It is currently Mon Mar 16, 2020 4:12 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 15 posts ] 
Author Message
Post subject: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 03, 2016 9:54 am
Offline
Hobbyist
Hobbyist

Joined: Sun Jul 17, 2016 3:11 pm
Posts: 7
Hi all,
I just bought a replacement set of tubes for my Bassbreaker 15 (Tung-Sol) but I haven't risked trying those out yet because I can't find anywhere if the amp is cathode-biased (not needing re-bias) or fixed biased...
Can anybody help?
Thanks.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 03, 2016 3:21 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
All kind of amp need a bias check with new tubes.

Cathode bias less than grid bias, but they need bias anyway.
I fix lots of these amps with wrong bias

Bass breaker schematic are not available yet. I don't know about their bias.


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Tue Aug 09, 2016 11:35 am
Offline
Amateur
Amateur

Joined: Thu Aug 02, 2007 5:13 pm
Posts: 190
Location: Taxachusetts
When I had my BB15 I checked the bias and they run those tubes very hot they were around 42 mA, tried to see if there was a bias adjust in that amp and it was a PITA just to see the circuit boards. So if you find your self going through power tubes that's one reason why. Blues Junior's runs the same HOT power tubes bias but I was able to easily change a resistor to get the bias current lowered!


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Tue Aug 09, 2016 11:56 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
J.LaGrassa wrote:
When I had my BB15 I checked the bias and they run those tubes very hot they were around 42 mA, tried to see if there was a bias adjust in that amp and it was a PITA just to see the circuit boards. So if you find your self going through power tubes that's one reason why. Blues Junior's runs the same HOT power tubes bias but I was able to easily change a resistor to get the bias current lowered!



What is the plate voltage to say 42 ma is very hot ?
Some Class A amp may run hot to have their tone. Is It a Class A amp ?


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Tue Aug 09, 2016 1:46 pm
Offline
Hobbyist
Hobbyist

Joined: Sun Jul 17, 2016 3:11 pm
Posts: 7
Hi all, thanks for the helpful replies. Some additional data I gathered:

Another amp in this series, the 007, is class A, but not this one. The Bassbreaker 15 is a class A/B: «Fender Bassbreaker 15 Head e-guitar head, 15 watt, class A/B, 3x 12AX7 and 2x EL84 tubes, 1 channel with selectable amp voice, control for bright, gain, ...»

I contacted Fender's customer support, asking for the circuit diagram but they replied that they couldn't share it:
«The schematics for our amplifiers moving forward will only be available to authorized service centers. Sorry about that, if I could I would certainly send one to you!»

Without the circuit diagram it will hard to understand what kind of amp this is...


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Tue Aug 09, 2016 1:51 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
rgrilo wrote:
Hi all, thanks for the helpful replies. Some additional data I gathered:

Another amp in this series, the 007, is class A, but not this one. The Bassbreaker 15 is a class A/B: «Fender Bassbreaker 15 Head e-guitar head, 15 watt, class A/B, 3x 12AX7 and 2x EL84 tubes, 1 channel with selectable amp voice, control for bright, gain, ...»

I contacted Fender's customer support, asking for the circuit diagram but they replied that they couldn't share it:
«The schematics for our amplifiers moving forward will only be available to authorized service centers. Sorry about that, if I could I would certainly send one to you!»

Without the circuit diagram it will hard to understand what kind of amp this is...


A class A/b amp tell it is not ( most of the time ) a cathode biased amp but a fixed bias amp


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Tue Aug 09, 2016 2:24 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
rgrilo wrote:
I contacted Fender's customer support, asking for the circuit diagram but they replied that they couldn't share it:
«The schematics for our amplifiers moving forward will only be available to authorized service centers. Sorry about that, if I could I would certainly send one to you!»


What a load of ABSOLUTE CRAP!

I remember when a schematic was supplied with every new Fender amp sold -- it came in the packet with the owner's manual and the warranty card.

:evil:

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: Are the new Bassbreaker amps cathode biased?
Posted: Tue Aug 09, 2016 5:24 pm
Offline
Amateur
Amateur

Joined: Sun Jul 22, 2007 9:29 am
Posts: 139
Yes,
Well if Fender wants to support their Authorized Service repair Centers,
and supply Fender OEM parts thru the Service centers, great!

Let the Service centers sell (make money) Fender parts to consumers, and sell the Schematics under technical support to the customer. Don't they do that already. It’s got to come back to the customer, full circle.
I read too many forum posts about people not being able to buy parts and having the Authorized Service center, unable to come to terms with the customer issues,, it happens. But it’s the internet forums,


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 10, 2016 6:35 am
Offline
Amateur
Amateur

Joined: Thu Aug 02, 2007 5:13 pm
Posts: 190
Location: Taxachusetts
stratele52 wrote:
J.LaGrassa wrote:
When I had my BB15 I checked the bias and they run those tubes very hot they were around 42 mA, tried to see if there was a bias adjust in that amp and it was a PITA just to see the circuit boards. So if you find your self going through power tubes that's one reason why. Blues Junior's runs the same HOT power tubes bias but I was able to easily change a resistor to get the bias current lowered!



What is the plate voltage to say 42 ma is very hot ?
Some Class A amp may run hot to have their tone. Is It a Class A amp ?



Been a while but it was about 320V, already been mentioned its a Class A/B power section.


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 10, 2016 7:12 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
42 mA, at 320 VDC, is about 13.5 watts. Sounds like the Bassbreaker 15 shares the same high idle wattage as the BJr. The tube layout and lineup seems the same in both amps.... and both amps are about the same size (the Bassbreaker slightly larger).... so, it is like the Bassbreaker 15 is a souped-up BJr. :idea:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 10, 2016 7:32 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
13.5 watts idle dissipation per EL84 is too high, no? No matter if the amp is designed for Class "A" or AB. This is even too high for 7189A tubes.

Did you reset the Blues Jr to ~70% max dissipation?

Thanks!


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 10, 2016 7:41 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Yes, 7189s idling around 9 watts. 8)

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 10, 2016 7:57 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Thanks! Did you place a bias pot at point C- (near power tranny)? 10k-ohm linear pot?

http://ampwares.com/schematics/blues_jr.pdf

Sorry, if you already posted this. Thanks! :)


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 10, 2016 9:42 am
Offline
Amateur
Amateur

Joined: Thu Aug 02, 2007 5:13 pm
Posts: 190
Location: Taxachusetts
BMW2002Ti wrote:
13.5 watts idle dissipation per EL84 is too high, no? No matter if the amp is designed for Class "A" or AB. This is even too high for 7189A tubes.

Did you reset the Blues Jr to ~70% max dissipation?

Thanks!


I replaced a resistors to get the bias in the 70% range in my BJIII


Top
Profile
Post subject: Re: Are the new Bassbreaker amps cathode biased?
Posted: Wed Aug 10, 2016 6:26 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
BMW2002Ti wrote:
Thanks! Did you place a bias pot at point C- (near power tranny)? 10k-ohm linear pot?

http://ampwares.com/schematics/blues_jr.pdf

Sorry, if you already posted this. Thanks! :)


Just replaced R52
Image

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 15 posts ] 

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: