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Old 23rd Aug 2006, 11:38 am   #1
adibrook
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Default Another crazy miniamp

Yup, i'm building another one! And even crazier than before.

The design is pretty normal. Ez80 or 81 rectifier, and a couple of stages of ECC83. I dont know what i should use for the power valve yet.

Its allredy got a B9A socket fitted, and i have EL84's, 6BW6's, ECL86's and other things.

I even thought of using a ECL80.

The miniamp will usually be connected as a preamp. It's output will connect to my bigger power amp. However, i decided to use an o/p transformer on the output, so that i can connect it to a speaker if i wanted to. This is quiet important as i sometimes need my crazy sound but without the power amp, for example for recording or for writing stuff.

As far as i know, there are no issues with connecting a low z output into a high z input. So when used as a preamp, the 8ohm transformer output can just be plugged into the input socket of the power amp instead of a speaker.

Most of the hardware is fitted. I'll post some pics when its finished. Its NOT made in a wiko baking tin...its somethign even crazier.

I ahve a couple of quick questions tho.

1) any idea about a power valve? An EL84 is supposed to be ''warmer'' than a 6BW6, right? How does an ECL86 compare to them? Or maybe even an ECL80? An ECL 80 will really get pushed hard, and thers nothign like the sound of a valve being pushed hard. The power transformer is small, so pushing an EL84 REALLY hard will stress it. But an ECL80 probably wont. Plus theyre easily avalible, so it doesnt matter it it doesnt live as long as it would in a radio.

2) i have several spare pots, with fittings, and knobs, but theyre 50K. Is this too low for valve stuff do you think? usually i use 1M.

Thanks.
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Old 23rd Aug 2006, 11:43 am   #2
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Default Re: Another crazy miniamp

Oh, oops, forgot to mention. I also thought of using a QQV03-10 with its anodes and control gids paralelled up. I like that valve, and its somehtign different. It'll definetly sound different to the stereotypical EL84 sound. AND it glows really nicely. This is important in this project especially.
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Old 23rd Aug 2006, 12:50 pm   #3
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Default Re: Another crazy miniamp

Quote:
Originally Posted by adibrook View Post
1) any idea about a power valve? An EL84 is supposed to be ''warmer'' than a 6BW6, right? How does an ECL86 compare to them? Or maybe even an ECL80? An ECL 80 will really get pushed hard, and thers nothign like the sound of a valve being pushed hard. The power transformer is small, so pushing an EL84 REALLY hard will stress it. But an ECL80 probably wont. Plus theyre easily avalible, so it doesnt matter it it doesnt live as long as it would in a radio.


Thanks.
Hi Adi,

The ECL86 is a lovely valve in an amp. I liken them to an EL84 with a triode conveniently provided for your use. I adore them.

I use one in my reverb unit. Just out of interest I tried using the ECL86 is a straight audio amp rather than as a reverb driver and it sounded really nice.

I've no experience of the 6BW6 is an audio valve but it should be OK although I believe it was not designed for audio service whereas the ECL86 very much was.

The ECL80 is not a good idea. It's puny and suffers by having a common cathode for the triode and pentode sections. That can cause instability problems when dealing with the sort of gain you will be interested in.

I love the idea of using a QQV03-10. Different, but again you have the common cathode problem. What about using a QQV06-40 if the QQV03-10 works. A 6-40 looks really nice and it'll glow a treat.

50K pots are a bit low really. The only place I've ever used one is as "top-cut" tone control in my reverb unit.

250, 500 and 1M pots is what you really want.

Have fun, looking forward to seeing the end result!
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Old 23rd Aug 2006, 1:04 pm   #4
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Default Re: Another crazy miniamp

The 6BW6 is a direct (but 9 pin) equivelant of the 6V6 i think? Thats definetly an audio valve.

With both the ECL valves i wouldnt even use the triode section. The gain of two ECC83 stages is plenty (and maybe even too much). The triode section can just sit there and glow.
So the common cathode of the ECL80 is no problem. I like the ECL80 precisely because its puny. Its so small that driving it to extreme levels is possibly without a huge power supply.

The QQV03-10 is a nice valve, tho i never tried it in s/e before. In p/p its nice powerfull and sounds good. For s/e i will paralell the anodes and control grids. Since it has a common cathode and screen grid, it'll act like a big pentode. Right?

Unfortunatly the ''shassis'' is too small for a QQV06-40.
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Old 23rd Aug 2006, 1:07 pm   #5
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Default Re: Another crazy miniamp

Hi Adi. The ECL80 might be a good idea because it has such a low power output. This will mean it will overdrive at only a watt or so which may be ideal for practice. You won't get the instability problems if you don't use the triode section for anything. Many people have junk boxes full of ECL80s pulled from old tellies so it's nice to find a use for them.

You *shouldn't* just plug the speaker output into a line input. You need to maintain the anode load on the o/p valve at more or less the right figure. You should load the output with a 4 ohm 5W resistor when a speaker isn't connected. There should still be plenty of output to drive a line input.

Have fun, Paul
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Old 23rd Aug 2006, 4:52 pm   #6
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Default Re: Another crazy miniamp

Quote:
Originally Posted by adibrook View Post
With both the ECL valves i wouldnt even use the triode section. The gain of two ECC83 stages is plenty (and maybe even too much). The triode section can just sit there and glow.
No, never waste a valve Adi

A spare triode can be used as a cathode follower for driving the tone stack or for providing a low impedance output from the amp.

Besides, running a section "open" will lead to cathode poisoning in time.

Paul, good point about using an ECL80 to get lots of distortion. I have a good selection of them so I shall give one a try.

Only problem is, I've never found driving a little amp into distortion sounds quite the same as a big amp being loudly driven into distortion. It's different somehow Lots of opportunity for experimenting though. Real valve distortion at low volumes is still something of a holy grail and to that end you can get a "speaker coffin" so that you can crank a big amp right up without worrying about blowing the tiles off the roof...
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Old 24th Aug 2006, 8:15 pm   #7
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Default Re: Another crazy miniamp

Ok. Here it is.

i was lookign for a shassis, and then i remembered that thers an old stainless steel dog bowl on my shed roof (i used it to feed seagulls). So i made a shassis out of it.

The pics arnt too clear, but you can see the o/p transformer and the c-r-c smoothing circuit. The valve linup hasnt been decided yet.

I'v had a slight change of plan. This will be a small power amp and will ahve no controls appart from an on off switch.

Because of this i think two stages of preamp is too much. This brings me to a familiar problem. All the pentodes i know that i can use (ef86, ef80, etc) are extremly boring and dont even glow alot.

I might just use an ECC83 with both triodes paralelled.

Does anyone know of a small singlan 9 pin pentode that actually glows?

The power amp will probably be an EL84 or a QQV03-10. Not sure about it yet.
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Old 24th Aug 2006, 8:48 pm   #8
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Default Re: Another crazy miniamp

Hi Folks
Bread boards and now dog bowls, where will it all end. It's a little like the "sauce pan" special radio or FJ Camms infamous and lethal "progressive baking tin " set in the 1950's PW.

But I like it!

Ed
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Old 24th Aug 2006, 8:56 pm   #9
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Default Re: Another crazy miniamp

That's looking good Adi, Now you need a decent "Woofer" to go with it , I must admit I keep looking at those shiny stainless steel bowls in the Pound shop................ .

Regards, Mick.
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Old 3rd Sep 2006, 11:50 am   #10
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Default Re: Another crazy miniamp

Instead of a "boring" pentode, you could use an ECC8_ type valve set up as a cascode. That will simulate a pentode pretty well, and will glow more as you know.
Why glow should be more important that tone though, I will never know...
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Old 4th Sep 2006, 3:40 pm   #11
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Default Re: Another crazy miniamp

Adi,
It looks great!

Keep doing the "crazy" things.

I'd stick with the ECC83/EL84, or half ECC83/ECL86.

Good luck!

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Old 8th Sep 2006, 1:45 am   #12
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Default Re: Another crazy miniamp

UPDATE

After alot of thinking, i finally decided that this thing should be both a pre amp and a power amp.

