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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 03, 2018 8:12 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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Post subject: Re: New to vintage amps (kind of)
Posted: Wed Apr 04, 2018 12:05 am
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Jimbojo13 wrote:
The '74 may get some more extensive mods...


If you carefully examine the AA371 schematic you'll notice that there is an unused half of a 7025 (V3) that can easily be adapted to function as a third gain stage for either channel or both, similar in layout to the 6G6-B circuit revision. Mod the bias supply to the traditional symmetric configuration and you'll have a nice ballsy guitar platform. Matched output tubes will be required of course.

Arjay

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"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


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Post subject: Re: New to vintage amps (kind of)
Posted: Wed Apr 04, 2018 1:10 am
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Those point to point amps are the most reliable amps made.
That is why there are a lots at 45 years old and more

Any tech can fix them easily on the road if needed, it would'nt happened


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Post subject: Re: New to vintage amps (kind of)
Posted: Wed Apr 04, 2018 7:58 pm
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Retroverbial wrote:
Jimbojo13 wrote:
The '74 may get some more extensive mods...


If you carefully examine the AA371 schematic you'll notice that there is an unused half of a 7025 (V3) that can easily be adapted to function as a third gain stage for either channel or both, similar in layout to the 6G6-B circuit revision. Mod the bias supply to the traditional symmetric configuration and you'll have a nice ballsy guitar platform. Matched output tubes will be required of course.

Arjay


That sounds like just the thing I might want to do. I wonder if that 3rd gain stage could be routed through the deep switch on the bass channel, what would I lose taking the wiring off that switch?

I will look at the schematic, if I can't figure it out may shoot you a PM.


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Post subject: Re: New to vintage amps (kind of)
Posted: Mon Apr 09, 2018 6:27 pm
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Just call me late to the party, both of these amps need cap jobs IMO.

The 68 has only some of the caps replaced in the doghouse, but not the bias or bypass caps, and one of the resistors in the doghouse looks "crispy".
Image

The other amp's filter caps show signs of dimpling, kind of look like there might be some leaking.
Image

Here's an example of what can happen when electrolytic caps go too long in a vintage amp.
Image

The Bassman 50 appears to be a 1975 according to the date code on the choke.
Image

The bias circuit has been modified by adding a trim pot and changing the 15k resistor to a 10k, allowing for some adjustment of bias, while keeping the balance pot adjustable as well.
Image

Just my 2₵ worth.

Bill


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 10, 2018 7:46 am
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vinyl wrote:
Just call me late to the party, both of these amps need cap jobs IMO.

The 68 has only some of the caps replaced in the doghouse, but not the bias or bypass caps, and one of the resistors in the doghouse looks "crispy".
Image

The other amp's filter caps show signs of dimpling, kind of look like there might be some leaking.
Image

Here's an example of what can happen when electrolytic caps go too long in a vintage amp.
Image

The Bassman 50 appears to be a 1975 according to the date code on the choke.
Image

The bias circuit has been modified by adding a trim pot and changing the 15k resistor to a 10k, allowing for some adjustment of bias, while keeping the balance pot adjustable as well.
Image

Just my 2₵ worth.

Bill


Thanks Bill,

I was wondering about the pot for sure and that was a good catch on the date I missed that one for sure.

My plan is to get the Drip Edge into a tech ASAP, I am not playing it right now. I don't know if you saw the picks of the transformer that looks like it got hot, but I am thinking it might need replaced as well as a full cap job.

The, '75 Bassman 50 will get some attention soon as well, I am thinking this one will be the one I mod more, leaving the "68 stock.

Thanks,

Jimbo


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 10, 2018 9:55 am
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Good to see I'm not the only one still using "Microsoft Paint". :lol:


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Post subject: Re: New to vintage amps (kind of)
Posted: Tue Apr 10, 2018 11:04 am
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Joined: Thu Dec 12, 2013 2:54 pm
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Busted!
:lol:


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