure seemed real 
> like bad stuff was happening right before.
> Twenty five years ago I changed C603A/B (30uF caps on 1st AF AMP) and the 
> PS electrolytics, so even though the originals are gone the "new" ones are 
> 25 years old. BTW the PS has the orig rectifier tubes in it; no solid 
> state.
> So to sum up, DIODE LOAD sounds fine, LOCAL and LINE audio are low and 
> distorted after blowing the fuse.
> Advice?
> Thanks in advance.Tom
>
>
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