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patrick-turner patrick-turner is offline
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There is an artical posted here about tubed phase shift oscilators at : -

http://www.rfcafe.com/references/pop...lectronics.htm

Its an old 1958 article with a hell of a lot of info to digest because unlike so many modern descriptions of anything technical, the old guys could say a lot, and not leave out very much. I think my father's generation were better communicators than many of today's website creators who just post a stupid brief plagerised picture of something, then think they are God's gift to the Universe of Information.
But I digress.

I do have a lot of 3 gang tuning caps from old radios which will never be used for radios again, and so its possible for me to mount maybe 8 of them in a box with so I'd get 3 caps with variable range 8 x ( 45 - 450pF ), ie, 360pF to 3,600pF.

To make a phase shift oscilator for 6 F ranges I need 6 sets of 3 R for each range, between perhaps 200ohms to 20Megohms, which isn't difficult.
I'd need 3 pole x 6 position switch for 6 F ranges, not difficult.

The paralleled tuning caps need not all be exactly the same type, or have the same C, although each gang in each cap should be the same, which all the ones I have are.

Has anyone else built a decent phase shift oscillator with wide range of F?

Patrick Turner.

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"patrick-turner"

There is an artical posted here about tubed phase shift oscilators at : -

http://www.rfcafe.com/references/pop...lectronics.htm

Its an old 1958 article with a hell of a lot of info to digest because
unlike so many modern descriptions of anything technical, the old guys could
say a lot, and not leave out very much. I think my father's generation were
better communicators than many of today's website creators who just post a
stupid brief plagerised picture of something, then think they are God's gift
to the Universe of Information.
But I digress.

I do have a lot of 3 gang tuning caps from old radios which will never be
used for radios again, and so its possible for me to mount maybe 8 of them
in a box with so I'd get 3 caps with variable range 8 x ( 45 - 450pF ), ie,
360pF to 3,600pF.

Has anyone else built a decent phase shift oscillator with wide range of F?


** Not me.

But I do have an all valve Wien Bridge oscillator using a dual gang
condenser, taken from a 1940s radio.

Owned it since I was 15 years old.

Tube line up: 2 x Mullard 6AM6, 1 x AWV 6BQ5 & 1 x Miniwatt 6V4
rectifier.

Three ranges: 9 to 218 Hz, 185 to 2158Hz & 1889 to 21,899Hz.

Two 18 megohm resistors used in the low frequency range.

The 6AM6s are wired as triodes.

Stabilisation is by an R53 NTC vacuum bead thermistor.

The condenser is electrically isolated from the chassis and lives in a steel
box of its own for shielding.

The shaft is driven by a backlash free, 60:1 worm reduction drive and a 200
point scale.

Verrry silky.

Once warmed up, it is remarkably stable.

THD is a modest 0.2%, pure 2nd harmonic.

Gave it a major renovation about 10 years back - including MF resistors,
new tag board, all electros and many poly film caps etc.

Nostalgia is a real bitch.



.... Phil



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"Phil Allison"

Tube line up: 2 x Mullard 6AM6,



** See this pdf link for more info that you ever wanted on the 6AM6 / EF91

http://www.aireradio.org/riviste_est...ola%20EF91.pdf

Really is worth a look, includes internal pics, magazine projects and facts
galore.



.... Phil


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Phil Allison[_3_] Phil Allison[_3_] is offline
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"Phil Allison"


** See this pdf link for more info that you ever wanted on the 6AM6 / EF91

http://www.aireradio.org/riviste_est...ola%20EF91.pdf

Really is worth a look, includes internal pics, magazine projects and
facts galore.



** Same article, much better presented:

http://www.r-type.org/articles/art-148.htm

http://www.r-type.org/articles/art148p.jpg






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"Phil Allison" wrote in message
...

"Phil Allison"

Tube line up: 2 x Mullard 6AM6,



** See this pdf link for more info that you ever wanted on the 6AM6 / EF91

http://www.aireradio.org/riviste_est...ola%20EF91.pdf

Really is worth a look, includes internal pics, magazine projects and
facts galore.


"Not the valve that won the war" but an interesting article indeed!

A comprehensive article about the EF50 that helped to win the war:
http://www.dos4ever.com/EF50/EF50.html

Lots of interesting projects at that site.

Gio Re




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***Phil replied to my article........
There is an artical posted here about tubed phase shift oscilators at : -

http://www.rfcafe.com/references/pop...lectronics.htm

Its an old 1958 article with a hell of a lot of info to digest because
unlike so many modern descriptions of anything technical, the old guys could
say a lot, and not leave out very much. I think my father's generation were
better communicators than many of today's website creators who just post a
stupid brief plagerised picture of something, then think they are God's gift
to the Universe of Information.
But I digress.
I do have a lot of 3 gang tuning caps from old radios which will never be
used for radios again, and so its possible for me to mount maybe 8 of them
in a box with so I'd get 3 caps with variable range 8 x ( 45 - 450pF ), ie,
360pF to 3,600pF.
Has anyone else built a decent phase shift oscillator with wide range of F?

** Not me.

But I do have an all valve Wien Bridge oscillator using a dual gang
condenser, taken from a 1940s radio. Owned it since I was 15 years old.

Tube line up: 2 x Mullard 6AM6, 1 x AWV 6BQ5 & 1 x Miniwatt 6V4
rectifier.
Three ranges: 9 to 218 Hz, 185 to 2158Hz & 1889 to 21,899Hz.
Two 18 megohm resistors used in the low frequency range.
The 6AM6s are wired as triodes.

***Yes, sounds like an AWA standard telephone tech's oscillator used by the PMG.
That was my first WB oscilator, with 20Hz to 20kHz, 3 ranges, and PP transformer at output from a 6SN7.

***I gutted it and rebuilt it with TWO 2 gang tuners, and made it go from about 2Hz to 200kHz. WB Circuit uses 6DJ8 diff input pair, 6CA7 gain pentode, then 6CM5follower OP stage. Goes well, and with series grain of wheat lamps, 'cos the thermistor was stuffed, along with the 3 pos switch when I examined it.

Stabilisation is by an R53 NTC vacuum bead thermistor.
The condenser is electrically isolated from the chassis and lives in a steel
box of its own for shielding.

***Common practice, because the cap chassis is NOT at 0V potential.

The shaft is driven by a backlash free, 60:1 worm reduction drive and a 200
point scale. Verrry silky.

***I have numerous old drives from that era. Some are works of art, others are cheap crap, from the days when we made things in Austraya, and hadn't yet gorn astray.

Once warmed up, it is remarkably stable. THD is a modest 0.2%, pure 2nd harmonic.
Gave it a major renovation about 10 years back - including MF resistors,
new tag board, all electros and many poly film caps etc.
Nostalgia is a real bitch.

***Ah, but we can learn from our father's generation. We can do better than they could. Much of the modern world disgusts me, and the gadgetry invented daily does not seem to make anyone much happier, so why be a slave to something like a mobile phone with 2 million transistors inside, so you yabbayabba to ppl who yababababa back, mostly about nothing meaningful.

***I quite like overcoming the shortcomings of the previous generations. They mostly did the best that they were allowed to do with available time and available wages from penny pinching bosses. Real good tubed test gear which is far more complex and difficult to understand was mostly made in USA by HP and only affordable by the rich, or military / govts. Its somewhat hard to feel nostalgia for my HP 606 HF oscilator 6 ranges from 50kHz to 65MHz, but it uses tuning gangs, by far the best I've ever clapped eyes on, and coils, and a PP oscilator, full AM mod. Somebody gave me a pile of such junk which is too good to strip down and maul, and the 606 is quit handy, although huge, about 2 cubic feet. The one I got had a few minor problems and a few crook tubes but once I fixed all faults it runs fine. Warms the shed a bit in winter.

***After reading the 1958 article on phase shift oscilator, I made one up, with 6BX6 / EF80 and one 6CM5 output buffer. It oscillated, but many problems occurred which the 1958 authors didn't dare mention. In fact, I take bak my praise for those authors because in fact very little analysis of understanding is offered at all, just like the ****wits you see after Googling "phase shift oscillators" There is not one single schematic with all working voltages at every electrode shown, but just blather without depth.

***For wide F range between 2Hz and perhaps 2MHz, maybe 3 parallel 3-gang caps are needed to life the C value so the R need not be too high for LF, while also giving low R value at HF not lower than say 820r so that the phase network isn't a horrible load to drive, even with tubes. I've converted a 1950 radio chassis to oscillator, with the phase network driven with 1.2 6DJ8 CF, and then its output feeding 1/2 6DJ8 CFF, so the network is buffered at both ends, and the 6BX6 can drive it effortlessly. The FB network needed is a combination of NFB and PFB using 10k0 plus 1k0 pot in what is a shunt network with oppositely phase signals at both ends, so that just the right amount of drive goes to the 6BX6, which has gain = 47. BUT, it remains to be seen what limits the Vo level and perhaps I have a use for the spare working P54 thermistor I have. I've never owned a phase shift oscillator, and the idea appeals, and I have lots of tuning caps. Its possible to have 4 x RC sections in the network and some designs use a follower buffer after each RC, so that the difference between network Vin and Vo is much less, so less amp gain is needed.
***I searched online for graphs of typical F response for 3 casacaded RC sections and found nobody offered a decent graph, so I made up a couple of networks and plotted the response to find where the phase shift = 180 degrees, and what the ratio was for Vin / Vo. Its not exactly 29.
Anyway, I build gear based on what I find and proove to be true rather than build junk based on inadequate ramblings of online junk-minded idiots. There are usually 200+ things to sort out when starting from scratch to design and build something and unless you sort out each issue, it just won't work properly.

***I'll try to read all the URLs ppl have posted up about such old gear. There's often some trick or two or three that you find lurking in the schematics that one would never think of by oneself.
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"Phil Allison"

But I do have an all valve Wien Bridge oscillator using a dual gang
condenser, taken from a 1940s radio.

Owned it since I was 15 years old.

Tube line up: 2 x Mullard 6AM6, 1 x AWV 6BQ5 & 1 x Miniwatt 6V4
rectifier.

Three ranges: 19 to 218 Hz, 185 to 2158Hz & 1889 to 21,899Hz.

Two 18 megohm resistors used in the low frequency range.

The 6AM6s are wired as triodes.

Stabilisation is by an R53 NTC vacuum bead thermistor.

The condenser is electrically isolated from the chassis and lives in a
steel box of its own for shielding.

The shaft is driven by a backlash free, 60:1 worm reduction drive and a
200 point scale.

Verrry silky.


** Ambiguity fix.

The 200 point scale is engraved on a 4.4 inch dia steel disk that rotates
with the worm drive, making 6000 setting points per range.

30 turns x 200 = 6000.


.... Phil




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"patrick-turner"

Phil mentioned the drive mech for the variable tuning cap in the wien bridge
oscilator he has....

The shaft is driven by a backlash free, 60:1 worm reduction drive and a
200 point scale.

Verrry silky.


** Ambiguity fix.

The 200 point scale is engraved on a 4.4 inch dia steel disk that rotates
with the worm drive, making 6000 setting points per range. 30 turns x 200 =
6000.

Well Phil, your dial certainly seems nice by what you say, but how accurate
are the 6,000 points on the dial? It would seem that the dial length around
the 4.4 inches is roughly 13.8 inches long, 351mm, so distance between each
"point" is 351 / 6,000 = 0.058mm and too small to be useful.

** ROTFLMAO !!!!!!!!!!!!!!

351 / 200 = 1.755mm

There a 30 turns of the dial for 180 degrees on the gang.



.... Phil



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I replied to Phil about his the oscilator dial mech.....

"""Well Phil, your dial certainly seems nice by what you say, but how accurate
are the 6,000 points on the dial? It would seem that the dial length around
the 4.4 inches is roughly 13.8 inches long, 351mm, so distance between each
"point" is 351 / 6,000 = 0.058mm and too small to be useful."""

Phil larfs 'is 'ed orf....

** ROTFLMAO !!!!!!!!!!!!!!

351 / 200 = 1.755mm

There a 30 turns of the dial for 180 degrees on the gang.

