Fender Bandmaster Reverb - 1969 - occasional "pop"

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gui_tarzan
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Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by gui_tarzan »

When you take it off standby it pops, maybe the switch? When you shut it off it pops pretty loudly. I re-capped (filters, bias and PI cathode) it a few months ago and it plays great, with a slight pop/pft noise and a little hiss now and then that just started recently.

I checked the voltage on the white Mallory cathode caps and they all show the normal 2.x (and 9.x on one of them) volts as the schematic shows and I have a rock-solid -52v on the bias.

The pop/pft sound is brief and usually happens every 8-10 minutes, like something's charging up and letting go, but I'm unsure about what would be causing it. It's not loud, in fact it's very quiet but you can hear it when it's idling.

Any ideas?
--Jim

"He's like a new set of strings, he just needs to be stretched a bit."
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cbass
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by cbass »

Might be a good spot for the upside down canned air trick.
I'm suspecting A solder joint maybe bad ground or a plate resistor
pdf64
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by pdf64 »

Try linking across the standby switch http://www.thegearpage.net/board/index. ... t-15220533
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Richie
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by Richie »

Are you running any sovtek preamp tubes in the amp? It is very common to hear 2 or 3 pops when coming off standby, then a pop every now and then using those tubes.

Other things could be CC resistors plate or cathodes.
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by Stevem »

Jump out the standby switch, does the issue go away?
Pull the phase inverter tube, does the issue go away?
Pull out one output tube at a time, does the issue go away?
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Not screaming like the passengers in his car!😊

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gui_tarzan
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by gui_tarzan »

I swapped out the 1w 100K resistors in the pre-amp and all the noise went away.

I've had to replace a lot of those over the years but these were the worst I've run into for noises.
--Jim

"He's like a new set of strings, he just needs to be stretched a bit."
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by Stevem »

Once I had the 68k resistor off of the input Jack on a Silvertone 1482 model make so much hiss / ocean noise all you needed was some sea gull sounds and you would swear you at the beach!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

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rooster
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by rooster »

Too bad on those 100K CC 1 watt plate resistors. Those are considered TONE things to many. Steve at ApexJr has a few, BTW.

But still, and interesting fix to the problem. I would have thought the power supply resistors - the ones you disturbed when you replaced your power supply caps - a more likely problem. 8)
Most people stall out when fixing a mistake that they've made. Why?
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gui_tarzan
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by gui_tarzan »

So my customer is VERY happy with the amp now, and the resistors I subbed into it didn't seem to make any difference in the tone. It sounds clear, Fendery and very quiet.
--Jim

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rooster
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by rooster »

I'm sure it sounds good, no worries. I myself like the CF type resistors but have recently purchased 10 of the 100K 1 watt AB resistors from Steve @ Apex, $1.85@. I need to have them around for the anal Fender guys. I also have a friend who is building amps and using these AB CCs throughout and his amps sound great actually, without any added hiss.

But everything is based on the build type. I wouldn't be using them in my Express' for example.
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by Stevem »

CC type resistors only add there resistive distortion into the tone mix when they have at least 150 volts across them, as such I much preferred to have less hiss / noise from a metal film type resistor esspecially in a high gain build!

These jerks that build SS type stomp boxes and tout that they use good souring CC type resistors leve me chuckling and wondering just how much the know about what they are doing!
When I encounter a amp with bad plate load resistors I also change out the power suppy dropping resistors to cover all the base's.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Richie
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by Richie »

Stevem wrote:CC type resistors only add there resistive distortion into the tone mix when they have at least 150 volts across them, as such I much preferred to have less hiss / noise from a metal film type resistor esspecially in a high gain build!

These jerks that build SS type stomp boxes and tout that they use good souring CC type resistors leve me chuckling and wondering just how much the know about what they are doing!
When I encounter a amp with bad plate load resistors I also change out the power suppy dropping resistors to cover all the base's.
How did you come up with the 150v for resistive distortion?

The CC cathode resistors in a tube amp with only a few volts can cause the same type hiss and noise problems if they are bad. You can have SS pedals with CC resistors, and have the noise problems with only 9v.
I think the mix up is if they are bad, or noise, hiss, pop or crackle, as compared to the resistive distortion sound.

Maybe those people you called jerks, ment they use good resistors that do not have the bad hiss noise problems.
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JazzGuitarGimp
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by JazzGuitarGimp »

I build pedals! But I don't use CC resistors! I use SMT resistors! And now I am so glad I do! Because I just couldn't live with myself if someone on the east coast thought I was a jerk! :D !
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Re: Fender Bandmaster Reverb - 1969 - occasional "pop"

Post by Stevem »

I would reference R G keen's paper on carbon comp resistor mojo magic.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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