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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Sun 03, 2013 1:24 am 
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Unfortunately, they don't give any Thiele parameters so I can't model the speaker to see how it behaves in an enclosure.

On the hum, you make a chassis and mount it all there so the wire lengths are small and the components mounted point to point.
Sort of like this http://flipper.cu.cc/Tin%20Man.htm

Also, I don't see an earth ground and the heater ground.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Sun 03, 2013 3:06 am 
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Joined: Dec Tue 04, 2012 9:31 am
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Hello

Ok thanks i will insert the earth ground wires again too

Warm Regards
Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Wed 06, 2013 5:45 pm 
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here is a video of the amp :) pls see the link. still to make a nice housing.

http://www.flickr.com/photos/27171557@N ... /#comments
thanks again for yr support guys:) :D

warm regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Thu 07, 2013 8:17 am 
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Congratulations. Fun isn't it? :D

Next you need a second tube for stereo.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Thu 07, 2013 11:48 am 
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Joined: Dec Tue 04, 2012 9:31 am
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Thank you !! :D

Its all because of the advice i have been getting from you and other friends here. and Yes its fun.

I noticed that i get much better sound quality when i am feeding FM radio from my cell into the amp as compared to the MP3 songs on it. The tube sound is clearly different and awesome.

Yes, now i need a schematic to put in a second tube into the circuit for stereo. Any ideas how to do this with the UCL82 ??

It would also be great if you could point me to a nice sounding simple stereo schematic using EL84 and a 12ax7. I have both these tubes (4 each).

Is there a converter cable with a stereo to" mono" jack to feed input signal my UCL82 single tube single channel amp??how are the connections in such a cable in case i need to make one? At present i think i am getting only one channel fed into my amp.

In the meantime,I am going to duplicate the UCL82 single tube amp as a gift to my friend also.

Warm Regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Fri 08, 2013 1:44 am 
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There are a couple of reasons why FM may 'sound better' than your MP3s with the first being MP3 quality varies tremendously and they're lossy, meaning the music is inherently distorted, to some degree, depending on bit rate and other factors. Second, FM is compressed and highly processed (both technically 'distortion' as well since it's 'not the same' as the original), which makes it sound 'fuller' (the purpose of it).

To make it stereo you simply make a second amp like the first and if the power supply can handle the load (mainly the transformer) you use it to power both. For something this simple I wouldn't worry about a balance control, nor tone, volume, etc, since you can use the source (cellphone) to do that.

The simplest way to combine stereo into mono is to put two resistors (10k being common) in series with each line and then tie the two ends together. I use that on all my (mono) transmitters like, for example, this one http://flipper.cu.cc/Twin%20Triode%20AM%20Transmitter.htm I used 100ks there because there's also feedback involved but the 'two resistor mixer' part is the same thing.

As for an EL84 amp, I'm rather partial to mine :mrgreen: http://flipper.cu.cc/StealthAX.htm That might be a little ambitious as a second amp but the reason behind the design was to 1. use a single 12AX7 per channel and 2. allow the use of a cheap line transformer as OPT. The first goal is done using a rather sneaky bootstrap (the preamp triode plate load under the phase splitter cathode) and positive feedback (R12 feeding into R6) to increase preamp gain and the second goal is accomplished with the transistor current mirror bias that keeps current through both sides of the OPT matched so the DC magnetic flux cancels in the OPT. It could be simplified if one uses 'real' OPTs by replacing the current mirror with a plain old single common resistor, cap bypassed, cathode bias. The 'optional' 1 Meg input grid leak is for when it's like your amp with no volume or balance control but, in mine, I added both and they serve as the grid leak. The volume/balance 'passive preamp' is like this one http://flipper.cu.cc/6gk6%20balanced%20fixed.htm (the two pots on the front end). The volume pot is audio taper with the balance pot being linear. The 22k makes the balance control 'volume neutral' as it's adjusted left to right.

At one time I thought of selling the PCB and do have a PDF 'manual' explaining the whole thing that I could email you.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Fri 08, 2013 8:37 am 
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Joined: Dec Tue 04, 2012 9:31 am
Posts: 90
Hi thanks!
My email is

.it will be great to have your expertise on the EL84 project as we'll !!

Warm regards
Amit


Last edited by an2727 on Feb Fri 08, 2013 5:56 pm, edited 2 times in total.

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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Fri 08, 2013 8:39 am 
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Joined: Dec Tue 04, 2012 9:31 am
Posts: 90
Hi thanks!

.it will be great to have your expertise on the EL84 project as we'll !!

Warm regards
Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Wed 13, 2013 7:47 pm 
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Joined: Dec Tue 04, 2012 9:31 am
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OK here is another test video clip. The UCL82 single tube amp plays fine but i feel it has more detail in the high frequency than in lower ones. I am wondering what could be done. I changed the speaker back to the sony column from SONY V40 and it was better . But i also feel that i am not connecting the 3.5 stereo jack properly from my fon into the mono input of the amp . The connection of the wire maybe wrong. I get fairly loud sound if i pull the3.5 mm pin out a little and only half the sound if the 3.5mm pin is fully pushed in.

Is there a wiring diagram for a wire that connects stereo cellfon socket to mono RCA input/ Mono 3.5 pin sicket??. i have both these installed on the amp for input signal.

here is a link to the sample video with the pin only partially inside the 3.5 mm socket.

http://www.flickr.com/photos/27171557@N ... hotostream

Warm Regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Thu 14, 2013 12:48 am 
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Can't tell because you didn't say how you wired it but the standard for a 3 wire 3.5mm stereo jack is left channel on tip, right channel on ring (which is how you can remember, Right-Ring, both an 'R') and ground on the sleeve.

Odds are, however, that your Nokia uses a 4 conductor jack (to add the microphone input) and they also used multiple, different, pinouts of that type so I can't tell without knowing the model number and looking it up.

This is an example of the 'logical' extension but that doesn't mean yours uses it, depending on the model number. http://pinoutsguide.com/HeadsetsHeadphones/nokia_handsfree_pinout.shtml


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Thu 14, 2013 5:39 am 
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Joined: Dec Tue 04, 2012 9:31 am
Posts: 90
Hello,

thanks for the pinout details. I will reconnect and test again :)

Warm Regards

Amt


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Tue 05, 2013 3:56 am 
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Joined: Dec Tue 04, 2012 9:31 am
Posts: 90
Hello,

The UCL82 amp is working fine now. No hum. Took a while to fix it.

Meanwhile i have got another old radio. Heres a link to my post about that. Glad if someone can help

viewtopic.php?f=6&t=217587

Warm Regards,

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Thu 07, 2013 9:13 am 
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Congrats. Glad to hear you got it sorted out.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Tue 19, 2013 5:18 pm 
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Joined: Dec Tue 04, 2012 9:31 am
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Thanks.

I been busy with work and building a second UCL 82 SE amp. This one has distortion and with my tube -ears :lol: i could tell that the sound isnt good as the first amp. We checked with the signal generator. The only difference in this one was the smaller OPT. I think the OPT in the second amp is cause of the distortion and poor sound. Is that usually the reason or it is some other part. The tube is New and it plays fine in the first amp.

Theres another difference on the second amp. The plate voltage is in range of 180 volts. The first one had final voltage after filtering of 240 volts coz we got that large voltage after ordering a transformer for step down to 180 a/c volts. So the next one was ordered for step down to 120 volts which gave us a final voltage after rectifying of around 180 volts.

I'm getting done a study of the frequency response of both amps.

here is the photo of the wave at the output of the second amp( the one with the distortion.)

let me know what you think please

And below is a link to the video of the second amp. I cobbled together a housing by cutting in half an industrial drawer.

http://www.flickr.com/photos/27171557@N ... hotostream

Warm Regards

Amit


Attachments:
2013-03-19-1799 - Copy.jpg
2013-03-19-1799 - Copy.jpg [ 80.53 KiB | Viewed 2345 times ]
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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Wed 20, 2013 10:12 pm 
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That's certainly a horrid waveform but, to start, you need to post the 'as built' schematic and specs on your custom built OPTs? What is the impedance and are you sure they're gapped for DC?

Presuming you used the Kaiser I put together a simulation and it's not quite right either. For one, the cathode resistor under the output pentode is too small leading to an idle current of around 51 mA and with plate sitting near 217 V (after drop through the OPT) the plate dissipation is 11 Watt and it should be under 7 Watt. A 680 (or 750) Ohm instead of 330 ohm cathode resistor is advisable. OPT impedance on the first should be 8k.

The 'large' B+ on the first was correct, at least as far as 'copying' the Kaiser schematic, and by changing it everything else changes. With 180 V B+ the OPT impedance should then be around 4k-5k, because now there's less voltage swing to drive it, and, ironically, the output tube cathode resistor should be about 330 Ohm because we both can have, and need, more current at the smaller voltage swing.

None of that would explain the horrid waveform but my first guess would be either there's a wiring error or the OPT isn't gapped for DC.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Thu 21, 2013 2:15 pm 
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Joined: Dec Tue 04, 2012 9:31 am
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Hello,

Thanks for the reply and explanation! I will look into it along the lines you mentioned and post a schematics of both amps.

In the meanwhile my colleague tinkered with some wiring/cap values and now he says that waveform is good. I will post the schematics and share yr feedback with him. What we noticed was poor low frequency gain in both amps. worse in the second one.

The second amp with the lower plate voltage is only half as loud .

Warm Regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Fri 22, 2013 2:49 am 
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Although a couple of cap values look a bit small the low end frequency response is mostly due to the OPT. That's one reason why I recommended something like my Tin Man topology with negative feedback, which improves distortion and over all frequency response. An example (not tested) would be something like
Attachment:
50BM8 SE v3.jpg
50BM8 SE v3.jpg [ 59.58 KiB | Viewed 2321 times ]
You see there is a signal taken from the speaker output that is 'fed back' to the input so it tries to 'correct' if the output deviates from the input. The gain was picked to be 'just enough' for a cell phone, I think.

I have also revised my original comment about 8k. With tweaking, like the above, I think a 5k OPT would work satisfactorily with 240V B+. 'Ideal' would probably be around 6k, but that's not a standard value and is why I originally suggested 8k because I think it's usually better to be on the high side rather than low, but I'm not so sure that's the case with this one.

To explain the OPT frequency response, the plate impedance is the speaker ohms multiplied by the square of the OPT turns ratio IN PARALLEL WITH the impedance from primary inductance. Now, at high frequencies the inductive impedance is so high that it can be ignored but as frequency decreases it gets lower and lower until, at some point, it equals the reflected impedance, which is the 'half' -3 dB point and below that response continues to get less and less. For 'real bass' you need 'lots of Henries', which means lots of turns, lots of iron, large size, and large cost, made worse because it has to be gapped for DC, which means even more turns, more iron, larger size, and larger cost.

Negative feedback can get another octave, maybe even two depending on the source material, since, when the low end 'droops off', it boosts preamp drive to the output tube attempting to compensate. Past an octave, or two, the plate impedance has dropped so low that the 'boost' can't produce enough output power to keep up but you'd be surprised how well it sounds.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Fri 22, 2013 1:01 pm 
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Joined: Dec Tue 04, 2012 9:31 am
Posts: 90
Hello

thanks for the schematic as a guide.

here is the schematic of the first amp. we will start with thet first one again first. pls have a look . This is exactly how this amp is wired now. My coleague who made some changes in it recently sent me this updated schematic.
OPT:
primary impedance = 5000 ohms
secondary impedance = 8 ohms

Warm regards

Amit


Attachments:
UCL82  amp schematic.jpg
UCL82 amp schematic.jpg [ 16.28 KiB | Viewed 2317 times ]
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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Fri 22, 2013 2:08 pm 
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Well, it's a bit difficult to read but if that schematic is accurate that would explain the poor bass and distorted waveform. And I’m not sure how the first one could sound okay.

Let's start by recalling the original at http://kaizerpowerelectronics.dk/wp-content/gallery/2008_11_26_-_2W_UCL82_SE/2W_UCL82_SE_amplifier.gif .
To begin with, C5 to the junction of the 2.2k and 220k is missing. That will reduce power output and increase distortion because the output tube screen is not held constant. As an interesting side note it also tries to act as negative feedback to the triode, since its B+ is now screen driven, but that's a lousy place to put negative feedback as it actually makes distortion worse. It also cuts the preamp tube gain (and for no purpose since distortion is worse).

An even bigger problem is the change in R1 from 10 Meg to 47k. That kills the grid leak bias, making the preamp tube act like a rectifier, and raises the R1C1 time constant to around 170 Hz, so it only passes higher frequencies. (I can only surmise the higher B+ of the first amp shifts the triode’s grid conduction point enough that it passes ‘some’ audio before turning into a rectifier [the onset of positive grid drive is seldom at ‘exactly’ 0 V].)

R4 matches the original but I've already mentioned that looks to me to be too low a value and 680 Ohm would be more appropriate.

B+ is higher than the previously mentioned 240 V and that’s enough to make the 5k OPT a tad low, but not enough to worry about (8k would definitely be too much).

So, add C5, change R1 to 10 Meg, and change R4 to 680 Ohm (for the first one with 257 V B+).


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Mar Fri 22, 2013 4:25 pm 
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Joined: Dec Tue 04, 2012 9:31 am
Posts: 90
Ok Thanks a lot! Will get back to you with the results next weekend on this. going to have busy weekend and busy week ahead.

thanks again!

Warm Regards

Amit


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