On another forum, mention was made of the 1T4. I did radio projects before that used the type, so I took another look at the spec sheet over at Frank's (1T4).
The spec sheet identifies this as a remote cutoff pentode that was used in battery powered radios (and making it very useful for noobs as it doesn't require lethal voltages). Included are characteristics for use as a pentode and pseudotriode. Ran some loadlines. The h2 estimate looks very good indeed.
Being that this is a low gain device, it looks like it could prove quite useful as a pre-amp. Since this is also a DH type, with VHH= 1.4V @ 50mA it would lend itself to filament bias quite well. No glowey bottle coolness points as the "heater" is a hair thin wire that can't be seen unless you're in a dark room.
The constant voltage line (used to calculate gm) shows the same sort of funkiness that the 6BQ7A does, even though the latter has no mention of any sort of remote cutoff characteristic in the spec sheet, so it does look like this is an undocumented feature.
The spec sheet identifies this as a remote cutoff pentode that was used in battery powered radios (and making it very useful for noobs as it doesn't require lethal voltages). Included are characteristics for use as a pentode and pseudotriode. Ran some loadlines. The h2 estimate looks very good indeed.
Being that this is a low gain device, it looks like it could prove quite useful as a pre-amp. Since this is also a DH type, with VHH= 1.4V @ 50mA it would lend itself to filament bias quite well. No glowey bottle coolness points as the "heater" is a hair thin wire that can't be seen unless you're in a dark room.
The constant voltage line (used to calculate gm) shows the same sort of funkiness that the 6BQ7A does, even though the latter has no mention of any sort of remote cutoff characteristic in the spec sheet, so it does look like this is an undocumented feature.
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I also played with these for radio projects a long long time ago. I revisited the "battery tubes" several years ago when looking at a battery powered portable guitar amp project. The project killer proved to be the horrendous microphonics provides by that hair thin filament vibrating.
I don't remember the specifics as to why, but I had picked the 1S5 out of the collection I had, which included the 1T4. It could have been as simple as the fact that I had more of them.
I decided to use a bigger battery and, a 12AX7 and a 6AK5 driving a pair of 6AK6's for the amp project. It made about 3 watts at full crank and would play for 2 to 3 hours on a 7.2 volt NiCad RC car battery (cheap and easy to change).
I have recently revisited "battery tubes" again, this time with size and power requirements, so my search includes subminiature tubes. The 6418 makes a nice preamp, but that really thin 10 mA filament will vibrate all by itself making the tube prone to singing.
So far the winner here is the 5678 with a 50 mA filament. Works good in triode mode and as a "high gain" pentode. Note with a Gm in the 1000 range, none of these tubes can have really high gain.
Yep, true.
BUT: as there is nearly no heat introduced (50mA * 1.4V) into this tube, I did the experiment depicted below:
I simply put the 1T4 into (real) sand.
You see only the thin leads from the sockets into the sand for two 1T4's, as well as the other channels tubes in the pictures foreground.
"Burring" the tubes in sand reduced the micro-phonic behavior to a really acceptable level and had -also long term tested- no further disadvantages. Rubber or felt (wrapped around the tube) did not prove to work nearly as effective.
My 2 cents,
Ulrich
Maybe use silica gel for a lighter weight damper.
Can get a Watt or two out of a pair of 5902 or 5639 sub-mini beamers.
Why settle for a remote cut-off sleeper? Curves look like it got a flat tire.
Perfect: Mu 10, 3 Watt combined, octal, double-DHP, $4
Can get a Watt or two out of a pair of 5902 or 5639 sub-mini beamers.
Why settle for a remote cut-off sleeper? Curves look like it got a flat tire.
Perfect: Mu 10, 3 Watt combined, octal, double-DHP, $4
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Yep, I just meant 3 Watt (1.5 + 1.5 W) plate dissipation.
Not a lot of power output or much gain either at only 10. One of those in-between tubes that's not quite good enough at any one thing to qualify. Useful as an emulation tube for SE sound from a P-P amp, use as the Global NFDBK attenuator ( in reverse).
Someone must like it though:
Not a lot of power output or much gain either at only 10. One of those in-between tubes that's not quite good enough at any one thing to qualify. Useful as an emulation tube for SE sound from a P-P amp, use as the Global NFDBK attenuator ( in reverse).
Someone must like it though:
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