I have seen solid state versions for days, and even built a few back in the day for driving analog VU meters. But I want to do something "different" mainly because I can.
So in my DIY Tube amp build, I want to use a pair of analog VU meters. But I dont want any solid-state diodes or transistors/op-amps for the VU drivers.
Is there a schematic out there (I cant find one) that is pure tube for driving analog VU meters?
I am thinking a simple 12AX7 or maybe even a 6T8 using its triode as a meter amp, and then the single diode as the rectifier for the meter. But most meter drivers are full-wave. So not sure
any ideas?
So in my DIY Tube amp build, I want to use a pair of analog VU meters. But I dont want any solid-state diodes or transistors/op-amps for the VU drivers.
Is there a schematic out there (I cant find one) that is pure tube for driving analog VU meters?
I am thinking a simple 12AX7 or maybe even a 6T8 using its triode as a meter amp, and then the single diode as the rectifier for the meter. But most meter drivers are full-wave. So not sure
any ideas?
Yeah, it takes some looking. I did find this reference (in the response) with links to schematic. I might try to do it with subminiature tubes.
Also, if you have the stuff for it, look at the Wireless World archive on american radio history .
The BBC also has a technical archive.
Also, if you have the stuff for it, look at the Wireless World archive on american radio history .
The BBC also has a technical archive.
If you want to ad a "real" analog VU meter, then no external diodes are required as they have an internal copper-oxide diode bridge rectifier. These meters are a 200 microamp D'Arsonval movement with special ballistics and an internal resistance of 3900 ohms which are designed to operate across a terminated 600 ohm source, which was usually a transformer. When used in this manor they will read zero VU with 1 milliwatt (.773v) of power applied. But they usually use an additional 3600 ohm series resistor to bring the total resistance to 7500 ohms so as to not excessively load the source. This lowers the sensitivity by 4dB requiring 1.228v to read zero dBm. This is pretty much the standard headroom in the industry back when such things were adhered too.
On the other hand if all you want to do is use an el-cheapo Hong Kong milli or microamp meter that happens to have a VU scale on it (but is not a true VU meter) then just use a full wave half bridge tube rectifier (6AL5) and any appropriate series resistor to upscale the meter to where you want it to go.
On the other hand if all you want to do is use an el-cheapo Hong Kong milli or microamp meter that happens to have a VU scale on it (but is not a true VU meter) then just use a full wave half bridge tube rectifier (6AL5) and any appropriate series resistor to upscale the meter to where you want it to go.
The schematic they link to has a VU meter in series with the plate of a tube, that would be dangerous IMHO. That one is probably one of those "real" VU meters though.
it goes on the output with several Ge diodes, capacitor and input resistor.
you could use tube diodes but you would need to apply a much larger signal then the speaker output.
I use SS for enhancement of tube performance where necessary.
ie. regulated B+ from voltage tripler 132v @ 20ma with 112 db of 120hz attenuation.
you could use tube diodes but you would need to apply a much larger signal then the speaker output.
I use SS for enhancement of tube performance where necessary.
ie. regulated B+ from voltage tripler 132v @ 20ma with 112 db of 120hz attenuation.
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I was thinking of the old HP oscillators when I suggested a diode half bridge. Go to the HP Archive and look at the type 205AG schematic as an example. Keep it simple like that one. Feedback circuits complicate things and aren't necessary. If you need more signal, I'd build a simple common cathode amplifier stage feeding a cathode follower which would then drive the meter. A 6DJ8 would do the job very nicely. And you might not even need the CF.
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Feedback linearizes diodes, so the scale is smooth at the beginning, and does not depend on temperature. Also, such a meter would not add own distortions to the source.
Here's a link for the GR 1551-B Sound Level Meter manual with schematic. It looks to me the meter driver is pretty small, though it's got a single BJT you might want to get rid of.
All well and good for a lab grade instrument taking absolute measurements. Pretty much irrelevant for an ersatz VU meter.
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