UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Success Stories

Notices

Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

Closed Thread
 
Thread Tools
Old 10th Mar 2017, 6:34 pm   #1
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Ekco AC77 - well on the way - not there yet!

As mentioned in another thread, I bought this set back in 1985 with a view to restoring it, but when I took the back off and looked inside, I put it in a dark corner of the left and forgot about it till it resurfaced when we move house in 1991, when it went back up into the loft again and was once more, forgotten about. Then in 2013, when fumbling about it the loft, I came across it again, and dithered about whether to offer it for spares, or do a total strip-down and rebuild.

The only thing I'd ever done that came close to that was to used an R1155 as a donor set, saving only the 'switchery', coils, IFTs and so forth, fitting an integral power supply, output stage, speaker, BFO and S Meter, a new front panel and fitting more modern valves. That was based on an article in Short-Wave mag, and served me well for several years.

There were a number of factors to weigh up before jumping in:

Firstly, the screen-printed glass dial had lost more of its lettering and a scan wasn't available to attempt to replicate it with a waterslide transfer. Without a new dial it would have been a non-starter. Luckily, someone alerted me to the fact that Ben Djikman in the Netherlands had them on his website, albeit with continental spelling of some stations. I contacted Ben to see if he could do the dial with English spellings throughout, and he said only if I could get orders for a batch of ten to be made. With an uncommon set such as the AC77, of no great value and not sought after, that seemed unlikely, so I opted for the one that he had, and excellent it is too.

Secondly, was the mains transformer and output transformer windings intact? Had they not been, rewinds would have been too expensive to contemplate. Luckily, they were both intact, though the mains transformer voltage selector panel needed replacement.

Lastly, was the field coil on the mains-energised speaker intact? No, it wasn't, but otherwise, though rusty, the speaker was in sound condition. I figured that I could rewind the field coil, as indeed I did. But with 2.3kms of wire and 20,000 or so turns, that sidetracked me into designing and building a coil winder, powered by a sewing machine motor. More of that later.

I decided to set about restoring the power supply chassis first. This is connected to the upper receiver chassis via a wiring loom, which terminates on a crude tagstrip arrangement at the rear of the power supply chassis, which has a mating tagstrip, the two being soldered together. For me, this was an example where originality had to be sacrificed for reasons of safety and serviceability, so I designed a new tagstrip with screw terminals, and a safety cover. This entailed turning brass terminals on the lathe, and making a printed circuit board strip into which the terminals were soldered. Pictures will make this clearer later.

The chassis had one electrolytic can mounted above chassis, and a two 8uF caps in a cardboard box which was a 'service replacement' probably fitted during the war years beneath the chassis, either on a DIY basis or by an unskilled bodger. The clip meant to hold it in place was missing, crudely soldered live connections had been covered with fabric insulation tape, and the box was swinging loose on the wires. I decided that the best solution here was to make a new 'box' with double sided PCB material, and to create a brown paper label to roughly replicate the old one, then to make a clip to fit the new box in place.

The vertical 16uF can above chassis was scruffy, so I decided to clean it up, re-stuff it and to create and fix a waterslide transfer to say what the cap is.

The first task was to remove everything from the chassis, to de-rust it using a 'power file' and rust inhibitor, then to use an acid etch primer. Gary Tempest tipped me off that the nearest colour to Ekco chassis was Halfords own brand Ford Dove Grey, so I gave it a couple of liberal cots, then when dry, set about fitting the components back, fit the new tagstrip, and rewire the chassis.

The first pic shows the PSU as found. Second pic shows the unsoldered two-part tag-strip which joins the power loom to the receiver chassis. Third pic shows the underside of the chassis with the service replacement twin 8uF paper box capacitors hanging loose on taped up perished wiring. Fourth pic shows the poor state of under chassis wiring, and the last pic is the power supply stripped ready for de-rusting with a power file and priming with acid etch primer.

