It is currently Mon Mar 16, 2020 5:48 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 54 posts ]  Go to page Previous  1, 2, 3, 4  Next
Go to page Previous  1, 2, 3, 4  Next
Author Message
Post subject: Re: ? on 1973 super reverb
Posted: Tue Jan 11, 2011 4:00 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Ok Scanner is working. I hope is clear and the right circuit ?

Image


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: ? on 1973 super reverb
Posted: Wed Jan 12, 2011 4:08 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
If you do this modification, before you put amp to ON, remove power tubes and mesure negative voltage at their grids , pin 5. You should have -30 to -50 volts DC. Turn your bias pot see if voltage change. Test that on each tube.
-----------------------------------------------------------
Nota: removing power tubes will protect them in case your bias circuit won't work.
-----------------------------------------------------------
If voltage change normaly, turn your pot for maximun negative voltage. This will keep your tubes cold bias.

Put your amp to OFF, plug power tubes in their sockets. Now you are ready to do proper bias.


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Wed Jan 12, 2011 2:25 pm
Offline
Hobbyist
Hobbyist
User avatar

Joined: Sun Jan 09, 2011 12:29 pm
Posts: 81
Location: Charlottsville
Thanks so much for all the help. Its going to take a while for me to get to it but I'll let you know how it turns out.


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Wed Jan 12, 2011 2:39 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Don't forget, there are lethal voltage on the amp even is disconect for many days.


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Wed Jan 12, 2011 5:39 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Just to speak to Tissan's discription of the filament voltage; yes the two resistors reference that voltage to ground, near zero. This also serves to keep the filament voltage lower than the cathode voltage, just as you suggested. The extra resistance to ground also lowers the chance of an arc in the power transformer, should the speaker be unplugged. Very good explanations, Louis ! Art

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


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Thu Jan 13, 2011 3:23 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
"This also serves to keep the filament voltage lower than the cathode voltage, just as you suggested. The extra resistance to ground also lowers the chance of an arc in the power transformer, should the speaker be unplugged"---aclempoppy

I never heard about that and never mesure any lower filament voltage ( than the cathode) with or without resistance.
Thank's for information, I 'll keep my ears and eyes wide open

Louis


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Thu Jan 13, 2011 9:48 am
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
I mistakenly said the filament voltage should be lower than the cathode voltage. The opposite is what we would want to avoid hum. Sorry,my bad ! Art

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


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Fri Jan 14, 2011 11:35 am
Offline
Professional Musician
Professional Musician

Joined: Sun Dec 19, 2010 12:00 pm
Posts: 1389
Fully aggreing with Aclempopi, if the filament voltage is lower than the kathode, the electron beam is from the filament to the cathode and it is exactly what we want to avoid :? .

_________________
Tissan

*'52 Telecaster RI, '57 Stratocaster RI, Gibson ES175 RI, Washburn Hawk 1980, Epiphone Casino MIK 2000, 57' Deluxe Knotty Alder, BDRI ...*
https://soundcloud.com/pierrou
http://www.youtube.com/user/Jazzenfamille


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Fri Jan 14, 2011 1:42 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
That not this way it work for no hum with the 2 resistors.

With or without those two resistor the filament voltage is the same


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Fri Jan 14, 2011 4:21 pm
Offline
Professional Musician
Professional Musician

Joined: Sun Dec 19, 2010 12:00 pm
Posts: 1389
You're right Stratele about absolute 6.3V AC, what we are talking about is the potential between filament "average voltage =DC" and kathode, like the potential between the kathode and the plate or grilles.

_________________
Tissan

*'52 Telecaster RI, '57 Stratocaster RI, Gibson ES175 RI, Washburn Hawk 1980, Epiphone Casino MIK 2000, 57' Deluxe Knotty Alder, BDRI ...*
https://soundcloud.com/pierrou
http://www.youtube.com/user/Jazzenfamille


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Fri Jan 14, 2011 4:43 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
I don't know what the use of the potential fialament average voltage and kathode ?


And this is something to do with filament hum ?


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Sat Jan 15, 2011 2:03 am
Offline
Professional Musician
Professional Musician

Joined: Sun Dec 19, 2010 12:00 pm
Posts: 1389
Actually, the secondary coil transformer of 6.3V AC is floating regarding ground, which should be connected to earth. The DC voltage of a valve kathode is imposed by the idle current through the" kathode to ground" resistor (2.2k for instance) or directly grounded (0V).
As the 6.3V is "floating", the DC voltage between the kathode and filament is the consequence of leakeage and or capacitor bridge divider... Sometimes by pure chance, it could in favor, but it could be not in favor at all. By putting 2 resistors on the ouput of transformer coil, you impose a reference voltage to the filament (rougly 0V). Then no voltage between filament and kathode or better a voltage that push back the electrons from the filament.
(BTW if you use spice simulator, with no reference to ground, the simulation of such schematic does not converge, it is necessary to put parasitic components)

_________________
Tissan

*'52 Telecaster RI, '57 Stratocaster RI, Gibson ES175 RI, Washburn Hawk 1980, Epiphone Casino MIK 2000, 57' Deluxe Knotty Alder, BDRI ...*
https://soundcloud.com/pierrou
http://www.youtube.com/user/Jazzenfamille


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Sat Jan 15, 2011 3:19 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Tis-san,

I am very surprise by your knowledge. These informations that I realy don't know about the voltage relation filament\ Kathode. ( I think I write a very bad english ?)

Where you got this information ? Your study in your life, a book you read now , experience ?

Same for Aclempopy.


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Sat Jan 15, 2011 10:27 am
Offline
Rock Star
Rock Star
User avatar

Joined: Wed Feb 17, 2010 11:38 am
Posts: 4333
Location: Tennessee
stratele52 wrote:
Tis-san,

I am very surprise by your knowledge. These informations that I realy don't know about the voltage relation filament\ Kathode. ( I think I write a very bad english ?)

Where you got this information ? Your study in your life, a book you read now , experience ?

Same for Aclempopy.

stratele52..I don't have your answer but you write English good enough for us to understand you,that's all that matters! :)
if you heard some of us speak here in Tennessee,you would not think we were speaking English. :lol:


Top
Profile
Post subject: Re: ? on 1973 super reverb
Posted: Sat Jan 15, 2011 3:05 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Rebelsoul, I wish one day go to visit Tennessee, I'm sure I like it.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 54 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: