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Post subject: Re: 76 Deluxe Reverb
Posted: Sun May 22, 2016 7:31 am
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I finally got some time to pull the chassis. Looks pretty clean on the inside. Also some message that I should have taken a photo of when I still had the chassis out. Looks like some of the caps were removed or replaced.
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Post subject: Re: 76 Deluxe Reverb
Posted: Sun May 22, 2016 9:27 am
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Retroverbial wrote:
I'd say your 1976 hunch is correct......

"1970-1989 -Most amps do not have a date code stamped on the tube location chart. These codes are for amps with the serial number beginning with a letter:

B+5---digits - 1975-1976
A6+5-digits - 1976
A7+5-digits - 1977
A8+5-digits - 1978
A9+5-digits - 1979
F0+5--digits - 1980
F1+5--digits - 1981
F2+5-digits - 1982/83
F3+5-digits - 1983/84
F4+5-digits - 1984/85
F9+5-digits - 1979-1980"


Arjay


So, I've got a Champ that is stamped A30418. What does that make it?

_________________
1963 Princeton
1965 Twin Reverb
1968 Bandmaster
1970 Champ
1983 (?) Musicmaster
2012 Mustang III
West Grande (x2)
Acoustic G60-T
Marshall JTM 60


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Post subject: Re: 76 Deluxe Reverb
Posted: Sun May 22, 2016 10:44 am
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Posts: 26415
Location: Tombstone Territory
Champ AA764 (silverface)
A12200 to A13900 - 1968
A13900 to A18000 - 1969
A18000 to A30500 - 1970
A30500 to A32000 - 1971
A32000 to A35000 - 1972
A32000 to A42000 - 1973
A42000 to A50000 - 1974
A50000 to A63000 - 1975
A63000 to A85000 - 1976

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: 76 Deluxe Reverb
Posted: Sun May 22, 2016 8:41 pm
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Retroverbial wrote:
Champ AA764 (silverface)
A12200 to A13900 - 1968
A13900 to A18000 - 1969
A18000 to A30500 - 1970
A30500 to A32000 - 1971
A32000 to A35000 - 1972
A32000 to A42000 - 1973
A42000 to A50000 - 1974
A50000 to A63000 - 1975
A63000 to A85000 - 1976

Arjay


Did they really make that many Champs in 1970, or were they using that block of numbers for some other purpose?

_________________
1963 Princeton
1965 Twin Reverb
1968 Bandmaster
1970 Champ
1983 (?) Musicmaster
2012 Mustang III
West Grande (x2)
Acoustic G60-T
Marshall JTM 60


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Post subject: Re: 76 Deluxe Reverb
Posted: Sun May 22, 2016 8:56 pm
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s3mamill wrote:
I finally got some time to pull the chassis. Looks pretty clean on the inside. Also some message that I should have taken a photo of when I still had the chassis out. Looks like some of the caps were removed or replaced.
Image
ImageImage
Image


I just happened to notice the sticker on the inside of that amp. At some point, that amp was in Indianapolis. I've known the owner of Uncle Albert's for years, and he is one of the absolute best amp techs around.

_________________
1963 Princeton
1965 Twin Reverb
1968 Bandmaster
1970 Champ
1983 (?) Musicmaster
2012 Mustang III
West Grande (x2)
Acoustic G60-T
Marshall JTM 60


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Post subject: Re: 76 Deluxe Reverb
Posted: Tue Aug 01, 2017 1:42 pm
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Posts: 145
Location: Cambridge, MA
Hey guys. Got some free time on my hands and I got a book called "how to hot rod your fender amp" and it got me inspired to get out the soldering iron and get inside in this amp.

I see that Its been "blackfaced" some, in that the bias set up seems to be blackface style.
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The phase inverter section has some weird resistor values compared to the blackface values. Not a big deal if I change these to 1M and 470 resistors? The author says to change that orange drop and try different values here (its a 916, he says try a 716) to see how they sound. Any suggestions about what to try here?
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I'm confused about the reverb section. It looks like it should have 2 pairs of caps and resistors, but only has one pair. He says to change the cathode resistor on the reverb driver to 2.2k ohm, but I cant figure out which resistor that is.
Image
Image

Any help would be appreciated!


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Post subject: Re: 76 Deluxe Reverb
Posted: Tue Aug 01, 2017 2:11 pm
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Location: Coastal Bend, Tx.
There may a cap wired to the socket and grounded to the back of the chassis.
You don't have to change the PI values, you can try the 330k's(orange-orange-yellow) or switch them to 1meg's & 470ohm.
The reverb driver is V3(third tube from the right) the cathode is pin 8. The bypass resistor in conjunction with the bypass cap(25uf x 25vdc) controls the cathode voltage. As far as I've read, and Timsaudio I think recommend changing the electrolytic cap to a poly 2.2 to get better tone. Cant say I've tried it but perhaps he'll respond to your questions. Although he may be in the midst of retiring.
just my .02 I'm still quite the novice myself, GL w/ the BF'ing.


