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> 100 philips egc nos 6205 pentode vacuum tubes
100 philips egc nos 6205 pentode vacuum tubes
Some background info; In the 40's and 50's guitar amps (and most other audio amps) employed larger octal style preamp and power tubes. In the late 50's and 60's these Octal preamp types were replaced by smaller 9 pin miniature tubes such as the 12AX7. The 12AX7 was equivilent to the common 12AX7 dual triode. I.E. the 6CS7 dual triode was used in early Fender amps but later directly replaced by the common 12AX7. The new smaller types had less adverse microphonics, used less space and power, but still had the same gain as the larger Octal types they were replacing...all this was a good thing for audio amp designers.
Then came the "latest advance" in preamp and power tubes with the introduction of the "sub-miniature" tube family of tube types, commonly called the "peanut" tube. As before, these were developed to replace the (now) larger 9 pin miniature tubes AND much parger Octal power pentodes (like the 6L6) to make much smaller compact audio amplifiers (NOTE: peanut tubes were originally exclusively developed for military communications due to their MUCH higher cost...who else could afford the development costs!). Most common 9 pin types such as 12AX7, 12AT7, and even EL34/6L6 pentodes have a peanut tube equivalent with similar gain, useful for making smaller versions of all kinds of audio products and as a family of tubes they have greatly reduced adverse microphonics. lower space and voltage requirements and increased life cycle and reliability as compared to their "big brother" equivalents.
The 6205 is the rough equivalent for a a power pentode such as a 6L6 (but of course it has no where near the power output!), but as aPentode it came be used for a small power stage, or can n be sued as a preamp stage too. Many designers only hook up the 3 primary pins for use in a single stage class A triode design such as those used in many modern tube mics and FX pedals They offer a more rugged construction, low power requirements, virtually no squealing adverse microphonics yet high quality audio performance. Using a 6112 as a front end audio gain stage (such as in a Fender tone stack arrangement) and a second one as the phase inverter driving two 6205 sub-miniature pentodes in a class A/B arrangement and presto, you have a killer small recording amp or recording preamp stage.
Our military grade 6205 tubes are individually vacuum sealed in plastic, then packed in single boxes, then 100 are master packed sealed in a larger box more than 25 years ago! The quality of these tubes is far higher than other tubes from this era, or tubes made today in Russia or China. Actually, we have NEVER experienced a bad military grade peanut tube when we were commonly using these these in our (now closed) audio manufacturing factory. We used peanut tubes like these for our studio audio electronics, such as inst/mic preamps or tube mics. Many music industry manufactures such as Seymour Duncan use these tubes in their award winning tube based FX pedals, and they are the usual tube for most the tube recording mics and smaller tube preamps on the market today. This more recent high demand for sub-miniatures has stripped the wholesalers of all their NOS NIB supplies, and they will likely never be manufactured again due to the increased cost to make these miniature tubes...so you will rarely see a factory master packed box of 100 available anywhere at any price.
These tubes only need 6.3 heater volts @ low amperage so the power supply can be a wall wart with an internal step up transformer. They use 7.5mA at 100 plate volts (a 12AX7 is 1.2mA at 250 plate volts by comparison) Gm of 5000 and a plate resistance of 260K ohms.
Due to the high cost of retooling and manufacture, and because there are no tube factories in the world even capable of reproducing this high quality miniature US military grade tube design, they will never be produced again. They are the last great advance of vacuum tubes, get them while you can!
Here's the 6205 technical specs:
Subminiature type used as a rf or if amplifier in subminiature equipment. Requires either a subminiature socket or direct soldering of the wires from the tube to circuit components.
Outline ....................................... 3-1
EIA Base ...................................... 8DC
Heater Voltage ................................ 6.3 V
Heater Current ................................ 0.15 A
Direct Interelectrode Capacitances (approx)
Input ......................................... 4.2 pf
Output ........................................ 3.4 pf
Grid to Plate ................................. 0.015 pf
Maximum Ratings (Design Center Values)
Plate Voltage ................................. 165 V
Grid No. 2 Voltage ............................ 155 V
Plate Dissipation ............................. 0.9 W
Grid No. 2 Dissipation ........................ 0.55 W
Characteristics and Typical Operation
Plate Voltage ................................. 100 V
Grid No. 2 Voltage ............................ 100 V
Grid No. 1 Voltage Derived from
Cathode Bias Resistor ....................... 150
Plate Resistance (approx) ..................... 260K
Transconductance .............................. 5000 Mho
Plate Current ................................. 7.5 mA
Grid No. 2 Current ............................ 2.4 mA
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