Fender 68 Custom Deluxe Reverb

[bsco]

Hi guys..Have a question....(a couple actually)...I have this one here and the complaint was low headroom and low bottom end....when A/B with another brand new one at the local store this indeed was the case....I changed the outpot tubes but same thing...I didn't have a 12AT7 on hand so I swapped the reverb driver with the phase inverter...the headroom and low bottom end came back but now there is a hiss in the backround that was not there before...and some low level crackling as well...I re-installed the original output tubes and nothing changed....so i guess the output tubes were not the cause of the low headroom and low bottom end....I swapped the two 12AT7's and back to their original positions and now that low level crackling sound is gone but the backround hiss is still there......and during this tube swapping back and forth, when you flick the amp into stand-by, you get a loud crack in the speaker which if I remember correctly was not there before when we were a/B ing the two amps....any thoughts, comments, etc, anybody
Cheers
I forgot to mention. I had asked Fender for a schematic and they sent me in one for a 68 Custom Twin Reverb.......

[Steve A.]

Here's the correct schematic (I hope):



Good luck!



Steve Ahola

[bsco]

Thanks Steve......that looks like the right one...Thank you very much.
Cheers

[Steve A.]

This is a fairly new amp and should still be covered by the 5 year mfg warranty (which I believe is transferable- maybe not.) Or does that not apply here?

Steve Ahola

[bsco]

This is a fairly new amp and should still be covered by the 5 year mfg warranty (which I believe is transferable- maybe not.) Or does that not apply here?

Steve Ahola

Yes it is a fairly new amp as far as I know...When I saw it I thought it was brand new....somebody named Randall had made a comment here about the filter caps.....I got an email notice but that post is not showing up here.....anyway.......I will look over this schematic as this si the correct one.....
Cheers

[The Dude]

I would do a quick check of all of the preamp plate resistors. There may be one going towards open and it takes all of about 2 minutes to check them.

[bsco]

I would do a quick check of all of the preamp plate resistors. There may be one going towards open and it takes all of about 2 minutes to check them.

Will do....I will go through the amp tomorrow...

[Tom Phillips]

Before you start trying other things, I recommend that you obtain a good 12AT7 and put it in the PI stage.
You said that the the headroom and low bottom end came back when you swapped the reverb driver with the PI so you seem to have identified at least one problem. If you fix that first then everything else may fall in place.

[bsco]

Before you start trying other things, I recommend that you obtain a good 12AT7 and put it in the PI stage.
You said that the the headroom and low bottom end came back when you swapped the reverb driver with the PI so you seem to have identified at least one problem. If you fix that first then everything else may fall in place.

Thanks Tom..Actually I am going to pick up 2 of them today as when the reverb send tube was installed in the PI position I got some crackling noises...so I am going to replace both of them first and see where everything stands.......but that has nothing to do with the loud popping when switching the standby switch....I'l post here my findings after I replace those two tubes....
Thanks

[mhuss]

I have a DRRI and it pops pretty good when you switch it on/off standby. Thought it just went with the territory...

[bsco]

I have a DRRI and it pops pretty good when you switch it on/off standby. Thought it just went with the territory...

Apparently it does but there is a mod which I am going to try as the owner would like for me to try and eliminate it.....a .047UF/600V cap in parallel with a 250k/2Watt resistor connected across the switch caps....this is supposed to eliminate the pop....I will let you know if it works or not......
Cheers

[Tom Phillips]

Thanks Tom..Actually I am going to pick up 2 of them today as when the reverb send tube was installed in the PI position I got some crackling noises...so I am going to replace both of them first and see where everything stands...

Bernie,
It is best to change only one thing at a time to keep your troubleshooting process organized and to give you a clear understanding of the effect of each individual change. Therefore, I recommend that your first step be to change only the PI 12AT7. Then evaluate and move on as required.
Cheers,
Tom

[bsco]

Bernie,
It is best to change only one thing at a time to keep your troubleshooting process organized and to give you a clear understanding of the effect of each individual change. Therefore, I recommend that your first step be to change only the PI 12AT7. Then evaluate and move on as required.
Cheers,
Tom

Yes sir....I will.....and I will let you know how it works out.....
Cheers

[bsco]

Hi Tom...I switched the PI 12AT7A tube out and that clicking sound went away....I am not sure but maybe this backround hiss I am hearing is natural for these amps?? same as the pop in the speaker..The noise reminds me of the type associated when you increase volume levels and hear a hiss in the speaker.....but this is there with all controls at minimum...I plugged in a guitar and the amp sounds good.......I also checked the bias....22mA in each tube.......good match....I will have to compare it against another 68 Custom Deluxe in the store....
Cheers