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Just finished construction of a Keppinger Theremin, need advice.
Posted: 12/28/2010 10:38:41 AM
[i]Nice clean 100V? Plate voltage??? Thats very low. I believe you need 150V for the B+.[/i]
Not forcibly at the plate of the Hartley oscillators... +B is 150V and there is a 10k resistor in series, which will eat up 50V at a plate current of 5mA...
Not forcibly at the plate of the Hartley oscillators... +B is 150V and there is a 10k resistor in series, which will eat up 50V at a plate current of 5mA...
Posted: 12/28/2010 12:24:36 PM
Welcome to the insanity part. I see you used my temporary cabinet design. Be happy it is oscillating just a little. You will need to tune your oscillators such that there are not any mixing harmonics in the high end, ie the second harmonic of the pitch oscillator is greater than 20 KHz separated from the volume oscillator.
This part is frankly more black art than science. Try shorting then ends of the volume loop together. I did the bass mod and tuned mine at 192 and 400 KHz. You will have to work with the volume bias, etc. There are some combinations of frequencies where the volume loop action is not functional. I also suggest you post on Levnet as well.
I worry that the many wires all over the place may be introducing stray coupling. Also, did you twist your tube filament wires?
ALSO, I noted that your pitch rod appears to be run down the side of the cabinet for mounting, right next to the pitch coil. This may be causing issues via unwanted coupling. If you can't make any progress, I suggest logging onto the kepptheremins group, and looking for the guy making repro chassis sets. That is really the only way to go for tube point to point wiring.
GOTO
http://groups.yahoo.com/group/kepptheremins
http://www.neidlinger.us/keppinger.htm
Your problem from the video on Youtube sounds familiar. If your oscillators are not oscillating all the time, then try doubling the capacity of the 0.001 uF adjacent to the grid shunts, lowering the Xc and getting more kick to the tank to keep it working. I had(have) this identical problem. Thierry and I have discussed this issue. Try grasping the big coils. If the oscillators start back up then its the same issue.
There are LOTS of photos for point to point wiring, etc. Be aware there are errors in the early diagrams, etc., that have been documented by Jeff Sparks and myself.
Keep us posted on your progress.
Philip Neidlinger
Richmond Hill, GA
This part is frankly more black art than science. Try shorting then ends of the volume loop together. I did the bass mod and tuned mine at 192 and 400 KHz. You will have to work with the volume bias, etc. There are some combinations of frequencies where the volume loop action is not functional. I also suggest you post on Levnet as well.
I worry that the many wires all over the place may be introducing stray coupling. Also, did you twist your tube filament wires?
ALSO, I noted that your pitch rod appears to be run down the side of the cabinet for mounting, right next to the pitch coil. This may be causing issues via unwanted coupling. If you can't make any progress, I suggest logging onto the kepptheremins group, and looking for the guy making repro chassis sets. That is really the only way to go for tube point to point wiring.
GOTO
http://groups.yahoo.com/group/kepptheremins
http://www.neidlinger.us/keppinger.htm
Your problem from the video on Youtube sounds familiar. If your oscillators are not oscillating all the time, then try doubling the capacity of the 0.001 uF adjacent to the grid shunts, lowering the Xc and getting more kick to the tank to keep it working. I had(have) this identical problem. Thierry and I have discussed this issue. Try grasping the big coils. If the oscillators start back up then its the same issue.
There are LOTS of photos for point to point wiring, etc. Be aware there are errors in the early diagrams, etc., that have been documented by Jeff Sparks and myself.
Keep us posted on your progress.
Philip Neidlinger
Richmond Hill, GA
Posted: 12/28/2010 4:40:43 PM
You are correct in the statement that the photos of the chassis undersides do not seem to have all the connections. These were interim build photos. Goto the Yahoo group for more photos of completed chassis.
Philip
Philip
Posted: 12/28/2010 4:50:03 PM
Hi Philip - thanks for jumping in on the thread.
I listened to your audio clip the other day, and thought "Oh Man, I'm waaaaay off with this"
I shall be deconstructing the whole thing and trying again starting tonight - all the advice is greatly appreciated.
Steve
I listened to your audio clip the other day, and thought "Oh Man, I'm waaaaay off with this"
I shall be deconstructing the whole thing and trying again starting tonight - all the advice is greatly appreciated.
Steve
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