'68 Custom Deluxe Reverb Mod Question

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adamrobertt
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'68 Custom Deluxe Reverb Mod Question

Post by adamrobertt » Wed Aug 31, 2016 7:46 am

Hey there - I just got one of these amps and I love everything about it so far except for two issues I had with it when I got it. One, there was a fair amount of hum when the reverb was engaged. I fixed this by rotating the reverb tank 180 degrees as I had read online. Worked like a charm.

The second issue I'm having is that the amp is quite hissy, another issue which is pretty well discussed online. I understand that this is actually due to an intended design feature of the amp, where they changed a resistor value to give the amp less negative feedback and therefore make the amp more dynamically responsive.

That's a cool idea and all, but the hiss is really annoying to me. I understand that to change this to the '65 reissue specs, I only have to change R64 from a 1.5k ohm resistor to a 820k resistor. Is it that simple? I'm aware that this probably voids my warranty. Also, does the wattage of the resistor matter? Anyone ever try this mod?

I've done a similar mod to my Traynor YGM-3 where I clipped the bright cap to smooth it out, and I've built guitars and pedals so this isn't completely uncharted territory for me. I'm confident I could do it myself as long as I understand the mod correctly.

Thanks!

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OffYourFace
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Re: '68 Custom Deluxe Reverb Mod Question

Post by OffYourFace » Thu Sep 01, 2016 11:34 pm

don't use a 820k resistor.
use a 820 Ohm resistor ;)
1/2 watt should be the size.

it all depends how accessible that resistor is... I've been thinking about doing this to my 68 Princeton.

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sookwinder
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Re: '68 Custom Deluxe Reverb Mod Question

Post by sookwinder » Fri Sep 02, 2016 12:13 am

I would go on more step and add in a toggle switch (that you could mount on the bottom of the chassis and accessible from the rear opening) and that can be used to turn the NFB on or off (in or out).
I have that on all my home designs and use it quite often
relaxing alternative to doing actual work ...

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adamrobertt
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Re: '68 Custom Deluxe Reverb Mod Question

Post by adamrobertt » Fri Sep 02, 2016 3:50 pm

OffYourFace wrote:don't use a 820k resistor.
use a 820 Ohm resistor
1/2 watt should be the size.

it all depends how accessible that resistor is... I've been thinking about doing this to my 68 Princeton.
Thanks for setting me straight! I've seen photos of the circuit board and it looks pretty easy to get to. I haven't opened mine up yet though.

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adamrobertt
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Re: '68 Custom Deluxe Reverb Mod Question

Post by adamrobertt » Fri Sep 02, 2016 3:50 pm

sookwinder wrote:I would go on more step and add in a toggle switch (that you could mount on the bottom of the chassis and accessible from the rear opening) and that can be used to turn the NFB on or off (in or out).
I have that on all my home designs and use it quite often
Is this easy to do? Sounds kinda complicated but I'm not an expert

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