It is currently Mon Mar 16, 2020 7:43 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 71 posts ]  Go to page Previous  1, 2, 3, 4, 5
Go to page Previous  1, 2, 3, 4, 5
Author Message
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 8:44 am
Offline
Hobbyist
Hobbyist

Joined: Fri Nov 07, 2014 7:33 am
Posts: 77
Location: Iran - Tehran
i want to order this 7025 instead of 12ax7...because i think 7025 is more better than 12ax7 for audio systems and has less noise.
what is your idea about 7025 my friends?
https://m.thomannmusic.com/tad_rt080_tu ... 1570808257

whats is you idea about these 6l6's?
do you think which one is better for super reverb?

1 - https://m.thomannmusic.com/tad_rt212_ro ... 1570808280
2 - https://m.thomannmusic.com/sovtek_roehr ... 1570808280
3 - https://m.thomannmusic.com/ruby_tubes_6 ... 1570808280


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 8:59 am
Offline
Hobbyist
Hobbyist

Joined: Fri Nov 07, 2014 7:33 am
Posts: 77
Location: Iran - Tehran
vinyl wrote:
vinyl wrote:
I'm surprised it works at all.

You need to take this amp to a pro before you burn it up.
Image


So I'll try to explain it very specifically.

What is wrong with this picture?
1. The capacitance value is incorrect. It should be a at least a 70uF 70 volt capacitor according to the schematic. Not 22uF. That value and voltage rating is very difficult to find, but you can substitute a 100uF 100 volt capacitor.

2. The capacitor is shown in the wrong polarity, the positive end is not going to chassis ground.

3. Because of #2, operating the amplifier in this condition causes the capacitor to overheat causing the capacitor to vent some of its electrolytic fluid out of the end of the capacitor. (that brown stuff oozing out the end of the capacitor) That means the capacitor is "blown", and is no longer able to provide the necessary filtering (smoothing of the ripple current necessary to provide the power tubes with proper bias current) to operate the power tubes in a correct manner. Once that happens, you can't just simply reverse the "blown" capacitor in the circuit.

I can not tell exactly from from your later pictures, but it would appear that you just unsoldered the existing capacitor, and soldered it back in the correct polarity. If that is the case, then you need to replace it with the correct value.

I have the following questions:

1. You said there is "no pro around here" in a previous post. Where is "around here"? It might help us tell you how to get the correct capacitors that you need.

2. Your pictures indicate that your amp is a domestic (made for the U.S.) model. Are you operating it in the U.S., or are you plugging it into another transformer to allow you to operate it in a foreign country with a different voltage?

3. What is the fuse rating that is in the amplifier?

From your previous posts, my guess is English is not your first language. There is no shame in that, it still is pretty good. Maybe even better that Stratele52's :P (Sorry Louis, we still like your posts around here)

I admire your effort to solve how to get your amplifier to run in the way it was meant to run when it left Fender.

If you could answer those questions, it would be helpful. Be warned, you might not get the answers you want, but will get answers that will help you.

depending on this layout the bias cap is 25uf 50 volt, and not 100uf or 70uf.
Image


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 10:10 am
Offline
Aspiring Musician
Aspiring Musician

Joined: Thu Dec 12, 2013 2:54 pm
Posts: 618
ali_k wrote:
I'm really Sorry for my weak english. I'll improve it in near future.

I am not criticizing your English, it just means that I try to write my replies to make it easier for you to understand. Maybe I am not doing a good job of that.
This is the correct schematic for your amp: http://schematicheaven.net/fenderamps/s ... _schem.pdf
This means that you have a bias "balance pot".
ali_k wrote:
with this wrong cap position i measure the bias in it was about 45 volts.
After the correcting the cap direction
( wait for 15 minutes then check the bias) the bias is still 45 volts.
I'm so surprised....

If you read DC voltage across the same place with no capacitor you would still read -45 volts as long as the diode is functioning correctly. But it does not tell you how much "ripple" is present.
Use your meter to read the AC voltage at the same place. This will tell you how much ripple voltage is across the bias capacitor and how good a job the capacitor is doing. It should be a low voltage.

Before you change tubes, or try to adjust bias, you need to make sure the bias power supply is working correctly.


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 10:26 am
Offline
Hobbyist
Hobbyist

Joined: Fri Nov 07, 2014 7:33 am
Posts: 77
Location: Iran - Tehran
vinyl wrote:
ali_k wrote:
I'm really Sorry for my weak english. I'll improve it in near future.

