FHR Deluxe Circuit Mods

Fender Hot Rod Deluxe Mods            Rev 7/17/13

(Done on Nick Mondy’s Amps)

1)    Upgrade Speaker if desired. My personal preference is the Celestion V30. (This requires removing the amp chassis from the cabinet).

2)    New JJ 6L6 Power Tubes  (bias at 67mA).

3)    Upgrade speaker cable. (Use 16, 14, or 12 gauge cable).

4)    Hot Glue flex cables to circuit board before bending circuit board out to access solder side of PC board

5)    Reflow all solder joints on both circuit boards.

6)    Replace 47uf cap, C31 power supply filter cap with a 100uf, 500V. (You can also add a 2^nd 100uf Cap in C32. Be sure to insert a jumper across R70).

7)    Replace all C5 & C6 Tone caps with Sprague “Orange Drop” type, same values. C7 use Silver Mica cap:

     a) C5 – Bass: .1uf, 400V
     b) C6 – Mids: .022uf, 400V
     c) C7 – Treb: 250pf, 400V

8)    Replace all four - 100K plate resistors with Carbon Compound, 1W. (R4, R11, R16, R22).

9)    Replace 130K Tone slope resistor (R12) to 68K. (Makes tone controls more dynamic).

10) Replace 390pf C11 with a 50pf. (Allows more high’s thru the Drive/More Drive Channels).

11)  Replace cap C23 (1.5nf) with.0022uf Orange Drop cap.  (Improves Bass response in Drive/More Drive channels).

12) Replace C18 (.022uf) with .022uf – 400v Orange Drop cap. (Adds highs to More Drive Channel).

13) Replace C2 (.047uf) with .022uf -400v Orange Drop cap. (Adds just a little more highs to both Drive Channels).

14) Replace C3 (250pf) with 82pf -1Kv. (Adds highs to Drive Channel).

15) Replace cap C8 (1uf) with 22uf. (Overall tone of More Drive channel is less harsh).

16) Replace C9 (22uf) with 1uf - 100v. (Decreases slightly the amount of volume difference when switching between the Drive/More Drive Channels. Lessens the ”bite” of the More Drive channel).

17) Replace C10 (.047uf) with .022uf -400v Orange Drop cap. (Just sounds a little better in both Drive Channels).

18) Replace C33, C35, & C36, the three 22uf power supply filter caps with 40-47uf, 500V caps (Original caps are cheap, and I’ve seen them leak).

19) Clip R103 at either end, and lift it up, and leave it so that it doesn’t touch anything. (Reverb mod:  Makes reverb much warmer and fuller sounding).

20) Check R78 & R79. 470 ohm 16V power supply resistors. (Replace if necessary). Re-mount the resistors up, off the PC board a little to allow for some air flow underneath.

21) Replace Volume pot (R6, 250K) with 1M ohm. Replace Master (R26, 100K) pot with the 250K pot removed from the Volume control.  (Better volume adjustment for Clean & Drive channels).

22) Add Volume & Drive pot treble bypass Caps (Silver Mica). Volume pot=220pf. Drive pot=50pf.

23) Upgrade 6L6 bias 470 ohm resistors to 2W or 5W. (R61 & R62).

24) (Optional) May want to add 3/8 A pico fuses to 6L6 bias trace on tube PC board. Tube Pin#4. This will keep a runaway bias tube failure from frying the 470 ohm resistors on the tube PC board. So, you end up replacing the fuse, instead of a fried resistor, which also fry’s the PC board.

25) Add Snubber circuit to tube PC board. (http://www.guitarplayer.com/article/smooth-your-sonic-ride/5505 )

     a) (Qty=2 of each: [1.5K, 5W]; [8.2M, 1W]; [.01uf, 600V], Orange Drop caps).

26) Be sure to vacuum all the junk out of the bottom of the cassis after all of your mods & rework. You’ll need to get way back in there, under the tube socket PC board.

27) Reinstall and mount the PC boards back into position.

28) Check all of the Flex cable connections on the PC board. All of the flexing from removing and remounting the PC boards can stress the little solder pads on the PC boards. Gently wiggle each flex cable lead on the tube PC board to make sure the solder pad is not just hanging in mid air, broken loose from the PC board. Fix if needed.

29) Redress Power wires harness.

30) Hot Glue large capacitor(s) C31 (and C32, if added) to circuit board (and each other). Also, any additional components you want to stabilize.

