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Brimar CV4024 M8162 NOS-Matched Pair
(Per Duncan's Amp Pages and other resources, these are equivalent to, and interchangeable with, ECC81 E81CC 6201 B739 A2900 12AT7 ECC801S)
Very Low Microphonics - Beautiful Phono Preamp Grade Tubes
Tested and Graded by noted tube expert Andy Bouwman, of Vintage Tube Services
You are looking at a very nice pair of vintage Brimar mil-spec tubes, with small single-winged boxed 'ladder' black plates, large ring getter, and incredible 1/2" getter flash. (These are not labeled as Brimar, but look exactly like other Brimar ECC81 I have seen. They appear virtually identical to the unmatched duo of Brimar 6060 / 12AT7, which sold for $50 in item #160299152117.) The factory codes are 75.12, which I believe is December 1975. They are not in original boxes; these military tubes were typically bulk-packed.
These tubes have a beautiful, 'British' tone. If you are familiar with the Mullard sound, back off a bit from the lush midrange and improve the top a smidgen, and there you go. These might be just the ticket, if your system tends toward brightness on the top end.
Outstanding tubes - This pair has been tested at 6000/6600 and 6000/6200, a better than 10% matched pair, and above the 100% level of 5500. Tubes are both rated Green, for microphonics level as suitable for 'moving magnet phono' (as described below). The green rating appears in only about 5% of the hundreds of tubes I have had tested; as such, this is a very rare pair indeed.
These tubes have been thoroughly tested and graded by Andy Bouwman, a noted top tube expert. He has a comprehensive (and quite impressive) array of mint/ calibrated test equipment, including many pieces used by tube makers themselves in production and RD. The tubes undergo an array of tests, including:
Visual inspection for
Loose pieces, misaligned components, loose/ cracked bases, etc.
Noise test – tubes exceeding normal residual thermal noise level are rejected.
Electrical test – small signal tubes are tested for transconductance on one or more of the following:
Chris Haedt - calibrated Heath TT-1, Hickok-built Western Electric KS-15750-L1, RCA WT-100-A
tubes measuring outside the rated specs for that type are rejected
Power tubes are tested using a combination of Weston and RCA measuring equipment and actual amplifiers, including tests at rated voltages/ currents to reveal potentially weak tubes.
Life/ leakage/ gas tests –tubes even marginal on these tests are rejected.
Finally, to improve electrical conductivity and reduce noise, the hard oxide coating on small tube pins is removed using a multi-step process, which leaves a smooth, shiny surface on the pins (see third photo!).
Octal pins undergo a different process – they are polished using a Dremel buffing wheel, to remove surface dirt and corrosion.
(NOTE: For both pin types, I then finish the pins with De-Oxit Pro-Gold GXL (hi-temp), to protect them and further enhance conductivity.)
Following is more on the testing process, direct from Andy's web site:
... all tubes are tested for microphonics including power and output tubes. Small signal tubes (12AX7, 6DJ8, 6SN7, ect.) are selected… using a combination of
(A) Very special, custom made, ultra low noise floor, auditioning and measuring units
(B) Both vintage and current, commercial Hi - End gear
Using this equipment small signal tubes are separated into four categories reflecting the job they do in a system. In a system using a low output moving coil cartridge the amplification factor can run in excess of 100.000, by the time the signal reaches the output of the power amp! It is very important to get this selection process right and this is one of the reasons this company was founded (because no one was/is doing it right).
Each small signal tube… has a colored dot on the base or vacuum tip. This is enamel paint with an estimated 100 year life expectancy on the colorfastness so it won't rub off! The system is:
Color/ Recommended Circuit Type Use/ Recommended Circuit Gain Use
RED Low Mic. LINE level tube 100 X
RED-GREEN ULTRA LOW Mic. LINE level tube 1,000 X
GREEN Moving Magnet PHONO input tube 10,000 X
BLUE Moving Coil PHONO input tube 100,000 X
Note: The colors do not designate the quality of a tube, only the Microphonics level.
POWER OUTPUT TUBES
Power Output tubes are tested a minimum of two times at V.T.S.
(A) The first test is at the regular rated testing voltage. (Tube testers in general do not run the tubes at anywhere near the voltage and current that amps do).
(B) The second test is a full ratings, metered torture test at full current and voltage, done with amplifiers to make sure the tubes actually "work" properly (as compared to "measure" properly). Microphonics, noise, and other parameters such as plate and grid heating are also monitored continuously during this test.
All of my 12AU7 / 12AT7 / 12AX7 type tubes have been auditioned, in my highly modified Cayin tube amp with high resolution speakers, to further confirm their performance. Although I cannot provide any assurance or guarantee of how these tubes will perform in your application, you can be confident these are among the finest tested and graded tubes you will find anywhere.
Terms:
If your eBay rating is less than 10, please contact me prior to bidding, or you bid will be canceled. Because this item is a vintage electronic device, it is sold "as is". Test results are unique to Andy's professionally calibrated setup, and will not correspond to results you may get on other test equipment. No guarantees, implied or written except for item description. Full refund of purchase price, minus shipping to and from buyer. Must e-mail 48 hours after receipt for claim. No Returns except for item description guarantee. Payment must be received within 7 days of winning auction unless prior agreement is made otherwise buyer will be reported for non-payment, blocked from future auctions and very negative feedback left. PayPal or US Postal money orders accepted. Insured shipping to a US address $7.95. Additional tube auctions can be combined, for $2 per auction plus additional insurance as required. International bidders, PayPal only. Note that international shipping rates have gone up considerably of late, so please contact me for a shipping estimate before you bid. If paying by other than PayPal, then please send e-mail indicating how and when payment will be sent. We are willing to work with you, but due to recent non- payers, we have to implement this rule. Thanks for understanding! We only ship to confirmed addresses. Powered by eBay Turbo ListerThe free listing tool. List your items fast and easy and manage your active items.
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