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Dumble mods to the Fender AB763?

7/6/2000 5:24 PM
Dumble mods to the Fender AB763?
I wanted to get any input on any one that has done the Dumble channel mods to the fender twin reverb AB763 and to see what they thought about the sound after they did this mod? Looking at the schem for these mods the feedback loop fromn the anode to the grid looks like it would help keep the channel cleaner at higher volume but Im not sure about the tone stack? Thanks.
7/7/2000 12:57 PM

I did the "cool mod" from Steve Ahola's site. Here is the address:  
I used the mod with the 3 way switch on the feedback loop to switch in different resistors in the circuit. I was working with a 69 SR that is blackfaced. I added the middle control and reverb to the normal side. I like the sound a lot. Real clean, doesn't mush out at 9 and 10. This mod IMHO is great for playing out. Main reason is that the amp doesn't really respond until you are above 3 or 4. After that it really comes to life and honks. I left the vibrato side alone so I still have that classic SR tone. As a matter of fact, if I put the 3 way switch in the middle position on the feedback loop I have the same thing. You have to turn up your bass more to get a lower end than you normally would without the mod to the tone stack but I think that Fenders have way too much bass anyway and the 5uf cap makes it more controllable. This is one of my fave mods. I did a 77 vibrolux reverb the same way. Everyone knows how those amps suck with the pull boost and all. The VR was the first one I did and I used a 2 way switch. So in order to get that classic VR sound I have to plug in to the vibrato side on that one. I was going to get rid of that amp but decided to make it a project amp. I got rid of all the CBS trash in there and with the blackfacing and cool mod along with a nice set of 66 jensen c10q's this is one of my favorite amps. This amp also has the mid control mounted in the #2 hole of the normal side. Hope all this helps. If you have any more questions ask Steve. He is willing to help you along with any problems you might have. I say go for it!! You'll like it.  
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7/7/2000 1:00 PM
Steve A?
Whats wrong with your link. I just clicked on it to check that it was working and it doesn't.  
7/7/2000 6:03 PM
Re: Dumble mods to the Fender AB763?
Hi MJ,  
Steve had written on a post to me about it before and I was trying to get an Idea if any one elso had done the mod also. I trust steve as he seems to know what he is doing with amps. I will probably do this mod to a fender bassman first. I am from the rock style school and not the Larry Carlton school even though I dig Larrys playing. A dumble seemed to be something new and different to try for one of my amps. Who knows, It might just steer me to the more jazz/ rock side of the fence if I like it:)  
Thanks for the post.  
7/7/2000 2:17 PM
Bare Re: mods to the Fender AB763?
Did you notice that on the 'vintage' section there are postings claiming that the current vaue of a Reverb (BF though) are upwards of $1600. I certainly would think twice about installing a sqiggly retarded mess wiring mod into my amp if it was worth that many $. Just my thought.
7/8/2000 5:29 PM
Steve Ahola

... a squiggly retarded mess wiring mod...  
    I was just wondering if you have looked at the drawings? The only change to the eyelet board would be with the tone caps; as for the tone stack, carefully desolder the original tone stack, volume control and bright switch and save them in a baggie. If you really wanted to add the mid control you could pull out the original input jacks and use the #2 jack for the volume control. I would recommend using push-pull pots to add in some of the switches (definitely the rock/jazz and mid boost; without the OD stages the P.A.Boost and Deep switches are optional). All of this is reversible if you wanted to restore the amp to the original circuit later. I have good reason to believe that H.A.D. did mods very similar to this for some of his customers  
    Now if someone were to try to add in the two OD stages I'd agree with you completely about it being a "squiggly mess wiring mod"... :D  
    Here is a link to the drawings:  
    As for a "squiggly mess wiring mod" here is a pic of the SF bassman head I converted into an ODS (*NOT* recommended for a valuable collectable amp!):  
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    Thanks for your post!  
Steve Ahola
7/8/2000 5:42 PM

Steve, Cool Pics, hows the amp sound? Ive got a bassman Ill do the same to. Thanks.
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