Bassman export amp silverface 1970 circuit

[bismarel]

Hi , i'm new and have a ?
Is there a way to find out which circuit the amp has ?
To make a long story short , i lost the tube chart .
TIA
rudi

[Jazz P Bass]

Amp Guide » Fender Bassman (Silverface)

[bismarel]

Thanks for the quick reply , but thats not what i was looking for .
To make the short story long , I rehoused the amp in a combo cab .
The empty head cab was stored in the basement .
In the meantime i devorced and moved away , left the head in the basement .
The bitch had a little campfire and burned the cab .
So now i'm " headless " , and no tube chart to find out the circuit .

[bismarel]

Ok , found it on a other website .
Thanks anyway

[Tom Phillips]

If you will post detailed photos of the inside of the amp. I will take a look and should be able to recognize unique features and identify the exact model number. Post cleat whole chassis shots and 3 or 4 closeups of the circuitry.
Regards,
Tom

[bismarel]

Here are some photos , i hope you recognize something .

[bismarel]

i think its a '69
the serial is A58059
and the transformers are 606-9-24 , 25 and 32

[Tom Phillips]

Rudi,
I agree with your assessment that the Amp was made in 1969. Both the transformer date codes and the internal cosmetics support that conclusion. The parts look to be all original.
I believe that the circuit is the Bassman AC 568. One tip off is the large rectangular resistors attached between pin 8 of the power tubes and the chassis. This variant of the Bassman has a power amp circuit that uses a combination of cathode and fixed bias. I had one customer that liked the sound of this circuit but most preferred to re-configure the circuit back to earlier blackface versions such as the AA 864. There is a copy of the AC 568 schematic posted at http://web.archive.org/web/200610201...sman_ac568.pdf
Regards,
Tom

[bismarel]

Tom ,
Thank u very much .
I bought the amp back in '89 for about 30 euros from a guy who bought it new but didn't use it much because it was to loud to play at home . Everything , including the tubes are still original stock from the Fender factory . Never needed a service .
Changed it to a combo with a Fane 15x200watt and used it for about 5 years as a rehearsal amp . Lost the original cab in '91 (that u new already ) Very clean sound .
Last week i came across this site and was reading about the bassman and remembered i had one in the basement sitting for about 16 years now . lol .
I plugged it in , besides the dust noise in the pots , it was still working . Unbelievable ! Unbreakable !
Now it needs a service for sure .....
Regards ,
rudi

[bismarel]

1 more ?
Do you think i could apply this fix ? http://music-electronics-forum.com/t21797-2/#post181696
I want to make sure before to start messing around .
Gonna change to 1x12 speaker and re-configure to blackface .
Thanks to the internet .
Thank u .

[Tom Phillips]

There is a lot of convoluted information in that thread.
The original noise complaint was traced to "The problem was a broken solder tab # 7 on one of the power tube sockets"
Further down they discuss re-voicing the pre-amp which is a common mod to improve the sound of the amp for guitar. There are lots of choices for that and the recommendations seem OK.

Note: There is no AC568 Blackface so what exactly do you mean by "re-configure to blackface"

[bismarel]

Tom
Yes that tread has some confusing information but i was only referring to the akimball442 post
And probably i didn't expressed myself well .
The changing of the combo cab to 1x12 and the " blackfacing " is gonna be my future project .
First i'm gonna let it checked by a technician , to be in good shape to start with .
There is a site were i can order a bassman ac568 conversion kit with instructions .
I'm gonna look around for more information on how to do the " blackfacing ".and search for the components over here .
For now i'm only gonna do the modification how it's explained in that particular post .
And don't worry , if you're gonna warn me about the capacitors , i have some basic electronic skills .
Unfortunately no schematics reading .
Regards
rudi

[Amp Kat]

The AC-568 has Cathode and fixed bias resistors and if you look on you're amps power tubes on pin 1& 8 and they don't have those 150 ohm resistors going to ground then you don't have an AC-568 or if pins 1 & 8 are tied to chassis ground. I also agree with Tom that you would have to change circuits to blackface it because there is not a Blackface AC568. IMO the AA864 is the best model of that amp and is what I would personally change it to if I were to go that route. The two 2000pf capps should be removed and the Cathode resistors in that scenario. I would consider leaving it as is and changing the filter and bypass caps and giving it a go and see how it sounds. Bassmans tend to do funny things when changing there circuits so just a warning before you venture into that sea.

[bismarel]

Thanks , much appreciate your opinion .

rudi