Tuesday, December 14, 2010

Feedback and the Rectifiers

[Hmmmm. That would be a great name for a band.]

A reader emailed me to ask if it is true that changing to a copper plug-in solid state rectifier “will get you more power without feedback.”

The short answer is, No.

Let’s review feedback for a moment: We all know it well. When your amp starts to howl the very first thing you do is turn down either your amp or your mic. In other words, you reduce the amplitude of your entire system: harp, mic, and amp.

Also, we all know that if we crank up the treble on our amp it is more likely to start howling feedback, so we usually have the treble set relatively low.

Swapping your tube rectifier for a copper recto of the same value will result in a slightly increased B+ voltage and a reduction in vintage sag tone, which gives the perception of a tighter, more present sound. Does it make your amp truly louder? Maybe very slightly louder, but it would be hard to hear.

Will it reduce feedback? How could it? All the remedies we know of for feedback involve reduced amplitude and/or EQ filters. The rectifier does neither. The claim is bogus.


Rick Davis said...

I've used the copper SS rectos in several of my amps over the last two or three years. I am very familiar with their sound and characteristics: They have less sag and make an amp seem brighter. If feedback is a problem in your amp, the copper rectos won't help. In fact, they can make it worse.

tmfharpking said...

The Weber CC actually mimics the rectifier it is meant to replace-the plate volatge acutally drops,and the ma reading at the tubes is lower as well,in effect reducing feedback. You may also bias,if the amp is so equipped,accordingly in effect with the CC will get you back the heat at the tubes.

Rick Davis said...

If what you say is true, then the copper recto does not "get you more power."

The promise of more power and lower feedback is a myth. And, as you say, the copper sold state recto "mimics" the tube. They do not sound the same.

Some people prefer the stiffer tone of the solid state rectos. I think it sounds harsh in big amps, but very pleasing in small 5-watt amps.

Jennifer said...


I found an old post from Bruce regarding the Weber WY3 vs the 5Y3:

Bruce / Mission Amps ( )
Sun Jul 4 23:55:35 2004

Yes, I did the beta testing of all the Copper Cap rectifiers for WeberVST a couple years ago (before they hit the market) and the only thing different I noticed with the WY3 over all the different brands of NOS 5Y3GTs I tried was that it always made about 8-16vdc less then a real vacuum tube rectifier when under a 60ma-90ma load.
However, that's just fine in the MA-5E3.
Now, if you end up taking that to Europe and you rewire the PT for 220v-240v (like we talked about) you might find that you do not need the zener diode with the WY3 and a 220v-240v primary.


This seems to conflict with your statement that a copper cap will increase B+ slightly. I know copper caps don't work exactly like tube rectifiers, but wouldn't lower B+ get an amp running closer to vintage specs, and thus better "vintage tone" ?

Rich K.

Rick Davis said...


It also conflicts with Gary Onofrio's statement that the copper SS recto gives his amp "more power." How do you explain that?

Bruce Collins assures me that new copper plug-in SS rectos send slightly more power to the B+ rail when compared to their tube counterparts. I'm certain of this because I've seen it on the meter.

Perhaps things have changed since the Beta testing several years ago. Perhaps you are missing some context in your quote.

Since you chimed in, let me ask you this: How does the copper recto get "more power with less feedback" as Gary claims?

tmfharpking said...

It depends on a myriad of things-what are the volatge outputs and what power and output transformers is Gary using? What are the plate volatges of the Cruncher? What MA are the tubes biased at? What recifier tube is being replaced? GZ34,5Y3,5U4? Which Weber CC is he using? Maybe he has too much plate voltage and not enough sag-maybe he has too much sag,and not enough plate voltage-all of these can be fixed with a CC.

Rick Davis said...


Nope, none of those things can be "fixed" with a simple swap of a SS rectifier in place of a tube. The ONLY thing a rectifier does is convert AD to DC and send it along the B+ rail. You seem to be confusing the power tubes with the rectifier.

And I keep asking the question that is the subject of this article: How can a simple swap to a SS rectifier give your amp more power AND less feedback? Please be specific.

You've told me Gary is a close friend of yours. Why don't you ask him this question and relay the detailed answer to us?

tmfharpking said...

Gary found when he substituted a NOS GZ34 with a CC,it gave HIS particular amp more life-bottom end-and richness the tube could not.
My good friend Mike Easton sums it up best:
Gary gives us Avenger owners both the copper plug in and the tube rectifier.

I was amazed at the subtle yet noticeable underlining difference between the two. The Avenger came with the Copper installed.

I tried that for a few days then tried the tube rectifier. I switched back to the copper because I could get cleaner separation of the eq's.

I think the noticeable difference to my ears is the cooper tube tends to keep the eq's separated more whereas the glass tube tends to allow some bottom to bleed into the mids and highs almost acting
like a filter. I guess it didn't matter much when the bass, treble and mids were controlled by one knob on vintage amps.
Now that separating the tone controls are the norm adding the tube rectifier can allow you to dial in more like a single tone knob where there is always some
bottom or "warmth" in the mix.

Rick Davis said...


I am not surprised that the Cruncher amp has a need for more power and less feedback. It's just that I doubt a simple swap to a SS rectifier will do both.

Rick Davis said...

Hmmmm, you are still unable to answer the question: How can a simple swap to a SS rectifier give your amp more power AND less feedback, as Gary claimed on Harp-L?

As for your comment, yep... SS rectos sound different than tubes. SS rectos have less sag and more brightness. That is the "separation" you mentioned. Some players think it is harsh, while others like it. My experience it that the brighter sound gets annoying fast, and you find yourself wishing for the warmer vintage tone.

If you listen to this comparison you will understand what I mean: http://bluesharpamps.blogspot.com/2010/07/comparison-mission-chicago-amp-vs-sonny.html

Has Gary gotten back to you yet about the feedback thing he claimed? That, after all, is the topic at hand. No more off-point comments. Time to answer the question.

Jennifer said...


I can't answer the question about the copper cap providing more power and less feedback. I apologize for getting off topic, I probably should have commented after one of your previous posts on the topic. Anyway, with my particular amp, a 5C3 deluxe clone, I have not observed more power and less feedback by using a CC WY3. What I did find is that the voltages were lower with the CC vs several NOS 5Y3's. The voltages are very similar to the original 5C3 schematic. For me, power is not the issue, and I didn't notice any differences in tone or sag. I prefer the CC WY3 because it runs the amp very close to original specs, so I suppose tube life would be longer and the amp is doing it's job as originally intended. I came across another post from awhile back, that indicated that Ted Weber designed the CC's to produce voltages more in line with the old 117 V wall voltage rather than 120-125V. I suspect the design hasn't changed over the years. Now, having said all that, I'm not doubting the readings you observed with Bruce, as I'm sure there are a wide variety of outcomes possible depending on the amp and components.I'm also not casting aspertions (sp?)on your observations of the differences in tube/CC. I just haven't noticed any in my particular amp.

I enjoy your blog...especially liked the post and detailed pics on the ME-18, as I am struggling to re-vamp mine and get some of the odd noises under control.

Rich K.