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Post subject: 1993 Concert Amp
Posted: Wed Jan 27, 2016 8:47 pm
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I've taken on the role of amp repair for a hobby. If I can't fix it, I don't charge anything.

I have a 1993 Concert Amp on the table right now. Here's the service manual and schematic for reference. http://bmamps.com/Schematics/fender/93_ ... Manual.pdf

Reverb doesn't work in any channel. It is hissing, and pops occasionally. Upon inspecting the board, around C44 and the surrounding area was burnt black. C44 was also bulging and leaking a little. I replaced it and C45.

I also replaced these resistors. Some did not read correct and the rest looked faded and old.
R18, R55, R116, R29, R30, R43, R60, R61, R56, R57, R73, R99, R100, R107, R108.

Also, V5 was microphonic. Threw in JJ ECC83s I had lying around.

Not sure what else it could be. I check the values of damn near everything on the board. Giving special attention to the reverb circuit. How do you go about checking the reverb tank?

Any help would greatly be appreciated.

Thanks everyone!

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Post subject: Re: 1993 Concert Amp
Posted: Thu Jan 28, 2016 1:53 am
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First you have to find if trouble is in reverb send or reverb recovery.
Reverb recovery ( the tank output ) ;

Put your finger on the positive at the input jack ( amp ) where the reverb tank ouput go , no tank connected , amp on , volume to 2,3 or more .
You should hear a buzz , no voltage there it is safe.

If you hear buzz , trouble is before the thank , the reverb send circuit or it is the tank. it self. No buzz ; trouble is in recovery circuit.

The tank ; how many ohms did you read at input ant output at the tank ?

My memory (?) 2 to 5 ohms one side , 100 ohms other side , not sure .


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Post subject: Re: 1993 Concert Amp
Posted: Thu Jan 28, 2016 2:10 am
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In addition to checking to see if reverb tank is working (described above by Stratele)... check to be sure that the driver tube (V4) 12AT7 and the recovery tube (V5A) 12AX7 are getting voltage to the anodes.

For anodes: V4 should be ~400 VDC on both plates (either pins 1 or 6 to ground). V4 duo-triode anodes are tied together. V5A ~ 225-250 VDC (on pin 1 to ground).

For cathodes: V4 = ~5-10 VDC (either pin 3 or eight). Cathodes also tied. V5A ~1.5-2.0 VDC. Pin 3 to ground.

Just to insure you are getting proper voltage to each tube. And each tube is conducting.

:)


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Post subject: Re: 1993 Concert Amp
Posted: Thu Jan 28, 2016 2:39 am
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TEXASBLUEZMAN wrote:

Reverb doesn't work in any channel. It is hissing, and pops occasionally. Upon inspecting the board, around C44 and the surrounding area was burnt black. C44 was also bulging and leaking a little. I replaced it and C45.

I also replaced these resistors. Some did not read correct and the rest looked faded and old.
R18, R55, R116, R29, R30, R43, R60, R61, R56, R57, R73, R99, R100, R107, R108.

Also, V5 was microphonic. Threw in JJ ECC83s I had lying around.


Thanks everyone!


No reverb mean one or few parts not working , nothing ; completely broken or disconnected

Resistors not reading correct ( how many ohms ? ) or looking fade and old can't be the issue.

You may do more some damage when working on printed circuit .


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Post subject: Re: 1993 Concert Amp
Posted: Fri Jan 29, 2016 7:18 pm
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OK! After checking everything that was suggested. Some readings weren't right. So, I switched the cable ends on the tank. Voila! Reverb is working! But is noisy. Noise gets louder the more I crank up the reverb knob.

And there's this static and popping noise when on and stand by off, ie. ready to play. ???????

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Post subject: Re: 1993 Concert Amp
Posted: Fri Jan 29, 2016 11:04 pm
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TEXASBLUEZMAN wrote:
And there's this static and popping noise when on and stand by off, ie. ready to play. ???????


Possible DC leakage in one or more of the cathode bypass caps -- relatively common for amps of this age.

Arjay

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Post subject: Re: 1993 Concert Amp
Posted: Sat Jan 30, 2016 2:54 am
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TEXASBLUEZMAN wrote:
OK! After checking everything that was suggested. Some readings weren't right. So, I switched the cable ends on the tank. Voila! Reverb is working! But is noisy. Noise gets louder the more I crank up the reverb knob.

And there's this static and popping noise when on and stand by off, ie. ready to play. ???????



Noise; Check with NOTHING plug in the amp. Amp alone.

Bad reverb cable. Dirty connector , check rca jacks.
Some wire with bad routing in the amp.
Tubes.
Input guitar jack defective, dirty shorting contact to ground


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Post subject: Re: 1993 Concert Amp
Posted: Sat Jan 30, 2016 12:56 pm
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This time I checked what BMW2002Ti suggested, but with the standby off. DUH! This is what I got:

V4 anode - 308v DC, below what it should be
V5A anode - 241v DC, within range

V4 cathode - 4.24v DC, again, below what it should be
V5A cathode - 1.92v DC, within range.

stratele52:

The output measures 197.5 ohms. Input measures 1.9 ohms.

Quote:
Resistors not reading correct ( how many ohms ? ) or looking fade and old can't be the issue.


I realize this wasn't an issue with the reverb, but overall, they needed to be changed out.

About the static and popping, checked with nothing plugged in. Still makes the same noises.

Checked with a new rca cable, had the same results. The reverb is working, though the higher I turn it up, it wants to sound like it is getting feedback. A high pitched feedback.

It sucks that I do not have any 12AT7 tubes to check that. Only have 12AX7's lying around. Still working other things.

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2011 Gibson Les Paul Trad Pro 50's
2007 Epi Les Paul Custom
90's ESP Eclipse
JH-1B Jimi Hendrix Crybaby
Analogman KOT
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Boss NS-2 PH-2
Blues Deluxe Reissue
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Post subject: Re: 1993 Concert Amp
Posted: Sat Jan 30, 2016 1:03 pm
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High pitch feedback ; how is the wiring / connector , what kind you have on your amp ?
Somme ribbon wiring/ connector may do some "noise" if not bend like they should.
Photo inside will help

The output measures 197.5 ohms. Input measures 1.9 ohms. Good, anyway reverb work this say all :D

IMO all your voltage are good and you won't find why the high pitch with voltage reading .

You can use 12AX7 if no 12AT7 available .


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Post subject: Re: 1993 Concert Amp
Posted: Sat Jan 30, 2016 7:31 pm
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Quote:
You can use 12AX7 if no 12AT7 available .


That is good to know. I was thinking that since this was a reverb driver, that it needed to be a 12AT7. I tried a 12AX7, and there was still the same popping.

I had the lights off one time, checking the tubes. Every time there was a pop, there seemed to be a surge to the power tubes. It had a flash, or something like that, inside the tube every time the amp popped.

I also cleaned every pot with contact cleaner. The mix and reverb pots still have some static in them. The reverb pot is a different kind of pot, it has no place to squirt cleaner into. I'm gonna take some pics. I'll have them up shortly.

*Edit*- Photobucket seems to be having problems. Photos won't upload. I'll keep trying though.

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2000 American Deluxe Stratocaster
2011 Gibson Les Paul Trad Pro 50's
2007 Epi Les Paul Custom
90's ESP Eclipse
JH-1B Jimi Hendrix Crybaby
Analogman KOT
Korg Pitchblack
Boss NS-2 PH-2
Blues Deluxe Reissue
1999 & 2007 Marshall TSL 100 w/1960BV cab


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Post subject: Re: 1993 Concert Amp
Posted: Sun Jan 31, 2016 5:33 am
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TEXASBLUEZMAN wrote:


And there's this static and popping noise when on and stand by off, ie. ready to play. ???????


Your amp is ON and on STANBBY.
You switch Stanby to OFF ( play ) and you here a "pop" ( one" pop") at this time.

Or amp is ready to play and you hear all the time "pops and other noise ?


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Post subject: Re: 1993 Concert Amp
Posted: Sun Jan 31, 2016 1:01 pm
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I once owned a Fender Concert amp. Problematic little bugger for sure until I unleashed it while saying bye bye and have a good half life.

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Post subject: Re: 1993 Concert Amp
Posted: Sun Jan 31, 2016 6:44 pm
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Pops and noise all the time.

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2000 American Deluxe Stratocaster
2011 Gibson Les Paul Trad Pro 50's
2007 Epi Les Paul Custom
90's ESP Eclipse
JH-1B Jimi Hendrix Crybaby
Analogman KOT
Korg Pitchblack
Boss NS-2 PH-2
Blues Deluxe Reissue
1999 & 2007 Marshall TSL 100 w/1960BV cab


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Post subject: Re: 1993 Concert Amp
Posted: Sun Jan 31, 2016 7:55 pm
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Perhaps the off/on and standby/operate switches are worn out, causing them to arc intermittently......?

Arjay

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Post subject: Re: 1993 Concert Amp
Posted: Mon Feb 01, 2016 1:50 am
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Bad contacts, connexions , solders.
Tubes's socket contacts , dirty and / or loose.
Tubes issues .

+1 Retroverbial

TEXASBLUEZMAN , put jumper on these switches.

You had these "noise " before you work in the amp for reverb ?


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