Can I use an Orange Drop (non-polarized) in place of an electrolytic polarized cap?

[Panther35]

Here is the scenario:

I'm wanting to replace the C1 cap in a Fender Hot Rod Deluxe (it's originally a 47uf 16v polarized axial miniature electrolytic; right off the V1 12AX7 tube, #3 pin) with a .068uf cap... based on some good info I've heard about the resulting tone. Apparently the 47uf in the C1 position is serious overkill (I can post a link to a schematic if needed). In looking for a replacement, I'm having trouble finding a polarized capacitor in that range, either voltage or capacitance... I even looked for mica caps in that range with no success. I'm considering using a Sprague Orange Drop .068uf 200v in it's place... is that going to create problems?

Along the same vein, is using a much higher voltage rating in capacitor mods a bad idea? Obviously I wouldn't want to go lower, but can going higher affect tone or have any adverse effects?

[Jazz P Bass]

I would have to say that the 47uf/16 volt cap will pass all frequencies to the next stage.
That is called a bypass capacitor by the way.
If you are looking to cut back on the low frequencies, then lowering the value would help.
If it were mine to do, I would try a 25, 15, 10 & 4.7uf cap.
(Any lower & it won't be a Fender amp)
One at a time.
The voltage rating has nothing to do with tone.
25 volt has been the standard since Leo.
Maybe the 16v's cost less (damn been counters)
Marshall has used a .047 cap on the first stage.
It is non-polarized.
It passes very little bass.

[Sweetfinger]

Your only problem might be the physical size of the film/foil cap. Even at a low voltage rating and much lower capacitance it is probably going to be larger than the electrolytic.

[J M Fahey]

based on some good info I've heard about the resulting tone.

And the resulting new sound would be?
What´s the claimed effect after that mod?
Just curious.

[Jazz P Bass]

"Thin" for sure

[imaradiostar]

Maybe the OP meant .68uf a la Marshall? That would be a useful mod.

I always thought the HRD was ripe for mods. This one makes sense to me.

jamie

[big_teee]

Mojo sells a 25uf bipolar that should work good.
Mojo Capacitors » TAD 25uF @ 25V Bipolar
I am going to try some different ones on my amp.
You could switch them in and out.
The ValveWizard has a whole area on bypass caps.
full and partial bypass.
You can download and read it free.
http://valvewizard1.webs.com/Common_Gain_Stage.pdf
Starts on page 25.
T

[Panther35]

It was actually from an old post on blueguitar.org forum, as follows:

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Steve Ahola

P.S. Looking at the HRD schematic, there are a lot of tricks you could try. I think that the 47uF Ck cap on the first preamp stage is a bit high; if you can add a switch somewhere, I'd wire it so that you could have 22uF, 0uF, or 0.68uF. The 1.5nF cap that splits the signal between the two channels could be replaced with something like a 0.01uF or 0.022uF Orange Drop for a fuller and stronger sound. For the second preamp stage, get rid of the "bright" cap on the cathode and stick in something like a 0.68uF or 1.0uF mylar cap (hard wiring the switch to ground so that it would be active in the OD mode). If that gives you too much gain, try inserting a 470 to 4k7 resistor between the Ck cap and ground. The tone stack looks a bit bit unusual- I'd try BF-ing it with a smaller slope resistor (like 82k or maybe even 68k) and possibly raise the treble cap to a 330pF mica cap. I like changing out the bass and mid caps with a high quality cap like a Sprague Orange Drop; you might try changing them both to 0.022uF or 0.033uF. The 390pF "bright" cap on the MV looks a bit excessive- you might try something smaller like a 47pF. (I have to pass on the "More Drive" circuitry with the two FETS's; I don't have any idea what that is supposed to do.)

Good luck!
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Re: HR Deluxe schematic on-line!
Thu Mar 25 15:20 in reply to Steve A.
Tom

Steve:

Thanks for the Schem., anyway, last night I couldn’t resist the temptation, so I started fooling around with this thing and here’s the rundown: I replaced the 47uF cap on the first preamp stage with a .68uF. I replaced all coupling caps outright with orange drops of the same value. I replaced plate (100K) and input grid (68K) resistors with carbon comps of same value. On the tone stack I replaced the treble cap to silver mica 470pF, replaced bass and treble caps to .022 orange drops and the slope resistor to 68K (really wanted 56K but didn’t have one). In the PI and power amp I replaced all the ‘stock mylars” with Sprague orange drops, as well.

Well, I think I’ve improved the overdrive tone a whole lot. The tone got warmer and it has more definition at low AND high volume. That 47uF Kcap was definitely overkill - especially in drive mode. I’m going back in tonight to tweak a bit more. I’ll experiment with the 1.5nF off the 1st stage plate and the 390pF on the Mst Vol. as you suggested. I’ll post the results after I’m done.

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Thanks to advice from Jazz P Bass above, I ended up using a 10uf electroclytic Sprague (which is down from the stock 47uf). I didn't want to go too extreme and lose my Fender sound. I believe the .68uf is from the Marshall idea. Anyway, I've replaced all my power caps and did a couple of other mods including that one... sounds outstanding.

I've only come across one issue with the following mod:


1. Unsolder and remove C11 (this is right next to the Master control, a 390pf cap). Obtain a good quality 50k to 100k pot.

