ใครมีหรือเคยลองบ้างหรือยังครับ
ดูจากข้อมูลน่าสนใจครับ ขาทองซะด้วย (ผมไม่มี6BQ5/EL84 จึงอยากหาอะไรที่ใกล้เคียงมาลองเล่นครับ)
http://www.vacuumtube.com/issue5.htm2. 6094
This type seems more common than the others. Examine the photo carefully, and you will see nothing but wretched excess. This is a 12.5 watt beam tetrode, a small tube similar to a 6BQ5. Mica spacers would be more than adequate, yet all the spacers are made of ceramic. Note the numerous structural supports, just the ticket for 500g mechanical shocks in a missile. The glass envelope isn't regular glass at all, but Nonex, a type of silicon-boron "hard" glass only used for transmitting tubes and lamps which get very, very hot.
It's more difficult to see the cathode construction deep inside, but the heater isn't just coated with alumina, folded and inserted into the cathode sleeve. Instead, Red Bank engineers went back to 1928 for a vulgar, extravagant touch; the heater is threaded into tiny holes in a machined ceramic block, which is then inserted into the cathode. The only other place you'll see this is in very early indirectly-heated tubes
the UX-227. It was very costly, so as soon as the alumina coating was perfected, the ceramic block disappeared. Its use here is mute testimony to the purity of design practiced by Red Bank. It gives the 6094 a heater-cathode voltage rating of +-450 volts, and since the plate rating is 275 volts, you have to think that this tube is rated in a grossly conservative fashion. This also gives a very long warm-up time.
The photo shows some of the variations of the 6094. The original Bendix Red Bank was the 1950s original, while Tung-Sol made a version from the late 1950s until its purchase by Webster Electric in 1970, and up until it closed its doors in the late 70s. The Cetron starts in the 70s and looks suspiciously
the Tung-Sol; the same tooling may have been used. Cetron 6094s apparently were made until the late 1980s.
I made two adapters to allow plugging 6094s into EL84/6BQ5 sockets. Although the EL84 has much more gain, the 6094 is similar enough to work well in a variety of EL84 amps. (It is actually more similar in characteristics to the 6CW5/EL86 ญp; tech. ed.) But the pinout is different, as it is on most Red Banks. First a single-ended listening test was done, using the VTV test amp with no feedback and comparing with some EL84s.
We agreed in general on the EL84s; all had quite distorted and bloated bass, and highs that varied quite a bit. The Sylvania 6BQ5, from the 1970s, had modest detail and was very warm. The Sovtek EL84M was somewhat better balanced in sound, while the Yugoslavian EI EL84 had a glassy effect in the midrange and accentuated highs. All the 6094s were lower in voltage gain, but used virtually the same bias point at 300 volts. They were much clearer than any EL84, with clean bass, very nice highs and a slight nasal quality in the mids. There were some small differences between the versions, the Bendix was a little softer-sounding while the Cetron and Tung-Sol showed a bit more treble detail and the Tung-Sol gave a "forward" effect to the drums.
Then a matched pair of 6094s was plugged into one channel of an Eico HF-86 amp. This is one of the finest-sounding EL84 stereo amplifiers ever made. The example was in near-new condition and was provided by our publisher. Upon comparison with a pair of fresh Mullard EL84s from the 1960s, the 6094s gave slightly cleaner bass and a less congested midrange. Imaging was excellent with both tube types. The difference was not as dramatic as in the SE test, and the difference in tube gain was less noticeable, due to the considerable negative feedback in the Eico amp. Yet a small improvement was apparent.
Even though they sounded cleaner than EL84s, the 6094s gave considerably higher distortion readings on the test amplifier than typical EL84s. The distortion at 300v 40 mA, 1 watt into 3200 ohms, was on the order of 0.9% to 1.2%, while EL84s average around 0.9%. This load is rather severe for the 6094s and probably favors the EL84s. Peak power from the 6094s was about the same as from EL84s.
And for toughness, even the old 7189A is a toy. I put 500 volts at 40 milliamps on a 6094's plate, with 300 volts on the screen. It didn't even blink. No red spots on the plate or the screen, no creaking. Try that with any other 12-watt tube, and you'd better stand well back.
