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SHERWOOD S2100 "Motor Boating" on 3/4 of AM dial

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The tuner is working OK. FM sounds OK. AM sounds great too but only within the higher 1/3 of the dial. When tuning within the first 2/3 of the dial, there is motor boating. I'm going to sell the tuner. Would be great to have the motor boating fixed first but I don't want to put $ into this, as I have other components to service.

I think I'd be OK with just knowing why the motor boating only happens within part of the dial range.
 
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might be a weak oscillator tube. If you've got a 6BE6 laying around, try swapping it to see if anything changes.
 
Gadget,
Sounds like a good approach. To what extent do you think that the described 'motorboating' may be RF interference generated from wall warts, CFL's, LED switching power supplies, and the like. In my home, seems like the band is about half covered in hash all the time, regardless of receiver.
 
could be that too, but usually when I've had interference from that sort of thing its a loud hissing or buzzing, often peaking at different points. No guarantee that isn't the problem of course.
 
RF like I am describing is definitely a buzz with different peaks, not a fast or slow "putt putt" you associate with motorboating.
 
Thank you. This is definitely of the putt putt variety. I live in an apartment complex near downtown; so I deal with plenty RF hashery :crazy:
 
I had the same problem in all my gear on AM. Turns out it quit when the neighbor moved out of her Apt. I think it was her cable modem.....Hope you find it!
 
gadget73 said:
might be a weak oscillator tube. If you've got a 6BE6 laying around, try swapping it to see if anything changes.
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Well, I looked around. No 6BE6. But they're cheap enough. And I'm curious. I certainly don't have your knowledge but I did have a gut feeling it might be a tube issue. Found a NOS one for $5.35 shipped. May as well. And thank you.
 
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AlTinkster92 said:
I had the same problem in all my gear on AM. Turns out it quit when the neighbor moved out of her Apt. I think it was her cable modem.....Hope you find it!
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Yeah, I'm hearing this just on the lower section of the dial. Other AM radios sound fine here. But wow never knew a modem could cause such havoc. Good riddance to your neighbor!
 
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its a cheap tube. Won't guarantee that will do it, but its just my first thought. A lot of AM tuners have one too, so you may be able to borrow one out of a radio or something.

A lot of times on am/fm tuners, whichever one wasn't used much seems to have tubes that are wasted and it often seems to be the oscillator/mixer that is the worst.
 
gadget73 said:
its a cheap tube. Won't guarantee that will do it, but its just my first thought. A lot of AM tuners have one too, so you may be able to borrow one out of a radio or something.

A lot of times on am/fm tuners, whichever one wasn't used much seems to have tubes that are wasted and it often seems to be the oscillator/mixer that is the worst.
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Yes, I understand. Thanks for clarifying. That's interesting, how the least used goes bad. By the way, stupid me looked in all my radios except in my S-C 445A, and there is a 6BE6 :crazy:
But even with the good 6BE6 it's still motor boating. What perplexes me is why doesn't it motor boat over the entire band? Wouldn't that be a clue?
 
I was thinking if the tube was marginal it may work better at one end vs the other. I've had weak oscillators that would drop out at one end or the other but in the middle it would just do odd things. Random dropouts, fading, that sort of stupidity.

The un-used ones in tuners die if it shuts the plate voltage off. Its called cathode poisoning, basically the electrons boil off and have nowhere to go and it ends up damaging the tube long-term. If it doesn't switch off the voltage, the tubes don't die that way.

anyway, could be a bum decoupling cap on the AVC line or maybe the detector is getting flukey. It uses a diode inside one of the other tubes for that task.
 
They can motorboat when they need an alignment and really many things can make a radio motorboat. I've installed a cap wrong and had a radio motorboat. Chasing it down can be hassle.I wish you luck.
 
sanford12 said:
They can motorboat when they need an alignment and really many things can make a radio motorboat. I've installed a cap wrong and had a radio motorboat. Chasing it down can be hassle.I wish you luck.
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was wondering about alignment. thanks. i need to sell it to make room. may just sell as is.
 
gadget73 said:
I was thinking if the tube was marginal it may work better at one end vs the other. I've had weak oscillators that would drop out at one end or the other but in the middle it would just do odd things. Random dropouts, fading, that sort of stupidity.

The un-used ones in tuners die if it shuts the plate voltage off. Its called cathode poisoning, basically the electrons boil off and have nowhere to go and it ends up damaging the tube long-term. If it doesn't switch off the voltage, the tubes don't die that way.

anyway, could be a bum decoupling cap on the AVC line or maybe the detector is getting flukey. It uses a diode inside one of the other tubes for that task.
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thanks again for your insights. i may have a look at that avc line or i may just sell as is. gotta make room.
 
If you don't want to keep it, honestly I'd be inclined to let someone else deal with it. If FM works thats probably more important to most.

Does the S-2100 have MPX, or is it mono?
 
gadget73 said:
If you don't want to keep it, honestly I'd be inclined to let someone else deal with it. If FM works thats probably more important to most.

Does the S-2100 have MPX, or is it mono?
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Sensible advice, yes. And the FM is amazing, using a MPX adapter. No built in MPX. It would be nice to satisfy my curiosity and conquer the challenge of fixing it. But I'm so far behind in other keeper projects.
 
I'm better at dispensing advice than taking my own. my own half-done project pile is evidence of that.
 
gadget73 said:
I'm better at dispensing advice than taking my own. my own half-done project pile is evidence of that.
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Ah, yeah :D Funny how, even with a novice like me, sometimes a year later you come back to something that had you stumped and you lick it. Hey, at least you have room for piles! Piles would be a luxury in this studio shoe box apartment. I feel like it's a big storage bin and I'm just among the junk stored.
 
yeah thats kind of what its getting like around here, but I fortunately (unfortunately?) have space to accumulate more piles.
 
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