For me, half the fun is creating something 'new' from junk. If the transformers and tubes are good, why not reuse them in something new? That's my take, anyway.
I am aware that it's not 'plug and play' and I am competent enough not to hurt myself doing this. I am from an electrical background (not electronics!).
It's just a bit of fun as I enjoy tinkering. I want to learn more about the Theory behind these circuits and I learn by being hands on. I am also doing a lot of reading up and trying to make sense of the schematics etc. Slowly but surely it's going in 🙂.
I'm not expecting a top notch hifi experience out if this. It's just something to do for a bit of fun. I think this is a good staring point.
I am aware that it's not 'plug and play' and I am competent enough not to hurt myself doing this. I am from an electrical background (not electronics!).
It's just a bit of fun as I enjoy tinkering. I want to learn more about the Theory behind these circuits and I learn by being hands on. I am also doing a lot of reading up and trying to make sense of the schematics etc. Slowly but surely it's going in 🙂.
I'm not expecting a top notch hifi experience out if this. It's just something to do for a bit of fun. I think this is a good staring point.
Really? In contrast to their precedessors with zinc silicate coated, trough-shaped or conical plates inside the envelope (»real« magic eyes), the newer ones like EM84 etc. with zinc silicate plus zinc oxide plating right inside the glass do not wear out that rapidly. Even those with obvious discolorations usually display rather brightly.
Best regards!
This does not match with my experience. It is true that earlier tubes with internal light emitting element are less durable, but I've found many EM84 and EM87 tubes with weak light emission, usually they have a noticeable darkened band. On my reclaimed tubes drawer, I've more weak EM84 tubes than good ones. EM87 is more desirable as level meter but sadly far less common.
By the way, when they are mounted on the amplifier chassis as level meter, it is important to check the light emitting stripe orientation before drilling the socket screw mounting holes on the chassis. I've made a novice mistake the first time I used them, and drilled the holes parallel to the chassis sides.
By the way, when they are mounted on the amplifier chassis as level meter, it is important to check the light emitting stripe orientation before drilling the socket screw mounting holes on the chassis. I've made a novice mistake the first time I used them, and drilled the holes parallel to the chassis sides.
Still reading, watching, learning! Thinking about chassis layouts and materials to use. An easy and cheap source of sheet metal is obviously cake tins/pans and baking trays from the pound shop. How much of an issue is it using a magnetic material for the chassis?
Secondly a thought about power transformers. A lot of projects build from reclaimed parts like mine use power transformers on top of the chassis which are clearly not originally designed to be placed where they can be touched as they appear to leave the terminals/taps exposed. I suppose if it's designed to sit inside an enclosure then that's fine. But it looks like people are building Amps designed to be used open chassis with the transformer terminals exposed like that.
Obviously I want to avoid this. Thinking of ideas to try and cover or insulate or protect in some way.
Secondly a thought about power transformers. A lot of projects build from reclaimed parts like mine use power transformers on top of the chassis which are clearly not originally designed to be placed where they can be touched as they appear to leave the terminals/taps exposed. I suppose if it's designed to sit inside an enclosure then that's fine. But it looks like people are building Amps designed to be used open chassis with the transformer terminals exposed like that.
Obviously I want to avoid this. Thinking of ideas to try and cover or insulate or protect in some way.
Metal cover bells and cover cases for standard transformers sizes are available, but they aren't cheap. A cheaper option is a PVC electronic project box or electrical box: don't use the lid, and screw the box on the amplifier plate. Another option is to use a reclaimed tea or coffee can, the lid need to be placed over the top plate, under the transformer. This is actually a very, very old hack: I've found it in a Crosley radio from the 1930's. On my opinion, this does not look good and I rather put the transformer inside the chassis. The cake pan hack was very popular but there are better options now. The main drawback is the missing bottom cover. I build small prototypes inside clear, thick plastic food containers. Fast and easy to cut and drill; quite inexpensive; you can see if anything goes wrong or overheat; and it is easy to move things around. For regular builds I use metal plates for top and bottom and a thick wooden picture frame or bamboo container for the sides. I also use the "Economica" and "Galaxy" enclosoures from Modushop.