PARTS LIST

Description                                                      Qty          Description                                               Qty

100uf Cap (Replace C31. Add C32)             1 or 2     220pf Cap (Vol treble bypass)                         1

.022uf, Org Drp 400v Cap (C2, C6, C10 & C18) 4          22uf, 100V Cap (C8)                                      1

82pf, 1Kv Ceramic Disc (C3)                          1          250pf Cap, 500V (C7)             (Silver Mica)   1

.1uf, Org Drp 400v Cap (C5)                          1          22uf, 500V Cap           (C33, C35, & C36)     3

.0022uf, 400V (C23)                                       1          68K ohm, ½ W (R12)                                     1

50pf Cap (Drive treble bypass)                        1          470 ohm, 2W or 5W    (R61 & R62)              2

100K ohm, 1W (Carb Comp, R4, 11, 16, 22) 4         1M ohm Volume pot   (R6)                              1

470 ohm, 5W  (R78 & R79, if needed)           2          V2 = JJ - 12DW7                                            1

Snubber Ciruit :

Description                                                      Qty      Description                                                      Qty

.1uf, 400V (Orange Drop)                               2          1.5K ohm, 5W                                                 2

8.2M ohm, 1W                                                2

My Tubes:

I am currently using the following tubes, and I’m happy with the tone & the overall performance of the amp for gigging.  By using a 12DW7 in v2, the Drive/More Drive channels are definitely more pleasing and usable over the stock amp. That tube helps tame some of the horrible gain increase when switching from the Clean channel to More Drive, also.

v1 = GT 12AX7          v2 = JJ  12DW7            v3 = Mullard  12AX7A             v4 & 5 = JJ  6L6

INFO About Tubes:

1) Keep the 12AX7’s in V1& V3, and use a 12AT7 in V2. Considering V1 will shape the tone and give some gain, V2 will help tame the drive channel some (very nice), and give more clean, and V3 drives the phase inverter to the output tubes.

2) V1 is going to shape the tone the most. V2 is less important for tone shaping but will affect it some. It can help with more clean with a lower gain tube here, and half is used only for the drive channel. V3 (phase inverter) has little or no affect on tone, but can add to the clean using a lower gain tube there also.

3) V2 - middle small tube - install a good quality 12DW7 - this tube is a 12AX7 on one side and a 12AU7 on the other side. The 12AU7 side is the side of the tube that handles the Drive and More Drive sections. 12AU7 has less gain and will tame the over the top buzzy sound and make it creamy smooth.

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Some HRD III Mods for Tone  (from -steveneddy off the web)

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I also bought a HRD III in 2011. Nice amp with most of the mods already taken care of for this stock version.       But I still felt the Drive and More Drive sections were lacking. Too buzzy. Here are some changes you can make to all year models of this amp to wake it up.

First - I tell every tube amp owner to simply try some different tubes. My choices for THIS amp and for the HR Deville are:

V1 - looking at the back of the amp this will be on your right - one of the little tubes - install a Mullard ECC83 in this position. This mainly handles your clean channel and will make the tone better and well defined.

V2 - middle small tube - install a good quality 12DW7 - this tube is a 12AX7 on one side and a 12AU7 on the other side. The 12AU7 side is the side of the tube that handles the Drive and More Drive sections. 12AU7 has less gain and will tame the over the top buzzy sound and make it creamy smooth.

V3 - the left little tube if looking at the rear of the amp. this is called the Phase Inverter. It sends the signal to the power tubes. You want this tube to send a smooth and powerful signal to the power tubes. Install a 12ax7LPS in this slot. Your power tubes will be happy.

My choices for power tubes in the HRD III are:

* Sovtek 5881WXT - creamy smooth and a very nice break up when the amp reaches about 8 on either the clean or dirty channels. With these tubes and high volumes you can use the clean channel only and use the volume on the guitar to get varying degrees of distortion and overdrive, from clean to nasty and dirty.

* Tungsol 6L6-G - very sweet - very loud - added dynamics at high volumes. Much larger than 6L6's, so get the spring keepers that hold the tube down into the sockets because these are much taller and the bases will not work well with the stock bear clamp keeper. Clean, kinda, up to 8, then all Hell breaks loose! One of my favs. This tube sounds almost like the Sovtek 6L6WXT+ - but this tube is much warmer and dynamic.

* Gold Lion KT66 - the golden tubes of clean goodness! These tubes are AWESOME in a HRD III! These tubes will turn your box into a different amp altogether. The tonal range is so huge with these tubes - the crystal Fender highs mixed with your new preamp tubes make this amp sing! And if you have added the preamp tubes mantioned above with these tubes you will get the dirty sounds of Rock-n-Roll, baby! Some people may feel that an extra 6.3v, 6ma transformer needs to be added to the HRD III because the KT66 tube does draw more amperage than a 6L6 tube.

** Power tube changes REQUIRE a bias adjust be performed with EACH power tube change. If you cannot perform this tack, take your amp to a well qualified technician. **

-steveneddy ******************************************************************************************************************