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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Mon Jun 09, 2014 8:34 am
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BMW2002Ti,
Here is something I noticed yesterday working on the amp.
TR 4 has 4 wires. black to ground, Blue to pin 6 of V3. Red
to circuit board and green to the reverb input phono jack.
I found that pushing the wires on V4 around on pin 1 and 2
made a difference in the tone of this scream. Then I checked
the connections to the the phono jacks, with my
meter on continuity and the green wire soldered to the center
tab of the input jack gave me the continuity tone to ground.
Only the body of the jack should be ground not the green wire....correct?
It appears the inside of that jack looks as if it is sorta broken some.
Anyway just out of my curiosity I am going to install a new jack and see.
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Mon Jun 09, 2014 9:17 am
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Green does go to ground, via the secondary winding to the black wire. There should be some static DC resistance, though. Like 1-5 ohms. The primary should be in the thousands of ohm (DC). You should pull all four wires and measure the DCR. Red/Blue = primary side. Green/Black = secondary side.

Now, that noise from pins 1 and 2 of the 12AT7 is troublesome. Sounds like the socket is bad or there is overflow of solder at the base. Causing a temporary short between the pins. Pull the tube and check continuity between the socket tangs. There should be around 100k-ohm DCR between hole 1 & 2 (anode and grid, respectively), with the socket wired in the circuit. If you press the reverb foot switch off, the resistance should go close to infinity. If not, you may have an issue with the footswitch.

One last thing, your amp may have a 2000 pico-farad cap (usually a disc cap) bypassing the 220k-ohm grid-to-ground resistor tied to pin 2 of V4. I dunno if this is the cap you replaced. Fender sometimes placed the 220k-ohm resistor and the 2000 pico-farad bypass cap on the reverb footswitch RCA jack (either for input or output) on the backside of the chassis. You may want to check these.

Good luck. Keep us posted.


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Mon Jun 09, 2014 10:50 am
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BMW2002Ti,
Thanks for taking the time. I will check the socket......
The thing is this amp started this verb screaming while
owner was playing at home.
With no pedal no verb tank hooked up...screaming when verb
control turned to 5. It does this with everything hooked up.
I have even used one of my ANOS 12AT7 and 7025..same problem.
The switching of the disc caps made no difference.
The only thing left is the testing of TR4.
We'll see.
Thanks again man!!!
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri Jun 13, 2014 7:24 am
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Well,
Here is my latest thought...this amp has the original cardboard covered 16uf@450v caps.
Could this cause a parasitic oscillation?
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Fri Jun 13, 2014 7:36 am
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Possible but unlikely. In any case, the amp is ready for new electrolytics all around -- filter array, bias supply, cathode bypass. There's an Ebay vendor who sells pre-assembled cap kits for Fender amps, consisting of F&T's (the gold standard for quality electrolytics). I just installed a set in my '66 Vibrolux Reverb and they cost around $58, with free S&H. I'd assume the price for a Deluxe Reverb would be similar. And upon reviewing the DR schematic, it's possible that the bypass caps in your reverb driver/recovery circuit *may* be the culprit.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Wed Jun 18, 2014 2:31 pm
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Arjay,
Well I did replace the PS caps.
Now I haven't disconnected TR 4 wires but I have taken some readings.
Red to Ground=450v
Black is ground
Green to ground=0
Blue to ground=452v
Then
Red to Blue=10ish
Red to green=452v
Black to blue=436v
Should I disconnect the red and blue from the circuit board and
turn on the amp and take those readings?
This is giving me a big headache!...LOL!

BMW2002Ti had this to say: your amp may have a 2000 pico-farad cap (usually a disc cap) bypassing the 220k-ohm grid-to-ground resistor tied to pin 2 of V4.
I do not find this cap he is referring to. Pin 2 of V4 goes to reverb out jack and tied to one end of the 220k. The only 2000 or .02 I see goes to pin 6 of V2 and pin 1 of V5.
This is all very weird! With of without the verb tank plugged in......the scream is there.
Thanks for your help!
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Thu Jun 19, 2014 6:45 am
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tube dude, 2000 pico-farads = 0.002 mfd. Not 0.02mfd.