This is the kind of thing I'm aiming to build (pic bellow). The cake pan is literally a source for the flat sheet metal as it's so cheap in Poundland etc (UK). I would just cut the sides off and cut the flat part down to required size. I want the transformers to sit on top. I'll have have a think about ways to cover the transformers as the ones in using are definitely not designed to be exposed. The tea/coffee tin idea is a good one. Or something of the same principle but more aesthetically pleasing.
I'm still not sure whether to make 2 separate mono amps in separate chassis or build them both into 1.
As I don't think the mono power transformers from the tape recorders will handle stereo setup, I might ditch them all together and use buck, boost converters and linear regulators instead like this build on YouTube.
I'm still not sure whether to make 2 separate mono amps in separate chassis or build them both into 1.
As I don't think the mono power transformers from the tape recorders will handle stereo setup, I might ditch them all together and use buck, boost converters and linear regulators instead like this build on YouTube.
Do those exposed transformer termnals protrude from the same side of the bobbin? Then you may cut a rectangular hole into the top metal sheet that is big enough to let the tranny sit flat and have the terminals beneath the sheet.
Best regards!
Best regards!
Hey, Kay. I haven't cracked these tape recorders open yet to liberate the parts. The machines are no here with me yet. Will take some pics when I've dismantled them.
I've decided to go with the Schematic bellow
https://www.experimental-engineering.co.uk/wp-content/uploads/2019/02/ecl82.jpg
Don't know if this can be improved on so I'm open to suggestions! Seems like a good starting place. I'm planning to use a DC-DC boost converter in place of the tape recorders MT and bridge rectifiers for the 200v anode supply so I can make it one stereo circuit rather than having to use the 2 MT's for 2 mono amps in the same chassis. I am also planning to use a buck converter for the 6.3v filament supplies.
I've started looking for the caps. For the 50uf 450v I've found these: https://www.electrotechdrives.co.uk...electric-motor-run-capacitor-50-uf-or-5-450v/
These seem a bit pricey. I can't find much in that exact voltage and uf. Any ideas here?
The 50uf 50v seem cheap and abundant
the resistors shouldn't be a problem. Looking at te schematic for the tape recorders some the resistors are the same values so hopefully I cam reuse some of those. I will measure them first, whatever else I need I can buy.
https://www.experimental-engineering.co.uk/wp-content/uploads/2019/02/ecl82.jpg
Don't know if this can be improved on so I'm open to suggestions! Seems like a good starting place. I'm planning to use a DC-DC boost converter in place of the tape recorders MT and bridge rectifiers for the 200v anode supply so I can make it one stereo circuit rather than having to use the 2 MT's for 2 mono amps in the same chassis. I am also planning to use a buck converter for the 6.3v filament supplies.
I've started looking for the caps. For the 50uf 450v I've found these: https://www.electrotechdrives.co.uk...electric-motor-run-capacitor-50-uf-or-5-450v/
These seem a bit pricey. I can't find much in that exact voltage and uf. Any ideas here?
The 50uf 50v seem cheap and abundant
the resistors shouldn't be a problem. Looking at te schematic for the tape recorders some the resistors are the same values so hopefully I cam reuse some of those. I will measure them first, whatever else I need I can buy.
The motor run capacitor you linked to is 'overkill'. Although the site doesn't mention this, the voltage rating of 450 V is most likely the rating for AC, so not the DC rating. The DC rating of these type of capacitors is much higher than their AC rating.
Since the B+ (= supply voltage) of the amplifier you want to build is only 200 Vdc, you can safely use capacitors with a 400 or 350 Vdc rating.
The capacitance of the capacitor on the left side of the schematic is not so critical. A value of 22 uF will still do fine, so anything between 22 and 50 uF is OK. The value of the capacitor on the right side of the schematic can just as well be 47 uF (or even 33 uF), especially when using a well filtered power supply that provides the B+ of 200 Vdc.
I hope this helps you to find somewhat less expensive capacitors for your project.
Addition: Search for "electrolytic" capacitors.
Since the B+ (= supply voltage) of the amplifier you want to build is only 200 Vdc, you can safely use capacitors with a 400 or 350 Vdc rating.
The capacitance of the capacitor on the left side of the schematic is not so critical. A value of 22 uF will still do fine, so anything between 22 and 50 uF is OK. The value of the capacitor on the right side of the schematic can just as well be 47 uF (or even 33 uF), especially when using a well filtered power supply that provides the B+ of 200 Vdc.
I hope this helps you to find somewhat less expensive capacitors for your project.
Addition: Search for "electrolytic" capacitors.
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I have also been down this road, renovating two Tandberg 74's, one with ECL86s in SE, the other EL84s (74B).
In both cases I just recapped them throughout (they had tons of split Rifa and Hunts capacitors), and that was not a trivial task. They had these 'tripod' Philips electrolytics that were the devil to remove sonce they had 4 soldered connections, and the 3 points on the metal case bridged some circuits on top of the PCB, so jumpers were needed when the replacements were fitted.
In both cases, they were stereo to start with. The internal broadband speakers were very pleasant (7x4 I think), and they had a 'PA' mode, so it was easy to connect a source and use them as Blue tooth player with adequate (and very nice) sound for a small room. They looked neat too, with their modern appearance and teak cabinets.
My point is that the single biggest resource is your time, and you have to consider what your expectations might be with investing that time with the raw meterials you will have. The SE transformer is not going to be big, and will be designed to work optimally with the internal speaker (3ohms maybe). The tubes are not expensive to buy new (unless you have an exotic ECC83, and only then if it had an easy life). You probably won't be able to salvage the sockets, or any of the passive components, so the danger is youend up putting a lot of effort creating something that is a compromise from the outset.
The alternative is looking at something like the Tubelab SPP, and creating something that has all the potential to be a great HIFI addition. The effort is predictable, the support is plentiful, and the outlay is not so much more than cobbling something together from your ECL82's. Alternatively, transplant the components from the taperecorders as intact as possible, and create a boom box or similar, with minimal change.
In both cases I just recapped them throughout (they had tons of split Rifa and Hunts capacitors), and that was not a trivial task. They had these 'tripod' Philips electrolytics that were the devil to remove sonce they had 4 soldered connections, and the 3 points on the metal case bridged some circuits on top of the PCB, so jumpers were needed when the replacements were fitted.
In both cases, they were stereo to start with. The internal broadband speakers were very pleasant (7x4 I think), and they had a 'PA' mode, so it was easy to connect a source and use them as Blue tooth player with adequate (and very nice) sound for a small room. They looked neat too, with their modern appearance and teak cabinets.
My point is that the single biggest resource is your time, and you have to consider what your expectations might be with investing that time with the raw meterials you will have. The SE transformer is not going to be big, and will be designed to work optimally with the internal speaker (3ohms maybe). The tubes are not expensive to buy new (unless you have an exotic ECC83, and only then if it had an easy life). You probably won't be able to salvage the sockets, or any of the passive components, so the danger is youend up putting a lot of effort creating something that is a compromise from the outset.
The alternative is looking at something like the Tubelab SPP, and creating something that has all the potential to be a great HIFI addition. The effort is predictable, the support is plentiful, and the outlay is not so much more than cobbling something together from your ECL82's. Alternatively, transplant the components from the taperecorders as intact as possible, and create a boom box or similar, with minimal change.
I take your point and you're right. But the thing is, I just enjoy tinkering with stuff and learning so it's not wasted time, it's fun for me. Anything I have to buy I can reuse again if I'm not happy with the end result. I'm getting the tape players for nothing so whatever I can salvage is a bonus. I can upgrade the output transformers later and the tubes if they're stuffed.
Why would the tube sockets be unusable, by the way? I'd imagined they'd be good for reusing??
Why would the tube sockets be unusable, by the way? I'd imagined they'd be good for reusing??
Depends on the chassis. If they are wafer style, or PCB mounted, it might be tricky to reuse them.
If you intend to discard the donor PCB anyway, the quickest way to harvest the tube sockets is to point a soldering torch's flame at the copper side.
Best regards!
Best regards!