Couldn't find any, sorry. What's the need for a 6888? 
Probably old equipment, isn't it? Otherwise, if you are building something, better to switch to more available types.
This thread might be of interest:
http://www.diyaudio.com/forums/showthread/t-19368.html
Probably old equipment, isn't it? Otherwise, if you are building something, better to switch to more available types.
This thread might be of interest:
http://www.diyaudio.com/forums/showthread/t-19368.html
E180F and E280F are still around... They seem to be used in
Microphone preamps. In such cases, the Amperex SQ low noise
product seem to be preferred.
Why not use an EF86 as a substitute. This is a low noise pentode
also often used in phono and microphone applications. Sovtek
produces an excellent current product.
-- Jim
Microphone preamps. In such cases, the Amperex SQ low noise
product seem to be preferred.
Why not use an EF86 as a substitute. This is a low noise pentode
also often used in phono and microphone applications. Sovtek
produces an excellent current product.
-- Jim
coresta said:Eli, is the 6AC7 really usefull in audio ? It seems to but did you try them ? i have some NOS left ...
I don't have hands on experience. There are some interesting tidbits in the GE data sheet. Notice the warning against use in low level audio circuits unless DC is used on the heater. Perhaps simply biasing the heater to + 40 V. is enough to control hum at line levels. Also, notice the remark about either sharp or remote cutoff character depending on how g2 is set up. 300 V. on the plate and 150 V. on the screen (VR150?) looks good.
Current and power capability are reasonably high. 40 dB. of gain from a single stage looks quite doable. Use a 12 KOhm load resistor and buffer with a DC coupled cathode follower.
Eli Duttman said:
Well, no they didn't. The 5963 is a nine pin mini that's a dual triode with characteristics much like a 12AU7. The 5963 was intended for digital use, but, ironically enough, has a characteristic that makes it a better audio tube than a 12AU7.
Regarding the 6AC7, that applies to all pentodes. Use a series dropping resistor to set the screen voltage will give a remote cutoff characteristic. Usually, this is not a problem when using a pentode to amplify a low level signal since the current won't vary all that much with signal swing. Combine a series dropping resistor with cathode bias gives enough "sloppiness" to easily accomodate different tube operating conditions and tube ageing. Stiffening up the screen voltage will give better results if you need a larger plate and screen current swing. In that case, voltage dividers, VR tubes (or more likely those little neon bulbs will be better since the current demand isn't all that high) or Zeners are useful.
The 5963 is a 9 pin twin triode similar to the 12AU7. The 5693 is the "RED" equivalent to the 6SJ7. It is also available in brown, and basic black. I have seen them in red and black. Both were metal cased tubes. I can't find any evidence of a glass 5693. The 6SJ7 came in glass and metal envelopes.
Ryssen said:
I think he means the "Special Red" series from RCA.
An externally hosted image should be here but it was not working when we last tested it.
As the picture above shows I mean red, as in the color of a fire engine. They were RCA's premium "long life" industrial tubes. I have seen some brown colored ones, although I can't find any now (I have some brown based 5962's), and I have some black metal 5963's although I think that they are GE's.
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