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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 01, 2014 2:18 pm
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BMW2002Ti wrote:
Still, the wooden chopstick maybe the best method to find the issue(s).


I concur.

Also, I'd take a look at the lead dress and see if anyone has been horsing around in there. Compare the wiring layout with photos of similar-vintage amps and note any differences.

Arjay

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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Mon Jun 02, 2014 12:48 am
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Retroverbial wrote:
[
Also, I'd take a look at the lead dress and see if anyone has been horsing around in there. Compare the wiring layout with photos of similar-vintage amps and note any differences.

Arjay



+1


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Mon Jun 02, 2014 4:23 am
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BMW2002Ti,
I used my probe/chopstick at the beginning. I have noticed how touching some of the wires of V1 and V2 produce noise when the volume pots of channel 1 or 2 is turned up.
Yes, the reverb tank is not connected. The screaming is still there, having removed and replaced a .003 cap and the .1 made no difference.
The only thing left is the pot...have you ever known of a pot to cause a problem like this?
That is something I will try today...install a new 100k linear pot and go from there.
Besides trying the caps I have also unsoldered several of the resistors and two of the dual 25uf-25uf caps and no problem with any of them.
Man I am stumped.
Remember with or without the verb tank connected...the scream is there starting at 5 on the verb control pot.
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Mon Jun 02, 2014 5:03 am
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tube dude wrote:
BMW2002Ti,
I used my probe/chopstick at the beginning. I have noticed how touching some of the wires of V1 and V2 produce noise when the volume pots of channel 1 or 2 is turned up.
normal

Yes, the reverb tank is not connected. The screaming is still there, haoving removed and replaced a .003 cap and the .1 made no difference.
The only thing left is the pot...have you ever known of a pot to cause a problem like this?
That is something I will try today...install a new 100k linear pot and go from there.
canot be a pot

Besides trying the caps I have also unsoldered several of the resistors and two of the dual 25uf-25uf caps and no problem with any of them.
Man I am stumped. are you sure tubes are good ?
Remember with or without the verb tank connected...the scream is there starting at 5 on the verb control pot.
tube dude


it look a bad lead dress , any picture of inside the amp?


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Mon Jun 02, 2014 5:30 am
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tube dude wrote:
BMW2002Ti,
The screaming is still there, having removed and replaced a .003 cap and the .1 made no difference.
The only thing left is the pot...have you ever known of a pot to cause a problem like this?
That is something I will try today...install a new 100k linear pot and go from there.
Besides trying the caps I have also unsoldered several of the resistors and two of the dual 25uf-25uf caps and no problem with any of them.
Man I am stumped.
Remember with or without the verb tank connected...the scream is there starting at 5 on the verb control pot.
tube dude



How about the 500 pico-farad disc cap that feeds the grids of the 12AT7 reverb driver? It's on the circuit board.

http://ampwares.com/schematics/deluxereverb_ab868.pdf


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Tue Jun 03, 2014 4:59 am
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Okay,
I have worn down the chopstick and haven't found any cold joints/loose wire or parts. I have removed and replaced the .003, 10pf just to see. Not the problem.
What should one expect to find when using a chopstick/probe?
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Tue Jun 03, 2014 6:46 am
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You are trying to generate the problem noise with the chopstick. To help narrow down which component(s) maybe the issue. A component that is setting up resonance vibrations and inducing microphony.

I take it, you tapped the 500 pico-farad disc cap, too? I only ask, because ceramic caps can become microphonic. I'm not sure where the 0.003 mfd and 10 pico-farad caps are, that you mention. But, the 500 pico-farad cap is in the tremolo/vibrato circuit. It supplies the signal from the gain stage to the 12AT7's grids.

The 500 pico-farad cap is the brown disc cap circled in red. [the green circle highlights the phase inverter tail resistors --- topic of another post :mrgreen: ].

If you can't generate the noise with the chopstick and have access to a signal generator and scope, you might be able to locate the offender more accurately. Otherwise, this is sounding like an out-of-whack electronic issue. Perhaps, positive feedback? Or a coupling issue with the filter caps? Leaky coupling cap feeding excess DC to a signal tube grid, making it unstable?

Good luck! Keep us posted.

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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Tue Jun 03, 2014 8:15 pm
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My amp tech also replaced the ceramic cap for the reverb driver in my Vibrolux. It got better tone wise but would still go crazy once you turn it up. When I brought it back he examined the reverb pot and realized it was the wrong value. The pot looked original just like the rest of the pots from '67, so he never thought it could be that. I have no idea why it was replaced... so please take a closer look and see if it is the pot.


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri Jun 06, 2014 11:57 am
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Well, I have removed and replaced and put back everything suggested from you folks..Thanks, I mean it.
What has my curiosity is the voltage readings on V4.
Pin 1(plate 2)…220v. Schematic shows 170v.
Pin 2(grid 2) .03ish.
Pins 3-8…1.59v
Pin 6(plate 1)…231v.
Pin 7(grid 1) .04.
Pin 4-5 tied together.
Pin 9 not connected
I am wondering also if the small transformer may be the culprit. Its blue wire is connected to V3 on pin 6, green to reverb input, for push button switch, red to the board,and black to ground.
Haven't stooped the screaming!
Oh well onward through the fog!
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri Jun 06, 2014 9:37 pm
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Im not even going to pretend I know $@!& about this.

I had a similar problem with my Victoria making a screaming or a bad tube noise. It would to it more so when I used the vibrato or reverb switch.

I thought the switch was bad. I called Mark,he told me to clean the amps input jacks. I thought he was crazy. I did it and the problem stopped.

Im not saying that is your problem because I dont know $@!& about it,but when I read this thread it reminded me of what was going on with my amp.

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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat Jun 07, 2014 1:16 am
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tube dude wrote:
Well, I have removed and replaced and put back everything suggested from you folks..Thanks, I mean it.
What has my curiosity is the voltage readings on V4.
Pin 1(plate 2)…220v. Schematic shows 170v.
Pin 2(grid 2) .03ish.
Pins 3-8…1.59v
Pin 6(plate 1)…231v.
Pin 7(grid 1) .04.
Pin 4-5 tied together.
Pin 9 not connected
I am wondering also if the small transformer may be the culprit. Its blue wire is connected to V3 on pin 6, green to reverb input, for push button switch, red to the board,and black to ground.
Haven't stooped the screaming!
Oh well onward through the fog!
tube dude


For the reverb driver, 12AT7:

Pin 9 has to be connected to the heater line (green wire). Pins 4 & 5 to the other heater line.

Pin 3 & 8 are the tied cathodes, and should have about a +8.5 to 10VDC reading.


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat Jun 07, 2014 10:01 am
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BMW2002Ti,
Thanks for the info. I stand corrected about pin 9..yes it's connected to filament line.
Anyway, I have done all I know to do and what has been suggested.
Why would I get such low voltage on the cathodes and such high voltages on the plates?
I honestly don't know where to go from here.
Thanks!
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat Jun 07, 2014 10:20 am
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" Why would I get such low voltage on the cathodes and such high voltages on the plates? "


My first guess would be a weak testing tube. Second would be the cathode tied resistor and bypass cap are way outta spec. Your anode voltage is fine. So, the limiting factor is how much current the 12AT7 can pass.

Do you have a strong testing 12AT7? Could be a new one or a nice NOS (or ANOS) one. My experience is that many true NOS tubes test higher than brand new ones.

Of course, this won't help the noise issue with your reverb circuit. Did you ever change that 500 pico-farad cap?


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat Jun 07, 2014 8:53 pm
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BMW2002Ti,
I do have some ANOS AT7's..I'll try that..
Yes I changed out the 500 pico no change.
Thanks for the suggestions!
Take Care!
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 08, 2014 3:51 am
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tube dude wrote:
Well, I have removed and replaced and put back everything suggested from you folks..Thanks, I mean it.
What has my curiosity is the voltage readings on V4.
Pin 1(plate 2)…220v. Schematic shows 170v.
Pin 2(grid 2) .03ish.
Pins 3-8…1.59v
Pin 6(plate 1)…231v.
Pin 7(grid 1) .04.
Pin 4-5 tied together.
Pin 9 not connected
I am wondering also if the small transformer may be the culprit. Its blue wire is connected to V3 on pin 6, green to reverb input, for push button switch, red to the board,and black to ground.
Haven't stooped the screaming!
Oh well onward through the fog!
tube dude


Sorry. I thought you were measuring the voltages off the reverb driver (V3) and not the recovery tube (V4).

These voltages for the 12AX7, V4 are fine. Did you measure the voltages off the 12AT7, (V3)? This tends to be the more critical of the two tubes. As, it is really a single-ended, output triode amplifier which drives the reverb transformer and the tank.

Now, since the 500 pico-farad cap feeding this 12AT7 is ok, I suspect the noise maybe socket or pot related. Try cleaning both V3 and V4's sockets. And use some good cleaner on the DEPTH and SPEED pots. I like Deoxit Fader Lube. Esp for original pots. Fader Lube won't dry out old OEM lubricant within the pots.

Trying a new 12AT7, in V3, is a good idea. Fender amps tend to be very hard on the reverb driver tube. So, this should be the first rule-out. High testing, quiet 12AT7 is a must. Tough ones, like the Sylvania/Philips 12AT7WA, or -WC, last much longer in this position, IME.

Good luck! Keep us posted. :D


http://store.caig.com/s.nl/sc.2/category.293/.f


http://bmamps.com/Schematics/fender/del ... _schem.pdf


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