Sound Practices Magazine, lots of useful information like the attached.
Done by real people & well documented.
Just checked on the iNet, many hits listing back copies available.
I got them all when they were published. I was on Joe Roberts
subscription list in the 90's.
Done by real people & well documented.
Just checked on the iNet, many hits listing back copies available.
I got them all when they were published. I was on Joe Roberts
subscription list in the 90's.
Attachments
John Stewart, Joelist? I have all the SP issues as well. I think there's a download available. I haven't built this 300B amp but I've built a number of Joe's 91A versions.
The 300B acoustic resonance graphs were interesting.
Here is a 1J6 DHT producing 75 mV 2nd harmonic from acoustic vibration ( the large sine wave is the acoustic signal at around 274 Hz, and the small sine wave is the 2nd harmonic 1J6 plate current ).
The filament vibrates back and forth, coming near to the grid twice for each acoustic cycle, producing the 2nd harmonic in the plate current.
Setup: 4inch speaker, 8 Ohm, 4 V P-P drive, 1/2 inch of cotton on speaker, with tube resting on the cotton.
Here is a 1J6 DHT producing 75 mV 2nd harmonic from acoustic vibration ( the large sine wave is the acoustic signal at around 274 Hz, and the small sine wave is the 2nd harmonic 1J6 plate current ).
The filament vibrates back and forth, coming near to the grid twice for each acoustic cycle, producing the 2nd harmonic in the plate current.
Setup: 4inch speaker, 8 Ohm, 4 V P-P drive, 1/2 inch of cotton on speaker, with tube resting on the cotton.
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Few years ago I done some tests for Audioreview magazine in Italy, only withh ECC88 family just to put in evidence the microphonic
The one set up
A secodn with a ittle bookshelf
Interesting results
Walter
The one set up
A secodn with a ittle bookshelf
Interesting results
Walter
Enjoy 300Bs without worrying about mechanical resonances. Mount the UX socket with Elsa + Ganter soft coupling links:
Elesa + Ganter at TME
The magazine article is nearly 30 years old, and improved 300B variants are available.
The EML 300B is well made and gives little or no mechanical noise, and sounds better.
The JJ 300B sounds good too, and has little microphony in practice. The 1998 version mechanically coupled the filament to the mica - and mica to the glass bulb, which left room for improvement.
Maybe they fixed it now; or fix it yourself with the soft coupling dampers.
Elesa + Ganter at TME
The magazine article is nearly 30 years old, and improved 300B variants are available.
The EML 300B is well made and gives little or no mechanical noise, and sounds better.
The JJ 300B sounds good too, and has little microphony in practice. The 1998 version mechanically coupled the filament to the mica - and mica to the glass bulb, which left room for improvement.
Maybe they fixed it now; or fix it yourself with the soft coupling dampers.