Amps Fender Bassman 100T

[CapnDenny1]

I upgraded the Bassman VT-100 2x15 speaker cab with 2 JBL E140-8 speakers. It's much louder now.

But now the Bassman 100T amp has a weird fizz on the decay of the notes on the clean vintage channel?

It doesn't seem to do it on the OD or overdrive channel, so I don't think it's an issue with the speakers. I'm pretty sure I heard it with the old speakers. I replaced the V1 tube that is unique to the vintage channel, and I thought it went away, but it's back now.

I've been studying the schematic and using google to try and get wise.

I will do a little testing from outside first.

1. Try another bass amp on the speaker cab.
2. Try another speaker cab on the Bassman 100T.

That will prove it is in the speaker cab, or the amp itself.

The fact that it isn't in th eoverdrive channel pretty much says it's in the vintage channel preamp section, not the power amp, or the speakers. But I will do the tests anyway.

I have read on google, it's a common issue with bad caps, bad solder, bad tubes,....

Nice that they narrowed it down for me?

 

[PapaRaptor]

Nice that they narrowed it down for me?

 

[CapnDenny1]

The speaker cab is a Bassman VT-15 actually.

 

[CaptainMoto]

Whoa...........that must move a lot of air

 

[CapnDenny1]

Really weird? I did some testing, and got some crazy results.

I could either try another cab with the Fender 100T amp, or try the 2x15 cab with another amp. I was going to hook up other speakers, but everything within easy reach was 16 ohms. So I had another Ampeg bass amp, a B2, 300W, so I tried that out. It worked just fine. No lingering noise. Ok, I figured that since the Overdrive channel on the 100T didn't make the 2x15 cab buzz?

So I tried put the 100T back into the 2x15 cab, and verified the noise was still there, and it was. I tried plugging my bass guitar directly into the "Power Amp In" jack on the back of the 100T amp. As expected I did not hear any noise. It didn't get very loud, but no buzzing or fizzing. It was at a level that caused the issue before going thru the Vintage preamp input on the 100T.

So connected back into the Vintage input and was listening to the fizz. I would strike a note on the bass, and it sounded OK, but as the note started to die down and almost disappear, that's when the fizz started. That's when I noticed something weird. I hit the note and waited for it to die down, and heard the noise, and then I muted the string. Instantly the noise and the sound from the string stopped dead? That's telling me the source of the noise is the bass itself.

Now this is a $50 bass, a Squier P Bass. It was unplayable when I got it. The jack was corroded and caused it to go wide open 60 Hz noise while trying to play it, so I cleaned the jack and it seemed OK. The pot is also really scratchy.

So i go one of my Strats and hooked that up, and no noise? No fizz, nothing. I even lowered the pitch on the low E to bass guitar pitch and again, not fizz, or buzz.

So I was looking at the bass and it occurred to me that the single P bass pickup was pretty low. So I adjusted it a little bit, and could only move it an 1/8", because the metal pickguard hole is too tight for the pickup to go through it easily. (Who worked on this thing anyway?) So I went ahead and tried it with the pickup raised a little bit, and I'll be darned if it doesn't seem like the buzz is gone?

So before I tear into the amp, I am going to adjust the pickup height and replace the jack and pots in the bass. Is it possible that having the pickup too far away causes the pickup to distort when the string vibration starts to die down? I've never heard of that before, but at this point that's what it looks like. As I said I need to fix the bass and then re-test. Maybe it's time to get a decent pickup for this P Bass as well?

 

[CapnDenny1]

OK, I put a new pot and jack in the bass, and raised the pickups to maybe 1/8" away from the strings. Guess what, the fizz is gone! That's a new one for me?

Phew! I'm glad I'm not chasing it inside the amp!

The bass is a lot louder too now. Duh!

So I will get it back on Craigslist and ebay and reverb. I need to get my son to come over and make another demo with the JBL speakers in the VT-15 cab. This time we will do some of the Overdrive channel as well as the Vintage.

 

[CapnDenny1]

So my son came over last night with his bass. Nice Ibanez BTB with a natural Danish Oil finish. Looks identical to one I used to have. (Merry Christmas to him.).

I wanted to make a new recording and video to relist it for sale. About 10 minutes into the recording that darned fizz sound came back! So I guess I will have to open this baby up and go find the fizz!

 

[TwoNotesSolo]

Looks identical to one I used to have.

LOL

 

[CapnDenny1]

So I spent a good 3 hours chasing this issue. I had my self convinced it was the bass guitar, then the speaker, then the amp. I tried 3 other bass amps and 2 other bass speaker cabs. I even opened up the amp and traced the signal thru the amp and tried swapping tubes into the preamp, and wiggled the board to board connectors. By the end of the night I was hearing buzz everywhere and from everything.

Today I went back and re-tested and decided the amp was ok. Perhaps it was one of the cables I wiggled, or I replaced the bad tube? Or it’s just waiting to make me crazy later. So I buttoned it all up and tested it, and it is sounding awesome. It’s disgusting how much better my Squire P-Bass sounds when my son plays it?

So I have been selling some gear that I repaired and doing a few customer repairs, so I decided to spend my earnings a bought a used PRS Kingfisher bass from Guitar Center. It has headstock damage, but just at the very tip. A little glue and good as new. It was $329, and new they are $800. Te next cheapestI saw was $450. I will post pics in another thread when I get it.

 

[CapnDenny1]

We made this video last week. I was recording on the PC with the mics, but after a few minutes I started hearing that noise. This is what made me work on it to try and fix this issue, as described in the post above. I thought people might enjoy hearing the noise. It's most evident towards the end, when on the Vintage channel, and my son has a weird expression. He said he heard it, but didn't want to say anything on the recording. I heard it and stopped recording. I was pretty disgusted too.

This is the kind of subtle issues I get sometimes. I just hate them, because if ti comes and goes you never really know if you've fixed it. It sounds like a bad tube, or a bad connection as in a cable, or the input jack, or the effects loop, or ....? Even on the audio just using the iphone it's pretty evident if you turn it up a bit.

https://youtu.be/f8Hyxb7LCus

 

[Iheartbacon]

Is the dust cap on the top JBL pushed in or is that a shadow of illusion?

That noise is strange, and I definitely don’t hear it at the start of the video. I have no insight into what it could be other than what you are already thinking, but I will say, other than that it sounds pretty darn good over YouTube!

 

[CapnDenny1]

Yes, the dust cap is pushed in. It shouldn't hurt anything, other than appearance. There is more risk of hurting the cone trying to pop it back out, or so I've read. I thought using a piece of tape to stick to it and pull on it?

I ordered a set of tubes for the amp. I figure it deserves a set of decent tubes. I have 4x6l6 and 2x7025 Tube Store Select tubes, and a Mullard 12AT7 that The Tube Store claims is crazy good in the phase inverter position.

https://www.thetubestore.com/fender-bassman-100t-premium-package

I have been pleased with their Tube Store Select tubes.

If I end up selling it, I can move the expensive tubes into my Twin, or my other Twin I need to build a cab for.

 

[Iheartbacon]

. I thought using a piece of tape to stick to it and pull on it?

I would research that more before attempting since you will be pulling on more than the dust cap, and unless your motor skills are a lot better than mine, you won’t be pulling perfectly straight.

 

[CapnDenny1]

Probably going to just leave it alone.

 

[MarkDyson]

 

[CapnDenny1]

Oh JEEEZ!

Um, thanks for the suggestion? ;-)

 

[gpower]

I've used a vacuum cleaner many times... hold the cone with your fingers as you slowly bring the nozzle up to the dust cap... works pretty good but, you do have to be careful.