In the next post I'll cover the rebuild of the power supply.
Attached Thumbnails
Click image for larger version

Name:	Power Supply of AC77.jpg
Views:	195
Size:	94.7 KB
ID:	138973   Click image for larger version

Name:	Tag-strip unsoldered.jpg
Views:	184
Size:	116.0 KB
ID:	138974   Click image for larger version

Name:	Underside of PSU chassis as found.jpg
Views:	181
Size:	89.9 KB
ID:	138975   Click image for larger version

Name:	Poor state of PSU under chassis wiring.jpg
Views:	165
Size:	105.4 KB
ID:	138977   Click image for larger version

Name:	AC77 PSU Chasiss stripped ready for de rusting and repainting.jpg
Views:	154
Size:	87.4 KB
ID:	138978  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 10th Mar 2017, 6:46 pm   #2
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

So, time to rebuild the PSU.

First pic is a replica box made from double sided PCB sheet soldered together, prior to soldering the lid on.

Second pic is the label I made and fitted along the lines of the original.

Third pic shows the 16uF can as found. Some may say 'leave it like that - it's patina'. No it's not - it's decay. 'Patina' is what you get on a Chippendale chair!

Fourth pic is the can cut open near the base with a 500V 16uF high ripple rated cap in place, and a new waterslide transfer applied.

Fifth pic is the can refitted to the base with an internal aluminium sleeve and 'Super Steel' two-part epoxy cement.

Next task was to make and fit the new tag-strip prior to re-wiring.
Attached Thumbnails
Click image for larger version

Name:	Replica Smoothing Cap block.jpg
Views:	137
Size:	68.0 KB
ID:	138979   Click image for larger version

Name:	Replica Smottihng Cap Block finished.jpg
Views:	141
Size:	103.4 KB
ID:	138980   Click image for larger version

Name:	16 uF electrolytic can.jpg
Views:	137
Size:	39.3 KB
ID:	138981   Click image for larger version

Name:	Smoothing cap can ready to stuff.jpg
Views:	146
Size:	39.0 KB
ID:	138982   Click image for larger version

Name:	Smoothing cap can with waterslide tranfer.jpg
Views:	134
Size:	28.2 KB
ID:	138983  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 10th Mar 2017, 7:07 pm   #3
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

So here's the power supply terminal-strip detail:

First pic is the PCB I etched to secure the terminals in place on the rear apron.

Second pic is of the brass terminals that I turned on the lathe, tapped 4 BA for external eye tags to be fitted, and internally, as solder points for the wiring.

Third pic shows the terminals soldered to the PCB.

Fourth pic shows the outside of the terminal strip, with the terminals passing through a paxolin strip which secures the PCB to the rear apron. The wiring loom to the receiver chassis will be fixed to those terminals, then a Paxolin safety strip fitted over them.

Fifth pic shows the internal wiring completed and a bracket made and fitted to hold the replica twin cap box in place, as it would have been originally.
Attached Thumbnails
Click image for larger version

Name:	Terminal strip pic1.jpg
Views:	112
Size:	17.7 KB
ID:	138984   Click image for larger version

Name:	Terminals for PSU Chassis take-off.jpg
Views:	114
Size:	20.1 KB
ID:	138985   Click image for larger version

Name:	Terminal srtrip pic3.jpg
Views:	115
Size:	21.4 KB
ID:	138986   Click image for larger version

Name:	Terminal strip for eyelet tags.jpg
Views:	138
Size:	69.2 KB
ID:	138987   Click image for larger version

Name:	Terminal strip on inside of PSU_edited-2.jpg
Views:	125
Size:	66.6 KB
ID:	138988  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 10th Mar 2017, 7:31 pm   #4
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

The Paxolin Voltage Selector strip on the mains transformer was too bowed as will be seen in the first picture. I'd made a new brass screw as can be seen, but as soon as it was finger tight, the original Paxolin selector panel bowed, so using that as a pattern, I made a new panel. (In the second pic, the old one is at the bottom).

When powered up, the PSU worked fine, that that's a success story at least!

Next, the speaker refurbishment and rewinding of the field coil.

The third pic shows the poor state of the speaker with the field coil removed and the hum bucking coil now hanging loose.

Fourth pic shows the heavily rusted pole piece with the field coil in place.

