Must do mods for a Hot Rod Deluxe or Deville !

Ken Fox · Post by **Ken Fox** » 3 Dec 2006 8:53 am

The overwhelming bass in these amps is a huge issue. For a long time I thought it was the choice of speaker! Not at all, it was the departure from the traditional values used in the tone stack. I checked the mods before hand on the Duncan Tone Stack calculator and could see the difference was going to be very significant.

I did the following to a Hot Rod Deluxe and the results were astounding! Sounds like an old Blackface era amp to my ear now. No more boomy bass!!!

1- "changing the bass cap (C5) to .022uF, changing the treble cap (C7) to 500pF, silver mica, and changing the slope resistor (R12) from 130K to 56K."

2- "The Mid control on this amp is a 25kA pot. (“A” stands for audio taper). Thus, the stock circuit in this amp puts 25,000 ohms at all times between the bottom of the bass control and ground. On vintage Fenders without a mid control, the resistor in its place was usually only 6.8k. On models with a mid control, such as the Twin Reverb, the pot was only 10k, so even with the mid turned up all the way, it didn’t have the same low-end response as the stock circuit in this HR Deluxe. The larger the value of this midrange resistor, the more bass and low-mid the amp has, regardless of the setting of the bass control.

Have you ever seen a “Loudness” switch on an older stereo? The Loudness circuit boosts the bass and treble and is intended for low-volume situations to compensate for the fact that the human ear hears midrange frequencies (where most speech resides) more acutely at low levels than deep lows or high trebles. As volume increases, this effect reduces. If you play a stereo at high volume with the Loudness switch engaged, it can sound flabby because the bass frequencies are now over-amplified for our ears. This is precisely what’s happening with this Fender HR Deluxe. It sounds great at low levels, but the bass overwhelms the tone at higher volumes.
Justin's comments: Instead of using wire I took a small piece of solder and melted it into place. This creates a very unobtrusive jumper that's easy to remove. Be sure to test your jumper with an ohm meter to make sure it passes current.

Fixing this takes very little effort:

Follow steps 1 and 2 above. Solder a jumper between the left and middle terminals of the mid control (when facing the amp from the rear, as you would be when working on it). That’s it. You can now reverse steps 1 and 2 and try it out. If you did it right, you should now be able to turn your volume down to 0 by turning all of your tone controls to 0. More importantly, you can now dial in just the right amount of low end with the mid and Bass controls. Remember, they’re interactive. The higher you set the mid control, the more bass you will get."

link to web site: http://studentweb.eku.edu/justin_holton/jvmods.html#bass

Other changes I ahve made to many of these amps is to replace teh input jacks with Switchcraft shorting jacks, the real deal!

Also the false channel switching is these amps is due to overheating of resistors in the + and - 16 volts supplies. The resistor change out and jacks mods can be fopund onthe same website.[This message was edited by Ken Fox on 03 December 2006 at 08:57 AM.][This message was edited by Ken Fox on 03 December 2006 at 08:58 AM.]

Ron Randall · Post by **Ron Randall** » 3 Dec 2006 7:26 pm

Ken,
Would this include the Fender Blues Deluxe?

Thanks,

Ron

Ken Fox · Post by **Ken Fox** » 4 Dec 2006 5:46 am

I just looked a the schematic for the Blues Deluxe and yes it would, but refer to the schematic as the part numbers are different.

Michael Johnstone · Post by **Michael Johnstone** » 4 Dec 2006 7:33 am

Another great mod which I had done to my Blues DeVille is to replace the power tubes with 6550s. Of course then you have transformer issues which in my case were resolved by adding a second small transformer - just to heat the power tubes.Now I have headroom for days.Another useful mod is to have adjustable bias instead of fixed. The really slick way to do it is to be able to bias each tube independently so the power tubes don't have to match. Bob Metzger did the mods BTW.

Ken Fox · Post by **Ken Fox** » 4 Dec 2006 7:49 am

I agree, the adjustable bias is a great idea on the older Blues Deluxe and Deville. Fortunately they changed that on the Hot Rod Series to an adjustable bias.

