It is currently Mon Mar 16, 2020 2:19 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 687 posts ]  Go to page Previous  1 ... 7, 8, 9, 10, 11, 12, 13 ... 46  Next
Go to page Previous  1 ... 7, 8, 9, 10, 11, 12, 13 ... 46  Next
Author Message
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Jan 29, 2013 11:42 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Chris,

Static DC resistance readings will not jive with the dynamic AC impedance values. It's these impedance values that are important for ID'ing a tranny.

You need a sine-wave signal generator, or some 1kHz source with a known AC voltage output ----placed onto the SECONDARY WINDING. Then, measure the resultant AC voltages on each half of the PRIMARY SIDE (each end to the center tap).

You plug the values into an equation (I need to look up, if you are interested) --- to find the impedance of the primary side (which determines what output tubes to use and in which arrangement). And the secondary's impedance (or which speaker impedance type to use).


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Jan 29, 2013 2:27 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Its installed and wired !
mail truck should be bringing me some resistors, Caps and a power cord tomorrow !!! and then.......
We Be Jamm'n 8)
I did have to add a bit of lead to the new transformer, Brown and red wire were Just a tiny bit short, i stole it from the little guy that was in there, i did however leave plenty on it in case someone needs an 8 ohm tranny for something.

Image

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: Tue Jan 29, 2013 5:05 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Tue Mar 01, 2011 3:10 pm
Posts: 5646
Location: Gateway to the West
blues bondsman wrote:
No Arjay I haven't given it much attention

there are no codes
Hand written notes unreadable except 8 ohms and "hole" on the bottom
Looks paper wound if that's the correct terminology ?
It is in working order so.......


Image


Blues...Maybe you have the long lost Courtney Love Commemorative transformer? :lol: :lol:

T2

_________________
-----------------------------------------------------------
What time is it? It's Fender Time.


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Jan 29, 2013 5:15 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Courtney Love. Hole. LOL! :lol:

Now that there is a real Diesel Engine in that amp... careful with those speakers!

http://www.youtube.com/watch?v=iR8-NYTLh8c

Chris I have one suggestion (really one of many, to date). Put heat shink insulation over those threads coming into the chassis from the new OPT. I've had amps wear & short out leads from heavy vibrations (no,,, not the kind from Dildoes). :D


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Tue Jan 29, 2013 5:53 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Glad it's working out, Chris!!! Thought that I unsoldered those leads, but you've got it in hand. 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: Tue Jan 29, 2013 6:19 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Thanks Art !!!!!
Be sure to allow me to return the favor !
I just flat can't over the fact that it's a 69 too, that my friend is pretty cool 8)

I'll let you all know (Good Lord Willing) when I fire her up tomorrow.
My guess is its gonna sound SWEET !!!!

_________________
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: Tue Jan 29, 2013 11:22 pm
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Chris, I'm sure a couple of guys,here, would have been happy to shoot you a part for the amp. Just don't forget about the possibility of positive feedback(loud hum) with a different trans. Maybe, Beemer or Bill can speak to this situation? Happy Pickin'!!! 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: Wed Jan 30, 2013 11:39 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
:x Danged old post office !
Says: expected delivery by 1-30-2013
Mail came and no parts :roll:

So looks like another day of waiting :mrgreen:

And a week long lull in my other business means my poor wife has to put up with me :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: Wed Jan 30, 2013 11:58 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Art,

That output tranny had been working fine in a Bassman circuit before? It should ok, as long as Chris retrofits the proper global negative feedback circuit into the amp. And uses a proper impedance load.

First thing to do is check the B+ voltages, with no tubes in. STANDBY SWITCH to on. Each tap point should read within 25% of schematic values. Usually consistent and RELATIVELY higher at each tap point, due to today's outlet voltages. The key is each tap-off point should drop by same relative amount from the first filter stage to the next. After each dropping resistor or the choke in the PS rail. Which is about a 10VDC drop from tap to 6L6GC to the next tap (after the choke), to the next (12AT7 tap). Then a 20-30VDC drop to the tap for the 7025's tap.

For example, you may see 475VDC after the standby switch. 460VDC after the choke. 450VDC tap point to the 12AT7 phase inverter. 425VDC tap to the 7025s. Since you have not changed the power supply setup from the original specs. The voltages at the PS tap points should be close to the original AC568 specs.

http://www.webphix.com/schematic%20heav ... _ac568.pdf


Next thing to do read the bias supply voltage at the junction of the two 220k-ohm grid-to-ground resistors. Should be a ROCK STEADY negative 43-46 VDC. Since you have changed the bias supply back to AA864, the bias supply voltage should be close to values in that amp. To get the reading to be -44VDC at midpoint of the pot --- you may need to juggle the 15k-ohm resistor value. Due to today's outlet votlages.

http://www.webphix.com/schematic%20heav ... _schem.pdf


Read this point before plugging in any tube. If the voltage varies or jumps when you touch the bias pot or components within the bias supply circuit with a wooden chopstick... stop! Turn off amp and fix the problem(s). Usually, it is a bad pot or solder point. Alternatively, poor contact to ground.