.... Phil

OK,OK, whatever.

Meanwhile, after I got back from a 115km bike ride I had a look at the ancient ex PMG Wien Bridge oscillator I must have re-wired for the 3rd time maybe 8 years ago or more.

I last made it with 5 ranges, 1Hz to 22Hz, 10-220, 100-2,200, 1kHz-22kHz, 10k-220k. I figured some overlap of F in the ranges was easy to do and useful, but not absolutely necessary.
Dial is 125mm dia and has around 300 degrees of turn, and no reduction drive was used - not deemed necessary, but there could be one.
I did once try two twin gang tuning caps for the first time I re-wired the unit before 2000.
The tunings caps have been replaced with an Alps "Black" 27mm mm square body normal direction 49.2k dual log pot, which means lowest F is with maximum clockwise turn of the F control knob. You get used to that in 2 seconds.

The pot tracks have a series R = 2k2, so the R range is actually 2k2 up to 51k2 giving C values of 3u3 for 1Hz up to 330pF for 220kHz. The dial was calibrated in pencil and later in blank ink on cream cardboard, then glued to front fact and then varnished. Its accurate within +/- 3%, mostly better..

The Alps pot gives "silky" F adjustment with very little Vo jitter, and no bounce occurs. I have ZDs back to back to clamp the voltage across the fixed R of the NFB network. No clamp between Vo and 0V was necessary. The operation is actually better than subsequent oscilators i made with opamps and pots or switched R, although the latest switched R type are quite nice to use.

The NFB network has 12 seriesed 12V x 50mA lamps.

Vo at output of tube stages = 16.4Vrms, and 5.46Vrms is acoss the lamps, and the current = 9.1mA, so the lamp R = 600r, so each lamp R average = 50r, and cold they measure about 27r, so they are operating at twice their cold R with average of only 0.45Vrms across each lamp, enough to cause a doubling of the cold R, and into the non linear region of lamp R increase..

The fixed R ( with parallel trimming Vr = 1,200r, and so the NFB network has total R = 1,800 r at normal operation.
The PFB network minimum Zin occurs when R = 2k2, and is a total of 4.67k and I in = 3.51mArms. The output attenuators are 10 log pot in series with 1k0 log pot so I get 0V to 1.4V, or 1.4V to 14.0Vrms. Ouput attenuator current = 1.26mA, rather feeble, but OK for most high Zin amps. No output buffer is used after the output level pots.
So the current max = 9.1 + 3.51 + 1.26 = 13.87mArms, or 19.5mA peak.

The tube line up = 12AU7 V1, V2 differential pair with one anode bypassed to 0V, gain approx 14 with other anode feeding V3 gain tube. PFB feeds V1 g, and NFB feeds V2 g, and commoned cathodes taken to current 8mA sink with MJE340. V3 = 6AC7, old metal jacket tube made maybe 1940. it was a high gain+gm octal pentode used commonly on instruments and for HF. Still very usable. Gain approx 200. Total amp gain = 14 x 200 = 2,800.
V3 feeds a White Cathode Follower with V4, V5 = 2 x 6CM5 with +250V anode supply and Ia = 25mA. This gives a surprisingly low Z class A output to drive the loads.

THD is not obviously noticeable on the CRO, and there no sign of any clipping, so I guess THD 0.5%, mainly 2H.

I do recall TRYING to get F higher to 1MHz, and only getting to 800kHz with a 6DJ8 input pair, and C would have needed to be 72pF in theory where R minimum = 2k2.
But trouble was that oscillations and Vo become unstable and slew rate limited at the high Vo level and the dial accuracy wasn't good above 300kHz. Maybe more Ia in white follower and and less Vo would have been more sensible, and an additional output cathode follower after the attenuators, but room in the box is a bit limited. The 5 pos range switch has one more position blocked, could be 100kHz to 2.2MHz maybe.

So this unit does the 1Hz to 220Khz very well, but I could have a tuning gang and a dial for a separate high range 100kHz up to whatever I might get. For this range, if the R ( fixed ) = 1k2 then C minimum for 1Mhz C mimumum = 132pF, and then oscillations should not become unstable and trim caps can adjust it for optimum because there is stray C lurking, plus input C of the tube grid. But then to get a decade of F the max C of a single gang would need to be 1,320pF, and that would require 3 gangs at say 445pF each, so there's a job for 2 x 3gang caps.

Depending how well the two triple gang caps worked, I could use the tuning caps for top 5 ranges and the largest fixed R = 12Megohms. The 50k pot can work to do the 1Hz to 10Hz. My experience is that the tuning caps can give surprising accuracy with 1 dial for 5 ranges because its easier to get accurate R than fiddle around with paralleling C to just the right C value.

The beauty of halving the Vo to 7Vrms means that if loads remain the same R, then the amp current output is halved. But loads can be reduced, for better HF, and same Ia in white follower should work OK, although maybe 35mA would be better.
The NFB network for 7Vrms would use 600r in series with 6 x 12V lamps in series, so that NFB network is a load = 900r. The attenuator can be lower value, and mimimum R value in PFB network.

I'll prepare a schematic of what I have now for my website because its not a bad oscillator even without the extension to 1MHz, and anyone could build it without any hard to get parts. The 6CM5 could be replaced with say 2 x EL84 in triode, and 6AC7 replaced with EF80/6BX6 or EF184/6EJ7. Plenty of these around, and the 12V x 50mA lamps are around, or better still, the type 327 lamp, 28V x 40mA are also easily getable. in a box fulla toobes, a j-fet or opto coupler would seem out of place.
The oscilator circuit would fit on an old AM radio chassis. The wooden box or bakelite box would be removed, and a new metal box made to fit. RF coild, tuning cap, and IF trannies and audio amp and speaker are all removed. There are plenty of such radio chassis around which are not at all worth restoring. Perhaps the dial mech parts could be saved to make a horizontal sliding dial, but to get 300mm of movement you need a wheel just the right size fixed on the pot shaft. Much thought needs to be applied. But I leave such imaginative craftwork to the thousands of old guys who like nothing better than to farnarkle around in their sheds with old gear.
Patrick Turner




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On Tuesday, September 10, 2013 1:36:27 AM UTC-4, patrick-turner wrote:
There is an artical posted here about tubed phase shift oscilators....


Good article. One thing that isn't mentioned, though, is the calculation for
f: = 1/(2π·R·C·ˆš6) (although the nomogram helps).

...unlike so many modern descriptions of anything technical, the old guys could
say a lot, and not leave out very much. I think my father's generation were
better communicators than many of today's website creators...


I concur. I think that people (authors AND readers) were a good deal more
patient back then than they are now. Today, we absorb (or disseminate) just
enough information to IMPLEMENT, but not enough to truly UNDERSTAND. Hence,
the "sound bite" method of teaching circuit theory. Even in educational
settings, truly expository explanations (such as that article) are rare.

The irony that exists between the early and modern ages of electronics is that
today, we have (particularly passive) parts that are quite a bit better than
what was available "back in the day", but what's lacking is the workmanship,
attention to detail, and the "make it as good as humanly possible regardless of
the effort involved" attitude that prevailed during that era.

It's no secret that the best equipment available is being produced on garage
workbenches and kitchen tables €“ DIY'ers combining the best of today's
components with the diligence and perfectionism of yesteryears' craftsman.

Has anyone else built a decent phase shift oscillator with wide range of F?


I guess it would depend on what's considered a "wide range of F". I've built an op-amp-based PSO that goes to just under 1MHz (from about 1KHz). But the tube PSO's I've made were all LFO's for guitar amp vibrato (1-10Hz).


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Oct 21
Other recipients:
Good article. One thing that isn't mentioned, though, is the calculation for f: = 1/(2π·R·C·ˆš6) (although the nomogram helps). ...unlike so many modern descriptions of anything technical, the old guys could
On Tuesday, September 10, 2013 1:36:27 AM UTC-4, patrick-turner wrote:
There is an artical posted here about tubed phase shift oscilators....


Good article. One thing that isn't mentioned, though, is the calculation for
f: = 1/(2π·R·C·ˆš6) (although the nomogram helps).