I am not criticizing your English, it just means that I try to write my replies to make it easier for you to understand. Maybe I am not doing a good job of that.
This is the correct schematic for your amp: http://schematicheaven.net/fenderamps/s ... _schem.pdf
This means that you have a bias "balance pot".
ali_k wrote:
with this wrong cap position i measure the bias in it was about 45 volts.
After the correcting the cap direction
( wait for 15 minutes then check the bias) the bias is still 45 volts.
I'm so surprised....

If you read DC voltage across the same place with no capacitor you would still read -45 volts as long as the diode is functioning correctly. But it does not tell you how much "ripple" is present.
Use your meter to read the AC voltage at the same place. This will tell you how much ripple voltage is across the bias capacitor and how good a job the capacitor is doing. It should be a low voltage.

Before you change tubes, or try to adjust bias, you need to make sure the bias power supply is working correctly.

inside the cab has written AB763 but you are think that was not correct and the "real" circuit is AB568?

Image

https://www.mediafire.com/view/22x59bfw ... 1i4x0lbons


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 10:43 am
Offline
Aspiring Musician
Aspiring Musician

Joined: Thu Dec 12, 2013 2:54 pm
Posts: 618
ali_k wrote:
inside the cab has written AB763 but you are think that was not correct and the "real" circuit is AB568?

Yes.


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 10:52 am
Offline
Hobbyist
Hobbyist

Joined: Fri Nov 07, 2014 7:33 am
Posts: 77
Location: Iran - Tehran
vinyl wrote:
ali_k wrote:
inside the cab has written AB763 but you are think that was not correct and the "real" circuit is AB568?

Yes.

So can i put gz34 instead of 5u4 on rectifier ?
Do you know what is the main difference between ab763 and ab568?
Which one has better sounding?


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 11:02 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
ali_k wrote:
inside the cab has written AB763 but you are think that was not correct and the "real" circuit is AB568?


We told you that nearly FIVE YEARS AGO.

:roll:
Arjay

_________________
"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


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 11:07 am
Offline
Hobbyist
Hobbyist

Joined: Fri Nov 07, 2014 7:33 am
Posts: 77
Location: Iran - Tehran
Retroverbial wrote:
ali_k wrote:
inside the cab has written AB763 but you are think that was not correct and the "real" circuit is AB568?


We told you that nearly FIVE YEARS AGO.

:roll:
Arjay

You are right


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Fri Oct 11, 2019 6:58 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14045
Location: Province de Québec, Canada
ali_k wrote:
i decide to order new tubes...for both power and preamp section.
i think 99% problem will be solved after using new tubes.

.


NO :shock:

New tubes won't fix these issues;

Posted: 07 Oct 2019 12:40 by Ali_K

1- after turning down the volume knob in both channells, the amp is not silent and it has very little sound, and the sound of guitar is already coming out from the amp even though the volume is totally off.
( i cleaned the pot with volume cleaner but the problem is not solve)

2- when i rotating the middle knob, the amp sound is affeceted with mentioned knob and volume begins to raise up or raise down along side the middle knob.

3- when i put the volume knob on 1; the amp sound is super huge loud. And i forced to put volume near 0 for getting low and bedroom volume.


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Sun Oct 13, 2019 10:48 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Ali, you do not have an AB763 circuit (modified or not modified). It's prolly an AB568. Look at the resistors hanging off the balance pot. Looks like two 10K and one 15K to ground on pot body. With one 100K going from branch point on standoff to the circuit board. just like the AB568. I had to blow-up your photo a bit, maybe you can take a better closeup of the circuitry --- in sections.

Image

Image


Top
Profile
Post subject: Re: Fender super reverb SF ab763 modification
Posted: Mon Oct 14, 2019 3:29 am
Offline
Hobbyist
Hobbyist

Joined: Fri Nov 07, 2014 7:33 am
Posts: 77
Location: Iran - Tehran
BMW2002Ti wrote:
Ali, you do not have an AB763 circuit (modified or not modified). It's prolly an AB568. Look at the resistors hanging off the balance pot. Looks like two 10K and one 15K to ground on pot body. With one 100K going from branch point on standoff to the circuit board. just like the AB568. I had to blow-up your photo a bit, maybe you can take a better closeup of the circuitry --- in sections.

Image

Image

Yes,,,You are right


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 71 posts ]  Go to page Previous  1, 2, 3, 4, 5
Go to page Previous  1, 2, 3, 4, 5

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: