Replace the tubes and it still after playing for a while will get a short pop or crackle. Then clean again for a while. I replaced 2 of the fat caps. 2 looked like they'd been replaced and look god. It looks like someone has already done a Blackface Mod to the amp to.
I'm thinking the rest of the caps should be replaced?
I'm thinking the rest of the caps should be replaced?
+1
They are the 100K ohm reistors. They are the larger resistors
on the rear side of the eyelet board. This is a different amp
Silver Face Vibrolux Reverb, but Most all Fender amps have
the same basic pre amp configuration.
This was the way I received the amp, before I did any work on it.
There are 3 pair of 100K resistors and I think two additional 100K
resistors that wouldn't hurt replacing while you are in there:
Post pics of what you have please. It always helps everyone
as this is a DIY site. Other people will be following along.
Cheers,
Sync
I generally upload them to postimage.org and then click the "Insert Image" button in the editor and put in the URL from postimage.
You can also do the "Manage Attachments" button under the editor in the "Additional Options" area. This is only in editor you get to from the blue "Post Reply", not the "Quick Reply" editor at the bottom of the thread.
An externally hosted image should be here but it was not working when we last tested it.
if I did it correctly- here's a shot of the amp.
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An externally hosted image should be here but it was not working when we last tested it.
[/url][/IMG]Hope I did the pic correctly this time. First of all Thanks! Replaced the plate resistors and it did the trick. No more crackle-pop. however - It's making strange sounds and braking up when pushed at high volumes after it's been on for a few hours. If I play 3 notes at once and bend them, it makes false tones and barks. Any thoughts? There's an 12 AT in there that tested ok but the other tubes are new. Could it be the tube? possibly needs caps?Still can't see the pic 
Increasing wattage rating is not your issue.
My advice, replacing parts and just listening isn't going to be enough. You need to take voltage readings to check each stage's operating conditions at the very least. This way you can see if any of the old molded capacitors are passing DC and throwing off the bias of the valves causing them to prematurely fail. Basically the tube's grid needs to be negative with respect to it's cathode, so previous stages passing DC can throw off the bias and make the tube conduct too much current. Also if a grid isn't referenced to ground via a bad connection etc.....
Take voltage readings at each pin of every tube and post results.
Pictures are also nice
Increasing wattage rating is not your issue.
My advice, replacing parts and just listening isn't going to be enough. You need to take voltage readings to check each stage's operating conditions at the very least. This way you can see if any of the old molded capacitors are passing DC and throwing off the bias of the valves causing them to prematurely fail. Basically the tube's grid needs to be negative with respect to it's cathode, so previous stages passing DC can throw off the bias and make the tube conduct too much current. Also if a grid isn't referenced to ground via a bad connection etc.....
Take voltage readings at each pin of every tube and post results.
Pictures are also nice
Ok- starting with the 12AX7 socket on the far right I'll call V1:
V1: 1- 435, 2- 0, 3- 0, 4- 0, 5- 436, 6- 0, 7- 0, 8- 0 9- .2
V2: 436 0 0 .2 436 0 0 0 .1
V3: 439 0 0 .1 439 0 0 0 .1
V4: 435 0 0 .1 435 0 0 0 .1
V5: 431 18.4 0 .1 385 18.4 0 0 .1
V6: 437 0 0 .1 438 0 0 0 .1
V7: 18.9 .1 216 0 18.9 443 .2 0
V8: 18.9 .2 444 443 18.9 .1 .2 0
V9: - 445 - 78 - 78 - 448
The only tube in it was the GZ34
V1: 1- 435, 2- 0, 3- 0, 4- 0, 5- 436, 6- 0, 7- 0, 8- 0 9- .2
V2: 436 0 0 .2 436 0 0 0 .1
V3: 439 0 0 .1 439 0 0 0 .1
V4: 435 0 0 .1 435 0 0 0 .1
V5: 431 18.4 0 .1 385 18.4 0 0 .1
V6: 437 0 0 .1 438 0 0 0 .1
V7: 18.9 .1 216 0 18.9 443 .2 0
V8: 18.9 .2 444 443 18.9 .1 .2 0
V9: - 445 - 78 - 78 - 448
The only tube in it was the GZ34
Attachments
+1 famousmockingbird.
Not sure if you have a schematic and layout. This is for
the AB763 amp. It has the lay out.
AB763 LINK
I think this is model that you have:
A1172 LINK
There should be no doubt as to which tube
is V1. As you look at the Fender amp, V1 should always be farthest
to the right, as you look from the back.
You should be working on these amps generally from the back side of the amp.
