It is currently Mon Mar 16, 2020 1:07 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 687 posts ]  Go to page Previous  1 ... 5, 6, 7, 8, 9, 10, 11 ... 46  Next
Go to page Previous  1 ... 5, 6, 7, 8, 9, 10, 11 ... 46  Next
Author Message
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Jan 25, 2013 8:48 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
I did find that the big 150 ohm sandbox resistors need to be changes to 1 ohm 5 to 10 watt.
just picked up a pair of 1 ohm ten watt sandbox type resistors at Radio Shack tonight.

The caps that were on pin # 8 with the big 150's have also been removed.
Other than that we should be up and running !!!!!
Well as soon as I find a single 4 ohm tap OPT :cry: that isn't on back order or from a place of business with decent customer service.

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Jan 25, 2013 10:53 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Chris, not sure what you're gettin' at with those resistors( I'm lookiing at the 568 schemo and your amp). But if you want, I can send you an OT(Fender PN:022671-606913). It's from my Bassman(4ohm). It's just fine, rust free. If you're going to keep the amp, then there is no charge. Art....OK, now I see the reasoning for the 1ohm guys!

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


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Fri Jan 25, 2013 11:13 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
I sent you a PM
Its even the correct year !!!
WOW !!!
Thank you !!!
Yes I'm keeping this one

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Jan 26, 2013 8:54 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Chris, if you have an Idle Bias Kit or some such device to read the idle bias supply --- you won't need those 1-ohm resiistors. If you want to insert these, you need PRECISE (1%) flame-proof, resistors.

I do not use any resistor above 5-watt rating. Really, you only need 1-watt rating --- as this is the DC power draw through the cathode of 6L6GC even at "10" with a 1-ohm load.

I like Riken or Kiwame flame-proof 1% resistors.

The reason you don't need 5-10 watt resistors, if the greater the load (150ohms) the greater the current draw and thus the power load on those resistors---in this part of the circuit. The cathode DC current draw on the 6L6GC. Ohm's Law and power equation and such jazz.


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Jan 26, 2013 11:37 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Ah !
So the big sandbox resistors are measure points for bias.

So since I use this rig (see picture) I can do away with them all together.

Thanks !
Image

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Jan 26, 2013 12:02 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
It does look like pin * does need to go to ground in the AA-165 layout I'm using.
Is that correct ?

There is a small cap connecting the two #8 pins also.
Is that waste too ???
Image

Thanks !!!!!!

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Jan 26, 2013 4:32 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Chris, pin 8 will go straight to ground (now) and the cap is also history. Art

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


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Jan 26, 2013 6:56 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Thanks art !
I was pretty sure that was the deal after consulting the schematic

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sat Jan 26, 2013 9:47 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Just so you all know.
There is no way I would get anywhere without your help
Thanks !

I've gone from a casual tube changer , to a restoration guy (on my way) in a couple of years of hanging with this crowd.

Man if this bad boy fires up and sounds sweet, you will all hear a Yippee from Hoosier land !

Thanks for all the great friends here !!!!!!!!
:) :D :) :D :lol:

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sun Jan 27, 2013 9:29 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
blues bondsman wrote:
Ah !
So the big sandbox resistors are measure points for bias.

So since I use this rig (see picture) I can do away with them all together.

Thanks !
Image


Chris, the 150-ohm, 7 watt resistor is part of CATHODE-BIAS portion of this amp (AC568). The amp also has a standard BF/SF era negative voltage FIXED-BIAS circuit. The are a few amps that use both types of biasing (hybrid). The idea was to get the-best-of-both world's tone. A sort of combo Vox and Fender tone in one amp. Or a very early tweed breakup (in those amps with cathode-biasing) and later BF or SF clean crunchy tone.

Problem is, you get neither. So, like 99.9%, of ppl that own Fender amps with this hybrid style of biasing revert them back to the 100% FIXED-BIAS blackface circuit.

In a hybrid circuit you could measure the voltage drop across that 150-ohm resistor. But, you need to insert "150-ohms" into Ohm's Law and power equations to get the actual idle power value of that tube. That's why ppl use precise 1-ohm resistors. The mV measured = the mA draw across that 1-ohm resistor.

Then, all you need is the plate voltage and you can calculate the power (watts), at idle, of your output tube. Adjust the bias to get 60-70% manufacturer's max rated output for the specific output tube (for typical Class AB1, push-pull).


E (volts) = I (current, in amps) TIMES R (resistance)

Watts (Power) = E (plate volts) TIMES I (current draw, in amps)

Since you own a BIAS PROBE KIT to measure the bias... do as Art says and run a ground strap for the cathode (pin #8) to the chassis. Keep those sandbox resistors stowed away, for when or if you re-sell the amp (I guarantee you will not be reverting this amp back to AC568) and sentimental value.

Also, if you fix that crazy PI section you can do away with those 2000 pico-farad snubber caps. These are put into the AC568 cricuit to stabilize the amp. Once you've dropped the PI section to more sane blackface plate voltage values, that section will be much more stable. Have better voltage swing. And need LESS negative feedback voltage.

:mrgreen:


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sun Jan 27, 2013 2:22 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
This is fun :mrgreen:

Fixing the PI may come later.
and I sure hope it does !!!!

All the caps (brown lumps) are either .1 or .047 other than those two .047 you (Beemer) already told me to swap out for .1's will I need to change values if I should I decide to order all new caps ?

Can't wait to hear it for the first time (fire extinguishers in hand) :lol:

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Sun Jan 27, 2013 3:37 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
blues bondsman wrote:
Can't wait to hear it for the first time (fire extinguishers in hand)


Your confidence is both ebullient and inspiring......

:mrgreen:

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: 68-69 drip edge Bassman /circuit changes
Posted: Sun Jan 27, 2013 7:10 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Chris, yes you need two good quality 600VDC rated 0.1 mfd non-polar caps for this project.

The reason for the change to 0.047mfd/600VDC in the AC568 circuit is prolly to let less bass (and AC voltage) through. Because, I'm sure when those CBS boys ran the AC568 style PI-output stage with standard 0.1mfd caps, they got very unstable looking tracings on the old scope.

That AC568 circuit is a study in fix-its. Whole bunch of extra feedback, both locally and globally. And added "after-the-fact" components. This is usually a sign of poor engineering.

Good luck with the amp. And those extinguishers are in the "green"-- right?

:D


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Jan 28, 2013 6:52 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Now for the good news !

remember the bad service from Amp Parts Direct and the poor attitude ?

This morning at 7:30 am my time I called Mojotone not one time but twice to add to a small order I had made over the weekend.
The fine folks at Mojo not only helped me out but seemed happy to have my business.

I guess its true there is the South and then there is Florida :mrgreen:

Kudos to Mojotone

_________________
Keepn' the Blues Alive

2004 50th Ann. Limited edition AMSE Stratocaster
2017 50's Baja Telecaster BSB

1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

Visual Sound Route 66
Cmatmods Signa Drive


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Mon Jan 28, 2013 9:28 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Thu Oct 14, 2010 8:54 am
Posts: 1179
Location: Florida
blues bondsman wrote:
Now for the good news !

I guess its true there is the South and then there is Florida :mrgreen:




Hey! :lol:

Art


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 687 posts ]  Go to page Previous  1 ... 5, 6, 7, 8, 9, 10, 11 ... 46  Next
Go to page Previous  1 ... 5, 6, 7, 8, 9, 10, 11 ... 46  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 1 guest


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: