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There was a 'before the internet nostalgia' thread on another forum that got me thinking. I used to do a lot of things before the internet, which I don't do now, and one of them was building home hi-fi and PA equipment. I built a stereo Maplin Millennium valve amp in 1996, which is a pair of EL34 valves in push-pull like the old Mullard amps. I ran it for a year or so until the mains transformer blew and replaced it in my final year at university. It eventually blew again but I couldn't get another new transformer because Maplin discontinued them, so it has sat on the sideboard at home ever since. A couple of years ago I noticed the guy who originally designed the Millennium amp had a website so I contacted him about it. He basically said the original spec was downgraded by Maplin to save money and the transformer was only powerful enough to supply a mono amplifier. I'd been driving a stereo pair which was constantly overloading it, hence it kept blowing. He did however have some proper spec ones. I didn't buy one at the time, but I returned a few weeks ago to find he's now got a Paypal plugin and so I ordered away... Here is the amp, pre-meddling: I thought I'd start a valve related thread because I've got a couple of valve projects up my sleeve and I'll keep them in one place. Hopefully a couple of you will also be into your valve amps and post your stuff up as well
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Bet that's 'kin loud!! How many EL34s do you need for your front room?? haha I'm a gigging guitarist and have taken out two of the four EL34s in my Marshall because it was too loud for every venue I played at Guitar amps are a bit different though I guess, they're designed to push the valves into saturation and sound better the harder (louder) they're pushed. Unfortunately most sound guys don't understand hence the removal of valves to obtain higher saturation at lower volumes. When I get my new amp (little 15 watt class A Laney) this week I'll join in the modding Marshall did a far better job on my main amp than I ever could, so that is staying standard bar the Mullards I've put in.
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I've got Rovers.
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Once the transformer turned up I fitted it up like-for-like with the old one, but didn't seem to be able to get it to work. There was a pop when I switch it on but no glow from the heaters. On further inspection the HT fuse inside had blown (HT = the one on the high-voltage line) so I wasn't sure what was up. The heaters are powered by 6V and just over 6V showed on the low tension - good. A shade over 500V AC showed on the transformer, so it's a bit higher than rated, but this is open load so it will read a fair bit higher than the loaded voltage. Well over 750V DC once rectified though - which was a bit scary watching the multimeter needle fly off the scale but, again, no problems there. I plugged the valves in one amp with a fresh fuse and fired it up. There was a blue flash inside one of the output valves which popped the fuse, so I'm assuming that was a dead valve, so I swapped it out. However, I still wasn't getting any heater glow from them. I looked up all the valve datasheets for the pin-outs so I could check for continuity on all the heater coils. All were fine. I then checked for voltage at the valve bases and only one at the far end was showing voltage. So I had to open the amp up again. On valve amps you've got to be EXTREMELY careful because of the high voltage, so I unplugged it completely and put the multimeter across the HT and waited for the voltage to drop off. Once safe I could start pulling wires. I found the heater wire was loose in the connector, so the connector was showing 6V but the wire going off to the valves wasn't connected. Once reattached I connected it all back up and flicked on the power. This time it all lit up properly and started kicking out heat like it should do. I forgot to polish the valves before I turned it on so it quickly started smelling of burning fingerprints, but it officially works again! I scored 4 nice matched EL34 output valves on eBay and it was finally all up and running again. To put a strange perspective on things, the last time I ran this was before I had MP3s. Old meets new... I'm planning to incorporate a switch-box so I can run multiple inputs, which means I'll be able to hook up the DVD player, TV and an aux input. I'm also quite tempted to wire up a tone control once I've deciphered the circuits in my GEC book, since most of them include a pre-amp stage that I won't want.