The amp fully supported by a "cradle" or on blocks so it won't
tip of fall over.
Also, the voltage in these amps if "Lethal". If you care for your
dog, don't let it near that amp.
At some point, before you put the tubes back in and test it,
from the picture that you posted, turn that over so that you
see a cover with 4 screws on it. This is called the dog house
and contains 4 or 5 filter capacitors for the B+ in your amp.
Remove the cover, don't touch anything and take a couple of
pics showing the caps, and their ends. They store an electrical
charge for your amp. You can put the cover back on and screw
it down for now. You'll probably end up back here later
but better to get all the pics out of the way first.
Also, on the pic that you've posted does it show the resistors
that you replaced or the original resistors?
Note that about 98 percent of the time popping and crackling
of an amp is those old carbon comp resistors.
Not to get ahead of ourselves, you should have a full set of new tubes
and a full set of replacement capacitors. The amp is 45 years old.
Do you have access to a tube tester?
Feel free to PM me if you have other questions or about parts etc.
Not sure if you have a schematic and layout. This is for
the AB763 amp. It has the lay out.
AB763 LINK
I think this is model that you have:
A1172 LINK
There should be no doubt as to which tube
is V1. As you look at the Fender amp, V1 should always be farthest
to the right, as you look from the back.
You should be working on these amps generally from the back side of the amp.
The amp fully supported by a "cradle" or on blocks so it won't
tip of fall over.
Also, the voltage in these amps if "Lethal". If you care for your
dog, don't let it near that amp.
At some point, before you put the tubes back in and test it,
from the picture that you posted, turn that over so that you
see a cover with 4 screws on it. This is called the dog house
and contains 4 or 5 filter capacitors for the B+ in your amp.
Remove the cover, don't touch anything and take a couple of
pics showing the caps, and their ends. They store an electrical
charge for your amp. You can put the cover back on and screw
it down for now. You'll probably end up back here later
but better to get all the pics out of the way first.
Also, on the pic that you've posted does it show the resistors
that you replaced or the original resistors?
Note that about 98 percent of the time popping and crackling
of an amp is those old carbon comp resistors.
Not to get ahead of ourselves, you should have a full set of new tubes
and a full set of replacement capacitors. The amp is 45 years old.
Do you have access to a tube tester?
Feel free to PM me if you have other questions or about parts etc.
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Thanks- I have attached the pics of the amp with the new resistors I installed and took of pic of the fat caps. I had already installed the 3 black ones cause they had some old silver ones that showed signs of oozing.
the amp doesn't like the note "d" especially. (5th fret/ 5th string) The tubes are only a few months old except for the one that fried so I put a known to be good one in place (12ax7). There's also an AT7 that is know to be good. I tested all the tubes in my Heathkit- not that I trust it, but it's all I have.....that's another issue. Oh- BTW- I had drained the amp before I let the pup in the room.
So here's what a I got from readings of my pins with all tubes in it:
V9 V8 V7 V6 V5 V4 V3 V2 V1
1 - 0 0 0 0 0 0 1.3 0
2 0 3.3 3.2 0hums 0 23.5 101 7 6.5
3 - 0 0 0 0 1 0 1.3 1.2
4 356 0 0 3.2 3.2 3.2 3.2 3.2 3.2
5 - 0 0 " " " " " "
6 356 0 0 0 0 0 0 0 0
7 - 3.2 3.2 0 0 0hums 102 1.3 1.2
8 0 0 0 0 0 0 0 0 1.4
9 3.2 3.2 3.2 3.2 3.2 3.2
Thanks in advance- you folks are Great!
the amp doesn't like the note "d" especially. (5th fret/ 5th string) The tubes are only a few months old except for the one that fried so I put a known to be good one in place (12ax7). There's also an AT7 that is know to be good. I tested all the tubes in my Heathkit- not that I trust it, but it's all I have.....that's another issue. Oh- BTW- I had drained the amp before I let the pup in the room.
So here's what a I got from readings of my pins with all tubes in it:
V9 V8 V7 V6 V5 V4 V3 V2 V1
1 - 0 0 0 0 0 0 1.3 0
2 0 3.3 3.2 0hums 0 23.5 101 7 6.5
3 - 0 0 0 0 1 0 1.3 1.2
4 356 0 0 3.2 3.2 3.2 3.2 3.2 3.2
5 - 0 0 " " " " " "
6 356 0 0 0 0 0 0 0 0
7 - 3.2 3.2 0 0 0hums 102 1.3 1.2
8 0 0 0 0 0 0 0 0 1.4
9 3.2 3.2 3.2 3.2 3.2 3.2
Thanks in advance- you folks are Great!
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