If bias supply has good, steady reading -- then turn off amp and plug in the 6L6GCs. I usually check the idle bias current draw of some known-good 6L6GC "bogey" tubes :D or tubes that I know are good, but not $$$. Kinda like tubes just to test amps. Plug in the 6L6GC only. No phase inverter or gain stage/input tubes.

If you start to see drifting, esp upward and upward and upward creeping of the mV readings --- could be an indication of instability. Changing the negative feedback voltage and/or lead dressings and tensioning or changing sockets maybe in order.

If the idle bias is steady. Turn amp off. Place in the phase inverter (12AT7). Recheck the bias for steady readings. Repeat process with each 12AX7 (7025). If any of the added tube gives you unstable idle bias ---- you stop. Check that stage for wiring and/or component problems.

If you can't get a steady idle bias, no matter what you try --- a signal generator/scope combo maybe needed to find the culprit.

I rarely see this with proper tranny setups in those Pro-level old Fender amps. Usually it's due to lead dressing, bad grounding, or instabilities in the gain stage or phase inverter section.

Whew! HTH!

Sorry for the Shaggy Dog Story description. :lol:


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Wed Jan 30, 2013 9:39 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Sure hope you guys are online tomorrow at about 1pm Central time !
My guess is I'll be ready to test and test run this amp ! :wink:

This has been very educational !
I have learned more in the last week or so that I have in the last two years.
Thanks for the help, the parts and for making me dig in for some theory and
now I'm beginning to understand more and more of what an amp does and why !

There is a guitar making school in Chicago that has a week long class where you build a Champ tweed or a 5E3, might just have to invest in it this year !

_________________
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: Thu Jan 31, 2013 12:35 am
Offline
Professional Musician
Professional Musician

Joined: Fri Jun 26, 2009 6:53 pm
Posts: 2252
Location: Harvard IL
Chris, depends on snow removal up at church tomorrow!!! But Beemer is probably the guy, anyway!!! 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: Thu Jan 31, 2013 6:24 am
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
I ended up at the county jail a few times last night, not a bunch of snow, however it rained then froze then snowed and our roads were like an ice rink !!!

Then the WNW winds hit !!!
Lets just say it was an interesting ride home :shock: :shock: :shock:

Gotta love living at the very south end of that big lake !

I keep checking my work and I'm pretty sure I've kept up with all of the suggestions so far and all the while rechecking my Tube amp books, that all seem to echo the advice from all of you.

My only question was on pin 8 of the 6L6's I ran them both to the same ground point.
Any problem with that ?

_________________
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: Thu Jan 31, 2013 10:35 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Chris,

I got a PST from Art re: phasing of that Bassman output tranny versus the one that was previously in the amp.

I have seen a signal generator and scope used to check polarity WRT the global negative feedback (GNFB) voltage. I posted a message on another amp board. And will get back to you with any answers.

From my experience, if anything is funky with the phasing of ANY stage in the amp --- the GNFB voltage MAYBE altered, as well as the phasing of the speakers. If the GNFB voltage is altered, you MAY have stable biasing issues. Resulting in a drop of output wattage.

Also, the speakers will traverse INWARD instead of OUTWARD with a single hit to the Low E string. What I do is have someone hit the E string, while I GENTLY touch the speaker. Then feel for the initial movement. Sometimes, just flipping on the STANDBY SWITCH, you can see or feel the initial movement. It should be OUTWARD.

Good luck. Will get back to you.


Top
Profile
Post subject: Re: 68-69 drip edge Bassman /circuit changes
Posted: Thu Jan 31, 2013 12:53 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Well !!!
not so good
Hum, flash, popped fuse

_________________
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: Thu Jan 31, 2013 1:24 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Tue Jul 17, 2007 3:08 pm
Posts: 2889
Image

Image

Image

Today's work
Did I flub ???

_________________
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
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 687 posts ]  Go to page Previous  1 ... 7, 8, 9, 10, 11, 12, 13 ... 46  Next
Go to page Previous  1 ... 7, 8, 9, 10, 11, 12, 13 ... 46  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: