Re: Tube TC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: robert heidlebaugh <rheidlebaugh@xxxxxxxxxxxxxx>

Tuning the colpitts osc to match your secondary will be NO SMALL  task. Use
a more forgiving circuit . Follow the wise councel  of the KISS  principle.
(Keep If Simpel Stupid) and avoid a lot of problens.
   Robert   H
--


> From: "Tesla list" <tesla@xxxxxxxxxx>
> Date: Fri, 14 Oct 2005 14:03:03 -0600
> To: tesla@xxxxxxxxxx
> Subject: Re: Tube TC
> Resent-From: tesla@xxxxxxxxxx
> Resent-Date: Fri, 14 Oct 2005 14:05:45 -0600 (MDT)
>
> Original poster: "Dan" <DUllfig@xxxxxxxxxxxxx>
>
> John:
>
> Ok, I don't know that much about electronics (enough to be
> dangerous), but I thought that in a colpitts oscillator, the
> cappacitors and _primary_ winding formed the LC tank circuit. In this
> schematic, the capacitors are connected in parallel with the
> _secondary_ ! Unless I don't understand the operation of this
> oscillator, seems something's fishy...
>
> Dan
>
> ----- Original Message -----
> From: <mailto:tesla@xxxxxxxxxx>Tesla list
> To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
> Sent: Thursday, October 13, 2005 7:06 PM
> Subject: RE: Tube TC
>
> Original poster: <mailto:Sparktron01@xxxxxxxxxxx>Sparktron01@xxxxxxxxxxx
>
> Jim
>
> Tubes can absolutely be made to operate as a push-pull power oscillator.
> I have built both types (Armstrong, Hartley), and recently (see 
below) posted
> a
> URL concerning a 50kW (!!!!) Colpits push-pull unit used for a linear
> accelerator
> HVDC multipler stack.
>
> 
<http://www.veccal.ernet.in/~vecpage/inpac2005/CD/Contributory%20paper/C-027.p> 
df>http://www.veccal.ernet.in/~vecpage/inpac2005/CD/Contributory%20paper/C-027
> .pdf
>
> NOTES
> I.  There is a schematic error in the above URL, can anyone catch
> it??? (and it is
> NOT minor...  :^D )
> II.  The above URL may or may not work, try "push pull colpits" as
> key words in GOOGLE
> then look for title:
> _CONSTRUCTION & TESTING OF 50kW/120kHz OSCILLATOR FOR 3MeV, 30kW DC ..._
>
> The difference between the three oscillator types are:
> Colpitts uses a series capacitor voltage divider network to establish
> grid drive power.
> Hartley uses a tapped inductor (dual of Colpitts) to derive grid 
drive power.
> Armstrong uses a grid feedback (tickler) coil to establish 180 deg
> phase shift and
> derive grid drive power.  There is a now with Armstrong (3)
> degrees of magnetic
> freedom in oscillator (1. Plate Tank to GFB, 2. Plate Tank to
> Sec., 3. GFB to Sec.)
>
> I personally like the Hartley (or Colpits) over an Armstrong because...
> 1.  Grid drive is derived directly from the tank circuit, rather 
then magnetic
> coupling from a tickelr coil.  It's just one less "fiddle
> factor" to deal with.
> 2.  Push-pull was used in early induction heating due to lack of high
> power tubes, and there is significant history and references (IEEE, IRE)
> concerning use, design, etc.
> 3.  Double the voltage swing and half the current would equate to ~1/4
> i^2r heating loss in tank circuit, versus a parallel connected
> circuit of equal
> power.  Tank caps have to handle 2X the tank voltage, however.
> (TINSTAAFL- There is no such thing as a free lunch).
> 4.  My experience with PP suggests significantly improved 
stability, and less
> likelihood of the oscillator to pull off frequency, even with
> significant loading.
> 5.  I've not tried a Colpitts oscillator (as above URL), however,
> with HV vacuum
> tuning caps (feedback/drive control) and a MMC array to handle HV and
> high RMS currents, may have considerable design advantage over a Hartley
> PPO at HV, high power.
> 6.  An excellent power oscillator tube for a VTTC would be a air
> cooled 3CX2500H3
> or water cooled Amperex 6960.  Alex Tanjsek and I have culled some
> 6960's with socket and water jacket hardware from boneyard high power
> LEPEL IH units.  Fils are intact (12V, 30A), have not built up
> a constant current
> test fixture to determine operational parameters.
> 7.  Staccato mode power control can allow significant pulse power
> capability out of
> tubes without overheating; I believe I would now use high power
> IGBT's instead
> of SCR's for cathode modulation control.  Much higher voltage,
> pulse current
> rating in a cheaper package (IMO).
>
> Regards
> Dave Sharpe, TCBOR/HEAS
> Chesterfield, VA. USA
>
>
>> Original poster: "Jim Mora" <<mailto:jmora@xxxxxxxxxxx>jmora@xxxxxxxxxxx>
>>
>> John or Dan or ?, I have 4 833a's with original Johnson Sockets and have
>> wondered if way down the road they could be made to Push Pull. I haven't
>> studied Tubes since 74. Can you elaborate on the Culpits vrs. The Armstrong
>> oscillators. One thing I was reading stated that 2 Triodes in
> parallel cause
>> Capacitance problems but there were work arounds? Any Ideas?
>>
>> They are not in my theory or family of curves text books.
>>
>> I net:
>>
>> "Colpitts oscillators are somewhat similar to the shunt fed Hartley circuit
>> except the Colpitts oscillator, instead of having a tapped inductor,
>> utilises two series capacitors in its LC circuit. With the Colpitts
>> oscillator the connection between these two capacitors is used as
> the centre
>> tap for the circuit.
>>
>> Regards,
>> Jim Mora
>> Ojai Ca.
>>
>>
>> -----Original Message-----
>> From: Tesla list [mailto:tesla@xxxxxxxxxx]
>> Sent: Wednesday, October 12, 2005 8:16 PM
>> To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
>> Subject: Re: Tube TC
>>
>> Original poster: <mailto:FutureT@xxxxxxx>FutureT@xxxxxxx
>>
>> In a message dated 10/12/05 8:14:26 PM Eastern Daylight Time,
>> <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx writes:
>>
>>
>>> All:
>>>
>>> I have been looking at different VTTC's, and noticed that most all of
>>> them are variations of the Armstrong tuned grid oscillator. Nowhere
>>> is it explained the merits of using such an oscillator. Why isn't the
>>> Colpitts, for example, used? what is the advantage? or drawback? has
>>> anyone built a VTTC that is wired differently?
>>>
>>> It would seem to me that a colpitts oscillator would give you a tuned
>>> primary; since the DRSSTC coil works so much better on account of
>>> having the primary tank tuned, wouldn't a tuned primary benefit a VTTC
>> also?
>>>
>>> By the way, I just bought a 833a tube on ebay, and plan on building a
>>> coil around it.
>>>
>>> Dan
>>
>>
>> Dan,
>>
>> The traditional modified armstrong VTTC's also use a tuned primary.
>> A number of folks have built Hartley VTTC's but I never saw any actual
>> efficiency advantage over the armstrong despite theoretical advantages.
>> I believe oscillation instabilities of the armstrong may actually be
>> an advantage
>> but I'm not sure.
>>
>> The 833A is a good tube for a VTTC and can give 21" sparks
>> or so without staccaco (pulsed) operation.  Longer sparks can
>> be obtained with staccato operation of course with suitable
>> decreases in tank impedance.
>>
>> John
>>
>>
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