In the end i used a EABC80 as the driver triode, since one triode is enough. I could have used a EF86, but the EABC80 actually glows!

I'm using the EABC80 with cathode biasing...not how its usually used in radios. It seems to work quiet well tho.

Notice how the speaker has a switch to connect a 4.7ohm load to it. This switch also turns on a indicator light to show that that function is definetly on or off.

This is so it can be connected to a bigger amp, with the valve still being loaded.

Tonight we tried this at a small local show. It worked really well. It worked throug two bands sets (our touring buddies palingenesis also used it). It got warm, but thats about it. No smoke, no funny noises.

Palingenesis used it to add a epic, warm ''plong'' effect to their bass, combined with reverb it sounded really cool. It only clipped a little bit.

The we used it, and i of course put everythign to max. Max distortion on my pedal, max output from my pedal, max preamp gain on my pedal. So there were 5 distortions involves. My pedals preamp beign overdriven, the pedals actual distortion, the dog bowl amp being overdriven my the pedal, and the power amp (my JHS 120W bass head) overdrivign...and i pushed it so hard even the speakers distorted. The sound was phenominal!

So, the 1st prototype works and works really well.

http://img.photobucket.com/albums/v4...ok/dogbowl.gif
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Old 8th Sep 2006, 7:27 am   #13
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Default Re: Another crazy miniamp

Excellent work Adi. Great that you got some results you like.

Frank N.
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Old 8th Sep 2006, 8:50 am   #14
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Well done Adi, you're a real trooper!

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Old 8th Sep 2006, 1:19 pm   #15
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Default Re: Another crazy miniamp

Oh yeah, forgot to mention. Unfortunatly there are no photos. During our last song, the video camera decided to get very hot, melt some of the tape, then chew it and break the tape extraction mechanism. Eventually the whole tape cradle fell out. The tape is half melted and ripped...so no footage . How wierd. The camera dude is a very reliable person and is both experienced and sober, and he says it just suddenly got really hot and stopped working.

So anyway, unfortunatly thers no pics of the amp. But it looked different. Everybody kept saying whats that, and after the show there was a big crowd of peoplecoming up to me to look at it.

Imagine what will happen when i finish the power amp .
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Old 11th Sep 2006, 2:05 pm   #16
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Default Re: Another crazy miniamp

Hi Adi,

You could try the 6BW6 as it is an output valve, look on TDSL on Duncans amp pages. Believe it or not the 6BW6 is identical in charecteristics as the 6V6 octal tube! My Kolster Brandes GR10 uses one of these in the output.
Keep up the crazy designs, they rock!
Regards
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Old 19th Sep 2006, 12:37 am   #17
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Default Re: Another crazy miniamp

Update:

We hired out some little community hall or somethign to try out some new gear, and we decided to video it.

The dog bowl is used in this, and is behind the mic stand, so you can only see it when i move away from the mic. Its the silvery thing on the right of the mic stand. The video is very bad quality webcam.

The gear we used wasnt very big, and thers only about half the drumkit there. But i think the preamp worked well.

http://media.putfile.com/Dodsferd-video

Warning:
This song is not so offensive. Especially if you dont speak norwegain. But other song on that putfile profile ARE. The one that begins with Chainsaw have soem great use of the preamp, and generally good music, but has extreme content unsuitable for you nice people. Watch at your own risk.

Enjoy
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Old 20th Sep 2006, 12:10 pm   #18
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Default Re: Another crazy miniamp

"This next song is about death!"
Well it's nice to see you experimenting with themes within your music genre!..
Shame I can't hear decent aduio on those vids, no idea how that preamp sounds!
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Old 25th Sep 2006, 7:51 pm   #19
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Default Re: Another crazy miniamp

I'm impressed, you have many good ideas. I know very few people who would keep going at something without soon giving up.
Not to mention the fantastic music!

Keep at it,

Matt
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Old 25th Sep 2006, 8:07 pm   #20
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Default Re: Another crazy miniamp

I assume that you are the guy on the left of the video. The movements somehow look like your avatar

As Merlin says, shame we can't even begin to judge the sound from your preamp.
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