Tube or SS, which is more EMI/RFI prone?

Tyson · « **on:** 5 Jun 2009, 09:39 pm »

Hi all,
After a successful completion of building a pair of speakers, I'm thinking about trying my hand at building an amp or preamp. One big consideration for me is that I live in a very high EMI/RFI area. I'm in downtown Denver, with several Cell Phone towers on top of my building, wireless networks from people all around me, several television broadcast station within a few blocks, etc....

Sooo, I'm curious whether SS or Tube designs are more resistant to this type of environment, and what can be done for each of them to guard against it.

Bob in St. Louis · « **Reply #1 on:** 5 Jun 2009, 09:46 pm »

Interesting thread Tyson. I'm curious to hear the results.

Integrating boiler plate would be my best guess to block interference.

Bob

Tyson · « **Reply #2 on:** 5 Jun 2009, 10:01 pm »

I read somewhere that the new refrigerators make good faraday cages. It would keep the amps cool, too. Of course the amps would eventually start to smell like leftover lasagna.... and there'd need to be really, really long speaker wires coming from the kitchen.

Bob in St. Louis · « **Reply #3 on:** 5 Jun 2009, 10:10 pm »

Well, you could always build the cage (refrigerator) in a box close to the audio room.
Kinda like an IB enclosure in the floor. aa

Bob

tekwiz · « **Reply #4 on:** 6 Jun 2009, 01:14 am »

JoshK · « **Reply #5 on:** 6 Jun 2009, 01:39 am »

Tyson,

Tubes are probably more succeptible to RFI/EMI, in a couple ways, but none-the-least that the tube is exposed whereas a SS circuit is usually in a conductive box (at least partially conductive) and that is an effective shield against RFI, but not EMI. There are ways to build tube circuits to avoid RFI pickup.

I highly recommend Building Valve Amplifiers by Morgan Jones! He goes through all of this. It is an easy read for the most part, focusing on the practical side rather than theory (theory is more focused on in Valve Amplifiers). Your an intellectual so I think you'd enjoy engaging in the learning process while building your first. I gaurantee it won't be your last if you succeed, which I am assured you will.

I recommend the VA book too, but it probably isn't as directly applicable in this specific problem.

Basically to cut to the chase, you can build electrostatic shields for your tubes if you have problems with RFI pickup. You generally only need to shield the bottom 1/3 of the tube where the the tiny leads are. That are orienting the plates at right angles to the transformers goes a long way.

*Scotty* · « **Reply #6 on:** 6 Jun 2009, 07:01 am »

Another concern in high RFI areas is the power bandwidth of the amplifier. The faster the amp is or the wider its small signal bandwidth is, the more likely it is to have problems from RF interference. It will come in the backdoor on the negative feedback loop and it will come in on the inputs at the front end of the amp. Also a differential input circuit using a balanced XLR into it really doesn't do any good because it is the nature of the beast to be increasingly ineffective at rejecting noise as the frequency increases. It is sometimes necessary to decrease the bandwidth of the amplifier to suppress the problem in areas where high RFI exists. This is sort of a last resort after all other possible points of RF injection into the circuitry have been eliminated. What bandwith limiting does is dumb down the amplifier if applied too aggressively. Too much amounts to throwing the baby out with the bath water. The drawback to putting those snap on shields on the tubes is to increase the operating temperature of the tube which can lead to substantially shorter tube life. Most tube power amplifiers are by nature bandwidth limited to a degree by the output transformer. The output transformer is also an effective filter mechanism for preventing RF from entering the amplifier via the negative feedback loop. Assuming of course that the amplifier uses a degree of global negative feedback. If you address the issues mentioned in connection with tube power amplifiers raised by the other posters on this thread a tube power amp might be a good first project for you to tackle.
Scotty

awe-d-o-file · « **Reply #7 on:** 7 Jun 2009, 01:04 am »

I'm gonna say overall design is more important then tube v ss. From circuit to shielding to case design and whether or not it has an earth ground. I lifted all my grounds after reading a Charles Hansen post and that made a big improvment.

ET

Tyson · « **Reply #8 on:** 7 Jun 2009, 02:57 am »

Tube cage, something like this?

http://thetubestore.com/tubecage.html

The info so far has been great, I think I might have to go for a tube amp design

JoshK · « **Reply #9 on:** 7 Jun 2009, 04:06 pm »

Yeah those are tube shields. Those look to be boutique types, you can get NOS ones off ebay and tube seller sites a lot cheaper.

Shields are particularly useful with high gm (transconductance) tubes.

stereocilia · « **Reply #10 on:** 10 Jun 2009, 12:23 am »

This may be a folk tale, but I've heard that cold-war era military circuits were built using tubes because solid state devices would be destroyed by the huge EMP of a nuclear detonation. I'm not saying tubes are less prone to RFI, I'll defer to the experts who say they are not. But, if the folk tale is true true then it's a little ironic.

Steve · « **Reply #11 on:** 10 Jun 2009, 01:27 am »

Quote from: Tyson on 5 Jun 2009, 09:39 pm

Hi all,
After a successful completion of building a pair of speakers, I'm thinking about trying my hand at building an amp or preamp. One big consideration for me is that I live in a very high EMI/RFI area. I'm in downtown Denver, with several Cell Phone towers on top of my building, wireless networks from people all around me, several television broadcast station within a few blocks, etc....

Sooo, I'm curious whether SS or Tube designs are more resistant to this type of environment, and what can be done for each of them to guard against it.

Hi Tyson,

Alot depends upon the design and shielding, both can give great performance but I prefer tubes.

My tube preamp is totally enclosed. My tube amps, only two stages so not super input sensitive, has the tubes on top of the chassis with no shielding. I have lived at two locations within one mile of each other for the past 16 years. I currently live on the second floor of an apartment complex approx 4-5 miles from two 2.2 megawatt video, 200kw aural TV stations (I am sure less power now). The single ended ICs I am running are not shielded. Not a lick of interference, no phantom anything ever.

I would not be afraid to build either type amplifier but make sure you use a good shielding.

Hope this helps.

Niteshade · « **Reply #12 on:** 10 Jun 2009, 10:57 pm »

I have ran Amateur radio stations before and most of the time it was shielding problems and it did not matter whether the electronics involved were tube or transistor. Like was said earlier, small caps going to ground att he amp's inputs are a good idea. Tube shields are great too.

As far as which one to build- I dunno. Tube amps are great- but if you're relatively new to soldering, etc... then a $30.00 chip amp kit might be a good place to start. Parts Express has a nice one for that price and I think the power transformer is another $25.00. It puts out around 15 watts/channel and has good reviews.

If your skill level is good, by all means build a tube amp.

JerryM · « **Reply #13 on:** 11 Jun 2009, 03:07 am »

Quote from: stereocilia on 10 Jun 2009, 12:23 am

This may be a folk tale, but I've heard that cold-war era military circuits were built using tubes because solid state devices would be destroyed by the huge EMP of a nuclear detonation. I'm not saying tubes are less prone to RFI, I'll defer to the experts who say they are not. But, if the folk tale is true true then it's a little ironic.

It's not a folk tale.

In 1976, Viktor Belenko defected from the USSR by flying his MIG-25 from Siberia to Japan. He essentially traded a fighter the West had never seen for safe passage to America.

Of course, the plane was completely reverse-engineered. Military engineers at first found it laughable that vacuum tubes, rather than solid state circuitry, were used throughout the avionics and electronics. Clearly these folks were well behind the times.

However, once questioned regarding the antiquated circuits, Viktor explained that tubes were used as they were virtually impervious to EMP, heat, cold, and extremely easy to change "on the fly".

Have fun,
Jerry

Bob in St. Louis · « **Reply #14 on:** 12 Jun 2009, 03:36 pm »

I'd bet my life the F-22 doesn't use tubes. This, despite the fact that EMP, heat and cold are still as much of a problem as it was 30 years ago. That being said, I wonder how we've overcome those issues using solid state technology. Knowing that may help to design a solid state amp.

Bob

Johnny2Bad · « **Reply #15 on:** 18 Sep 2010, 05:09 am »

Quote from: Bob in St. Louis on 12 Jun 2009, 03:36 pm

I'd bet my life the F-22 doesn't use tubes.
Bob

I'm going to decline the bet; don't say I never do anything for 'ya

I think the F-22 has radar. Radar, like your microwave oven, is always done with at least one vacuum tube (the transmitter).

Ericus Rex · « **Reply #16 on:** 18 Sep 2010, 12:47 pm »

That and the tubed radar system was 10X stronger than ours at the time. I sure hope those issues have now been addressed!

I know it's true too. A buddy of mine was working for Lockheed Martin at the time.

Quote from: JerryM on 11 Jun 2009, 03:07 am

It's not a folk tale.

In 1976, Viktor Belenko defected from the USSR by flying his MIG-25 from Siberia to Japan. He essentially traded a fighter the West had never seen for safe passage to America.

Of course, the plane was completely reverse-engineered. Military engineers at first found it laughable that vacuum tubes, rather than solid state circuitry, were used throughout the avionics and electronics. Clearly these folks were well behind the times.

However, once questioned regarding the antiquated circuits, Viktor explained that tubes were used as they were virtually impervious to EMP, heat, cold, and extremely easy to change "on the fly".

Have fun,
Jerry

Bob in St. Louis · « **Reply #17 on:** 18 Sep 2010, 01:19 pm »

Quote from: Johnny2Bad on 18 Sep 2010, 05:09 am

Radar, like your microwave oven, is always done with at least one vacuum tube (the transmitter).

Microwave ovens all have a tube in them?

chlorofille · « **Reply #18 on:** 18 Sep 2010, 01:22 pm »

I own a small preamp using mini tubes that will shriek when a cell phone is pointed and dialling a number.

JohnR · « **Reply #19 on:** 18 Sep 2010, 01:44 pm »

Tube circuits often operate at higher impedances than solid state, which may make them a little more prone to RF pickup. Personally I wouldn't worry about it.