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FDP Forum / Fender Amps: Vintage (before 1985) / Trouble with BFVR

twofish

United States

Mar 4th, 2016 07:28 PM   Edit   Profile   Print Topic   Search Topic

Hi, I am new to your forum but have been a vintage fender lover for years. I am having an issue with one of my amps and am hoping for some help/advice/info.

The amp in question is a 65 BF Vibrolux Reverb. What happens is occasionally when I am playing it seems that the bass circuit just goes out (away) completely. Through experimentation I have found that if I dial the treble knob down when this happens I can actually hear the bass circuit come back in again. I then have control over the bass again. I have no idea how these things are related as I am no tech or electronics guru so any thoughts or help is greatly appreciated.

You guys have a great forum here. Hopefully I will be able to contribute something of value some point.

Cheers,

twofish

(This message was last edited by twofish at 09:34 AM, Mar 6th, 2016)

twofish

United States

Mar 6th, 2016 07:36 AM   Edit   Profile   Print Topic   Search Topic

Anybody have any advice? As stated I am no tech or electronics guy. I also have a BFDR and a BFPR that I have never experienced anything like this with.

Any help appreciated.

twofish

guitarcapo

U.S.A.

Mar 6th, 2016 08:28 AM   Edit   Profile   Print Topic   Search Topic

Sounds like a bad pot. Perhaps spray some contact cleaner in all pots?

twofish

United States

Mar 6th, 2016 02:22 PM   Edit   Profile   Print Topic   Search Topic

Thanks. I tried that. It is almost as if the signal with the bass up and the treble up (say around 7) makes it happen and then dialing back down the treble brings the bass back on. Moving the bass knob does nothing which is weird.

It also seems to happen more often if I am using a tube screamer or even a clean boost.

Thanks,

twofish

guitarcapo

U.S.A.

Mar 7th, 2016 10:29 AM   Edit   Profile   Print Topic   Search Topic

OK.... does this occur on BOTH channels or just one?

If it's just one I would replace the caps and resistors associated with the tone stack of that particular channel. The .1 uF one is the one I would be suspicious most of.

amphead4
Contributing Member
********

Cincinnati, USA

Mar 7th, 2016 11:42 AM   Edit   Profile   Print Topic   Search Topic

If Deoxit doesn't fix it, measure the pots for proper resistance across the full sweep.

twofish

United States

Mar 8th, 2016 05:24 AM   Edit   Profile   Print Topic   Search Topic

guitarcapo, it seems to occur on just the vibrato channel.

amhead4, the Deoxit did clean the pots up some but did not eliminate the problem. I have no way to test for resistance.

twofish

willie
Contributing Member
*******

Too Near Atlanta GA

Amp Tech Emeritus
Mar 8th, 2016 11:06 AM   Edit   Profile   Print Topic   Search Topic

I would check the connections on the 6.8K resistor from the end of the bass control pot to ground. Though you say you have no ohmmeter, look for a cold solder joint. It happens. :-)

Edit: In fact, take a close look at all the connections on all the control pots. Move the wires around gently with a pencil or wooden chopstick and watch closely the joint where they meet the pot connections.

willie

(This message was last edited by willie at 01:08 PM, Mar 8th, 2016)

twofish

United States

Mar 8th, 2016 01:22 PM   Edit   Profile   Print Topic   Search Topic

Thanks willie, will do!

guitarcapo

U.S.A.

Mar 8th, 2016 07:29 PM   Edit   Profile   Print Topic   Search Topic

Look for possibly a bare wire crossing and touching a grounded surface or other wire in that area.
The smaller caps and resistors in that area shouldn't drift much because they aren't under high voltages at the tone stack but it's a possibility.
But yea...make sure every lug off the bass pot isn't touching something it shouldn't to be shorted.

twofish

United States

Mar 9th, 2016 05:20 AM   Edit   Profile   Print Topic   Search Topic

Thanks to all.

Hammond101
Contributing Member
*********

So. Cal. USA

Mar 9th, 2016 10:03 AM   Edit   Profile   Print Topic   Search Topic

Looking at the back of the control pots, there is a wire that connects the left most lug of the treble pot to the wiper (center) lug of the bass pot. Check connections of this wire. It may be tucked in above the pots. It could also be shorting to the chassis or an end of it was left long causing a short.

The brown wire connected to the center lug of the bass pot connects to the end of the .1uf cap closest to the controls for the vibrato (tremolo) section tone controls. Note that the brown wire is connected under the board. You may be able to see the end of this wire sticking up through the eyelet. Check connections at both ends of this wire.

I've seen many amps lose bass control but rarely is it intermittent like yours. Typically the treble pot fails or has become shorted and signal fails to get to the balance of the tone stack. Yes, through the wire connecting wire connecting the treble and bass pots.

This is about all you can check without a ohm meter and an o-scope. Best of luck.

vanceen25
Contributing Member
***

United States

Vance Erickson
Mar 9th, 2016 04:30 PM   Edit   Profile   Print Topic   Search Topic

I had a very similar problem with a 64 SR, although some of the symptoms were slightly different. I found a bad solder joint in the tone circuit of the affected channel by prodding with a chopstick. In my case it was at the slope resistor.

Steve Dallman
Contributing Member
*********

Merrill, Wisconsin

Age is just a number...mine is big
Apr 22nd, 2016 03:07 PM   Edit   Profile   Print Topic   Search Topic

Our guitar player brought me a BFVR and a 67 Telecaster to fix up. The amp sounds awful...vibrato circuit snubs the volume of the vibrato channel (I suspect the neon bulb in the bug is on all the time) and lots of noise...likely dirty sockets and plate resistors.

We'll see when I open it up. This amp has never had a cap job, so a bit of work will be necessary. He wants new speakers too. Not sure what yet. He's trusting me.

Steve Dallman
Contributing Member
*********

Merrill, Wisconsin

Age is just a number...mine is big
Apr 22nd, 2016 03:07 PM   Edit   Profile   Print Topic   Search Topic

Our guitar player brought me a BFVR and a 67 Telecaster to fix up. The amp sounds awful...vibrato circuit snubs the volume of the vibrato channel (I suspect the neon bulb in the bug is on all the time) and lots of noise...likely dirty sockets and plate resistors.

We'll see when I open it up. This amp has never had a cap job, so a bit of work will be necessary. He wants new speakers too. Not sure what yet. He's trusting me.

jazzguy
Contributing Member
*********

Philly, B-3 Capital

don't dream it be it
Apr 22nd, 2016 03:12 PM   Edit   Profile   Print Topic   Search Topic

"He wants new speakers too. Not sure what yet."

pair of Weber 10F150's or 10f150T's

groovemaster
Contributing Member
**********

USA

watch sunrise from the bottom of the sea
Apr 22nd, 2016 03:30 PM   Edit   Profile   Print Topic   Search Topic

I have had a faulty treble pot cause the exact symptom twofish is troubleshooting.

Hammond101
Contributing Member
*********

So. Cal. USA

Apr 22nd, 2016 04:47 PM   Edit   Profile   Print Topic   Search Topic

GM, that is exactly why I mentioned the treble pot in my post above. Tone "Stack"...yes.

FDP Forum / Fender Amps: Vintage (before 1985) / Trouble with BFVR




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