...unlike so many modern descriptions of anything technical, the old guys could


say a lot, and not leave out very much. I think my father's generation were


better communicators than many of today's website creators...


I concur. I think that people (authors AND readers) were a good deal more
patient back then than they are now. Today, we absorb (or disseminate) just
enough information to IMPLEMENT, but not enough to truly UNDERSTAND. Hence,
the "sound bite" method of teaching circuit theory. Even in educational
settings, truly expository explanations (such as that article) are rare.

The irony that exists between the early and modern ages of electronics is that
today, we have (particularly passive) parts that are quite a bit better than
what was available "back in the day", but what's lacking is the workmanship,
attention to detail, and the "make it as good as humanly possible regardless of
the effort involved" attitude that prevailed during that era.

It's no secret that the best equipment available is being produced on garage
workbenches and kitchen tables €“ DIY'ers combining the best of today's
components with the diligence and perfectionism of yesteryears' craftsman.

Has anyone else built a decent phase shift oscillator with wide range of F?


I guess it would depend on what's considered a "wide range of F". I've built an op-amp-based PSO that goes to just under 1MHz (from about 1KHz). But the tube PSO's I've made were all LFO's for guitar amp vibrato (1-10Hz).

""""""""""""""""""""""""""

I didn't get anywhere with trying to make a wide band phase shift oscillator as dedicated bit of test gear with an accurate single dial for many decade ranges of F.

But I have now got my tubed wien bridge oscillator sorted and free of any instablity and which has open loop gain at 1kHz of about 2,000. Tubes are 6BX6 for V1, V2 gain, then White follower with 2 x EL86. NFB is to V1 6BX6 cathode from network using 4 x 12V-50mA "grain of wheat" lamps.

The high gain at 1kHz is reduced above 10kHz and below 100Hz by gain shelving R&C networks. I have nearly completed the schematic drawings for my next website page on wien bridge ocillators.
The unit gives 5 decade ranges of 20Hz-200Hz, and up to 200kHz - 2MHz. These ranges require fixed R between 2M8 to 253r, and a quad of 3 gang tuning C which gives about 2,500pF to 250pF. The changing of F by string dialcord and 4 wheels, one for each cap gives very stabgle Vo with no bounce that one gets with some pots. The sixth F range obtained by turning the rotary rage switch gives 1Hz to 20Hz, using a dual gang 25k log pot + 1k25 and fixed C = 6u6 approx.

I have yet to instal a rotary switch for the output Vo range levels, 7V,2.2V,0.70.22V,0.07V, and 0.022V if I have a suitable 6 pos switch in junk bin. Following this switch will be a 2k2 log pot for adjusting level, and then a solid state complementary darlington pair emitter follower buffer to maintain Rout at about 60r, from class A bjts working from +/- 15Vdc, and idle current 200mA. I had thought of using a tube CF but when output load is say 100r, the bjts give far less gain loss.

All R&C values are trimmed for wanted F range. There are two dials, one for the 5 tuning gang operated ranges and another for the LF pot range. I have to calibrate cardboard templates of the F outcomes, then scan into PC and tidy it all up in MS Paint. Then I print 3 copies of each about the right size by trial and error, OK, because the exact size is not critical for a dial with rotating pointer mving around a fixed centre point. Then the paper copies are soaked in varnish and laid on the front panel and the text shows good contrast when you have 3 layers all soaked in varnish.
I could have illuminated dials, but that is not necessary.

In my retirement, I can afford to fiddle around making gear if I want. Retirement is a wonderful change from my 20 year stint as volanteer amp worker fixing every other man's old junk for net wages less than the dole, currently $220 a week in Oz, while the mean gross wage in Oz is now about $1,280, giving over $800 net after tax. I live quite well on old age pension of $350. I owe the world SFA. What I found sickening was that all customers I ever had never ever made sure I got a socially just wage for which they would be prepared to work for themselves. I could not be friendly to any, because if I did, they'd just abuse the friendship by expecting me to fix gear for zilch. Nobody actually mixes business with pleasure ethically.
But I digress.

Patrick Turner.

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