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Bet that's 'kin loud!! How many EL34s do you need for your front room?? haha I'm a gigging guitarist and have taken out two of the four EL34s in my Marshall because it was too loud for every venue I played at Guitar amps are a bit different though I guess, they're designed to push the valves into saturation and sound better the harder (louder) they're pushed. Unfortunately most sound guys don't understand hence the removal of valves to obtain higher saturation at lower volumes. When I get my new amp (little 15 watt class A Laney) this week I'll join in the modding Marshall did a far better job on my main amp than I ever could, so that is staying standard bar the Mullards I've put in. Awesome, that didn't take long! You're right about the output. It's rated at 25W per channel (RMS) but it can easily keep up with my 100W per channel MOSFET amps. Like you say, you can overdrive them and the harmonics just make it sound better ;D You can also force the outputs up by increasing the voltages. I'm pretty sure EL34s are rated at 25W each when run at 450V, but this is for a reliable output and long life. Push the voltage up and the output goes up significantly, but they just don't last as long!
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Yeah, my Marshall was running a RMS output of 100W using 4 EL34s. Can't remember the plate voltage off the top of my head. I do know they produce a smaller version that gets 60W from 2 EL34s though so I guess they're running a bit hot An old sound tech friend of mine told me that's how Eddie Van Halen got the best tone in town back in the day... by using different transformers. His amps sounded awesome for about half a gig haha.
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I've got Rovers.
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Those look lovely. I'd love to build a valve amp having heard a couple of them. Quite a gentle sound - easy to listen to all day. I want to build one to replace the little Tripath2020 amp (Topping TP20 clone) which is great for the price and size, but it's a bit bright and does my ears in after a while.
I only need a fairly low wattage one (about 10W per channel) and while I know my way around solid state stuff, valves are completely new to me so I'd need my hand holding in the form of a kit. But, they all seem to be mega money.
Anyone know of a basic PCB and component "kit" that's <£80 ish including the tranformers? or am I asking too much for a pretty lousy budget?
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Last Edit: Feb 8, 2012 15:42:59 GMT by cobblers
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There's not much unfortunately, anything with valves in it allows the price to rocket. Any kind of wrecked old valve amp on ebay can make 50 quid or so. Tbf though, a lot of the cost is in the transformers. Valve amps need up and down transformers so you've double the cost off the bat compared to tranny amps. You might be able to get a kit without transformers and valves, then try to find these by other means
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I've got Rovers.
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Yeah, I figured as much.
Is there is anything to be gained by using these valve preamps in my situation? I don't actually need a preamp (All the audio comes from my PC) but I've read of people just putting one in line to make things sound "better"
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I don't know about domestic audio, but it never works out particularly well with guitar amps. If the signal is already at line level I can't see how another preamp could improve the sound... it can only amplify what it is given. See oversimplified, biased and opinionated flowchart... Rubbish sound created (PC card) ->-> Rubbish sound made a tiny bit louder (but without adding unpleasant harmonic distortion) by a valve preamp ->-> Rubbish sound made very loud (whilst adding unpleasant harmonic distortion) by tranny power amp. To simplify, I see it that amps are only able to distort sound. The fact a valve preamp doesn't distort the sound in an unpleasant way doesn't make it sound any better. I am of course willing to be corrected
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I've got Rovers.
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Hi, My name's James, and I Like Valves. ;D
Good to see so much activity in this thread - and I hope your input switch and tone control plans go well, Jonny. Any questions relating to the circuits, do shout - I recently finished a degree in electronic engineering and, while we didn't cover valves, the principles are the same.
I don't currently have a working valve amp - but I do have a couple of vintage stereogram amps to scavange transformers from, and I'm planning to build a few amps (RIAA phono amp, preamp, p-p EL84 power amp to start with).
Cobblers, I'm afraid you won't find anything new for £80. There are a few reasons:
*The transformers are probably the biggest expense. Edcor in the USA make the cheapest new production, starting at ~£20 per output tranformer (OPT), but there's shipping on top - so you'd struggle even to get the transformers for £80. Vintage transformers tend to be coveted by audiophiles and radio collectors, again increasing the price.
*The voltages are high, which means that the components have to be rated to take them - this increases the cost of both resistors and capacitors especially.
*These are low-production items, with no economies of scale to speak of.
A valve pre might give some of the character, but it's not something I've tried. Another option is finding a stereogram, and liberating the valve amp from that. They tend to be simple but competant designs, and are often around 10w output. Of course, you'd have to replace all the electrolytic capacitors, any leaky film capacitors, any suspect resistors and maybe some of the valves, but it would be a good place to start. If you do chose this option, make sure that it has a mains transformer - many old bits of kit didn't, so if they are wired incorrectly the chassis becomes live with potentially letal results.
Finally, you could build an amp up from scratch, and careful component sourceing should result in something inexpensive. A mains toroidal transformer can actually be used as an output transformer, for example, or you could just build around scavanged transformers. However, this is not a quick and easy option - I'm still pursuing this option about 5 years after starting, and I've not made any progress...
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Yeah. I figured you'd need to actually push a valve a bit for it to "show itself" properly.
The signal from the PC is actually pretty good, After being sick of the noise and general awfulness of onboard audio, I bought an M-Audio external USB soundcard which was like night and day!
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MiataMark
Club Retro Rides Member
Posts: 2,970
Club RR Member Number: 29
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Valve amp enthusiasts?MiataMark
@garra
Club Retro Rides Member 29
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1990 Mazda MX-52012 BMW 118i (170bhp) - white appliance 2011 Land Rover Freelander 2 TD4 2003 Land Rover Discovery II TD52007 Alfa Romeo 159 Sportwagon JTDm
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Davenger
Club Retro Rides Member
It's only metal
Posts: 7,272
Club RR Member Number: 140
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Valve amp enthusiasts?Davenger
@dminifreak
Club Retro Rides Member 140
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You should build a guitar amp Jonny. I'd use one. Who wouldn't like a bright red amp with a big 69 on the grille cloth
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Those look lovely. I'd love to build a valve amp having heard a couple of them. Quite a gentle sound - easy to listen to all day. I want to build one to replace the little Tripath2020 amp (Topping TP20 clone) which is great for the price and size, but it's a bit bright and does my ears in after a while. I only need a fairly low wattage one (about 10W per channel) and while I know my way around solid state stuff, valves are completely new to me so I'd need my hand holding in the form of a kit. But, they all seem to be mega money. Anyone know of a basic PCB and component "kit" that's <£80 ish including the tranformers? or am I asking too much for a pretty lousy budget? I don't know of a PCB based one any more, except maybe something from these guys: www.ampmaker.com/store/The main problem with valve amps on a budget is the transformers. You need three of them for a stereo pair and the output transformers are critical. Second hand is a good option if you know what you're looking for, but unfortunately it looks like most of them are raped from old valve equipment that would otherwise be left intact, so I don't agree with the ethics. You used to be able to buy them from Maplin, but they discontinued them a long time ago. An alternative is these (he is the guy who designed the Maplin amp) but I might be onto something because RS seem to keep one in stock for a class A EL84 (5W output) and Rapid and Farnell still list it even though they don't keep it in stock. They are about £15 each. The second problem seems to be the valves themselves. Not many people make them any more and the prices have leapt up. There are bargains out there though and don't get suckered into spending big money on eBay. I got my 4 matched EL34s for £25 and eBay sellers have crappy ones up at £15 each, the cheeky sods. Don't worry to much about the output. 5W from a valve is a LOT more than 5W from a transistor because they can handle being overdriven. They don't clip like a transistor does. I don't know about domestic audio, but it never works out particularly well with guitar amps. If the signal is already at line level I can't see how another preamp could improve the sound... it can only amplify what it is given. See oversimplified, biased and opinionated flowchart... Rubbish sound created (PC card) ->-> Rubbish sound made a tiny bit louder (but without adding unpleasant harmonic distortion) by a valve preamp ->-> Rubbish sound made very loud (whilst adding unpleasant harmonic distortion) by tranny power amp. To simplify, I see it that amps are only able to distort sound. The fact a valve preamp doesn't distort the sound in an unpleasant way doesn't make it sound any better. I am of course willing to be corrected That sounds about right. The valve amp appears to be particularly good at pointing out how bad some of my MP3s are ;D
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Yeah, my Marshall was running a RMS output of 100W using 4 EL34s. Can't remember the plate voltage off the top of my head. I do know they produce a smaller version that gets 60W from 2 EL34s though so I guess they're running a bit hot An old sound tech friend of mine told me that's how Eddie Van Halen got the best tone in town back in the day... by using different transformers. His amps sounded awesome for about half a gig haha. I thought EVH's sound came from running a plexi 100w head through a variac to lower the plate voltage, and get more clipping at lower volume? I am also a valve amp fan - I have a 30 watt (2x EL84) WEM dominator and a bunch of leftover parts from old radios and tape players that I intend to make "something" out of "sometime"....
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To get a standard A40 this low, you'd have to dig a hole to put it in
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I thought EVH's sound came from running a plexi 100w head through a variac to lower the plate voltage, and get more clipping at lower volume? Possibly so, he was known to exaggerate time to time I've never heard a 'hot plate' style variac that improved the sound though. Regarding transformers, this guy does very reasonable rates on his repair work and makes his own transformers. I don't know how much custom transformers would cost, copper is expensive however you do it. www.chambonino.com/
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I've got Rovers.
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scruff
Part of things
Posts: 621
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Wish I had a use for a valve amp... I love building this old stuff but I only sporadically listen to music and don't play guitar!
I try and limit myself to Nixie tube clocks instead. Plus most projects never get finished...
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1994 Lotus Esprit - Fragile red turbo with pop up lights. 1980 Porsche 924 - Fragile red turbo with pop up lights.
I spy a trend...
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Nixie clocks are amazing. I REALLY want to make one.
Sam: Thanks for that link. I've pretty much read the whole site today!!!
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scruff
Part of things
Posts: 621
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Feb 10, 2012 12:31:45 GMT
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Mike's Electric stuff has schematics and lpans for basic nixie clocks. Pretty straight forward design as long as you can make PCBs. www.electricstuff.co.uk/nixclock.htmlHow about a 100% valve driven nixe clock: (Not mine!) Or a rev counter: Couldn't make the software work properly though. Might have another go.
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1994 Lotus Esprit - Fragile red turbo with pop up lights. 1980 Porsche 924 - Fragile red turbo with pop up lights.
I spy a trend...
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Feb 27, 2012 18:49:09 GMT
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Some improvements to the EL34 amp and a sneak preview into the new portable AA-powered EL84 amp project There are quite a few things on the EL34 amp that I never sorted out when I first built it and I decided to sort them all out. You might be able to see in the first pictures that it's built in three ally boxes that are screwed together, but it has a sag in the middle. This is because it's only got 4 feet on the outside edges and there was never a proper front and rear panel available to hold it all straight. One day I might make a new panel, but in the meantime it just needs some more feet: You'll see the outside ones aren't straight. I occasionally used to move them back into place but the whole amp gets so hot the adhesive goes soft and they move around! Next up is the volume control. I'd originally fitted a cheap Maplin dual gang potentiometer as the volume control. I can't remember if it went crackly or caused the amp to hum but I disconnected it some years ago and used to use a preamp for the volume control. My setup is different these days and it needs a decent volume control so I can hook it up to the CD player, DVD, TV etc. I didn't want another cheap pot because they don't last long so I splashed out on a pair of good quality guitar pots, which are bigger and have metal shafts. Old pot in place: The replacements: Fitting them was a matter of drilling a new hole in the left hand amp case. I was really hoping the existing wiring would reach, because cutting, stripping and soldering coax cable is an utter chore and I hate doing it. No such luck: Time to cut up a Cambridge Audio phono lead. Expensive, but I have a box of these that I've 'acquired' so this hasn't cost me £20... And fitted: This took hours, but it's done now and I don't have to worry about it any more. It's made the amp a lot more useable and all I need to do now is make up a switch box for multiple inputs. What it looks like from the front: I just need a pair of matching volume knobs now
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