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Post subject: Re: 76 Deluxe Reverb
Posted: Tue Aug 01, 2017 9:48 pm
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Think you are best off following the schemo & layout from Fender.

I believe this is yours:

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

And this is what you want to revert the circuit back to:

http://ampwares.com/schematics/deluxe_reverb_ab763.pdf

Going back to the 1M, 1M, 470ohm, 22k-ohm phase inverter tail is a good move.

Check to be sure the anode plates of the 12AT7 phase inverter are loaded with 82k/100k-ohm resistors. I have seen some volume-boost era DR with a different resistor pair (like 100k/100k).

The reverb recovery 12AX7's 25mfd/25VDC cathode-resistor network (off pin 3) to ground, is on the OTHER side of the 0.01-0.01-0.02mfd disc cap lineup of the tremolo/vibrato section. So it looks like it's part of the tremolo circuit.

One other note... Fender in the Silverface era, sometimes ran grounded parts (like cathode tied networks-to ground) to the BACK SIDE of the chassis. The speaker, pedal switch jacks, and aux outlet side.

Image


Good luck! Great little amp, for sure.

:mrgreen:


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Post subject: Re: 76 Deluxe Reverb
Posted: Thu Aug 03, 2017 1:21 pm
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Thanks for the info Beemer. Yeah, there is a cap in my amp in the same spot as your photo. Tied to the tremolo pedal foot switch jack.

Mine ins't a pull boost circuit (as far as i can tell, none of the pots pull out, which is what I think the pull boost does).

I'll update the thread as things go along. Waiting for some stuff to come in the mail right now.


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Post subject: Re: 76 Deluxe Reverb
Posted: Sat Aug 05, 2017 2:03 pm
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I replaced the ceramic disk treble caps (the bypass cap on the volume pot, and the treble cap in the vibrato channel and the reverb coupling cap) with silver mica and the treble sounds smoother and more pronounced. Its an improvement.

I had a question about the normal channel. I read about lifting the ground on the mid resistor on the bass pot and I did this on the normal channel. It lifts the tone stack from the circuit and the character is louder and tweedy/crunchy. I like it, but I need more time to see if I really like it. Is it okay (i.e. will it hurt anything) if I leave it this way for a while?

Thanks guys!


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Post subject: Re: 76 Deluxe Reverb
Posted: Sat Aug 05, 2017 2:24 pm
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Location: Coastal Bend, Tx.
Some folks that use pedals remove the bright cap(volume control)completely, saying it opens up the highs when driven w/ pedals.

As long as the tail of the resistor is protected from contacting other parts of the circuit w/(shrink tubing or sleeved somehow)it should be fine.


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Post subject: Re: 76 Deluxe Reverb
Posted: Wed Aug 09, 2017 5:39 am
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Hey guys: I'm doing a negative feedback mod on my amp. There is a wire that runs from the negative feedback circuit on the board to the ext speaker jack. I'm taking the jumper wire that runs from that wire on the ext speaker jack to the main speaker jack and replacing it with a resistor. The book I'm looking at says you can use a 1.5K to 10K resistor to reduce the negative feedback, like turning up the presence control on my '63 bassman. Which resistor will give me less neg feedback (i.e. which will get me closer to the presence knob being all the way up)? Or will it not make a difference?

Thanks, sorry for the newb questions!


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Post subject: Re: 76 Deluxe Reverb
Posted: Wed Aug 09, 2017 7:43 am
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From AB763 layout. I believe the GNFB line is the same, through most of the SF era DR amps. Green arrows and red resistor labels.

Line should be yellow in color (if cloth covered). Could be white (if plastic covered). Will try to get photo, a little later.

:)

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Post subject: Re: 76 Deluxe Reverb
Posted: Wed Aug 09, 2017 7:50 am
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Photo of above VLR chassis. GNFB line is next to red arrows.

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Post subject: Re: 76 Deluxe Reverb
Posted: Wed Aug 09, 2017 3:08 pm
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yeah beemer, thats right. So where the white plastic covered wire (in my amp anyway) meets the ext speaker jack, there is a jumper from the ext speaker jack to the main one. One mod I read (in Gerald Weber's book) is to just take the jumper off and I guess this removes all the negative feedback in the circuit. This might make the amp unstable I read, so another mod is to add a resistor (suggested 1.5k ohm to 10k ohm) in place of the jumper cable.

My guess is a 10k ohm resistor will allow less negative feedback into the circuit than a 1.5k Ohm (like turning the presence knob up), but I'm not the most savvy with this stuff, still being new-ish to it, so I thought I would double check with you guys.

Any thoughts? Thanks!


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