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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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23rd May 2017, 10:17 pm | #21 | |
Retired Dormant Member
Join Date: Dec 2015
Location: Barnsley, South Yorkshire, UK.
Posts: 172
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Re: Advice stereo valve amp kit or scratch ?
Quote:
I get a lot of pleasure building stuff even better when it works first time. My Son and family went to my brothers wedding recently I couldn't go because of a heart attack on the day before, he met my aunt (same age as me) she asked my son if I still take things apart and make stuff like a mad scientist something she remembers when we were growing up together, its nice to be remembered this way. Steve |
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24th May 2017, 1:04 am | #22 |
Banned
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Location: Mareeba, North Queensland, Australia
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Re: Advice stereo valve amp kit or scratch ?
I liked your last post captainking I myself am still known as "the black sheep/mad scientist" of the family.
Back to output transformers and your idea of DIY amps. WITH care, and some advice your home made amp can equal, and even exceed a ready made purchased one. Unobtainium parts are usually un necessary. Mains transformers and output transformers are the "critical parts". The statement will get me shot, but as a transformer winder for over 50 years (Im 64 tomorrow) I understand how they work. Forget trying to wind your own unless you are a REAL masochist. When specifying the ratings, allow a "little extra" in both heater windings and high tension windings. This will ensure that any "additions" you make will be catered for with unduly over loading the basic unit. With output transformers, specify a low flux density at low frequencies. 1. Choosing a mains transformer: Be generous!!! Big is beautiful, BUT keep it sensible. A welding transformer size is stupid and un necessary. A DECENT design is whats required. A custom wound toroid is today a very big improvement with very little increase in cost. There are a few SPECIAL rules that apply to toroids though. hint, hint. 2. Choosing output transformers: Be generous!!! Once again big is beautiful, and as Ed has already mentioned, be wary of "super steel" there ISNT ANY!! Britain and Australia have different commercial names for transformer iron, but the thing to look for, and is widely available is 5% silicon, grain oriented steel laminations. A rule my father taught me years ago: A big transformer using ordinary cheap laminations will ALWAYS be better than a small transformer of special laminations . Comes down to several things! A smaller transfomer passing the same amount of electricity will almost always create more heat than a large one. A smaller transformer running high flux densities can/may have higher distortion levels at lower frequencies, and less high frequency response due to losses in both iron and wire size. A smaller transformer is generally "harder" to make, takes more time and therefore costs more. For Hi-Fi transformers I generally specify a design that does not exceed 1 Tesla at 50 Hz at maximum power. I also try and make a design that is at least 7 sections of interleaved pri/secondary layers with staggered interconnections to partly equalize ohmic resistances. ( Turns are shorter on the core than on the outside of the transfomer) I recommend approaching Ed Dinning about your requirements as he has been doing all types of transformers for many years. (WE actually spoke when he was in Melbourne, and our designs and ideas are very similar). There will be a new amp of my own going into the DIY section shortly, and I am waiting with bated breath for Andrew to start his new amp that has excellent iron Joe |
24th May 2017, 10:49 am | #23 |
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Re: Advice stereo valve amp kit or scratch ?
Cheers Joe.
For wise words I wouldn't dream of trying to wind my own something for the expert and yes I am very likely to take up the off made by Ed BTW my other aunt who I grew up with lives in Western Australia her name is Sheila no pun intended All the best, Steve. PS if you do a lot of reading check out Captain's French Adventures on Amazon will give an insight what makes me tick sold quite a few in Australia |
25th May 2017, 12:07 am | #24 | |
Octode
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
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Re: Advice stereo valve amp kit or scratch ?
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But I'll speak via email rather than hijack Captain King's thread. Andy. |
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25th May 2017, 12:29 am | #25 |
Octode
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
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Re: Advice stereo valve amp kit or scratch ?
Captain King, I may have missed a reply but you mention looking for stereo versions?
