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Post subject: Hearing Distortion on Fender Bassman 10
Posted: Mon Oct 23, 2017 8:13 pm
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Hi all.

I have had a used 70s Fender Bassman 10 for probably 5-7 years. I've used it pretty sparingly overall, but over the past year have used it more. During prep for my last gig I started noticing a distorted / scratchy sound. This distortion seems to only happen when I play notes (it's not just happening with the amp on but nothing being played). It also seems to happen more and less often in certain note ranges. I wouldn't say it ALWAYS or NEVER happens when playing a particular note, just that it's more or less likely to happen at certain notes. I hear this when using all 4 inputs.

I don't know much about this stuff and have no idea what the cause is. Any chance this could be an issue of worn tubes? I have replaced the 6L6 tubes recently but as far as I know the 12AT7 and 7025 (12ATX) tubes are the original ones and never been changed. I'm thinking this would be best case (cheapest) scenario.

I just don't want to unnecessarily have to lug it into a shop (I live in NYC so that would be a pain), or pay money just to have somebody look at it and tell me it'll cost $1,000 to repair.

Thanks in advance for any replies / help!


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Post subject: Re: Hearing Distortion on Fender Bassman 10
Posted: Tue Oct 24, 2017 11:14 am
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Joined: Fri Feb 05, 2010 4:31 am
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Location: Province de Québec, Canada
Be sure it is not the guitar or cable

Check
1- The speakers
2- 12XX7 tubes
3- Phase inverter resistors, 12AT7 is the phase inverter
4- Output transformer
5- 6L6 bias.
6- Filter caps

Schematic here;

http://www.ampwares.com/schematics/bassman_10.pdf


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Post subject: Re: Hearing Distortion on Fender Bassman 10
Posted: Tue Oct 24, 2017 8:44 pm
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I've seen/heard plenty of output tubes make the noise you're describing, especially on certain notes. Doesn't matter if they're new or not, give them a tap test. Same deal for the 12AX7's and 12AT7.

Free for nothin' - If a tech tells you it'll be 1K to fix, grab your amp and run, fast.

UN


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Post subject: Re: Hearing Distortion on Fender Bassman 10
Posted: Wed Oct 25, 2017 1:16 am
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upnorth2 wrote:

Free for nothin' - If a tech tells you it'll be 1K to fix, grab your amp and run, fast.

UN


+1 , this make no sense $1K :lol:


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Post subject: Re: Hearing Distortion on Fender Bassman 10
Posted: Wed Oct 25, 2017 6:45 am
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"Ghost notes" can indicate main power supply caps are failing. When was the last time they were changed?


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Post subject: Re: Hearing Distortion on Fender Bassman 10
Posted: Sun Oct 29, 2017 7:29 pm
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Thanks to all for your responses. After further research, I saw enough people describing issues similar to mine being tube-related, that I got a brand new set and installed today. I played around for 15 minutes and didn't hear any of the distortion.

As I said, this distortion wasn't permanently present, so I don't know if I'm out of the weeds yet, but it's certainly promising. I will test further and if it returns I'll check back here.

Thanks again all!

ps - the $1,000 thing was just a hypothetical example. I was only saying that tubes would seem to be the cheapest and simplest fix so I was hoping that to be the issue and not something more expensive / internal.


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Post subject: Re: Hearing Distortion on Fender Bassman 10
Posted: Mon Oct 30, 2017 3:54 am
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bats8711 wrote:
Thanks to all for your responses. After further research, I saw enough people describing issues similar to mine being tube-related, that I got a brand new set and installed today.



Wich tubes ? 12XX7s ?
You had replaced 6L6s recently


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