It is currently Mon Mar 16, 2020 3:32 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4  Next
Go to page Previous  1, 2, 3, 4  Next
Author Message
Post subject:
Posted: Wed Mar 24, 2010 4:20 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
If the hiss come louder in both channels when you turn the volumes, that's mean the problems is in V1 and circuits before volume pots on first channel and V3 and circuit before the pot on second channel.

Probably the plates resistors , pin 1 and 6 of all preamp tubes but in your case V1 and V3

And about your center plastic guide on your 6L6 you cannot glue it. Be carefull when you plug tube in the socket , look at the one is ok an you can put the same way.

I brake some over the years and no problem to plug it

Look trought the glass see how it's look.

Have you tried leaving the amps "on" couple hours ?

That's could fix your hiss. I see it few times


Top
Profile
Fender Play Winter Sale 2020
Post subject:
Posted: Wed Mar 24, 2010 4:39 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Yeah, you're dodgin' bullets like crazy! But now you know the drill. OK, replace V5 and test. If no hiss, remove V2 and V3, and plug V4 back in and test. If no hiss, plug V3 back in and test. If no hiss, plug V2 back in and test. If no hiss, plug V1 back in and test. Obviously, you can see the step by step method. When the noise returns that tube is suspect, but so are the components surrounding that tube. But we always have to make sure that the tube is good, before moving on. You know what I mean? Work slowly and carefully. Use reference marks on pre amp tubes and sockets to help with pin alignment. Most of us have busted the plastic key off power tubes( they get brittle with heat). Super glue it back on, if you want. Usually, I'll just carefully replace the tube, using the pins and the adjacent tubes as guides(the retaining claw marks should also help). There are replacement pieces made, if you want one, they slip over the tube pins. Art PS:I didn't see Stratele"s post until mine was done. But you can see, we're talking about some of the same things

_________________
None of Us are free, if One of Us is chained !


Top
Profile
Post subject:
Posted: Wed Mar 24, 2010 5:36 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Jul 25, 2007 11:48 am
Posts: 53
Okay. We're getting there. This is probably a couple days worth of amp school already. Follwed the tests and it hisses when V4 is put in. So, I tried a couple of other 12AX7s there and the same result. I agree with stratele, it's probably the resistors and I'll pull the chassis and replace them. You guys are the best. Thank you


Top
Profile
Post subject:
Posted: Wed Mar 24, 2010 7:13 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Alright James, be sure to discharge the filter caps every time you go inside the chassis, OK? If you're going to replace the plate load resistors(100Kohm)with carbon comp, spend the cash for 1watt. Don't forget the cathode resistor(820ohm). As long as you're in there, you might want to check all solder joints and components by giving them a tug or push and watching very closely for any movement(even the component body on it's lead). Art

_________________
None of Us are free, if One of Us is chained !


Top
Profile
Post subject:
Posted: Thu Mar 25, 2010 8:28 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
I said something wrong :Yes, you can glue the plastic pins guide. I do with epoxy.

Sorry


Top
Profile
Post subject:
Posted: Sat Mar 27, 2010 12:15 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Jul 25, 2007 11:48 am
Posts: 53
Okay. I've pulled the chassis again and found no loose connections of cold solder joints. I'm confused (almost always) about the resistors. Which are which, what the colors really mean etc.
Art, you say to replace the plate load resistors with 1 watts. Okay. Which ones are they? And the cathode as well.
Stratele, when you say replace the resistors from pins 1 and 6, are they in pairs? For instance, on V1, the wire from pin 1 goes to the foot of a resistor and the wire from pin 6 goes to a different one. You're saying to replace both, right? are these the plate resistors? Thanks for your help, fellas. I'll wait until I hear from you before I go on.
James


Top
Profile
Post subject:
Posted: Sat Mar 27, 2010 9:08 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Hey James, which plate load resistors are you planning on replacing? There are nine 100kohm(brown-black-yellow-silver or gold).One 82kohm(grey-red-orange- silver or gold). One 220kohm(red-red-yellow- silver or gold). The last color band denotes the tolerance, 10%=silver, 5%=gold, 2%=red. Also, do you have the layout for the AB763 Twin Reverb? Art

_________________
None of Us are free, if One of Us is chained !


Top
Profile
Post subject:
Posted: Sun Mar 28, 2010 2:46 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
+ 1 aclempopy.


Top
Profile
Post subject:
Posted: Sun Mar 28, 2010 5:48 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
http://www.ampwares.com/schematics/twin ... _ab763.pdf

Go there to find a layout if you don' have one. You'll see easier all the parts

Don't forget to check and change the 470 ohms 1 watts ( big) resistors ( yellow,violet brown) on each of your 6L6 sockets.

