KEL80 EL34 Monoblock 80w amplifier

[IanG3XYV]

David

Thank you for that distillation of wisdom. I would have paid good money for it.

Ian

[Valvepower]

Hi,

Just came upon this thread and I’ve a similar ‘round tuit’ project on the list. Its fairly straight forward and no more adventurous than two pairs of UL connected EL34’s as per the Mullard 5-20, Leak TL25+ and EL34 data etc. From memory the output transformer anode to anode load is 3.3K. It’s on the furthest back burner, but I hope to do it sooner rather than later.

Looking at the earlier posts I didn’t know there was a cathode biased VOX AC100, I knew the AC50 came in cathode and fixed bias but not the AC100, mind you the AC100 is a rare beast!

Regards
Terry

[Aub]

Hi Terry,

Hard to believe but my mates and me used two AC100 amps for stereo, when we had our disco in the seventies. I wonder where they are now.

Cheers

Aub

[Diabolical Artificer]

"David...Thank you for that distillation of wisdom." Seconded.

"...no more adventurous than two pairs of UL connected EL34’s as per the Mullard 5-20, Leak TL25+ and EL34 data etc" I've been mucking about with similar OPT's wound by Joe in Oz - 3k4 Z pri for the last few weeks and have tried various OP configurations, EG Class AB1, Class AB2 (two valves only) and extended Class A ( where two valves are triode strapped, two as beam tetrodes), this has been an illuminating experience, in that the worse the amplifier performed as regards THD and F response, the better it sounded with a music test. I miss-wired the PS on one test and was applying PFB with the result of 8% THD, but this sounded lovely with test records like Take 5 - Dave Brubeck, ITCOTCK - King Crimson, The Russians are Coming - Val Bennet etc..

I then set about trying to create an amplifier that was wrong in a lot of respects but sounded good on a music test by making various parameters variable, IE AC balance into the OP stage, DC balance of the OP stage, varying NFB with added PFB to the voltage gain stage and a few other wrinkles. Obviously this isn't a straight wire with gain approach, more harmonic sculpturing and might raise ire from traditionally minded engineers, but it's fun.

Andy.

[Radio Wrangler]

Originally Posted by Diabolical Artificer

Obviously this isn't a straight wire with gain approach, more harmonic sculpturing and might raise ire from traditionally minded engineers, but it's fun.

It's not only fun, it's fundamental.

Let's use pictures as an analogy.

Take a photograph of somewhere and look at your result. Often it can look 'flat' and boring. Put on a tin, it wouldn't sell shortbread to yer granny.

So you need to do something.

There was a Soviet era camera brand called Lomo. They made truly grotty cameras. Lenses that could only focus in one area at once, ghosting, and no attempt at accurate metering - no metering at all. Just guess and push the button.

Do you know what? they're still on the go. They take quirky photographs where their distortions etc become a feature. They can make things stand out as being the only clear thing in a generally mucked-up frame. Words like Lomography and Lomographers have been coined. They are still bring out new models! They put some of the fun back into photography. It takes a lot of skill to get what you want out of them. A fair degree of luck is needed. It takes a lot of experience to even guess what you might get. In many ways these parallel the interest in early analogue guitar effects pedals where dramatic effects on overload and other misbehaviours become part of the performance.

Lomo cameras and those guitar pedals make no claims of accuracy and rightness. They set out to change things, and they deliver. The results of both, with a skillful operator can be wonderful. They are part of the performance.

Kodak made a film for the happy snapper. It had two aims in life, to make photos Joe Public would be pleased with, and to survive a long time in storage and left in the camera before it got developed and to still do well with fair amounts of under and over exposure in the hands of unskilled photographers.... and a fanatical devotion to Monty Python! It succeeded Kodacolor Gold The American spelling told you the colors were going to be a bit, shall we say, NTSC. It was successful. Fuji had a competing emulsion. Martin Parr is a famoud professional artistic photographer who specialises in somewhat everyday subjects for his photos, and he uses these films to make his photos pop. He makes no claims of accurately recording things, but his results are special and have won numerous awards.

Quirkiness and hyper-reality sell. Jack Vettriano painted it into pictures and did well out of it. No problems here, no claims of accurate renditions of real events. They pass the shortbread tin test. Some sneer at it, some like it. Wouldn''t the world be boring if we all liked the same thing... think of the queues for those things!

What if we wanted to do something for a bit of landscape photography for a shortbread tin? and we restricted ourselves to scrupulously accurate films, lenses and cameras. