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Post subject: question about aa270 layout
Posted: Mon Oct 24, 2011 9:47 am
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I took the chassie out to get ready to install the 1 ohm resistor and noticed a .002 k cap going from pin 5 to pin 8. I looked at the schematic and I can't see where anything is going to pin 8? If there is anything I can undo that would improve the sound I would. Arjay what you say?? Image[img]http://i840.photobucket.com/albums/zz326/freebird186/[IMG]http://i840.photobucket.com/albums/zz326/freebird186/aa270-3.jpg[/img]aa270-2.jpg[/IMG]


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 9:57 am
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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 10:02 am
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Image sorry about the picture size.


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 10:09 am
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Pardon the intrusion, that 220 pico-farad ceramic cap is going between the grid-and-ground, as part of a filter circuit with the 1500-ohm grid stopper resistor to help stabilize the amp. In theory the cap, helps filter out unstable oscillations-induced frequencies.

In general, the basic parameters or the desired tonal shaping of the amp may also have changed. The early 1970s saw some interesting circuit modification from Fender.

http://www.freeinfosociety.com/electron ... php?id=918


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 10:27 am
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BMW, hay man you know its no problem. I hold your opinions in high regard as well. I'm just a truck driver trying my best to understand what I can. I still say its not on the schematic. But Its still like chines to me. lol. I think as much as love old tube amps I should take one of those week long corses on how to build one from scratch.


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 1:18 pm
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BMW2002Ti wrote:
Pardon the intrusion, that 220 pico-farad ceramic cap is going between the grid-and-ground, as part of a filter circuit with the 1500-ohm grid stopper resistor to help stabilize the amp. In theory the cap, helps filter out unstable oscillations-induced frequencies.


Correct -- it's an isolation cap. Some AA270's had these caps installed -- others, not. I would leave it in situ, barring any suspected issues.

HTH

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: question about aa270 layout
Posted: Mon Oct 24, 2011 2:20 pm
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I'm wondering if all components look stock. Other than the trim pot I installed. I guess I should get around to removeing the death cap although I never move the switch, someone else could mess with it with out me knowing it. Any links to show how.


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 2:34 pm
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Everything seems to look pretty copacetic.

Do you have a grounded 3-conductor power cable correctly installed?

Arjay

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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 2:41 pm
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Retroverbial wrote:
Everything seems to look pretty copacetic.

Do you have a grounded 3-conductor power cable correctly installed?

Arjay

Yes ! I'm waiting on the 1 ohm resistors to come in. Looks like the old game of operation. Not much room to manuever a soldering iron in there.


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 2:47 pm
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Unplug the amp, ground the death cap (if charged, it will drain and be safe to handle), then either disconnect the lead that runs to the center terminal lug of the polarity switch or remove the cap altogether. I prefer leaving the cap in a chassis to preserve the amp's visual vibe but it can be excised altogether if desired.

HTH

Arjay

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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 3:02 pm
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Like BMW said this 220 pf capacitor is a filter because the poor wire dress in most amps of CBS area. This poor lead dress can act like antenna and produce parasitic oscillation

You can remove it and see if your amp have some parasitic oscillation.

Anyway those amp are very good amp


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 3:41 pm
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stratele52 wrote:
Like BMW said this 220 pf capacitor is a filter because the poor wire dress in most amps of CBS area. This poor lead dress can act like antenna and produce parasitic oscillation

You can remove it and see if your amp have some parasitic oscillation.

Anyway those amp are very good amp

Everyone thought it was cool that my amp was picking up a radio signal at the last jam session. Everyone except me. If removeing the caps could possably make that worse then they will not be removed.


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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 3:53 pm
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bluestrucker wrote:
Everyone thought it was cool that my amp was picking up a radio signal at the last jam session. Everyone except me. If removeing the caps could possably make that worse then they will not be removed.


Definitely not a good thing!

:shock:

Arjay

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Post subject: Re: question about aa270 layout
Posted: Mon Oct 24, 2011 7:11 pm
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I picked up a Canadian radio station one night on a Marshall amp I owned in the '70s. :lol:


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Post subject: Re: question about aa270 layout
Posted: Tue Oct 25, 2011 1:53 am
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Everyone thought it was cool that my amp was picking up a radio signal at the last jam session. Everyone except me. If removeing the caps could possably make that worse then they will not be removed. __Bluestrucker

On don't think capacitor is there to removing some radio signal. It is another problem from bad wiring.
I have an amp of this area and I shortened all wire , like Blackface . I remove the capacitor too.


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