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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Quick question about tube amps

rayma

Member
2011-04-29 8:37 pm
Try gently tapping each tube with an eraser. Probably the input tube will make noise in the speaker.
Sometimes the tube sockets need cleaning, sometimes it's the tube itself. If you can get the noise
by tapping the table that the amp is sitting on, try putting rubber decoupling feet under the amp.
 
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Are the tube amplifiers supposed to reflect sounds when the table they are on or the body of the amp is hit (like with the fingers)

I recently got a small tube amp and is doing this, not sure is a regular (bigger) amp will do it.

Thanks
No.
Its a defect of one tube that has become "microphonic" . This tube has to be

replaced.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
All tubes are microphonic. Some not much. Some way too much.

This fact limits the audio gain of radio sets (tubes in the speaker cabinet). Radio 1st-audio tube types are sometimes rated for minimum signal level to avoid hum and howl-round.

Low-low-level tubes in pro applications were often shock-mounted.

Many capacitors are microphonic. Some coax cable is too.
 
Found the issue... Like perturb said, one of the tubes was damaged. weird thing is that it is the "NOS" that I recently added. (note this was a Chinese made amp with cheap tubes) so adding the RCA should have improved. LOL, well back to buying tubes to see if there is something better out there.
 
All tubes are microphonic. Some not much. Some way too much.
Many capacitors are microphonic. Some coax cable is too.
THE SKY IS FALLING. WEAR SAFETY HELMET AT ALL TIMES.
I have 4 hammond organs three with 23 tubes and one with 14. I have a ST70 (7) & PAS2 (5). None of the above make noise in the speaker at idle when I tromped around on the wood floors of my houses. The 1961 AR turntable sure did, so I sold it off.
One of the Hammonds has 10 uf caps in it replaced with aerovox gold ceramic. No problem with those either.
So the stock of tubes I have are of the "not very much microphonic" category.
I buy used organs on craigslist instead of "NOS" tubes on ebay. Much better source of tubes never removed for cause or red plated for that "special sound".
 
weird thing is that it is the "NOS" that I recently added. (note this was a Chinese made amp with cheap tubes) so adding the RCA should have improved.
By definition, OS tubes are not being made any more.
When one tests bad or rejected by buyer, it is not smashed with a hammer but put back on a shelf, and hopefully being resold later.
Given enough time, only junk remains.
Natural selection.
 
LOL ... I buy all my tubes from eBay. You can figure out who the legitimate sellers are just look at their feedback and you can usually weed them out by how they post test results and what tester they used. I've bought hundreds of tubes that way and not sure I ever had a bad one yet.

What tube type does your amp take?

Current one is a headphone amp Little Bear p7 2x 5670 (2C51 396A 6N3P) TUBE) and a 6AS7
the 6AS7 was a RCA that has the problem.

I also have coming another headphone amp Darkvoice 336s, which I was going to use the RCA 6AS7.
 
So the question now is, if I only use the tube that is microphonic with a headphone, will it sound good or still its characteristics will be changed and sound worse?
Tubes (thanks God) age/wear sllloooowwwwllllyyyyy unless you redplate , overvolt or abuse them in some way.

Guess that´s not the case with Headphone amps (I might be surprised though) so if it "sounds good" today, it should still sound good a few years ahead.
 
THE SKY IS FALLING. WEAR SAFETY HELMET AT ALL TIMES.
I have 4 hammond organs three with 23 tubes and one with 14. I have a ST70 (7) & PAS2 (5). None of the above make noise in the speaker at idle when I tromped around on the wood floors of my houses. The 1961 AR turntable sure did, so I sold it off.
One of the Hammonds has 10 uf caps in it replaced with aerovox gold ceramic. No problem with those either.
So the stock of tubes I have are of the "not very much microphonic" category.
I buy used organs on craigslist instead of "NOS" tubes on ebay. Much better source of tubes never removed for cause or red plated for that "special sound".

You buy organs to remove the tubes?