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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Fri 25, 2013 8:26 pm 
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Well, my first instinct is, if you built that power supply as shown, that being directly on the AC line is likely the cause and the grid leak bias on V1 doesn't help either.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Fri 25, 2013 8:30 pm 
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an2727 wrote:
Btw, the link is fouled. It should be http://kaizerpowerelectronics.dk/wp-content/gallery/2008_11_26_-_2W_UCL82_SE/2W_UCL82_SE_amplifier.gif


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Fri 25, 2013 8:42 pm 
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Without a actual volume/gain control on the amp it's at max gain anytime there isn't a audio source connected, hum will be likely be present unless shielded conductors were used... For temporary, try connecting a 47K resistor from the input to ground, if that helps I'd recommend adding a pot to the circuit...

Tom


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sat 26, 2013 7:26 am 
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Well, it's at 'max gain' with an input connected too but that grid leak, at 10 Meg, might pick up whatever's floating in the air, unless the input is loaded down, like with the 47k or something driving it.

I can't see how that AC supply could be helping either because, being a full wave bridge, it's switching polarity relative to earth 60 times a second, which also means I'm not sure what you'd 'shield' the input with.

On top of that I'm nervous about a cellphone connected to a hot chassis. It might be case isolated but I'd bet they never dreamed 'ground' would be 'hot'.

Back in the 'good ole days' a direct mains supply was half wave so, depending on your plug luck, you had a 50-50 chance of it being at earth, with the 'instructions' being "if hum, reverse plug"; but that doesn't work full wave.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sun 27, 2013 7:26 am 
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Hello and thank you for the feedback


Sorry about goofing the link.

I must be more specific . 1
1 the sound an increasingly loud hum becomes a high pitched squeal if the amp is turned on with nothing connected (input connector being physically been cut away). with the connector there but not plugged in, the squeal sound still comes after the initial hum. The hum can be heard even when the music is playing( the squeal is gone though)

Pls see attached pictures. the circuit was spread out on the work bench. supply was varied with a variac. we noticed that the hum was somewhat lower when the supply was lower. but not gone.

The power supply part has 2x220 uF 450v caps on a board together with the diodes. the speaker( black portion on lower left corner) cant be seen fully. the twisted wires are going to the input socket.



I am going to relook at the whole think based on yr feedback.

How do i solve any oscillation issues which i suspect could also be there( squeal??) in this circuit??

thanks again!!!

Warm Wishes

Amit

I will post the actual circuit pictures soon.


Attachments:
File comment: UCL82 single tube amp
2013-01-25-1402 - Copy.jpg
2013-01-25-1402 - Copy.jpg [ 155.3 KiB | Viewed 1998 times ]
File comment: UCL82 caps and power supply diodes
2013-01-25-1404.jpg
2013-01-25-1404.jpg [ 131.84 KiB | Viewed 1997 times ]
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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sun 27, 2013 2:19 pm 
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'Squealing' is usually feedback, but the original circuit has no built in feedback, so that suggests either extraneous coupling from the wire nest or feedback through the power supply. My first guess would be the wire nest.

Your picture indicates you've got a 'real' transformer rather than the autotransformer so I don't know without seeing the wiring but this is what I was concerned with in the direct AC mains version.
Attachment:
240VAC hot power supply.jpg
240VAC hot power supply.jpg [ 71.11 KiB | Viewed 1993 times ]
As you see, the 'circuit' B+ and gnd are riding on AC and that suggests two problems to me. For one, the input is a very high impedance and who knows what the 'air' voltage pickup is but an electrically 'perfectly quiet' surrounding would appear to the input as 120VAC because IT is riding on AC. Second, circuit gnd is also 70VAC at -169V relative to the heater and could inject hum through there but its gnd relative to earth that concerns me the most.

This is what the 'typical' half wave diode direct main connection looks like.
Attachment:
240VAC hot power supply - HW.jpg
240VAC hot power supply - HW.jpg [ 56.68 KiB | Viewed 1993 times ]
Back in the 'good ole days' that's what it would look like if you luckly inserted your 2 prong plug with earth to the circuit ground side. If you got it reversed you'd have ground riding on AC like the full wave version and the 'instructions' were 'if hum then reverse plug', but reversing the plug on the full wave bridge version doesn't help.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sun 27, 2013 3:08 pm 
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You have far too much unshielded wiring, reduce length and connect input as close to tube socket as possible... If you still have hum with the input at ground, there is a power supply problem as well...

This should be built on a chassis with all leads as short as possible...


Tom


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sun 27, 2013 3:16 pm 
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Hello

Thanks again...Ok..yes i have a transormer that gives me two volatges on the secondary 50 v is for the heaters and the other is 180 volts for Anode ( B+). while the circuit was running we measured the plate /anode volatge it measured around 230 volts!! is that boost coming from the caps in the power supply that i made??

Also,what would u suggest that i start changing in my circuit and layout??


Warm Regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sun 27, 2013 5:50 pm 
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Drilling holes in the pref board for the tube pins to fit through would be a option, then you could have short leads... Still a gain control is almost going to be a necessity...

Tom


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sun 27, 2013 8:15 pm 
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Hello

Thank you. what exactly should i add into the circuit and where to get that gain things under control ?? resistor 47 k between ground and the input signal? or a potentiometer in the input??


warm regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Sun 27, 2013 9:04 pm 
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For a gain pot something like this would work... On your amp I would add a capacitor in series from the common point of the pot and negative input to ground(negative)... This will isolate the input totally from line...


http://pcbunn.cacr.caltech.edu/jjb/Tube ... ic_web.jpg


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Mon 28, 2013 3:41 am 
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Thank you! let me do this today and see what happens.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Mon 28, 2013 5:40 am 
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With a properly isolated power supply, I.E. a real transformer, you can do a proper circuit ground to earth. And I do mean earth, the third wire, and not AC neutral.

I can't tell for sure from the picture but it doesn't look like you have the heater ground referenced, and one end should be.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Mon 28, 2013 8:22 am 
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Hello,


we put the 47 k resistor between signal and ground and now the squeal is gone but the hum is still there.getting the heaters wires twisted properly and may also shield them if necessary.


warm regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Mon 28, 2013 8:56 am 
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The 47k stopping the squeal almost certainly confirms it’s the rat's nest of wires that's causing it. The 47k just loaded down the input making it less susceptible to pickup from the adjacent wiring.


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Mon 28, 2013 2:06 pm 
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Hello,

The hum is like that a motor running rrrrrrrrrrrrrrrrrr and clearly there when we give a small audio signal and even there when the input signal is large.( the song plays loud but the hum is clearly there in the background) By the nest of wires u mean the wires coming out of the tube at the base?? I put in a shielded 4 core cable for the heater and used two of the wires in it for the filamint. the hum went down by 1/4 or so. The length of the wires was also reduced to 1/3 but the hum has not gone down too much.


what else should i check. could this is be bad solder somewhere?? ground loop?

Warm Regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Tue 29, 2013 4:26 am 
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Yes, by rat's nest I mean not only the tube wires but all of them running all over the place and the worst thing you can do is run wires 'side by side' like the picture shows coming off the socket. Signal/noise couples from wire to wire and 'long' wires are antennas for whatever is 'in the air'.

Did you ground the heater and add the earth to ground like I previously mentioned?


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Tue 29, 2013 5:52 am 
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Joined: Dec Tue 04, 2012 9:31 am
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Hello,

Ok Im in the process of grounding the heater and also cutting short the wires and set them at 90 degrees( where ever possible)

and then get back to you with my results.


Warm Regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Jan Tue 29, 2013 6:59 am 
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Joined: Dec Tue 04, 2012 9:31 am
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Hello,

I think i found the problem. by urning the tube at right angles to the breadboard the noise was all gone. there could also be a loose contact somewhere that got working by moving the tube.

Now i know that there is zero hum if things are done proper way.


I will get back to you as soon as im finished with the new layout :D

Thanks Guys for all your Support!! :D

Warm Regards

Amit


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 Post subject: Re: DIY amp with ECC83 and 6L6 tubes
PostPosted: Feb Sat 02, 2013 9:10 pm 
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Joined: Dec Tue 04, 2012 9:31 am
Posts: 85
Hello again

Update on the UCL82 single tube amp

Saw the hum get completely killed while moving the tube around by hand with those maze of wires so we thought it cn be fixed by arranging the wires here or there to get rid if the hum. we shielded the important wires etc. but the hum got reduced a lot but never went away completely again. its there if u hear for it.

Anyway now i would like to try this speaker here with this small amp...simply becoz of the rated SPL.

pls see the link and do let me know whats the best enclosure and its dimensions that i should build.. this speaker would cost me no more than $6!!( driver only) . so if i can fabricate a good enclosure, then i can duplicate it for my next UCL82 push pull amp too. :D . open baffle?? dont have space for open baffle..

http://www.iwaispeakers.com/Fullrange/8_in_4_15W/

let me know the best design of enclosure and materials that i should use. by end of of coming week i post the picture of the amp in its complete form.

attached is also a picture of the ampin its original built, showing the position of the tube ( almost inverted. the hum reduced in proportion to my turning of the tube slowly upside down). in this position the hum was zero!( could not hear hum even if we tried hard and music played clearly too) but upon making it into a formal rig/box /base ,we did whatever we could do for shielding, reducing the wire lengths but now.the hum was there again and we could not get it back to zero hum again.( music though plays just fine)
the other pic shows the parts now placed on the base but as i said in this condition of wiriring which was done with all precautions for shielding but we now had hum again. hum did not go away no matter what we moved..here and there to get rid of it.. tube or parts
Warm Regards

Amit


Attachments:
File comment: no hum in this position of wires and the tube.
IMG_20130129_111100_0.jpg
IMG_20130129_111100_0.jpg [ 157.26 KiB | Viewed 1943 times ]
File comment: hum back again in this condition of amp wiring
2013-01-31 17.28.33.jpg
2013-01-31 17.28.33.jpg [ 130.73 KiB | Viewed 1943 times ]
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