2. Obtain a decent quality .01uF cap. It doesn’t need a high voltage rating. I used a 50V Mylar cap. Use anything but a ceramic type; they aren ’t very good for audio applications. They are only used in amps like this one because they are cheap. It’s rare to find ceramic caps in high-end amplifiers. Trim the cap’s leads to about ½ inch and solder one lead to the middle terminal of your new control. Solder a 3-inch jumper wire to the other lead of the cap. I recommend shrink tubing over this connection. Hold the new control with the shaft towards you and the terminals facing up. The terminal on the right needs a 3-inch jumper wire soldered to it. Solder the other end of this jumper to the right side hole where C11 used to be. Solder the lead attached to the cap to C11’s other hole. The third terminal of your control is not used in this circuit.

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It sounds great and works as intended in the lower range of the pot, but when I get up beyond the halfway point, I get a high pitched squeal. I'm curious as to why he recommends taking the value from 390pf to a .01uf and if that may possibly be a typo. My temptation is to go back in and replace his .01uf cap with something more like a 500pf or 1000pf. From doing some research, I understand that the C3 cap (a 250pf/1Kv cap right off of V1A) is there specifically to avoid this high pitch squeal when the amp is in "drive" mode (which is when I get the squeal). So, the only thing I did with the C3 was to replace the stock ceramic cap with a mica cap which was close to the same value (220pf/500v... didn't think I really needed 1kv, and I had the 500v close at hand). Again, my hunch is to reduce that C11 cap value and see if the squeal is tamed.

Am I on the right track?

[JoeM]

What is it exactly you want to do with this amp? I.e. do you want to trim the bass? less bright? If you can describe your goals, someone here may be better able to recommend some specific mods. There's a ton of stuff out on the Web, most is very subjective, but I dont recommend modding an amp just for moddings sake.

Personally, I've always felt the best sonic improvement in many cases is a speaker upgrade.

[Panther35]

What is it exactly you want to do with this amp? I.e. do you want to trim the bass? less bright? If you can describe your goals, someone here may be better able to recommend some specific mods. There's a ton of stuff out on the Web, most is very subjective, but I dont recommend modding an amp just for moddings sake.

Personally, I've always felt the best sonic improvement in many cases is a speaker upgrade.

I agree, I changed out my speaker a few years ago and am quite happy with that. I've actually gotten to where I want to be with the mods I just did. Of course the power caps were just routine, but there were a couple of goals I had in mind... one was to make the "drive" channel more usable, which I have definitely done. It sounds far richer than before. And I also wanted to get closer to an old Deluxe Reverb Blackface/early Silverface sound when using the clean channel, mostly brighten it up a bit and get some tube sag. I was trying to get it to be a bit more touch sensitive: I wanted it to break up a bit more when I would dig in during a lead, but go back to a shimmery sound during chords... and I wanted to get there without the use of pedals.

I'm there now... really happy with it. I just need to eliminate that squeal I'm getting on the high end of the master cap mod (see above post).

[JoeM]

.....

I'm there now... really happy with it. I just need to eliminate that squeal I'm getting on the high end of the master cap mod (see above post).

OK.

The squeal only happened after the mod right?

[Panther35]

Yes, wasn't occuring before it.

The mod itself works and sounds great, it's just that when I take the control to halfway and beyond, it begins to squeal... even sooner in the "more drive" mode. But don't get me wrong, I like where it's headed, just want to get it tweaked so that it won't squeal in any position. I could theoretically live with it the way it is, but there would always be a risk that someone else might use the amp and not understand what's happening... not to mention, it'll bug me forever :P

[hasserl]

I've messed with those Hot Rod Deluxe amps, modifying them for improved tone, and IMO 4.7uf cathode bypass cap at the first gain stage is a nice improvement. It does cut some of the bottom end response without getting too thin; 4.7uf with the standard Fender 100k plate load/1k5 Cathode resistor still provides full range bandwidth for guitar, but it does not swamp out the low frequencies as much as the larger 47uf cap, providing for a very nice roll off of the lower frequencies. IMO .68 is too small, not a good match for the 1k5 rK .068 would be pretty useless IMO. A polarized 4.7uf cap should be easily available at most any electronics supply supply source.

[Panther35]

Seems I've figured it out. I was swapping out different capacitor values just to see what would happen, got squealing no matter what I did. Then I wired a capacitor alone without running thru the pot and the squealing went away. But, when I moved the capacitor near where the pot was (I mounted it in the number 2 input spot), I got squealing again. When the cap was away from the input jack, everything was fine. I could actually move the capacitor back and forth near the potentiometer/input jack and it sounded like the world's most annoying metal detector (I had the cap wired to a wire lead of about 8", allowing me to move it around). So, I'm no electrical genius, but the terms "oscillation" and "feedback" come to mind... it does resemble super high pitched feedback. It would seem that the solution is simply to move the potentiometer elsewhere, away from the input jack. I'm guessing the cap is receiving or transmitting a signal that the input cable/guitar signal are picking up?

[Chuck H]

So what about that bypass cap your using??? Is it a .68uf or did you use a .068uf??? If it sounds good to you it's all good. But a .068uf will only be bypassing very high treble frequencies. You really only need to cut bass. Did you accidentally install a .068 cap in that circuit?