| skyraider |
hi gurus,
I recently bought a 'junk' tube amplifier over the internet auction. after several attempts to repair, I got fed up. I salvaged the valuable parts, and built a new one based on a schematic i've found on internet (http://nmwilliam.tripod.com/ecl82.html)
Even though this is the first time i tried this, the amp sings on the first time and im amazed how sweet tube sounds.-) byebye~silicons!!
Ive attached the schematics, and I highly recommend this amp for a newbie (if i could do it, i figured any idiots could) hahaha. At first, there was a little buzzing, but i finally got rid of it because i forgot to ground my heater.
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| skyraider |
There are several questions i would like to ask:
1. Can I 'triode-strap' this amp? My idea is to connect pin7 to pin6 with a 100 ohm resistor. Will this work? Is this modification worth it?
2. If I want to use 'exotic' components, which part would you gurus recommend to change first? (which parts would effect the sound the most)
3. My current power Tx is 300Vac. I am worried this may be a bit too high for the tube, even though it sounds ok. I am thinking of using 2k resistor in series to bring the voltage down, but this would require a large wattage resistor. Is there any way I could lower the supply voltage?
btw, after I 'salvaged' the parts, I have leftover of 10H choke(a gem find) , 2x ecl82 tubes and 1x ecc82 tubes -) |
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| powertriode |
Hi There,
and welcome to the wonderful world of tubes.
There is a thread called "is there a tube gainclone" or something and these little amps are discussed therein, do a search, this thread contains loads of links.
I currently have a variant of the Svetlana circuit breadboarded on the bench and it sounds pretty good. (for what it is) I have used junkbox parts and junkbox transformers. Follow this link, its 'figure2'
http://www.svetlana.com/docs/products/glass/6BM8.html
As for triode strapping the pentode, you will reduce the available output considerably (its only about 2 watts)
Don't worry about the B+, mine is connected to a bench supply and I have varied it between 200 upto 400VDC. To my ears the amp sounds better with a higher B+, even though you are on the limit of the curves for the pentodes.
Have fun!!! |
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| skyraider |
thanks
I have browsed through the website and i wanted to built this one initially:
however, i couldnt understand the notes about adjustable bias voltage, approx -25 volts. How do i adjust the bias if the 470k resistor is fixed? How did you build yours?
Thanks |
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| arnoldc |
| i believe you need to supply the -25 volts from another source (such as a bias tap on your transformer) |
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| SHiFTY |
1) I wouldn't bother. Triode mode would make it too low on power for most use (<1W) You could use EL84s though.
2) I would make use of that 10H choke in the power supply. What rectifier are you using? (Tube I hope :D) What is the layout of your power supply? I find that a choke in the power supply improves the sound... Apart from that, you could try some different output transformers...
3) Check the power dissipation of the PENTODE half. (CAREFULLY! READ THE SAFETY THREAD!!!)
Do this by measuring the voltage at the plate, then the voltage at the cathode. The dissipation is then the current across the cathode resistor (Vcat/R) x the voltage across the tube (Vplate-Vcat) where R is the value of the cathode resistor in ohms.
If this is less or equal to 7 Watts then no worries. If its 8 or more, then increase the cathode resistor appropriately. Use a 5W cathode resistor too...
You might want to also try building the classic Mullard ECL82 circuit, I really like it and it has stood the test of time really well...
LINK
Regarding that PP circuit, its referring to the power supply (not shown). PP circuits can be a lot trickier... |
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| skyraider |
thanks shifty
Actually I was saving the choke for a bigger project in future:D
Nothing fancy on the psu here, just plain 4007 bridge diode rectifiers, bypassed with 0.01uf caps. This is followed by two 50uF caps, exactly as shown in the original post. I am thinking of salvaging an unused transformer to be used as choke. problem is i cant measure the inductance though.
How will the choke effect the sound apart from less noise? I read that chokes pushes the soundstage behind, is that true? My amp is almost dead quiet allready, and if can, I want this amp to be as compact as possible. |
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| powertriode |
I built the SE circuit.
<img src="http://www.svetlana.com/graphics/TB/No10fig2.gif">
The 'adjustable' bias is meant to be from an adjustable source, behind the resistor.
I wouldn't go too mad with this tube, it was used as the output tube in many 1950's radios and grams and isn't exactly hifi. |
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| Fuling |
| quote: | | I wouldn't go too mad with this tube, it was used as the output tube in many 1950's radios and grams and isn't exactly hifi. |
I don´t really agree here. I own one ECL82 amp and one PCL82 amp, both SE, and I think this is a quite amazing little tube.
Even though I have a few amps with way fancier tubes (f.ex. 6B4G) and OPT´s, my little PCL 82 amp with TV output transformers still makes it into my system now and then without being ashamed.
Run them in triode mode and enjoy <1W of music :D
A great tube for beginners to play with, too. Only 200V B+ and they´re happy as pigs in sh*t!
Cheers
Fuling |
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| wwflyball |
The 6MB8 sounds great, comparable to any higher quality mass produced HIFI amps/receivers....but warmer :) However the 6MB8 is not really an "Audiophile" tube like 2A3 or 300B's etc....
I built the Lighthouse circuit with a few tweaks and designed my own PSU. I'm VERY happy with the sound quality . The dollars/sound ratio makes it a well worth project....you will be surprised how this little thing cranks.
I also build a Solo TQWP and mounted a pair of RS1194 in it.
IMHO this is a perfect match.
My neighbour (SS audio geek) was totally amazed over the sound quality and loudness of this small amp.
His jaw hit the floor and he started shaken his head in disbelief.
Needless to say he has a new found opinion on tubes!
Attached are a few pics..
http://www.flyballequip.com/pictures/6MB8front.jpg
http://www.flyballequip.com/pictures/RS1194soloTQWP.jpg
I'd be happy to share my tweeks, tips & build info if anyone wants it.
Mike
Langley B.C.
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| SHiFTY |
Regarding the choke, you should replace the 100 ohm resistor with it. Give it a try and see if it sounds better, it may make no difference.
You could also apply negative feedback as in the mullard circuit, might clean up the sound (if its a bit ragged).
Don't use a transformer as a choke, they have no air gap and will "saturate" quickly. Which means they won't have any inductive effect and is no better than a resistor. |
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| skyraider |
flyball,
nice work on the casing. I notices you didnt enclose the output transformers. No problem from there right? any exotic components you used on the inside?
I am still working on my casing:smash: :smash: :smash: I am repainting the old chasis. No such thing as 'audiophile' colours right? Right now its still ugly so im posting my pictures later on. :eek: |
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| wwflyball |
Thanks,
I've built many guitar tube amps and I wanted to build a "budget" tube HiFi to see what the fuss was about.
This project only cost me $250.00Can (+/-200US)
All the items were bought new from off-the-self-parts.
Nothing too exotic.
-JJ 50/50 filter cap can
-Solen caps
-NTE resitors
-ALPS dual gang volume contol
-Hammond 270DX PT
-Hammond CSE OT's
-Motarola (Made in Holland) ECL82 tubes
Point to point wiring on self made terminal strips.
The CSE OT is insulated and has no exposed terminals.
I see many people mount their ESE's externally so I didn't see or feel there was a problem with doing it as well.
If you decide to use the 125A-E series of OT...you might have some concerns since it has exposed terminals.
Two evenings of wiring and another two of listening and tweaking.
I first ran the amp though a pair of Mission 761 (+/-89DB) and a Sony CD player. Though it was not super loud the sound quailty was sure there. Then I made my Solo speakers which really took things up a notch.
I would highly reccomend this project for a first time HiFi builder.
This amp sounds pretty good to me and I wonder how much better a 2A3 or a 300A SE would sound :-)...I'll soon find out!
Mike
Langley B.C. |
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| Yugo |
[QUOTE]
How will the choke effect the sound apart from less noise? I read that chokes pushes the soundstage behind, is that true? My amp is almost dead quiet allready, and if can, I want this amp to be as compact as possible.
Skyraider,
using a well designed choke with enough or higher(better) inductance than the critical one in a power supply PI filter will bring many benefits as: better,deeper and stronger bass,less noise,more easy and liquid sound,better soundstage.Try it and you will be satisfied with the sound.
Regards,
Yugovitz |
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| skyraider |
well, still doesnt convince me to use my 10H choke for this small project. I will devour one of my cheap trafos and wound up a choke after this. :smash:
Anyway, I need help with another problem. The amp i'm building requires 5k output transformer impedance. But what I have is only these:
I am currently using 8k-8k, but I am afraid I might be wong. Or should I just use CT-8K connection?
thanks |
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| skyraider |
the bird is singing happily in my living room now. The soundstage is not as wide and focused as my gainclone monoblock, the estimated frequency response is 100Hz-12KHz. The high treble is not so liquid, almost like splatering glass. Nevertheless, Nat King Cole rose from the grave:D :D :D
Still no photos.. |
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| Yugo |
Skyraider,
did you used a PS choke?
Regards,
Yugovitz |
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| skyraider |
Previously I used a wire-wound 100R which has an air core in the PS. I guess it sort of acts as an inductor. After messing around, I broke one of the legs. I have it replaced using those white colour modern resistors. I guess the old one sounds better.
Im gonna put in the choke, and see if it helps with the bass. Or is it a fault with my OPT wiring? |
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| skyraider |
Yesterday I have it moded to ultra-linear mode.
The sound: heaven:angel: :angel: :angel:
:D :D :D :D :D
Previously SE pentode is a bit thick-sounding, female vocals doesnt sound right. Now its brought to a correct balance, and playing complex jazz parts is not a problem. Treble is now smoother, the grains are almost all gone.
If its not for the lack of bass, I would have thrown away my gainclone.:smash: :smash: :smash:
Im gonne try triode mode after this. |
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| skyraider |
| Inserting the choke improves bass a bit and lowering the rectifier noise. The sounds clearer now, with more spaces between instruments. But still I want my boom booom booom |
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| skyraider |
choke in, choke out, choke in, then the choke remained.
More liquid and better spacing.
Siemens MKV & Jensen caps arriving in two weeks. By now im happy enough not to be bothered about them. |
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| Yugo |
| quote: | Originally posted by skyraider
Yesterday I have it moded to ultra-linear mode.
The sound: heaven:angel: :angel: :angel:
:D :D :D :D :D
Previously SE pentode is a bit thick-sounding, female vocals doesnt sound right. Now its brought to a correct balance, and playing complex jazz parts is not a problem. Treble is now smoother, the grains are almost all gone.
If its not for the lack of bass, I would have thrown away my gainclone.:smash: :smash: :smash:
Im gonne try triode mode after this. |
Skyraider,
Leave the choke,use some oil caps for PSU and make it triode connected!You will never go back if you like that liquid soprano voices!And of course: Let the coupling caps be Jupiter Beeswax.They are for my taste little bit better than Jensens!
Regards,
Yugovitz |
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| king30 |
skyraider,
Can you post the updated schematic your using...Thanks Lee |
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| skyraider |
| This is my schematic, slight modified from the original |
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| skyraider |
the power supply is the most critical part.
The tube i'm using is matsushita, and I couldnt find the datasheet for it. I found out that with higher B+, the sound is more alive. The rest is adjusted by ear. Here is the chicken scribble version |
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| skyraider |
Finally the pics are here.
I present to you: Black Beauty |
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| Yugo |
| quote: | Originally posted by skyraider
the power supply is the most critical part.
The tube i'm using is matsushita, and I couldnt find the datasheet for it. I found out that with higher B+, the sound is more alive. The rest is adjusted by ear. Here is the chicken scribble version |
Skyraider,
try if you have opportunity (for the best sound) to change the rectifier with a valve one ex. 5U4G or GZ34 (I personally prefer directly heated rcf.),or maybe use some fast diodes but SOFT recovery.They will make sound closer to the valve rectifier.Anyway cheap 1N4007 will be my last choice.And use fast/soft diodes without any snubber!
Regards,
Yugovitz |
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| skyraider |
| quote: | | or maybe use some fast diodes but SOFT recovery. |
But I heard that fast diodes has higher switching noise? Any value you recommend?
| quote: | | without any snubber! |
snubber means bypass with small value caps right?
thanks yugo |
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| Yugo |
| quote: | Originally posted by skyraider
But I heard that fast diodes has higher switching noise? Any value you recommend?
Skyraider,
My experience is based only on listening tests on my amps and preamps I build myself and also gained through exchanging ideas and experience of other diy-iers and ofcourse including this great forum and many threads I've read.You can use even better( some claim) shootky diodes (UF 4007 ex.) .For fast/soft use Philips's BYV96E.They are not expensive you can try both .YMMV.
snubber means bypass with small value caps right?
Yes,bypassing each diode with caps.But it is not so simple to put only let's say 0.01 or 0.1 ceramic cap and say I've done.You can calculate some components of the PSU first and then make the snubber values.You even have to put cap with res. in series and in parralel in that connection put another resistor!But according to the more experienced members of this forum for shootkys and for fast/soft diodes it is better not to put anything in parralel with them!
Hope this will help you more:
http://www.hagtech.com/pdf/snubber.pdf
thanks yugo |
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