@shortbus and anyone who cares -- Below is the (too) long awaited LOPT disassembly discussion.

Please accept my sincere apologies for the cursory, frequently shamefully informal 'tone' of the following (my time has not been my own as of late - excuses, excuses...):oops:

All questions, comments and requests for clarification welcome! --- Please be advised, however, that while I may be unavailable for a few days, @Aleph(0) will be 'on hand' (granting the continued 'march' of her 'necroambulant' VPN:rolleyes:)

So... With no further ado...

LOPT Disassembly Discussion (27 Nov 2017)

1) The terms 'core' and 'form' are used interchangeably (and may be regarded as synonymous) for the purposes of this discussion.

For the reader's convenience, illustrations are both 'contextually linked' and attached as full-size images at the bottom of this post. For best results please return from linked images via your browser's 'back arrow' (⇐) 'button'...

The illustrations represent LOPTs and constituent components typical of the desired style but not necessarily from the same device.

LOPT Construction:

-As a 'point of reference' an unmodified LOPT of the desired 'form factor' is presented in illustration #1

-Illustration #2 shows the device following removal of the external (radial) auxiliary windings and clamping/mounting hardware (save for the frame ligature) -- Please regard this (sans the ligature) as the 'initial state' of the device prior to disassembly...

-Please see illustrations Nos. Three, Four, Five and Eight for definitions/depiction of terms and references.

The principal difficulty: Liability to core breakage during LOPT disassembly.
Ferrite consists of a rather brittle sintered ceramic possessed of only moderate strength - Indeed the tensile strength of the 'grade' employed in the devices under discussion only marginally exceeds that of (graphic) 'chalk sticks' of similar cross section.

While the lower core joint is directly accessible following destructive removal of the (inutile) external auxiliary windings whereupon the lower gap adhesive may readily be 'defeated' via direct heating or application of keytone solvents - Direct access to the upper joint is not possible owing to its envelopment by the EHT winding assembly.

The Desired Solution: Discovery of a 'pedagogically acceptable', 'novice friendly' method of upper core joint separation sans undue liability to damage to or degradation of the core or EHT winding proper.

A Summary of unsatisfactory methods (i.e. what we've tried):

Present (miserably failed) technique:

Step 1) Clear the lower joint gap of adhesive via steeping of the exposed lower core leg in a keytone solvent followed by mechanical removal of the degraded adhesive and gap spacer.

Potential difficulties with step #1:
Degradation of EHT assembly insulation and/or cladding secondary to keytone vapour/condensate exposure...

Step 2) Following removal of the wooden shims intervening the core sleeve and upper core leg, alternately play hot air upon each core rail distal to the EHT winding assembly such that temperatures sufficient to adequately soften the adhesive are attained at the upper core leg and joint (via thermal conduction in the ferrite) -- followed by 'working' the core pieces free of the adhesive via development of alternating torques coaxial to the upper form leg through manual application of simultaneous, appropriately directed 'differential' forces to each core rail.

Potential difficulties with step #2:
Although damage to the coaxial auxiliary windings (please see illustration #8) is of no consequence - the EHT winding is easily damaged via misdirected and/or otherwise 'stray' hot air...

B> Overheating of the core may result in a permanent shift of the ferrite's magnetic properties.

Uneven heating of the core may result in explosive stress fracturing..

It has been our observation that, for many (I daresay most) individuals, successful application of adequate --all the while non-excessive-- torque represents an experience-garnered skill... -- Please note that this is far and away the leading 'mode' of LOPT damage incurred in the course of optimization...

Other methods 'explored' and found to be unsatisfactory or otherwise deemed unacceptable:

1) Rapid, even heating of the core via 'induction' techniques.

--Rationale for rejection--
-While this method has proven to effectively and consistently 'release' the core pieces (within two minutes) sans significant heating of the EHT winding or overheating of the core -- it is, sadly, inadmissible (Re: inclusion in our Tutorial) for the 'disjuncture' of tuition necessarily attending early discussion of power oscillator circuits...

2) Removal of the coaxial Aux windings 'in situ' so as to abrogate core to sleeve adhesion and provide direct access to the upper core joint.

--Rationale for rejection--
-High liability to inadvertent damage to central EHT winding turns.
-Liability to severance/breakage of the EHT return.
-Value of access to the upper core joint (thus obtained) questionable owing to continued proximity of the (readily damaged) EHT winding.

-Method deemed more 'failure prone' than present (unsatisfactory) technique.

3) Ultrasonic delamination of the adhesive-ferrite interfaces.

--Rationale for rejection--
-Variable results.
-Unduly burdensome requirement of 'special' tools/equipment.

4) Protracted (hours to days) application of traction (via spring tension) to core pieces in a modestly heated environment (Ca. 100°C)

--Rationale for rejection--
-Burdensome requirement of arduous, tedious and 'critical' construction of 'traction apparatus'.
-Liability to core breakage secondary to (necessarily) 'uneven' yielding of adhesive.
-Liability to insulation/cladding degradation secondary to protracted exposure to elevated temperatures.

5) Destructive salvage of two similar LOPTs for production of each optimized unit
(i.e. salvage of the winding via destruction of the core of one unit and vise versa).

--Rationale for rejection--
-Maintenance of minimum allowable winding periphery to core clearance requires very similar source LOPT geometries.


Potentially useful information

1) Inasmuch as the coaxial auxiliary windings will be discarded, damage to same is of no consequence.

Appreciation of the coaxial auxiliary windings' position within the EHT winding assembly may be gained via study of the following linked images:

Illustration #8
(Unmodified EHT winding Assembly) - Note that all features central to and including the auxiliary shell will be discarded in the course of modification...

Illustration #9 (EHT winding assembly following removal of all auxiliary winding components except the auxiliary shell) - EHT return lead indicated by pen.

Illustration #10 (EHT winding assembly following removal of all auxiliary winding components) - EHT return lead indicated by pen.

2) The 'stock' reluctance gap spacers will not be reused and are, hence, 'expendable'.

3) Acceptable techniques will apply equally to cores defining cylindrical and polygonal cross-sections...


Illustration #1: Typical AC LOPT

Illustration #2: LOPT assembly following removal of external aux windings and frame

Illustration #3: 'Exploded' view of LOPT assembly components (sans external Aux windings)

Illustration #4 Form/Core detail

Illustration #5: Form piece detail

Illustration #6: Detail of lower core joint prior to removal of adhesive

Illustration #7: Sleeve to core adhesive/shims

Illustration #8: EHT winding assembly prior to removal of coaxial winding

Illustration #9: EHT winding following removal of coaxial Aux windings but prior to removal of aux shell

Illustration #10: EHT winding following removal of coaxial aux windings and aux shell

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