Awful noise from Fender Bantam Bass

[the.reveller]

well, I bought a silverface bantam bass amp last year. it still has the original rca tubes, i have been noticing a horrible noise or crackle everytime I play a G. This has never happened before, this is the first tube amp i've had for more than a couple of months and I have never encountered this particular problem before, is the noise related to the tubes becoming microphonic or could it be anything else? I would really appreciate your input.

[txstrat]

Easiest way of troubleshooting even a non tech could do, would be to replace the tubes with new (or known good) ones. First and second tubes are 7025 (12AX7) third is 12AT7, power tubes are 6L6 GC.

[the.reveller]

thanks man, i just didnīt want to buy new tubes if the problem was of another sort...that was my first instinct, the tubes are old enough..hehe

[Chuck H]

That particular amp may have a wierd feature not found on any other Fender product. A Yamaha speaker that is an odd shape and uses a styrofoam cone. Many of those speakers have already failed and there is no replacement other than to retrofit a normal round speaker on a new baffle. Just something to be aware of on that amp. FWIW the Bantam is said to be a pretty good guitar amp when fitted with a decent speaker.

If your amp has the wierd speaker you should at least plug into a different speaker and see if the problem persists. Other than that...

That amp is old. It may need tubes and new electrolytic capacitors. Both wear out. Electrolytic caps will wear out just sitting in the amp when it's not in use. If the electrolytic caps have never been replaced they are overdue.

Chuck

[Prairie Dawg]

That particular amp may have a wierd feature not found on any other Fender product. A Yamaha speaker that is an odd shape and uses a styrofoam cone. Many of those speakers have already failed and there is no replacement other than to retrofit a normal round speaker on a new baffle. Just something to be aware of on that amp. FWIW the Bantam is said to be a pretty good guitar amp when fitted with a decent speaker.

If your amp has the wierd speaker you should at least plug into a different speaker and see if the problem persists. Other than that...

That amp is old. It may need tubes and new electrolytic capacitors. Both wear out. Electrolytic caps will wear out just sitting in the amp when it's not in use. If the electrolytic caps have never been replaced they are overdue.

Chuck

I've got a Bantam that I picked up a few months ago that had all the stuff done I would have. It has had the weirdo Yamaha styrofoam speaker removed and replaced with a 15" Jensen and the wimpy output transformer was changed to a Twin Reverb output. It is a good sounding amp for guitar, a lot like a Pro without the vibrato. I am fascinated with 15 inch speakers.

[the.reveller]

That particular amp may have a wierd feature not found on any other Fender product. A Yamaha speaker that is an odd shape and uses a styrofoam cone. Many of those speakers have already failed and there is no replacement other than to retrofit a normal round speaker on a new baffle. Just something to be aware of on that amp. FWIW the Bantam is said to be a pretty good guitar amp when fitted with a decent speaker.

If your amp has the wierd speaker you should at least plug into a different speaker and see if the problem persists. Other than that...

That amp is old. It may need tubes and new electrolytic capacitors. Both wear out. Electrolytic caps will wear out just sitting in the amp when it's not in use. If the electrolytic caps have never been replaced they are overdue.

Chuck

I did the same thing and replaced the yamaha with a 15 inch jensen..its a great sounding amp but it might be ready for a tune up. by the way iīve been cheking tubestore.com for a couple of days now and have gotten an estimate of 88 bucks for new tube replacements... by the way chuck, how much would the new capacitators set me back?

[txstrat]

...by the way chuck, how much would the new capacitators set me back?

Although I'm not the one you asked I thought I'd chime in.
The schematic suggests two 70uF filter caps @ 350V in series and three 20uF filter caps @525V. The transformer is a 125P5D which has a secondary voltage of 325V (got this value from the Hammond replacement PT which is a 290DX). Rectified this would be around 460V at no load. So 500V caps would be sufficient IMHO. You might check your actual voltages to see if my calculation is OK.
Higher rated caps (600V) are more expensive.
Depending from where you order, it shouldn't be more than 30-35$. You need one 40uF@500V and three 20uF@500V. Besides you need 3 cathode bypass caps (for the preamp tubes) which should be no more than one or two bucks each.

[the.reveller]

Although I'm not the one you asked I thought I'd chime in.
The schematic suggests two 70uF filter caps @ 350V in series and three 20uF filter caps @525V. The transformer is a 125P5D which has a secondary voltage of 325V (got this value from the Hammond replacement PT which is a 290DX). Rectified this would be around 460V at no load. So 500V caps would be sufficient IMHO. You might check your actual voltages to see if my calculation is OK.
Higher rated caps (600V) are more expensive.
Depending from where you order, it shouldn't be more than 30-35$. You need one 40uF@500V and three 20uF@500V. Besides you need 3 cathode bypass caps (for the preamp tubes) which should be no more than one or two bucks each.

thanks man, Iīm really a begginner when it comes to electronics so i really appreciate your input. is there any particular brand of capacitors that you consider to be the best?

[txstrat]

Well, I like the German F+T caps, they seem to be very good. Easy to get and not too expensive where I come from.
Also Sprague Atom seem out of criticism. Some other brands might be fine too. Depends partly on how long you want to leave them in the amp. If you're willing to change them every 5 years they don't have to be reliable for 10 years, see what I mean? I just wouldn't use bargain caps. Paying a couple bucks more can save you a lot of bucks eventually.

[Chuck H]

Not looking a the schem, but...

Since the main filter is a "totem pole" arrangement with two 350V caps (good for 700V) I think you could even get away with 450V caps for the remainder of the rail. If you can use radial lead caps I've been spying the Nichicon PW series. They're small, good to 105*C, very low impedance and have an endurance of 8000 hours when treated correctly. That's more than triple that of most caps. They're only a little more expensive than average and not as expensive as Atoms. So the long term savings are huge.

Chuck

[Prairie Dawg]

Not looking a the schem, but...

Since the main filter is a "totem pole" arrangement with two 350V caps (good for 700V) I think you could even get away with 450V caps for the remainder of the rail. If you can use radial lead caps I've been spying the Nichicon PW series. They're small, good to 105*C, very low impedance and have an endurance of 8000 hours when treated correctly. That's more than triple that of most caps. They're only a little more expensive than average and not as expensive as Atoms. So the long term savings are huge.

Chuck

Mouser's site has links to the specification sheets for capacitors that they carry and they're very informative in making a purchase decision, even if you don't buy from them.

[the.reveller]

thanks guys...
itīs strange but i plugged the amp in another outlet in my house and the problem just disappeared...the amp is now super quiet...iīm pretty sure there is an electrical problem in my house, but even so i would like to do the whole recaping. i really donīt know much about electronics and there arenīt many places here in puerto rico where i can get an old tube amp serviced, so iīm wondering whatīs the average cost of this type of repair? I only ask cause i dont want to get screwed here in PR.

[ricach]

Cap replacement is a relatively easy thing to do, and a good introduction into servicing your own amps. If you are terrified of the high voltages, that's a good thing - it will make you extra careful. By following just a couple important rules, you'll be safe. And there are many very helpful people here who will be happy to provide you step by step instructions. If you're interested, just say the word and I'm sure somebody will jump in to help you out.

[the.reveller]

If you are terrified of the high voltages, that's a good thing - it will make you extra careful ...

If you're interested, just say the word and I'm sure somebody will jump in to help you out.

hahaha thanks,

[the.reveller]

hey guys: should I recap the amp before or after retubing it? and is the bantam a self biasing amp or should it be biased?