All a stereo amp is, as I am sure you know, is 2 mono amps on the same chassis. So you have a choice here. Build 2 identical mono amps and use them together. (more expensive as 2 mains transformers needed, but potentially much lighter to lift. This is not as daft as it sounds, a stereo EL34 amp chassis using decent sized transformers is going to be a heavy beast. it's unavoidable.) Build your 2 amps on one chassis and simply double up on the PSU rating. At this juncture I would STRONGLY advise using silicon rectifiers on the HT. Cheaper by a country mile, more reliable and cooler running and you won't need a hefty 5V at 4 amp winding for a pair of GZ34 heaters. Again saving weight and cost. Not to mention limitations on the size of the first capacitor off the rectifier. In fact if i was to build 2 mono amps I'd still use silicon rectifiers, recent experience with my home brew EL34 monos bore this out and GZ34's aint a cheap valve. Finally, consider other circuits as well as the admittedly excellent Mullard circuit. I adapted the Leak TL25plus circuit for my monos and I am highly chuffed with their performance especially after I tweaked them to use a triode input stage which reduced the sensitivity to a modern level and dropped the hum and noise to barely audible levels with my ear pressed to the speaker. Also consider alternatives to valves such as the expensive EF86. The Octal 6SJ7 is one that springs to mind being similar but cheaper by an order of magnitude for quality ex military russian NOS. Good luck and have fun! Andy |
25th May 2017, 7:18 am | #26 |
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Re: Advice stereo valve amp kit or scratch ?
While thinking big and considering all things, don't leave the word 'valve' in the title unchallenged. Designing a good transistor amplifier is a somewhat bigger challenge than doing it with valves, but you can go further and you'll learn more.
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
25th May 2017, 7:26 pm | #27 | |
Retired Dormant Member
Join Date: Dec 2015
Location: Barnsley, South Yorkshire, UK.
Posts: 172
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Re: Advice stereo valve amp kit or scratch ?
Quote:
you must have been reading my thoughts I was looking at an old tandy book from the 70's which has mullard and other am designs in it so was checking for leak circuits. Yes I will incorporate both amps on one chassis and like your input re silicone rectifiers. I am going to have a good search want to try and get it right. Thanks very much for your advice it makes the decision so much easier when deciding because people like you and everyone on this site has been there and done it and its so nice that you give advice freely All the very best Steve |
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25th May 2017, 9:42 pm | #28 | |
Retired Dormant Member
Join Date: Dec 2015
Location: Barnsley, South Yorkshire, UK.
Posts: 172
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Re: Advice stereo valve amp kit or scratch ?
Quote:
Built a few small amps with transistors but nothing HiFi topend Iv'e got some nice circuits for top end amps just never got round to building one, when i finally get to France and finish building my Moulin I will have time to do more in my workshop.....wife willing! Regards steve |
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28th May 2017, 8:32 am | #29 |
Heptode
Join Date: Oct 2008
Location: Aalborg, Denmark
Posts: 903
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Re: Advice stereo valve amp kit or scratch ?
I've used VVT-iron in the past and been very satisfied.
http://www.vvttransformers.co.uk/ They're now back in business with transformers for valve-amplifiers even if they shut down that department some years ago. My amplifier project is here and it is right from scratch. I didn't know the first thing about building with valves then. Possibly it wasn't a good idea to start out with doing a class AB2 amplifier but in the end everything worked out very well. The amplifier is still in daily use. http://www.vintage-radio.net/forum/s...ad.php?t=67511 The output valves I used are 2C34 or RK34. I didn't know much about them then. Mostly that they look good and were $1 a piece, NOS. Today I know a lot more about them and it's no longer any wonder the amplifier sounds good. They come from a prominent family: DET19 4074-A 33A-138A CV18 CV1061 VT61 VT224 And very similar to: 6A6 6N7 53 4074-B 5694 CV1573 10E-142 VT61A TV03-10 Good luck with the Mullard-project. |
29th May 2017, 2:21 am | #30 |
Hexode
Join Date: Apr 2017
Location: Buderim, Queensland, Australia.
Posts: 428
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Re: Advice stereo valve amp kit or scratch ?
Hi there,
the Australian magazine "Silicon Chip" had an article on a valve stereo amp a few years ago, and you could buy it as a kit. Started in November 2014 issue. http://www.siliconchip.com.au/Issue/...1?res=nonflash The different thing about this design is that they used PA line transformers. As a minimum, it may give you some ideas. Good luck. |
29th May 2017, 11:29 am | #31 | |
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Re: Advice stereo valve amp kit or scratch ?
Quote:
All the best Steve |
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29th May 2017, 11:39 am | #32 | |
Retired Dormant Member
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Location: Barnsley, South Yorkshire, UK.
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Re: Advice stereo valve amp kit or scratch ?
Quote:
I seem to remember EPE featuring this thanks for sparking my memory bank I will have to check my back issues All the best Steve |
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