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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 12:53 am
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Thanks, Mike, for the '68 CDR schematic.

I took a brief look at both the '68 CDR and DRRI reverb circuitry. There are differences. And it will not be easy to change.

Ok... the CDR and the DRRI have the same basic reverb circuitry. A 12AT7 (V3), with both halves tied-together to drive the reverb transformer, as a single-ended triode amp. The reverb tranny is the same unit (#037099). However, the reverb tank's part number for the DRRI is listed as (#063064). And the CDR is listed as (#064063). The CDR tank has a ferrite shield built into the wiring. Prolly to cancel out possible RF coupling and/or sonic instabilities (?).

But, the biggest difference I see is the voltages applied to the tank. The CDR schemo list 136mVAC signal voltage, while the DRRI lists 960mVAC. With the original AC signal reading applied to the 12AT7 grid as 230mVAC in the CDR and 1.9VAC in the DRRI. A big difference.

With the CDR there is an extra 10k-ohm resistor (R122) inline with the 12AX7 recovery tube's grid. And a 220 pico-farad disc cap running to ground from the tank's output to the 12AX7. These look like instability "fixes." The high number (R122) of the resistor part may indicated a post-production modification to address some inherit problem with the original design. Since other resistor numbers in the reverb circuit are in the R20's.

Why and how this signal voltage onto the reverb driver's grid is controlled between the two models is not simple. As the DC voltages applied to the anode of the 12AT7 is about the same between the CDR and DRRI (X branch point of the DRRI = 261VDC. CDR = 276VDC). V3 cathode resistor 2.2k-ohm (R27) and the bypass cap 22mfd/25VDC (C15) is the same in both models.

There are differences in how the phase inverter gets the signal. This is the main difference between the DRRI and CDR. So, I would not try any modifications on the circuitry --- as you may lose some of the CDR attributes (mixing channels).

HTH. Think you better try a bunch of CDR's at the shop and pick one with the reverb that you can live with. Or look for a good Reverb/Delay Unit.


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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 2:04 am
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BMW2002Ti wrote:
Thanks, Mike, for the '68 CDR schematic.

I took a brief look at both the '68 CDR and DRRI reverb circuitry. There are differences. And it will not be easy to change.

Ok... the CDR and the DRRI have the same basic reverb circuitry. A 12AT7 (V3), with both halves tied-together to drive the reverb transformer, as a single-ended triode amp. The reverb tranny is the same unit (#037099). However, the reverb tank's part number for the DRRI is listed as (#063064). And the CDR is listed as (#064063). The CDR tank has a ferrite shield built into the wiring. Prolly to cancel out possible RF coupling and/or sonic instabilities (?).

But, the biggest difference I see is the voltages applied to the tank. The CDR schemo list 136mVAC signal voltage, while the DRRI lists 960mVAC. With the original AC signal reading applied to the 12AT7 grid as 230mVAC in the CDR and 1.9VAC in the DRRI. A big difference.

With the CDR there is an extra 10k-ohm resistor (R122) inline with the 12AX7 recovery tube's grid. And a 220 pico-farad disc cap running to ground from the tank's output to the 12AX7. These look like instability "fixes." The high number (R122) of the resistor part may indicated a post-production modification to address some inherit problem with the original design. Since other resistor numbers in the reverb circuit are in the R20's.

Why and how this signal voltage onto the reverb driver's grid is controlled between the two models is not simple. As the DC voltages applied to the anode of the 12AT7 is about the same between the CDR and DRRI (X branch point of the DRRI = 261VDC. CDR = 276VDC). V3 cathode resistor 2.2k-ohm (R27) and the bypass cap 22mfd/25VDC (C15) is the same in both models.

There are differences in how the phase inverter gets the signal. This is the main difference between the DRRI and CDR. So, I would not try any modifications on the circuitry --- as you may lose some of the CDR attributes (mixing channels).

HTH. Think you better try a bunch of CDR's at the shop and pick one with the reverb that you can live with. Or look for a good Reverb/Delay Unit.


The "fixes" that whoeverthefuck came up with to address this nebulous "instability" within the Deluxe Reverb's reverb circuit are total crap. There is no instability -- not now, not in the past, not ever. I own them all: original AB763, B1270, and re-issue AB763. I've never had a scintilla's worth of problems with the reverb in any of them, nor with any reverb-equipped Fender amp (I've owned over fifty of them in the last forty-five years).

There was a time when I thought the CBS-era amps were the worst in Fender's history.

I was wrong......


:roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll: :roll:

Arjay

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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 7:12 am
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Arjay, these mods to the CDR's reverb section have me scratching my head, too. As the DRRI and original BF (AA763) DR's reverb section circuitry is identical.

Both DRRI and the CDR get the original signal from second half of V1 (V1B), as a cathode follower. And inject the reverb signal back into the second half of V4 (V4B) grid. So, the "why's" of the modification to the CDR circuit seems to be a mystery. :?:


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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 9:36 am
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Engineer thought process: "If it ain't broke......you can probably still fix it." :lol:

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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 10:21 am
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shimmilou wrote:
Engineer thought process: "If it ain't broke......you can probably still fix it." :lol:


+1

Very similar to a politician's philosophy.

:evil:

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: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 1:20 pm
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I brought my amp in for servicing today. It sounds like there is a significant difference then in the reverb circuit according to that schematic then. Is it possible that they changed things around to limit the amount of reverb? DRRI's have great reverb, but it really isn't useable beyond 6 IMO, even for surf. Maybe they got complaints or read forum posts and wanted to dial it back to a useable level? The princeton I tried had lush, amazing reverb and the deluxe I could tell would've had the amp been turned up louder. I don't think there's any question at this point that the custom has weaker reverb or that there will be variations in sound between any two amps. Especially ones made with analog circuitry.

With my amp, it's definitely got to be a case or something wrong rather then some small variation in values. I'll report how it is after servicing, but if it isn't fixed then I'll probably just return it and have to figure out getting a different unit elsewhere.


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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 3:49 pm
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Brianvonbondy wrote:
DRRI's have great reverb, but it really isn't useable beyond 6 IMO, even for surf. Maybe they got complaints or read forum posts and wanted to dial it back to a useable level?

With my amp, it's definitely got to be a case or something wrong rather then some small variation in values. I'll report how it is after servicing, but if it isn't fixed then I'll probably just return it and have to figure out getting a different unit elsewhere.


I really doubt that TOO MUCH reverb is the issue, as Fender has used that same reverb circuitry in nearly all Fender amps, from DR's to TR & Showman Reverbs. From blackface through silverface era. Including the DRRI, SRRI, & TRRI... AFAIK.


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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 4:12 pm
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BMW2002Ti wrote:
I really doubt that TOO MUCH reverb is the issue, as Fender has used that same reverb circuitry in nearly all Fender amps, from DR's to TR & Showman Reverbs. From blackface through silverface era. Including the DRRI, SRRI, & TRRI... AFAIK.


+1

Reverb problems with Fender combo amps seem to be endemic of late......

:shock:

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: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Jul 28, 2014 5:07 pm
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BMW2002Ti wrote:
Brianvonbondy wrote:
DRRI's have great reverb, but it really isn't useable beyond 6 IMO, even for surf. Maybe they got complaints or read forum posts and wanted to dial it back to a useable level?

With my amp, it's definitely got to be a case or something wrong rather then some small variation in values. I'll report how it is after servicing, but if it isn't fixed then I'll probably just return it and have to figure out getting a different unit elsewhere.


I really doubt that TOO MUCH reverb is the issue, as Fender has used that same reverb circuitry in nearly all Fender amps, from DR's to TR & Showman Reverbs. From blackface through silverface era. Including the DRRI, SRRI, & TRRI... AFAIK.


That's a really really good point. I'm really curious what their reasoning is.


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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Sun Aug 03, 2014 8:23 pm
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Picked up my amp from repairs on Friday. Just as I thought, they claimed nothing was wrong with it and that he played it "for an hour and couldn't get it to sound bad" but here's the thing. The reverb IS stronger now. Before it was basically off until 5, but now it's audible at 3. The other thing is, I had a chance to use another 68' custom at a proper volume and it did sound identical to mine. The reverb is probably strong enough now. It still does not get the surfy drip sound though. Neither deluxes did. Oddly, the princeton did. So clearly, for reasons unknown the Princeton's have different sounding reverb. I'm just going to try upgrading the tank and if need be I'll live without the surf drip. I have no idea what happened with my amp but so long as it works better?


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Post subject: Re: Reverb problem with a new '68 Deluxe Reverb Custom
Posted: Mon Aug 04, 2014 6:18 am
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My 68 twin reverb didnt work new, the spring popped out during shipping I guess so the store put a better one in they said. I usually run it at 4 and my 6 for messing around, dont need any more then that. The 68 deluxe seemed fine to me when I was testing it with a strat but I never really got into playing the RI amps very much.


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