Yes, they are on each tube socket. Mesure it before 470 ohms +/- 20 %
Those are very important parts and they are often wrong


Top
Profile
Post subject:
Posted: Sun Mar 28, 2010 9:05 am
Offline
Hobbyist
Hobbyist

Joined: Wed Jul 25, 2007 11:48 am
Posts: 53
Hey,
My copy of the Weber book came in the mail yesterday so I have a great clean copy of the schematic and layout and they look great. Can't read them yet, but they look nice. Anyway
aclempoppi. I'm changing the 100 kohms to try and get rid of hiss in both channels. While I'm inside, I'll probably change the others as well. I know I should boost the 100s up to 1 watt. Should I change the value of every resistor or leave most of the the same? Also, should I replace with carbon comps, carbon films, does it make a difference? Also, could you explain what the different tolerances mean? And last question (this time) do resisters have to go in a certain direction or does it matter? Thanks for all the guidance.
James


Top
Profile
Post subject:
Posted: Sun Mar 28, 2010 11:25 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
The layout in your Weber book or at ampware.com is the lead dress.
This how your amp look when YOU LOOK inside. It help to locate the parts.

Schematic diagram, it's another thing : maybe this is what you can't read.
Layout and schematic diagram come together in Fender amp.


Don't change de value ( ohms) of resistor, keep the same.
Resistor don't have a direction, does not matter.

Carbon comp and carbon film : could change the sound (different tone, noise) if you can ear the difference. I don't.
My opinion, in your amp no difference exept the look . Carbon comp look more vintage.

Tolerance is the difference(error) resistor can have. The maximum error.This is the third color on resistor usualy silver 20% .

So a plate resistor of 100,000 ohms can mesure 100,000 + 20%=120,000 or 100,000- 20%=80,000 ohms.

If difference is more, change resistor


Top
Profile
Post subject:
Posted: Sun Mar 28, 2010 12:50 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Jul 25, 2007 11:48 am
Posts: 53
Stratele,
Thanks. I measured the large resistors across the power tube sockets and they range from 492 to 554. That' one is a little high but still within the +/-20%. So I won't change them. Here's where I may have a problem. When working on the cap job, I broke a resistor in half. With the caps away from you and the pair of resistors closest to your body, it was the one on the left. I thought I replaced it with the right one but now I'm not so sure. Brown Black Red Yellow (Gold?) and it measures a little over 1000 ohms.
I don't have the broken one to compare it to. It could be wrong? And another question: where do I find the filter caps on the schematic? Thanks.


Top
Profile
Post subject:
Posted: Sun Mar 28, 2010 7:19 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
James, the 1Kohm 1watt power resistor is correct. To find the filter caps on the schematic: bottom right hand corner, the 70/350 caps & 220K1watt resistors are in a boxed or ladder looking figure. Follow the line up and past the standby switch, hang a left at the first junction. You'll run across the choke(TR2), next are the other20/525 filter caps(noted by B,C,and D) and the power(step-down) resistors between them. If you study the layout, you'll see (6) 100Kohm plate load resistors, just above the tube sockets. They look like a two-sided triangle. There are three sets of these. Their top apex is denoted by [D]. Above V1 & V2 are 100Kohm resistors connected to the right hand leg of the triangular figure, running across the bottom of the circuit board. Essentially, we have (3) 100K resistors for V1, and (3) for V2. For V4, we have (2) 100K resistors. Alright, you'll need to study the layout and the circuit board, until you're sure of what I've told you. Oh yeah, the green heater wires, off the pilot light to all the tubes, are not shown in either the layout or the schematic for the sake of legibility. Art

_________________
None of Us are free, if One of Us is chained !


Top
Profile
Post subject:
Posted: Wed Mar 31, 2010 1:22 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Jul 25, 2007 11:48 am
Posts: 53
Okay. Got my first shock today and it was.....scary as hell. Don't want to do that again.
I changed all the 100k resistors and the 82Kohm. The his is still there but I found out something else. All the wires from the socket of V2 seem 'hot' or microphonic? is that right? Tapping them with my wood stick makes noise through the speakers. I tapped each wire seperately and every one is noisy except pin 6. Tapping the tube itself also give off noise although it varies with different 12AX7s. The wires on socket V1 are also making noise but a lot less than socket V2. Could the socket be bad? How do I troubleshoot this?


Top
Profile
Post subject:
Posted: Wed Mar 31, 2010 4:25 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
All you eard is normal and tube socket is not defective.

Do you realy know how to discharge capacitor ? Or you just forget.

It can kill you, don't forget.

For your trouble, the hiss. I think a good tech must ear it for fix. And ear what kind of hiss.

Good luck


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4  Next
Go to page Previous  1, 2, 3, 4  Next

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: