just wanted to share my experience with the 1629 magic eye tube. Many years ago I fell upon Steve Bench's site -now can be found here- where he mentions his experience and measurements of the 1629.
Out of curiosity I ordered then a couple of tubes but after that I got busy with other projects and obligations and forgot about it.
Last week as was browsing my archive I remembered about it and decided to give it a try. I made a quick and dirty assembly on a small piece of plywood and went on to take some measurements. In this grounded cathode configuration the output impedance is very high, at about 13.4k, and so it it is unsuitable for driving any power amp with low input impedance. So I went on and added an ECC82 cathode follower, DC coupled. HV is at 305V regulated with LR83N, one per channel. Heater supply is DC elevated by 45V. Maximum output is a healthy 44Vrms before clipping.
The circuit is free of hum despite being so close to power xformer, however the 1629 has somewhat high thermal noise so I put the volume control at the output and now is totally silent even at high listening levels.
Listening experience was a very pleasant surprise and hence this post 🙂 Steve measured a predominant 2nd harmonic and this shows indeed in practice. The preamp is really sweet sounding but not to the expense of detail, I could say the exact opposite. It plays so nice that I am really tempted to built a proper chassis for it, despite the fact that I already have another three 🙄
And by the way an added advantage with this is that you have a pair of beautiful eyes to look at while enjoying your music 😀
Out of curiosity I ordered then a couple of tubes but after that I got busy with other projects and obligations and forgot about it.
Last week as was browsing my archive I remembered about it and decided to give it a try. I made a quick and dirty assembly on a small piece of plywood and went on to take some measurements. In this grounded cathode configuration the output impedance is very high, at about 13.4k, and so it it is unsuitable for driving any power amp with low input impedance. So I went on and added an ECC82 cathode follower, DC coupled. HV is at 305V regulated with LR83N, one per channel. Heater supply is DC elevated by 45V. Maximum output is a healthy 44Vrms before clipping.
The circuit is free of hum despite being so close to power xformer, however the 1629 has somewhat high thermal noise so I put the volume control at the output and now is totally silent even at high listening levels.
Listening experience was a very pleasant surprise and hence this post 🙂 Steve measured a predominant 2nd harmonic and this shows indeed in practice. The preamp is really sweet sounding but not to the expense of detail, I could say the exact opposite. It plays so nice that I am really tempted to built a proper chassis for it, despite the fact that I already have another three 🙄
And by the way an added advantage with this is that you have a pair of beautiful eyes to look at while enjoying your music 😀
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I am just waiting for a poster to say they have a CRT preamp as the principles are somewhat similar built on a mahogany base with "ironwood " tube sockets .
What about making the sockets with wormwood? That way we can make Absinthe with the stems & leaves!😀
yeah, that's the beauty of diy, you get to try things out of the box and sometimes you are rewarded 🙂
>The preamp is really sweet sounding but not to the expense of detail, I could say the exact opposite...
You creation better have the detail that those eye tubes "wink" with the music - otherwise?!?
You didnt happen to mention that those beautiful eyes wink. As a kid, I used to love watching them wink to a recording when used as a level indicator.
wink-wink! ;')
You creation better have the detail that those eye tubes "wink" with the music - otherwise?!?
You didnt happen to mention that those beautiful eyes wink. As a kid, I used to love watching them wink to a recording when used as a level indicator.
wink-wink! ;')
the 1629 schematic is in the Steve Bench link I posted, but here it is again for convenience 1629
As for the cathode follower that I added it is plain vanilla 😉 Attached is a scan of a quick schematic I drew in Proteus. You may ignore my comments on it
Edit: I just noticed that in the original schematic of 1629 Steve mentions that Rout is 5k. I am not sure how this was measured but the actual figure is about 13.4k as I write in my opening post. Gain is indeed x15
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I was also wondering about that but unfortunately no, they do not play to the music.
But as I love magic eyes I have installed a pair of EM83's (which is a beauty) in my main preamp
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It would need varying voltage on the grid to change its display, that was provided by the different signal strength provided by the RF stage ( initially ) in a radio.
My AVO VCM MK4 can provide different voltages to the grid to show the tube is functional.
My AVO VCM MK4 can provide different voltages to the grid to show the tube is functional.
I use "eye tubes" for their intended purpose - to show a visually changing signal level of radio I.F. strength.
Or, as a neat volume level (VU) meter.
They can also be used to visually indicate output tube bias changes.
Or, as a neat volume level (VU) meter.
They can also be used to visually indicate output tube bias changes.