Eye Tube (1629) controller help

[dsavitsk]

I am looking to put a pair of 1629 magic eye tubes in a preamp as crude level meters. I don't need to them to be accurate, only to pulse with the music.

The data sheet for the 1629 is here http://www.mif.pg.gda.pl/homepages/f...049/1/1629.pdf and a description of how to hook it up is here http://www.mif.pg.gda.pl/homepages/f...039/1/1629.gif

Essentially, the idea, as I understand it, is to put 250V on the plate, the cathode to ground, and vary the grid from 0 to -8V. This circuit I drew up is supposed to give the grid the 0 to -8V. Essentially, it takes the signal form the preamp output, runs it through an opamp with a variable resistor to control gain so one can increase the output when the volume is low and decrease it when it is high so that all listening levels can use the full range of the eyetube. This signal is then rectified and sent to the tube.

Will this work as a concept, and/or are there any changes I should make? The tube needs 12.6V for the heater, so I thought I'd also use +/-6.3V for the opamp.

The opamp portion is just a cmoy, btw.

Thanks,

-d

[Simpleton]

If you want to see some action, and not a simple "volume" indicator, use half wave rectification.

my 0,02€

[dsavitsk]

Originally posted by Simpleton
If you want to see some action, and not a simple "volume" indicator, use half wave rectification.

Really? Why?

Asside from the type of rectification to use, any other thoughts on the concept?

[heater]

Why not get serious about this? As in the following peak reading magic eye VU meter: http://koti.mbnet.fi/siliconf/JukkaT...r/peakmtr.html

[Simpleton]

OK, maybe not A volume indicator , but there is no need to read the (in this case, as we want negative grid bias) positive half cycle of the signal, as only the peak function is needed. You should consider getting a resistor connecting the grid cap to ground (the peak hold function).
One other thing ( and i may be wrong, as with the above), depending on the magic eye tube, and vaguely remembering the vaguely learnt theory of opamps, you might get only the signal to pass to -6.3V.

The link heater posted is very good.

[PRR]

What is that funny triangle-shape tube?

Your 4-D rectifier is dubious. It is full-wave (pointless for "to pulse with the music") but has has no peak-hold (nice for speech/music). It looks like when the cathode is driven, the grid floats, and vice versa?

The simplest way is to drop B+ to 100V and put audio direct on the grid. This will jiggle fine, at either CD-deck output or power-amp input levels. At 100V supply the eye closes around 2.5V.

You can, of course, if you must, put that triangle-tube (chip???) in front for variable gain.

Peak-hold is nice, but needs a rectifier. A proper full-wave rect is complex and will look the same for "pulse with the music" uses. While speech/music can be asymmetrical, it usually isn't too asymmetrical, and you are not asking for any precision, only jiggle.

Use your booster driving one diode onto a cap/resistor combination to ground. Say 0.01uFd and 1Meg. The eye-tube grid connects to the top of the R||C. Diode is polarized for negative output. A few-K in series with the diode will keep it from holding very-short transients and give more jiggle.

For less jiggle but no gain-knob, do a rude log conversion on the input. Opamp with diode feedback. Yeah it has crummy tempco, but you don't care.

[ALBQ]

dsavitsk,
How about his one. Is a design by MapleTree Audio that they had posted on their website for years. I would have just forwarded the link but, could no longer find the lin to the assembly manual. Should be realatively easy to build
Cheers -ALBQ

[dsavitsk]

Thanks for all the helpful suggestions.

[Simpleton]

What do you think of this schematic? One can use the full input signal with no diode.
As always, correct me if i'm wrong at something.

[kathodyne]

hey!

I have a nice one for you .... ALL TUBE

you can adapt it to use virtually all indicators that need a - voltage at the grid.......

http://www.aha.nl/tubelevel.aspx

here a picture of the vu-meter with
-EM84
-EM85
-EM71 (test)