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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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16th Jul 2013, 6:44 pm | #1 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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A Gramophone Amplifier from 'JUNK'.
I discovered an early 30's Columbia 'playing desk' a while back. It's fatal to put anything on the bench 'just to have a look' as one tends to get interested and one thing leads to another.
Well, it was much more of a saga than at first thought involving rewinding the ten million turns of hair like wire that is known as the pick up coil, redamping the needle holder, rewiring the arm, repairing the autostop mains switch and truing the turntable but that was just routine stuff and if you believe that... Well all was finished but what could I play it through? It was designed to connect to the pick up terminals of your EMI broadcast receiver thus turning it into a sort of radiogram and very well they worked too. Boring! I decided to build from scrap a suitable amplifier. An odd chassis was discovered in the 'stores' [Ha! ha!] and a hunt was undertaken to uncover suitable mains and output transformers.The mains was easy but the output transformer was slightly more elusive. Many were measured and sized up but as usual the most scruffy example proved to be the most suitable. It was decided to use octal valves as these were in a box with some other odds and ends on the workbench. A couple of holes were cut to accommodate the EL33 output valve and 5Y3G rectifier. I may well substitute pre war valves as there is a 4 volt heater tap on the transformer. Suitable valves would be an AC2/PEN and maybe a AC/SG as I have an ancient one. The old pick-up requires reasonable amplification to obtain full output so it was decided to employ a Mazda television IF/RF amplifier valve, the 6F13 as pre amp rather than the standard low impedance triode such as the 6LD20 or 6J5. I have a number of mouldy looking ones that soon cleaned up and look presentable. The 6F13 required a B8A holder so another hole was cut with care in the aluminium chassis. Yet more holes were required for the volume and tone controls, transformers, tag strips, loudspeaker sockets and the input connectors. The 6F13 is a high slope valve quoted a 9m/a per volt so I guessed it would have no problem dealing with humble audio frequencies. It was decided to use as much old junk as possible component wise. This included capacitors but of course they had to be of the correct value and no leaks even when warm! Some NOS electrolytics were discovered dated 1950. Surprisingly they didn't require reforming and look just the part on the old chassis secured with clips that were discovered in an old 'National Dried Milk' tin from the 1940's! I even used 4BA nuts and bolts removed from WW2 radio junk chassis and some lengths of cotton covered connecting wire. Some second hand valve holders were pressed into service together with some rather odd sleeving that smells like Rexine when warmed by the soldering iron. With a few suitable vintage looking resistors the component count was just about complete. The circuit was 'in my head' and just required a little tinkering with the values in the negative feedback loop to obtain full output without distortion and yes it works. The screen grid of the 6F13 is fed via a 1m resistor, the anode a 200k. This gives a good stage gain to the point where the valve actually becomes very slightly microphonic but you have to let her loose at full blast to hear the tiny trace of it. Negative feedback to the cathode is via a 10k in parallel with a .01uf. With the loudspeaker used this gives an excellent sound with very little needle scratch.[Soft Tone steel needles] The H.T. line is 295v smoothed via two 16uf cans and a choke that must have been saved from an old EMI radio. Hum level is very low but just enough to tell you the amp is switched on in a quiet room. This has been great fun and the amplifier only took a three evenings to complete. The sound quality is excellent with a good 4 watts of valve sound to play with. I usually take my '78 Disco' with my big boys toys [lorries] to the steam/vintage shows. I am going to add the amp and playing desk as it will be something new to display and the records and decks always attract a lot of attention. Regards, John. PS If you would like to see the circuit I can upload it in three parts. Power supply, output stage and pre amp. Oh...No Oxygen free cables were harmed while constructing this amplifier. |
16th Jul 2013, 8:37 pm | #2 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: A Gramophone amplifier from 'JUNK'.
Nice one! Always good when you can use stuff out of your junk drawer. Shows it's well stocked
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If I have seen further than others, it is because I was standing on a pile of failed experiments. |
16th Jul 2013, 8:49 pm | #3 |
Octode
Join Date: Jul 2011
Location: Stockport, Greater Manchester
Posts: 1,208
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Re: A Gramophone amplifier from 'JUNK'.
Well John, it properly looks the part!
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Robert |
16th Jul 2013, 9:25 pm | #4 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,550
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Re: A Gramophone amplifier from 'JUNK'.
Now that's what it was all about in the good old days! A couple of evenings with a box of bits, an old chassis and a soldering iron.....bliss!
Excellent stuff John. Rich PS. Just noticed you've even put pink 'inspection paint' on the solder connections! Talk about attention to detail.......!
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There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
17th Jul 2013, 7:53 am | #5 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: A Gramophone amplifier from 'JUNK'.
Yes Rich, the bottle of nail varnish is almost empty! I fear another embarrassing trip to the 'Boots' make up counter to replenish my stocks. J.
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17th Jul 2013, 8:22 am | #6 |
Hexode
Join Date: Jan 2013
Location: Ålesund, Norway
Posts: 361
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Re: A Gramophone amplifier from 'JUNK'.
Nice project John, I love seeing things like this too. When I was helping to clear out a garage after my friend passed away a few years ago I found several assorted gramaphone parts that I passed on to another friend of our "ilk" and these were put to similar use to repair other machines.
One item that did get taken into care was an amplifier from a jukebox, I know that it does or rather "did" work a few years ago and there was a large horn speaker amongst the treasures too. Didn't have the heart to let such treasures go to the recycling skip. Re the nail varnish: just tell them its for yourself because this worries them in the shop a whole lot more than a cover story ever would Tony |
17th Jul 2013, 10:13 am | #7 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: A Gramophone amplifier from 'JUNK'.
They do actually make special "men's" nail varnish. It's exactly the same stuff (basically, vehicle paint in a slightly-less-nasty solvent base) -- just in a narrower range of colours, and three times the price of the "ordinary" stuff marketed at women!
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If I have seen further than others, it is because I was standing on a pile of failed experiments. |
17th Jul 2013, 12:28 pm | #8 |
Dekatron
Join Date: Jul 2008
Location: Charmouth, Dorset, UK.
Posts: 3,601
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Re: A Gramophone amplifier from 'JUNK'.
Very nostalgic John, just the sort of thing I used to build in my tender years, the parts came from anything scrapped and of course the local government surplus store. I started off with a pair of 6V6s and eventually graduated to 6L6s, never made it to KT66s until I started work.
Peter |
17th Jul 2013, 12:33 pm | #9 | |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
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Re: A Gramophone amplifier from 'JUNK'.
Quote:
If bright red is OK, ISTR RS do some masquerading as "tamper evident seal" or some such bs but undoubtedly the local market or even a bootsale would be much cheaper....
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17th Jul 2013, 1:00 pm | #10 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: A Gramophone amplifier from 'JUNK'.
Hi John,
Classic Practical Wireless material. It's a pity that the magazine has gone, this would have made an excellent article. A spares box special. DFWB. |
17th Jul 2013, 1:39 pm | #11 |
Dekatron
Join Date: Mar 2008
Location: Worthing, West Sussex, UK
Posts: 5,185
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Re: A Gramophone amplifier from 'JUNK'.
Nice work John, The use of proper octal valves was a wise decision
It is about time I got back to finishing my amp project and stop messing with old tellies! Mark |
17th Jul 2013, 2:17 pm | #12 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
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Re: A Gramophone amplifier from 'JUNK'.
Lovely work John! But what about the gold-plated knobs and exotic hardwood end cheeks?!
What speaker(s) are you using? N. |
17th Jul 2013, 5:41 pm | #13 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: A Gramophone amplifier from 'JUNK'.
The speaker is a standard run of the mill Celestion 10 X 6 in a plywood box. [Ex WW2 factory speaker] I connected the output to a 100 ohm transformer and ran a lead down the garden to a small horn speaker. It set next doors farm dog barking and gave very good volume and clarity. Artie Shaw's 'Stardust' is amazing on HMV 78. Great entertainment value even 70 years on.
I thought that would apeal to you Peter. I get as much fun from a very simple project like this as I did when I was 14. At 65 I guess I should just brazen it out and pay my local Boots a visit. 'Nail varnish dear, what shade?' Quick exit from shop... Happy Days! John. |
18th Jul 2013, 8:11 pm | #14 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: A Gramophone amplifier from 'JUNK'.
Yes David! Do you remember F.G. Rayer? All his receivers were regenerative types in 1500 different presentations. Great stuff and it always worked. Very encouraging for a 12 year old. Oh Happy Days. John.
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18th Jul 2013, 9:57 pm | #15 |
Rest in Peace
Join Date: Feb 2008
Location: Dorset, UK.
Posts: 947
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Re: A Gramophone amplifier from 'JUNK'.
Practical Wireless is alive and flourishing.
The present editor, Ron Mannion is due to retire later this year, and his successor may well make some changes to expand the range of articles (or, perhaps, may not). I know they are looking for articles for the latter part of this and early next, year, so it might be worth writing. |
21st Jul 2013, 4:42 pm | #16 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: A Gramophone amplifier from 'JUNK'.
The amplifier has proved to be a bit of fun stimulating more interest than I would have thought. With that in mind I decided to continue the project..
I decided to incorporate the amplifier into a 'period' cabinet complete with record playing deck only requiring the addition of a suitable speaker. My school boy woodworking classes once again came to the rescue. [Thanks Mr Mathews] The 'Junk' theme had to continue so I decided to use some small sheets of 18mm ply pulled out of a skip last winter. Add to this some wood moulding, good old fashioned Rustins wood dye, screws, panel pins and even the wood glue itself, all pulled off a south coast tip years ago! The amplifier will be mounted at the bottom. The small holes in the panel at the top are drilled for ventilation and the pilot lamp. The two large ports are simply for decoration but may be incorporated into some internal cabinet lighting. A sheet of smoked Perspex [another dump find] was cut to size and used as a backing for the 'viewing window'. It is essential to be able to see the actual amplifier as so many displays are just DVD players playing into an old speaker in a vintage radio cabinet. URghh! I have yet to drill the top to incorporate the single 78 RPM motor. It is a most unusual arrangement and I have never seen anything like it before. [You think you have seen them all] I'll keep you guessing on this one. Once all the cutting is complete I intend to give it a few coats of durable varnish to protect it from the odd spots of rain. The pick up is a circa 1930 BTH [British Thompson Houston]. It had zero output when tried but the coil read around 3k so at least I didn't have the hair tangle I experienced with the Columbia.. On the bench it was soon discovered that all the damping rubbers had turned to concrete resulting in the needle holder being firmly attached to one of the pole pieces. With great care the pick up was dismantled and the needle armature removed. This was covered in white powder but was soon cleaned up with a mini brass wire brush and a miniature drill. New damping rubbers were cut to size and carefully reassembled. The horse shoe magnet is the strongest I have ever known in one of these old style pick ups. Amazing after 70 odd years. The results are truly amazing with plenty of output and bass. With new damping and soft tone needles it will be a lot kinder to records and is not too heavy. [I have some BEAST pick ups from the late 20's] More to come but not sure when. Regards, John. |
22nd Jul 2013, 11:25 am | #17 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: A Gramophone amplifier from 'JUNK'.
Hi John,
Absolutely wonderful. This what we should be all be doing, getting back to our engineering roots. To think we were constructing similar projects in our early teens. We both started about same age, around eleven years old. There's loads of bits and pieces lying about in this shop so later on this year I'll think about doing a similar grammohone amplifier project. Here's an idea for for someone. Find some bashed up old record player, chuck out the rubbishy one valve amplifier, you know the type, models with the single UL84 or EL84 and replace it with a Mullard 3-3 amplifier. Many of these cheap record players did have decent loudspeakers, just let down by the awful amplifier. Fit a stereo cartridge to the record deck and then construct a similar amplifier built into a matching cabinet. The 3-3 uses the EF86 which is getting expensive. There's loads of metal 6J7 valves available and I'm sure that valve would work OK as a substitute. Same goes for the EL84. I'm sure there is an octal power tetrode or pentode that has similar characteristics. Retain the 3-3's direct coupling between the amplifier and output valve if possible. Anyone keen on this idea? DFWB. |
22nd Jul 2013, 12:43 pm | #18 |
Dekatron
Join Date: Oct 2003
Location: Southport Lancashire, UK.
Posts: 3,221
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Re: A Gramophone amplifier from 'JUNK'.
I have an HMV badged version of the Columbia deck. It must be slightly later as it doesn't have the governor on the motor, but the pickup looks the same. I have to say that I have never been impressed with the sound quality I have got from it, and have experimented with new suspension (even though the old one seemed ok) and needles.
I had a later Garrard one and that sounded much fuller with less distortion. It is interesting that the BTH one sounds so good, even if older. |
22nd Jul 2013, 6:31 pm | #19 | |
Hexode
Join Date: Aug 2007
Location: S.W. London, UK.
Posts: 416
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Re: A Gramophone amplifier from 'JUNK'.
John, A superb project, well done.
Quote:
Vic
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22nd Jul 2013, 6:56 pm | #20 |
Retired Dormant Member
Join Date: Oct 2010
Location: Ipswich
Posts: 57
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Re: A Gramophone amplifier from 'JUNK'.
I too fondly remember the school workshop, it was still there by the late 1980s although my teacher did complain about increasing rules and looming budget cuts..
Why not use two turntables, build a mixer and create a modern day version of equipment I understand was used to provide sound for silent movies, or the installations that would have been used in discotheques since the 1970s? With the first I read in some old book about a dual turntable unit which had an inbuilt crossfader used in AV installations in the mid 20th century.. I've always been curious by what was used in the days before the Japanese Technics SL1200 became the main vinyl record deck used for DJ performances (would they have been called a "gramophone recital"?) Although not quite using completely home grown kit I've seen the folk from the Nederlands Gramofoon Genootschap do something similar at the photos of their events (I quite often read their website to practice my Dutch), showing some early setups predating Armin Van Buuren and Tiësto by a few years |