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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 6:06 pm
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Looks to be the AB165 circuit. I would assume it has a red switch on the back side that is a voltage selector?

T2

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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 6:08 pm
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Good catch, Tony!

It does appear to be an export model.

Arjay

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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 7:31 pm
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http://i251.photobucket.com/albums/gg30 ... bb661c.jpg

Tony, looks like you have a resistor tied from cathode to ground. Maybe a 1% tolerance one (final color band = brown). Bet this is a 1-ohm, 1% tolerance resistor to measure mV drop across. Each 1mV drop = 1mA current, or a resistor to measure idle bias.

Good find! Nice cab, indeed.


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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 8:03 pm
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Yeah Luzwei, that's a very nice cab!!! Seems like a 165, but I'd like to know how it sounds??? Looking at the pre amp photo, there is a toasted white ground wire(?) running off the dual Mallory 25uf bypass cap, for V1 and V2. The black ground wire looks normal. Just wondering where the white wire is terminated ? Has anyone ever seen this extra ground? Art

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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 9:56 pm
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aclempoppi wrote:
Seems like a 165......


Didn't anybody notice the "4668" build date stamped on the chassis?

The AB165 revision was supplanted by the AC568 in May -- this amp was made in November.

Arjay

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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 11:20 pm
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Arjay, I'm way good with your expertise for the dates and analysis of this chassis !!! It's that white wire off the bypass cap that gets my attention. I have never seen a solid core (wht) wire in this spot. Where does it go ? Maybe the Bass pot's low side ? Maybe to defeat the 8.2k ohm mid resistor or just someone's idea of an extra ground(noise elimination) ? Intent always gets my attention. Art

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Last edited by aclempoppi on Sat Mar 22, 2014 4:25 pm, edited 1 time in total.

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Post subject: Re: 1968 Bassman
Posted: Fri Mar 21, 2014 11:49 pm
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Indeed. It does look like someone has been rooting around in there. It also appears that the snubber caps were removed from the power-tube sockets (part of the hideous-sounding "improvements" that FMIC's whiz-kid engineers made). That white-jacketed wire does look wonky and should be investigated further. The OP should start a new thread dedicated to this apparent enigma.

Arjay

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Post subject: Re: 1968 Bassman
Posted: Sat Mar 22, 2014 1:54 am
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Retroverbial wrote:
Why not start a new Bassman thread to avoid confusion?
Arjay


Arjay,
I really didn't want to clog the forums with another topic with a same Bassman model. If someone will investigate this year of production, it will have all in one exhaustive topic.


Last edited by Luzwei on Sat Mar 22, 2014 2:45 am, edited 1 time in total.

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Post subject: Re: 1968 Bassman
Posted: Sat Mar 22, 2014 2:00 am
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T2Stratman wrote:
Looks to be the AB165 circuit. I would assume it has a red switch on the back side that is a voltage selector?

T2


Indeed it has, sir. It's an Export model. I live in EU.

Image


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Post subject: Re: 1968 Bassman
Posted: Sat Mar 22, 2014 2:23 am
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Retroverbial wrote:
aclempoppi wrote:
Seems like a 165......


Didn't anybody notice the "4668" build date stamped on the chassis?

The AB165 revision was supplanted by the AC568 in May -- this amp was made in November.

Arjay


If this helps, I have a chassis number. I know it doesn't say much more, but here goes:

Image


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Post subject: Re: 1968 Bassman
Posted: Sat Mar 22, 2014 2:37 am
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aclempoppi wrote:
Yeah Luzwei, that's a very nice cab!!!


Thank you, sir! Here are some more pics, before the service and before the pots had plastic caps.

Image

Image

Image



aclempoppi wrote:
Seems like a 165, but I'd like to know how it sounds???


I have a fairly great technician who I truly trust and has repaired stuff for me before (yeah, I really can't fix anything with my hands besides something to eat) and he said he is 100% this is a AA371 circuit.

aclempoppi wrote:
Looking at the pre amp photo, there is a toasted white ground wire(?) running off the dual Mallory 25uf bypass cap, for V1 and V2. The black ground wire looks normal. Just wondering where the white wire is terminated ?


Can you, please, make it visible for me on a pic? Can you highlight that wire on a pic? Thank you!


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Post subject: Re: 1968 Bassman
Posted: Sat Mar 22, 2014 2:58 am
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Luzwei wrote:
I have a fairly great technician who I truly trust and has repaired stuff for me before (yeah, I really can't fix anything with my hands besides something to eat) and he said he is 100% this is a AA371 circuit.


With original Mallory caps in the filter stage and bias-supply circuit dating to 1968 and you believe your tech who tells you the amp is a 1971 circuit revision?

Good luck with THAT!

I'm done.

:roll:

Arjay

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Post subject: Re: 1968 Bassman
Posted: Sat Mar 22, 2014 3:04 am
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Arjay, I'm sure he didn't mean to insult you personally with his observations. I'm sure he tried his best investigating this amp but with limited resources and knowledge, unlike you guys, he concluded what he concluded.

He might not be 100% correct, but he is still a damn good technician.


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Post subject: Re: 1968 Bassman
Posted: Sat Mar 22, 2014 8:17 pm
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Luzwei, Yeah, start a new Topic thread for your 1968 Bassman Export amp. I would like to learn more about this amp. Have only seen a couple of true Export amps on my bench, and they were a Deluxe Reverb and a Pro Reverb. As far as highlighting goes... I'm not good enough with computers to do that. Here is a site that might help you and the tech...http://el34world.com/Schematics1.php I noticed the voltage selector was set to 117 volts. Is that the wall voltage in your location? Keep us posted!!! Art

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