The Deville series has a lot more headroom, even though it is a 2-6L6GC amp. They ran the plate voltages hotter to get more power. A good choice if you need less distortion/early break-up in the sound.

Papa Joe Pollick · Post by **Papa Joe Pollick** » 4 Dec 2006 7:59 am

As usual,Ken Fox comes through again.Thanks for the heads up.PJ

Michael Brebes · Post by **Michael Brebes** » 4 Dec 2006 10:19 am

Most pots I've seen, the A is linear taper and B is log taper. I have a linear pot in mine. The tone stack values are more in line with the Fender Tweed era values. It really comes down to what your preference is. With the Mid pot, it just means that the range 1-5 of 12 is the same as the Blackface values. I actually like the option of more bass. The original speaker on my Blues Deluxe was a dog and the amp sounded much better with an EV12L or Celestion V30. Also put Winged C EL34's in and changed the bias, which brought the amp to life.

Ken Fox · Post by **Ken Fox** » 4 Dec 2006 11:18 am

Not all true about the 25K mid pot. Try it on the Duncan tone stack calculator, the 10K makes a big difference. By shorting the section of the pot out you get a 12.5K pot.

Mitch Druckman · Post by **Mitch Druckman** » 4 Dec 2006 4:15 pm

I'd love to hear from someone who has performed the mod on a Blues Deluxe.

I can't help but wonder if it would be the same kind of improvement as on a Hot Rod. I haven't experienced the heavy bass on my Blues Deluxe like I have on a Hot Rod Deluxe or Deville. I'd be afraid that it might thin out the tone of the Blues Deluxe even more than it already is.

Ken Fox · Post by **Ken Fox** » 4 Dec 2006 4:55 pm

I had a Blues Deluxe and found the tone very bassey. If yours is not I suspect you have Chinese preamp tubes! They take bass out in big bites!

The tone stack in the Blue Deluxe is identical to theh Hot Rod with exception that the slope reisitor is 100K (conventional Fender) not 125K.

The mid pot is the still a 25K. Traditional Fender tone stack was 10K. The mod makes it a 12.5 K.

[This message was edited by Ken Fox on 04 December 2006 at 04:55 PM.]

Michael Brebes · Post by **Michael Brebes** » 5 Dec 2006 9:21 am

I agree that the jumper across the Mid pot does help. Forgot that I did that also. It puts it back to Fender Blackface and late Tweed type circuits. Otherwise it will slightly increase bass as you drop the mids.

Al Moss · Post by **Al Moss** » 7 Dec 2006 5:46 pm

How much bass is left after the mod has been installed? Is it enough, or, more than enough, to cover the needs of the pedal steel? It's the mids in this amp that I usually have to battle to sweeten out the tone.

Ken Fox · Post by **Ken Fox** » 8 Dec 2006 6:26 am

Plenty of bass is left. The bass was alway too dominant in the amps. Now you can control it!

Al Moss · Post by **Al Moss** » 8 Dec 2006 7:37 am

-read with interest through the HR Deluxe/Deville site. There's a reverb mod on there that looks very useful also. Clips a low volume/high end boost from the reverb circuit. The sound of the reverb has always seemed "chirpy" to me, especially at low volume or practice levels. Maybe this is why. http://studentweb.eku.edu/justin_holton/reverb.html#dallman

Ken Fox · Post by **Ken Fox** » 9 Dec 2006 7:08 am

I have done three of these amps this week! All customers were very pleased with the tone mod.

Lowering the boomy bass adds more headroom for the mids and highs. It makes the amp feel far more powerful than prior to the mod.

Al Moss · Post by **Al Moss** » 9 Jan 2007 1:10 pm

Ken,
Were the mods that you've done, installed on a Deluxe or a Deville? ...and... does it make any difference anyway? I have my Deville in the shop at the moment for a checkup on the bias and I'm going to have the reverb mod done to it also. So, I was thinking that while it was there it might be a nice time to do the mid shift mod too. Any thoughts?