Fifth pic shows the open circuit field coil, which is a very naughty boy!
Attached Thumbnails
Click image for larger version

Name:	Power Supply above chassis restored.jpg
Views:	139
Size:	69.9 KB
ID:	138990   Click image for larger version

Name:	Voltage Selector old & new panels.jpg
Views:	132
Size:	41.5 KB
ID:	138991   Click image for larger version

Name:	Speaker as found.jpg
Views:	146
Size:	78.4 KB
ID:	138992   Click image for larger version

Name:	Field Coil off speaker rear.jpg
Views:	146
Size:	79.1 KB
ID:	138993   Click image for larger version

Name:	Field Coil removed AC77.jpg
Views:	139
Size:	71.1 KB
ID:	138994  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 10th Mar 2017, 7:32 pm   #5
Robert Darwent
Heptode
 
Robert Darwent's Avatar
 
Join Date: Aug 2006
Location: Sheffield, South Yorkshire, UK
Posts: 981
Default Re: Ekco AC77 - well on the way - not there yet!

Hi David,

Your rebuilt PSU board looks first rate! I can see that you've been heavily influenced by some of Gary Tempest's Ekco restorations, as if I didn't know otherwise when viewing the images I would have attributed the work as his - no denigration intended there, to emulate Gary's handiwork is no mean feat and is just exemplary! Particularly like your pcb terminal strip and brass terminals. Will look forward to the further updates.

Best wishes and regards
__________________

Robert G0UHF
www.wavesintheair.co.uk
Robert Darwent is offline  
Old 10th Mar 2017, 8:04 pm   #6
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

On with the field coil re-wind.

First I checked the gauge of the wire and weight it to see roughly how much I'd need to buy.
The resistance of the coil needed to be 2,000 Ohms and the gauge was 38SWG - 0.52mm. I calculated from the ohms per meter for that gauge that 2.3 KMs of wire would be needed, and that a 500g spool would be more than enough. I used the original coil tube, but not the cardboard end cheeks, as they were too flimsy, so I used them as a pattern to make new Paxolin cheeks which I fitted to the tube with two-part epoxy. I used solderable wire from wires&co.

The second pic shows the coil winder that I made which had adjustable tensioning springs on the feed spool shaft to keep the wire fed under tension so that the feed coil couldn't 'free-wheel' if I slowed or stopped the motor, the speed of which is controlled by a foot pedal. I won't go 'off piste' in this thread to bang on about the wider, which is a diffrent topic in its own right, and I've probably covered it in other threads, as well as in the BVWS Bulletin. Suffice to say that I wound on turns until the field coil former was full, figuring that I wouldn't be too far off the 2,000 Ohms needed. Not really critical as it's not an RF coil in a tuned circuit. 1,900 or 2,100 Ohms or whatever would do. (+/- 5%).

As the wire was solderable (the enamel acts like flux), I touched the wire with my soldering iron to tin it so I could check the resistance. had it been much less than 2,000 Ohms, I'd have insulated the tinned spot and added more turns - had it been more than 2,000 Ohms, I'd have removed turns, testing at intervals. Luck smiled on me that day - the coil was 1,997 Ohms! I fitted a lead out wire leaving the 38swg nice and slack and secured the lead out wire tightly so as not to fracture the joint.. As the original coil was wrapped in black plastic, I put a couple of turns of black Gaffa tape to finish off the coil.

I de-rusted the pole piece and sprayed it - see pic 3
I then fitted the field coil in place - see pic 4.
I re-sprayed the speaker body and fitted it back on the baffle board - pic 5.

Next, I tuned my attention to the main chassis - more of that later.
Attached Thumbnails
Click image for larger version

Name:	Field Coil unravelled!.jpg
Views:	137
Size:	67.6 KB
ID:	138995   Click image for larger version

Name:	Overhead view new counter.jpg
Views:	146
Size:	65.3 KB
ID:	138996   Click image for larger version

Name:	Field Coil Pole Piece Dove Grey, AC77.jpg
Views:	138
Size:	56.2 KB
ID:	138998   Click image for larger version

Name:	New field coil close up.jpg
Views:	145
Size:	61.9 KB
ID:	138999   Click image for larger version

Name:	Speaker & field coil restored.jpg
Views:	139
Size:	67.7 KB
ID:	139000  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 10th Mar 2017, 8:08 pm   #7
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

Quote:
Originally Posted by Robert Darwent View Post
Your rebuilt PSU board looks first rate! I can see that you've been heavily influenced by some of Gary Tempest's Ekco restorations, as if I didn't know otherwise when viewing the images I would have attributed the work as his - no denigration intended there, to emulate Gary's handiwork is no mean feat and is just exemplary!.
Thanks Robert - that's praise indeed - I walk in Gary's shadow!
__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 10th Mar 2017, 8:31 pm   #8
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 5,953
Default Re: Ekco AC77 - well on the way - not there yet!

Lovely job without a doubt. Concours De Elegance.
__________________
G8JET BVWS Member and V.M.A.R.S
HamishBoxer is online now  
Old 11th Mar 2017, 2:34 am   #9
Lloyd 1985
Octode
 
Lloyd 1985's Avatar
 
Join Date: Jun 2008
Location: Coningsby, Lincolnshire, UK.
Posts: 1,332
Default Re: Ekco AC77 - well on the way - not there yet!

Hi David,

The power chassis and speaker look like new! I like the replacement for the chassis interconnect, much better.

I have one of these sets too, and also a battery version that uses a vibrator to generate the HT from the 4V LT battery. That one was practically just a chassis hanging from 2/3rds of a cabinet! I was lucky enough to find an empty cabinet for sale to re-house it. It also needs a new tuning scale glass, as although it was intact, all the lettering had faded away! The scale is different on this one as it is painted white on the rear of the lettering, with just a thin strip in the middle through which you can see the scale pointer. I hope to get it working one day!

I'll be following this thread with interest!

Regards,
Lloyd.
Lloyd 1985 is online now  
Old 11th Mar 2017, 10:29 am   #10
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

Thanks for the encouraging comment on the work in progress guys.

Though I took lots of photos, that in itself isn't enough to use as a 'road-map' when rebuilding, so I also made lots of drawings showing the location and interconnections of components. Fortunately, the Ekco service data includes excellent diagrams of the underside and top of the chassis, but not in enough detail to complete the re-build. As will be seen from the first picture, (IFT1 and V2/3 valve-holders) the chassis and wiring were in such a state that it wasn't possible to do anything other than a complete strip-down and rebuild.

The pictures alone couldn't be relied upon so I drew lots of diagrams, which hopefully, with reference to the cicuit as well, should enable me to see the job through to a successful conclusion. There's little point in peppering these posts with copious drawings, so I've attached just one to give an idea.

With everything removed from the chassis, I set about de-rusting it, treating it with rust inhibitor, then as with the PSU chassis, spraying it with acid etch primer and two good coats of Halford's Ford Dove Grey (which doesn't actually look anything like 'grey', but certainly fits the bill). To remove the rust In used a cheap Aldi 'Workzone' adjustable speed 'power file' (see pic 3 below), which has abrasive belts which last quite a while. The fourth pic shows the chassis half de-rusted to show how effective the power file is, and the last pic shows the chassis after priming and two good coats of top coat. I did the spraying on a warm day in the greenhouse, which is as dust free as can be. As the paint - like almost all modern aerosols - is water based acrylic, no nasty fumes to breath in.
Attached Thumbnails
Click image for larger version

Name:	IFT2 V2 & V3.jpg
Views:	114
Size:	92.8 KB
ID:	139016   Click image for larger version

Name:	AC77 Output Transformer and C21 22 24 etc tagboard wiring.jpg
Views:	114
Size:	56.5 KB
ID:	139017   Click image for larger version

Name:	Aldi electric file.jpg
Views:	124
Size:	50.3 KB
ID:	139018   Click image for larger version

Name:	Chassi top part derusted.jpg
Views:	121
Size:	83.0 KB
ID:	139019   Click image for larger version

Name:	Chassis resprayed ready for rebuild.jpg
Views:	119
Size:	44.1 KB
ID:	139020  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 11th Mar 2017, 11:13 am   #11
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

Where possible, I used things like the old tag-boards to rebuild. I re-stuffed original capacitors and used 1Watt and 2 Watt metal film resistors to look as close as possible to original 1/2 Watt ones. The first pic shows two tag-boards before and after being rebuilt. I made two brackets to support them as I didn't like the original fitments. Where possible I re-stuffed the old caps, some of which had side connections rather than axial. The originals had been sealed with pitch at the ends so I used 'Super Steel' two-part epoxy to seal the ends, (which - despite its name, is non-conductive). If the label on the old cap was too far-gone, I created a new one as authentically as I could - see the electrolytic is the fourth pic, and the label in the last pic. Don't know what 11/07 signified - it was on the original).
Attached Thumbnails
Click image for larger version

Name:	Tagboards old & new.jpg
Views:	90
Size:	47.7 KB
ID:	139023   Click image for larger version

Name:	Old cap unstuffed.jpg
Views:	94
Size:	44.0 KB
ID:	139029   Click image for larger version

Name:	Stuffed cap1_edited-1.jpg
Views:	89
Size:	24.9 KB
ID:	139030   Click image for larger version

Name:	Six re-stuffed caps AC77.jpg
Views:	87
Size:	26.1 KB
ID:	139031   Click image for larger version

Name:	AC 77 C25 CAP LABEL.jpg
Views:	84
Size:	47.8 KB
ID:	139032  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 11th Mar 2017, 11:44 am   #12
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

The frame of the three-gang tuning capacitor was in quite a rusty state and had integral compression trimmers which I dismantled. I cleaned off as much rust as I could with 220g wet and dry and a brass bristled brush, then gave it half an hour in my ultrasonic bath. It came up well enough to mask the vanes and spray the framework. When reassembled and the bearings lubricated with silicone grease, it did what it's supposed to - varied the capacitance, and the trimmers worked too. I didn't take any pics after it was refurbished, other than with it back on the chassis.

At the time, I didn't know about electrostatic cleaning, and have not yet tried it, but on the face of things, it looks to be a very effective way of rust removal of iron and steel items. The appeal is that apart from a car battery charger, it only uses household items such as short lengths of re-bar for anodes, and washing soda as an electrolyte. See here as an example:

https://www.youtube.com/watch?v=54ADeB6V1rQ

I cleaned up the cans of the oscillator coil and IFTs, testing the continuity of the windings before refitting them to the chassis. The two existing valve top cap clips were a bit manky so I fashioned new ones from brass sheet. See old and two new clips in pic three.

Earlier I mentioned that had a new dial not been available, I'd have not embarked on the restoration. Pic 4 shows the state of the old dial - pic 5 is a pic of the reproduction screen printed dial I obtained from Ben Djikman. As will be seen, some words are in continental spelling, (EG: Britisch, Moscou, Bruxelles), but I can live with that. The dials is 5mm thick glass - same as the original, but of much higher quality. It's not a difficult dial to re-create in say Photoshop, but I think it would be really quite costly to get it screen printed, so I'm quite content and consider myself luck that I was able to get the dial. (Sorry the pic is a bit out of focus, and won't be easy to read).
Attached Thumbnails
Click image for larger version

Name:	Tuning cap trimmers dismantled.jpg
Views:	106
Size:	60.9 KB
ID:	139033   Click image for larger version

Name:	Reassembly back view.jpg
Views:	122
Size:	73.0 KB
ID:	139034   Click image for larger version

Name:	Top-cap clips.jpg
Views:	109
Size:	43.1 KB
ID:	139035   Click image for larger version

Name:	Dial view.jpg
Views:	106
Size:	64.7 KB
ID:	139036   Click image for larger version

Name:	Ekco AC77 Dail (Continental).jpg
Views:	102
Size:	24.6 KB
ID:	139041  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 11th Mar 2017, 12:15 pm   #13
Aerodyne
Octode
 
Aerodyne's Avatar
 
Join Date: Jun 2004
Location: Hampton Vale, Peterborough, UK.
Posts: 1,630
Default Re: Ekco AC77 - well on the way - not there yet!

Brilliant work, David. You walk in no-one's shadow. That Aldi power file certainly does the business. I only came across this thread today (Saturday) and already there's a lot of interest in it.
I am especially impressed with your thoroughness. 'It'll do' is not part o your vocabulary.
Great restoration.

Tony
Aerodyne is offline  
Old 11th Mar 2017, 4:35 pm   #14
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

Quote:
Originally Posted by Aerodyne View Post
I am especially impressed with your thoroughness. 'It'll do' is not part of your vocabulary.
Great restoration.
Tony
Thanks for your kind words of encouragement Tony.

Still some way to go with it yet till I get to the 'MOT' stage - 'moment of truth'!
__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Old 11th Mar 2017, 5:24 pm   #15
David G4EBT
Dekatron
 
David G4EBT's Avatar
 
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,151
Default Re: Ekco AC77 - well on the way - not there yet!

The last work I did on the set was to attend to the Band pass Filter Unit, which contains the wave-change switch.

Rather worryingly, the maker's service data states:

"The wave-change switch is incorporated in the same screening can as the bandpass input filter and normally should not be subject to atmospheric action.
Should the switch or bandpass filter give trouble, no attempt at repair should be made - the complete unit must be returned to EKCO works for replacement'.

Well it did give trouble - some connections on the switch were open circuit, and the shaft was hard to move. I fitted some heat shrink tube around the switch shaft to form a reservoir for Plus Gas penetrating fluid (never WD40 - ok for garden gate hinges, but not wave-change switches). (See pic I below). That enabled the switch to move freely, but on removing the cover from the filter, the wave-change switch appeared to be 'sealed'. On further examination, it was surrounded by a paper strip and coated in wax, (just visible in pic 2). On removing the paper there seemed to be as much congealed wax on the switch contacts as on the paper which had surrounded it.

I degreased the contacts and lubricated them with Servisol then fitted the cover back on. I made no attempt to disturb the fragile wires of the coils in the filter - wound on beech dowels and rather beyond my comprehension as to which coil is which as there is no diagram. (See pic 3). On testing the continuity and resistance of the coils and comparing them with the table, they seemed close enough to be acceptable, though the connections between 2 & 8 are a little high at 41R when the spec is 30R, albeit before cleaning the switch, between those point was open circuit.

Only time will tell if this unit is functioning correctly.

That's about the stage that I'm up to, so the next phase is to start wiring up the receiver chassis. The correct approach is of course to be single-minded and only deal with one project at a time, seeing it through to conclusion before starting another project. I've never really been able to do that as other projects pop up to catch my attention and off I go on a frolic. Last autumn I restored a little 'Figaro Special' which could have waited, then another one came along so I restored that for my younger son who shares my interest to an extent.

This week's sidetrack is a lathe rev counter I've just taken delivery of to fit to my woodturning lathe, which uses a magnetic proximity detector ('Hall Effect'). This is yet another act of frivolity on my part, as I can tell what speed my lathe is running at and I've got a non-contact rev counter which I just have to point at the lathe shaft anyway. But at only 12.00, I succumbed. Probably undiagnosed ADHD or something.

Really, having done so much at this AC77, which - as well as the Coil Winder project - has involved other ancillary projects such as making valve-base adaptors to enable me to test the AC77 valves on my Taylor 45 Valve tester, I should now get on with finishing the AC77, so that before the year is out, it qualifies as a 'success story' - not simply as 'work in progress!'
Attached Thumbnails
Click image for larger version

Name:	Bandpass Filter shaft oiling.jpg
Views:	102
Size:	36.0 KB
ID:	139059   Click image for larger version

Name:	Bandpass Filter rear of sealed switch.jpg
Views:	101
Size:	80.6 KB
ID:	139060   Click image for larger version

Name:	Bandpass Filter view2_edited-1.jpg
Views:	96
Size:	69.9 KB
ID:	139061   Click image for larger version

Name:	Bandpass Filter Resistance Chart.jpg
Views:	94
Size:	117.7 KB
ID:	139062   Click image for larger version

Name:	AC77 BANDPASS FILTER RESISTANCES.jpg
Views:	85
Size:	47.9 KB
ID:	139063  

__________________
David.
BVWS Member.
G-QRP Club member 1339.
David G4EBT is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:11 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.