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Post subject: New to vintage amps (kind of)
Posted: Wed Mar 28, 2018 10:11 am
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Hello,

New to vintage amps, well except for the Fender Brownface Deluxe I fried as a kid. Just picked these two up this week. Hope to learn more about them here.

Thanks,

Jimbo

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Post subject: Re: New to vintage amps (kind of)
Posted: Sat Mar 31, 2018 2:19 am
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Great amp the Bassman amp on the top , a real blackface desing in silverface cab

http://ampwares.com/amplifiers/fender-b ... ilverface/

______________________________________-
Bassman 50 schematic;

http://el34world.com/charts/Schematics/ ... sman50.pdf


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Post subject: Re: New to vintage amps (kind of)
Posted: Sat Mar 31, 2018 7:08 am
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Two in one go...nice!
This type of thing can become addictive...you'll see...and learn coping skills to control the GAS (gear acquisition syndrome...)

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If the voice inside your head says "you can't play guitar", then by all means play the guitar and that voice will be forever silenced. I know I can't play, I don't care


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Post subject: Re: New to vintage amps (kind of)
Posted: Sat Mar 31, 2018 10:12 am
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Thanks guys, but one thing I don't buy is that these forums in any way help curb GAS. Hahhahahah.

I have pulled these out of the cab to get a look, pretty sure the '68 is fairly early, it does have a black line face plate, circuit looks like AB165, only wired thing is tje two resistors to ground off of the pilot light, my schematics don't show that until later circuits.

The '74 sounds really good, supposedly had some type of bias mod done not sure what.

Anyway, I am running these through a closed back 2x12 cab and I am digging the tone, pushed 'em up to about 8 and the OD is wonderful, loud as hell but wonderful. Hahahhaha


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Post subject: Re: New to vintage amps (kind of)
Posted: Sun Apr 01, 2018 1:26 am
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Jimbojo13 wrote:
, only wired thing is tje two resistors to ground off of the pilot light, my schematics don't show that until later circuits.

This a artificial ground for tube's heaters. Power transformer may not have heater ground


The '74 sounds really good, supposedly had some type of bias mod done not sure what.

Post picture, we'll tell you. Good tone is more than a bias



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Post subject: Re: New to vintage amps (kind of)
Posted: Mon Apr 02, 2018 12:14 pm
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Here are some pics of the '68

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Post subject: Re: New to vintage amps (kind of)
Posted: Mon Apr 02, 2018 12:16 pm
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Here are some pics of the '74 with atleast a bias mod I've been told.

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Post subject: Re: New to vintage amps (kind of)
Posted: Mon Apr 02, 2018 3:48 pm
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Nice amp all original except 4 filter caps . These are not the best part available but they do the job.

And no mod on bias circuit .


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Post subject: Re: New to vintage amps (kind of)
Posted: Mon Apr 02, 2018 7:52 pm
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Yeah, the first one, the '68 does look mostly untouched. It is a little noisy, I have been told to get the electrolitics checked. I will probably get all of the filter caps replaced as well. I believe that one is an AB165 circuit.

Now on the second set of pics, the '74, that bias pot looks different than what I have seen on schematics, that is the one I was told had a bias mod. that one sounds real good though, I was told it is an AA371 circuit.


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 03, 2018 12:08 am
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I reverted my 1968 Bassman back to AA864 circuit. I used Tone Lizard's site to do the fixing. Good to follow his cues, as circuitry gets inverted with all the local and global feedback mods, which Fender did to this amp.

I'd put some shrink-wrap insulation on that power transformer line (which is soldered). Looks kinda dangerous. :wink:

http://tone-lizard.com/bassman-mods/

http://thevintagesound.com/ffg/schem/ba ... _schem.gif

Before (AB165):

Image

After (AA864 bias supply, grid-to-ground 6L6GC, and PI anode plate resistors):

Image

Image


Last edited by BMW2002Ti on Tue Apr 03, 2018 12:13 am, edited 1 time in total.

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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 03, 2018 12:12 am
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AA864 PI tail and feedback:

Image

My doghouse caps & resistors:

Image

:)


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 03, 2018 12:54 am
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Jimbojo13 wrote:
Yeah, the first one, the '68 does look mostly untouched. It is a little noisy, I have been told to get the electrolitics checked. I will probably get all of the filter caps replaced as well. I believe that one is an AB165 circuit.

Now on the second set of pics, the '74, that bias pot looks different than what I have seen on schematics, that is the one I was told had a bias mod. that one sounds real good though, I was told it is an AA371 circuit.


It is all original circuit too .
CBS / Fender use sometimes in late Silverface amps a balance bias circuit. You can't adjust bias grid voltage .
You just can balance this voltage between the two output tubes, No need matched pair.
Easy to mod for a "standard" bias adjustment.

https://forums.fender.com/viewtopic.php?f=12&t=62833

Mods circuits here; Scroll 1/4 screen down;
https://robrobinette.com/Silverface_Amp ... as_Balance


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 03, 2018 4:03 pm
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Looks like that CT on the '68 power tranny got hot enough at one point to melt the original. (maybe a puffed 6L6 in the past) I'd definitely give that amp a tune up.

UN


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 03, 2018 4:13 pm
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Vintage amps; always check for the right fuse.

Over years some owner may put a too much powerfull fuse and do some damage to P.T.

New buyers may not think to check :(


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 03, 2018 8:09 pm
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Thanks Guys, lots if great tips. I am not running the '68 at this,point, gonna get it into a tech for sure. I hadn't even noticed that wire on the tranny and I am a damn electrician, Hahhahah. But, either way my goal,is to get the drip edge up to snuff and run it pretty much original. The '74 may get some more extensive mods, but I want the '68 solid before I start down that road.


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