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Post subject: Re: 65 Pro Reverb Hiss
Posted: Sun Dec 29, 2013 10:57 pm
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The word "prophylactic" has never once entered my mind when looking at that old amp. That's a piece of advice I won't soon forget. :) Thanks Arjay.


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Post subject: Re: 65 Pro Reverb Hiss
Posted: Sun Dec 29, 2013 11:54 pm
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Randy, Arjay has the deal down. If it's a player, go for the 470 ohm 1watt metal oxide screen resistors on the power tube sockets. The 1500 ohm 1/2watt resistors on the sockets can either be carbon comp or carbon film(your call). As far as the plate load 100K ohm resistors goes, there's three on each pre amp tube(channel) and two for the reverb. They are easily located, if you look at the layout diagram for this amp. They are situated just north of each tube(V-1,V-2,and V-3 & V-4). Now, I will say that these guys can be worth the R&R, but it's not always necessary. Just saying! Art

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Post subject: Re: 65 Pro Reverb Hiss
Posted: Sun Dec 29, 2013 11:55 pm
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"Prophylactic: A preventive measure. The word comes from the Greek for "an advance guard," an apt term for a measure taken to fend off a disease or another unwanted consequence."

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: 65 Pro Reverb Hiss
Posted: Mon Dec 30, 2013 2:29 am
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If you are interested in original AB carbon comps, in the signal section:

http://www.partsconnexion.com/resistors ... _watt.html

As Arjay stated: Metal-oxide, fire resistant resistors for the screen grids & grid stoppers. Also, in the main power rail (resistors under the doghouse) and bias supply.


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Post subject: Re: 65 Pro Reverb Hiss
Posted: Mon Dec 30, 2013 3:08 am
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aclempoppi wrote:
Louis, I got to say, the noisy plate load resistors that I have run across, exhibit the snap-crackle-pop sound(arcing). Never got the hiss from them. I'm thinkin' a tube is the culprit. Possibly dirty tube sockets or an outside chance that a grid wire or such is picking up noise. But, you just never can tell :oops: JMO, Art



I often had hiss from these resistors. Hiss is sometimes very subtle and the notes after replacing the resistance how the amplifier is quiet.

A defect can have several causes, I agree with you , we just never can tell.


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Post subject: Re: 65 Pro Reverb Hiss
Posted: Mon Dec 30, 2013 7:05 pm
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Great info, Louis!!! Never thought of those resistors as a source of hiss. I'll definitely, keep that in mind. And Beemer, you're spot on about the metal oxide resistors. They are superior for the heat and stability aspects. It's just that some times, folks want that "old school" carbon comp in the signal chain(grid stopper). Art

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Post subject: Re: 65 Pro Reverb Hiss
Posted: Mon Dec 30, 2013 9:33 pm
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Some ppl no like all metal-oxide, because of wider bandwidth compared to carbon comp. All other characteristics are superior (drift and heat-resistance).

Anyhoo... I've made a couple of DIY (Deluxe Tweed & Princeton clone) with 100% metal oxide and wire-wound resistors and the amps sounded fine. Tubes, coupling caps, and speakers prolly play a bigger role in overall tone, than resistors.


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Post subject: Re: 65 Pro Reverb Hiss
Posted: Mon Dec 30, 2013 10:00 pm
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BMW2002Ti wrote:
Tubes, coupling caps, and speakers prolly play a bigger role in overall tone, than resistors.


+1000

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: 65 Pro Reverb Hiss
Posted: Mon Dec 30, 2013 10:21 pm
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For sure, Steve !!! Resistors are way low on the sonic totempole. Kind of like the use of stranded, solid core, and silver clad wire. It's all cool !!! Art

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