It is currently Mon Mar 16, 2020 9:04 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 12 posts ] 
Author Message
Post subject: Help Dating a Drip Edge Twin ?
Posted: Sat Apr 22, 2017 12:58 pm
Offline
Hobbyist
Hobbyist

Joined: Sat Apr 22, 2017 11:08 am
Posts: 4
Long time lurker and thankful for all the great reads here.

Not 100% sure what I got here.... the more I dig, the more confused I get.

What I do know:

Face Plate has the Black Lines
Serial # on back is A 24483
The JBL plate is on the Front
The Speakers are JBLs - D120Fs
Legs say Patent Pending w/ serial #
Caps were replaced and 3 prong Power cable installed
Came with Victoria Luggage Cover with Twin Reverb label
Date Stamps seem to indicate Shumacher from 1969 - 606-9-xx
Foot Switch is Chrome - not back
Tube Chart 90% missing... :

Thanks is advance!!!!


Image
Image
Image
Image
Image
Image
Image
Image
Image
Image
Image
Image


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 1:13 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Justin_Case wrote:
...Date Stamps seem to indicate Shumacher from 1969 - 606-9-xx...


There you go.

_________________
---> "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: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 1:56 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14045
Location: Province de Québec, Canada
1969 parts.

Nice amp , congrat.


Top
Profile
Post subject: Re: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 2:49 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
Your amp was built in the fall of 1969 and is wired to AA769 specs. It was factory-equipped with JBL's (a small logo shelf is required at the lower-right corner of the baffle board to facilitate installation of the Lansing logo). This revised circuit was deliberately strangled at the factory by reducing the plate voltage to a paltry 405 VDC. As a result, the amp only puts out about 60 watts, compared to the original AB763's 460 VDC and 85-watt output.

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: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 9:19 am
Offline
Hobbyist
Hobbyist

Joined: Sat Apr 22, 2017 11:08 am
Posts: 4
Thank you to one and all.

Time to do a lot of reading up on the AA769 specs.


Is it unusual to find the Black Line plate on a 1969?

ImageIMG_5312 by six strings, on Flickr


Top
Profile
Post subject: Re: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 9:38 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
That late in the '69 model year it is indeed rare to find a blackline front panel AND the drip-edge molding. But the silver/white/metallic-turquoise grill cloth is a hallmark for Fender that year. The previous 1968 amp line-up used a silver/black/pale-blue weave. And the 68's featured the last of the snowman knobs.

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: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 9:53 am
Offline
Hobbyist
Hobbyist

Joined: Sat Apr 22, 2017 11:08 am
Posts: 4
Thank you again!

So guess I do have an " Odd Bird " with this one.

Fender must have been clearing out the Parts Bin when doing up this one with the Black Line Face Plate.

Was there any logic behind the AA769 Circuit? Seems to me to be a rather large drop off in output?


Top
Profile
Post subject: Re: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 11:12 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
Justin_Case wrote:
Was there any logic behind the AA769 Circuit? Seems to me to be a rather large drop off in output?


Only insofar as the losers that CBS hired to run the newly-created Fender Musical Instruments wanted to leave their mark on history. When sales began to tank due to such nefarious diddling, the amp circuits were again revised to put some lead back into the pencil as it were and output power was restored. Ironically, many of Fender's amps would later be uprated when the "wattage wars" commenced in the early '70s. The amps themselves were largely unchanged -- FMI's engineers merely tapped into the intrinsic power reserve that already existed in most of Leo's designs.

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: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 11:27 am
Offline
Hobbyist
Hobbyist

Joined: Sat Apr 22, 2017 11:08 am
Posts: 4
Arjay,

Thanks for the insight. So much for logical reasons.

I guess I'm in the Catch 22 of leaving it original, or having it modded to get the most out of it.


Top
Profile
Post subject: Re: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 12:15 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
Converting the circuit back to the earlier AB763 revision isn't as daunting a task as you might think. The fundamental stuff is fine -- only a handful of small components need be changed, costing perhaps less than $30.00 in total. The trick would be to finding a competent tech who is familiar with vintage Fender amp architecture.

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: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 9:19 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Looking at the two schematics (AB763 and AA769), I can't immediately see how Fender dropped the plate voltages on the AA769 circuit. Both the BF and this SF circuit used the same PT & OPT models. There doesn't seem to be any added resistor in the PSU. Maybe, the diodes used in the PSU's rectification?

http://www.thevintagesound.com/ffg/sche ... _schem.gif

http://www.thevintagesound.com/ffg/sche ... _schem.gif

There is definitely some alterations to the phase inverter's plate and long-tailed, cathode resistor network. Plus, of course, the bias supply's control (bias versus balance-hum). All is fairly easily reversible. The PI section's mod in the later AA769 is going to alter the tone, for sure. The LT changes reminds me of the DR I reverted. Area circled in green in photo.

Image



:mrgreen:


Top
Profile
Post subject: Re: Help Dating a Drip Edge Twin ?
Posted: Mon Apr 24, 2017 10:46 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26415
Location: Tombstone Territory
BMW2002Ti wrote:
Looking at the two schematics (AB763 and AA769), I can't immediately see how Fender dropped the plate voltages on the AA769 circuit. Both the BF and this SF circuit used the same PT & OPT models. There doesn't seem to be any added resistor in the PSU. Maybe, the diodes used in the PSU's rectification?


+1

That's the only thing that came to mind with me as well (downgraded diodes in the rectifier circuit). The filter-cap array and power-rail resistors seem to be the same for both revisions. And the iron (PT and OT) is unchanged.

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
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 posts ] 

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: