![]() PS/Edit: the text on the Bottlehead archive page is the same as with my original version, just with the new tube mentioned: "One half is configured as an actively loaded voltage amplifier using our Camille Cascode Constant Current Source for super quiet, dynamic, linear performance. The Brimars I just got should be more relaxed and creamy. well not huge but clearly discernable upgrade to the clarity/resolution IMHO. All those didn't seem to change the sound much! As predicted by 'Doc' and Paul Joppa, but I had to try. Upgraded coupling and 'parafeed' caps to V-Caps and Mundorf Silver/Oil. ![]() I haven't had any issues so left it as-is. Mine do not have the soft-start circuit which was an upgrade offered later for mine. the newer ones (like on this archived page) use a different driver tube but the same topology. My amps are the 'original' versions of these Bottlehead Archives. ![]() !!! His web page is now a PITA to put payment/shipping info into, but I've bought several tubes from him over the years (long ago). Very desirable 12AT7/ECC81 type tube for both Audio and Guitar applications. I just ordered a backup matched pair of the Siemens tubes plus a MP of Brand New, MINT NOS NIB 1965-66 Brimar Military Production CV4024 12AT7WA tubes with Black Plates and copper posts. Anyway, still seems like the 'charts' might be useful. my 300B amps have a 12AT7 as a driver tube. PS/edit: OOPS I see you said 'preamp' tube(s). Of course, your amp may not 'respond' as the B'Head 300B amps do, but I hope so! The Bottlehead circuit is a bit unusual and uses 'modern' design, but the driver tube seemed to me to respond well to the change. I might try some others sometime as well, now that I have a SS Parasound P 7 preamp. I think in general this is a pretty good 'chart' to look at for flavors. but seems like the 12AT7 type S&H triple micas fit these descriptions very well (and I used the charts to pick out 12AX7 types for the C220 too). These charts (see below) are for 12AX7 and 12AU7s, from an old tube site. Pairs/M.Quads/Trios) seems to be the last few of this batch (SAME ones I got years ago when he first got them!). Siemens & Halske E81CC - 1960s MINT NOS NIB 3-MICA 6201 Munich W. I got some NOS Siemens & Halske triple mica 12AT7 types for the 300B amps. ![]() Got some Tesla NOS then new Gold Lion 12AX7s, which sounded the best of all, but still wanted something more. I got some used old stock tested good Tele ribbed plate 12AX7s for the C220, sounded better but I wanted more resolution/"crispness" to the sound. I got a McIntosh C220 preamp at that time, and things sounded a bit 'soft' for me. Not sure what they were, I have them stored away so can't look. ? "pulls" or something that had been tested. I have Bottlehead Paramount 300B amps (the version with 12AT7 type drivers, I know they changed this later). Hey! finally something I can comment on from experience (sort of). The tube requires a noval nine-contact socket and may be mounted in any position. By their design, they are inherently low noise, making them a good choice for these applications. They also turn up in line and microphone preamplifiers, musical instrument amps, and vacuum tube equipped recording equipment. The 12AT7 is found in many high fidelity applications, as each triode section in normal use operates as a class A amplifier. This tube has a mu factor of 60, as compared to the higher gain 12ax7 with a factor of 100, and the 12au7, with a mu of only 20. The 12AT7 is a miniature, high-mu twin triode designed for use as a grounded-grid radio-frequency amplifier or as a combined oscillator and mixer at frequencies below approx 300MHz. If you have any suggestions that would be great. I want to try something else maybe a different brand or tube number with different sound. So far I have a GE 12AT7 and sounds midrangey. I try to keep my mind open on different sounds. Seeking to try different 12AT7 NOS tube and 12AT7-substitutes (not 12ax7 or 12au7) to get some different flavor. I'm game-on to explore tube-rolling the 12AT7 preamp tube of my 300b amp.
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