Fisher 400 FM radio pops sometimes which causes the volume to increase

[red888]

I have a fisher 400 receiver. The phono stereo and aux output has no issues and the FM radio has no issues _most_ of the time, but sometimes it will make a popping sound and the sound will increase by a lot. Its only the radio. Its annoying because I'll have the volume up and then it will pop and the volume will increase a lot more and I'll have to turn it down. I thought it was just the reception, but it happens on any channel. Some days though, I'll have it on for hours and it won't happen at all so its pretty random.

I'm wondering if its this tube here (not my specific receiver just a photo for reference). I detoxit-ed all the other tube ports except this one because I'm not sure how to remove it correctly:


Does that tube have anything to do with the radio? Its currently super dusty as well because I haven't cleaned around there.

 

[gadget73]

That tube is the tuning indicator. Has nothing to do with receiving but if it jumps in reading it could be a clue

 

[red888]

What would a jump in reading look like? Should I check what the "eye" is doing when it pops? Because when it pops the eye does move around a lot in sync with the pops.

 

[PE9ZZ]

when it pops the eye does move around a lot in sync with the pops

That is an important clue. These receivers have self-limiting detectors. If its electrolytic capacitor is bad it will change the volume level. Albeit that I have never seen this cap behave like this. Usually they just go leaky.

Edit: can't be it because the EM84 is before the detector. It could be a cap in an IF can. They sometimes fail intermittently which would be more consistent with your complaint. Finding the bad cap will be a serious undertaking as the IF strip will need realignment. Try tapping IF cans, see if you can provoke it.

 

[gadget73]

Yeah, sort of wonder if its silver mica disease

 

[red888]

I'm totally new to audio equipment like this, any walkthroughs/guides for doing this? I don't even know what IF cans are.

 

[gadget73]

Not to be rude about it, but if you don't know what an IF can is, you probably shouldn't mess with them. Its the square aluminum boxes in the tuner section. If they have silver mica problems, the cans get removed, the internal caps removed, and replacements installed on the bottom. Then the tuner needs to be re aligned.

Tuner alignment is vaguely voodoo and needs special equipment.

 

[Dswankey]

As of this past Thursday you mentioned acquiring the Fisher and posted the following

How "good" are my speakers relative to my whole setup (LTV University series 200 model 312, fisher 400, elac 10h)

I bought a stereo cabinet a little while ago. I think everything is original because its all from around the same year: Fisher 400 receiver, elac 10h, university 312 speakers). I don't plan on upgrading because I think it sounds great, but I'm curious how good these speakers are for my setup-...

www.audiokarma.org

I bought a stereo cabinet a little while ago. I think everything is original because its all from around the same year: Fisher 400 receiver..

I don't plan on upgrading because I think it sounds great..I'm totally new to hifi stuff.

.. I don't know what I'm doing so there's probably good potential for me to make them sound worse if I start messing with their internals.

My guess is the unit is all original 60+yr parts, tubes etc; So if you plan on keeping this for an extended period of time it would behoove you to have the unit checked out and assessed by a competent tube technician.

Those are well thought of units here on AK and elsewhere and it would be a shame if you didn't have it serviced properly

 

[PE9ZZ]

Tuner alignment is vaguely voodoo and needs special equipment.

I'd put it more strongly: tuner alignment is totally voodoo for the uninitiated. Find a competent engineer to tackle this issue. It will cost a pretty dollar once you find them but you will be rewarded by a beautiful piece of equipment. Maybe your engineer can even HDRadio-proof it.

 

[gadget73]

I will toss in a low hanging fruit possibility here

pull and clean the pins and sockets for all of the tuner tubes if you haven't already. Maybe you'll get lucky. I've had a lot of funky tuner problems caused by dirty tube pins.

If that does nothing, at least it rules out one issue.

 

[red888]

Anything special I have to do to remove that tube? It's the only one I didn't detoxit. Does it just pull out like the other ones, it looks like it's clamped in or something?

 

[gadget73]

The socket unplugs from the bottom but problems with that tube will not cause audible issues.

 

[red888]

Have a little more info on this, found this thread: https://www.antiqueradios.com/forums/viewtopic.php?t=131499

".... No clicks means adequate signal strength."

I confirmed that on stations when the "eye" is totally closed (ie perfect signal strength right?) it doesn't seem to pop at all or extremely rarely. So I'm thinking I can just try to get a better antenna to improve reception for now.

Maybe I could find a cheap antique tube fm radio on ebay to experiment doing alignments on haha. Although the equipment required for that seems kinda pricey.