Your 220k-ohm grid-to-ground resistor may not be bypassed off the Pin2 (grid) of V4. Voltages on the reverb tranny seem high. Lift the black and red leads, only, from the circuit. Measure the STATIC (no power) DC resistance (DCR) across red-to-blue (primary windings). And green-to-black (secondary windings).

You should get about 1000 or more ohms across red-to-blue. And 1-10 ohm across green-to-black.

Look at this diagram to help visualize. Hammond uses same, appropriate colored wired as used in this era Fender amps.

http://www.digchip.com/datasheets/parts ... 0A-pdf.php


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 22, 2014 12:14 pm
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BMW2002Ti,
Well the resistance seems okay. Red to Blue= 2.05K. Blk to Grn= 1.2K.
Let me say this about V4. Pin 2 goes directly to reverb output jack. Pin 7
goes to to a 470K resistor. The other end of the resistor goes to the
brown wire back to the middle leg of the Reverb control pot.
Also, I can't locate a 2000pf cap. Where would this be?
Thanks again!
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sun Jun 22, 2014 11:21 pm
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" Blk to Grn= 1.2K. "

This is not right. Should be 1 to 5 ohms (not k-ohms).

Look at the V4B section on the schematic. See the 2000 pico-farad cap bypassing the 220k-ohm resistor, off the grid? This resistor/cap combo is often directly soldered to the reverb jack. And is not on the circuit board.


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


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Tue Jun 24, 2014 10:06 am
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BMW2002Ti,
I will re check the Blk-Grn resistance again.
Anyway, the 220K resistor, one end is tied to the verb pedal and verb output jack and then to ground. There is no 2000pf there at all. I will connect a 2000pf across the 220K and see what happens!
This is strange. The schematic shows it but the layout and this amp doesn't have it.
Interesting the amp did great up until a month ago. Original owner...
Weird!
thanks man!
I'll let you know.
tube dude


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Tue Jun 24, 2014 1:43 pm
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Some SF models were not given this cap. I believe that it is a HF filter cap that limits the bass. As desired frequency range is mid-to-high, for the reverb circuit. Anyhow, plenty of reverb sections, in Fender amps, work well without that 2000 pico-farad cap. I don't think that the lack of this cap in your amp, is the problem.


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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Thu Jun 26, 2014 7:12 pm
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Retroverbial wrote:
Possible but unlikely. In any case, the amp is ready for new electrolytics all around -- filter array, bias supply, cathode bypass.
-snip-
And upon reviewing the DR schematic, it's possible that the bypass caps in your reverb driver/recovery circuit *may* be the culprit.

Arjay


Seems to me you've pretty much eliminated V3, tank, and reverb tranny, at least as far as the screaming goes.

To paraphrase Arjay: Would you drive a 46 year old car with the original tires, hoses, and belts and expect to get very far?

Replace all the electrolytics, not just the PS caps. Especially the dual 25uF between v4 and v5.

Just my 2 cents.

vinyl

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Post subject: Re: Silver Faced Deluxe Reverb Screaming
Posted: Sat Nov 01, 2014 2:29 am
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tube dude wrote:
O

Stratele52, sorry you see tube testers in a bad way, but not to argue, we all have opinions about everything and anything..
tube dude



It is not my opinion , it is a proven fact . Gerald Weber talk about that in one of his book and I see by myself too . Just few one are more reliable but cost $$$$
Gerald Weber .Tube Amp Talk ,page 325 ;

http://books.google.ca/books?id=kxtcysX ... er&f=false


If I said put half power on a bulb light il will glow less , you say it is my opinion ?

I just said , use tube tester if yo want but if you can't find why your amp don't work and everything test good , try new good tubes :idea:


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