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Old 13th January 2010, 05:42 PM   #1
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Default Sub mini history question ...

I have been reading that the sub-mini tubes arose at the end of the tube era as a last ditch effort to compete with semiconductors...

Does anyone know or any 'analogs' between transistors and sub-mini tubes. Does anyone know of any "head-to-head" devices. These rivals would be great fun to play with (great fun for someone kinda strange like me anyway <grin>) thx much for your mental bandwidth!
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Old 13th January 2010, 06:06 PM   #2
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Quote:
Originally Posted by moonbird View Post
I have been reading that the sub-mini tubes arose at the end of the tube era as a last ditch effort to compete with semiconductors...
At the time, transistors were absolutely hideous when it came to high frequency performance. (And BJTs still are. If hfe=100, and the alpha cutoff is 200MHz (typical for many small signal BJTs) then the more important, and much less impressive, beta cutoff is 1.9MHz -- barely under the 180M band. Going higher in frequency (i.e. a "no tune" SW amplifier) will require NFB and/or other means of gain compensation.)

Quote:
Does anyone know or any 'analogs' between transistors and sub-mini tubes. Does anyone know of any "head-to-head" devices. These rivals would be great fun to play with (great fun for someone kinda strange like me anyway <grin>) thx much for your mental bandwidth!
There really are no "head-to-head" devices since these "nuvistors", while being about the same size as a transistor, are still hollow state devices with the same characteristics of larger triodes. Transistors have a very different sort of characteristic (more like pentodes). The closest analogs would be JFETs, same as for other types of VTs.

As for getting sockets to fit these, I haven't a clue.

Nuvistors can be used for small signal audio amplification, as Ampex used them in a studio tape recorder, though the intended application was VHF small signal amplification, and these were originated for the RF section of TV sets. A lot of them also appeared in 2M -- 10M ham service.

Nuvistor

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Last edited by Miles Prower; 13th January 2010 at 06:11 PM.
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Old 13th January 2010, 08:45 PM   #3
kevinkr is offline kevinkr  United States
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I'm not sure the OP was thinking of nuvistors, but more probably about subminiature glass tube types like the 6.3V IDHT single and dual triodes: 5744, 5703, and 6021, 6111, 6112, respectively, etc.

Battery operated DHP pentodes like the 6088, and 6418 are commonly triode connected for audio use and have low voltage/low current filaments. See Steve Bench site for an example of an entire pre using these two types: http://greygum.net/sbench/sbench/6088pre1.html

The battery operated 5676 DHT is an interesting little low mu device with mediocre linearity, but with some care can sound pretty good in a simple battery powered line stage. I designed several variants years ago and several of my friends and I built these - some sounded better than others, but they all sounded reasonably good. (They didn't necessarily measure all that great though.)

My experiments with the 5744 (questionable linearity except in low level phono stages) and the 6021 indicate that they have some promise in appropriate applications.

Other types like the 6111 and 6112 have achieved cult status in the audio world. They quickly priced out of my zone of comfort when I was mass acquiring subminiatures some years ago so I have none. I have heard tuners and cd players that use the 6111 and they sound fine as far as I can tell. (No critical listening or measurements.)

There are lots of other types suitable for audio use, none as Miles points out are really analogous to transistors, they are merely shrunken analogs of the families of devices they belong to; triodes or pentodes.

Most have reduced ratings compared to standard miniature or octal types with similar parameters.

None require sockets, they may be socketed or directly soldered into a pcb if desired.

They tend to be surprisingly microphonic and should be restrained/isolated from their surroundings so they don't ring.

They run very hot compared to larger types and should be properly ventilated. (With the exception of the battery operated DHT types which run pretty cool.) Metal mounting clips or modified TO-5 heatsinks are a good investment for longevity.
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Last edited by kevinkr; 13th January 2010 at 09:04 PM.
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Old 13th January 2010, 09:17 PM   #4
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Of course, some would be used in hearing aids (Hivac made a lot), some diodes in the probes of valve voltmeters and some, presumably, in proximity fuzes (well, this last use would make sense to me).
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Old 13th January 2010, 10:02 PM   #5
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Quote:
Originally Posted by kevinkr View Post
more probably [thinking] about subminiature glass tube types like the 6.3V IDHT single and dual triodes: 5744, 5703, and 6021, 6111, 6112, respectively, etc.

Battery operated DHP pentodes like the 6088, and 6418 are commonly triode connected for audio use and have low voltage/low current filaments. See Steve Bench site for an example of an entire pre using these two types: 6088 Based Battery Powered Full Feature Preamp
Great site thx much!

Quote:
Originally Posted by kevinkr View Post
The battery operated 5676 DHT is an interesting little low mu device with mediocre linearity, but with some care can sound pretty good in a simple battery powered line stage. I designed several variants years ago and several of my friends and I built these - some sounded better than others, but they all sounded reasonably good. (They didn't necessarily measure all that great though.)
I have some -- any schematics you could share?? What measurements do you mean here?

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Originally Posted by kevinkr View Post
Other types like the 6111 and 6112 have achieved cult status in the audio world. They quickly priced out of my zone of comfort ...
Agreed

Quote:
Originally Posted by kevinkr View Post
They run very hot compared to larger types and should be properly ventilated. (With the exception of the battery operated DHT types which run pretty cool.) Metal mounting clips or modified TO-5 heatsinks are a good investment for longevity.
Great tip thx!
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Old 13th January 2010, 10:06 PM   #6
Jeb-D. is offline Jeb-D.  United States
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Speaking of which, I have some NOS Phillips 6021 and 6112's for sale. $4 each, in original packaging.
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Old 13th January 2010, 10:09 PM   #7
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One thing that does buffalo me a bit is the stuff I've read about the 6418's. Supposidly these were used in high-end condenser mics - but supposidly VERY microphonic too. Anybody ever take one of these mics apart (crazy I know) to see how the microphonic problem was overcome? I have heard about grommets -- any other suggestions?

So if I am looking at a circuit using an 'old' transistor - is there any 'shade-tree' rule of thumb I can use to perform a quick 'sanity check' about maybe using a sub-mini instead? I don't understand transistor specs (not sure I really want to either) for gain -- so when I look at the datasheets they doan make much sense to me. Thx again for your time.
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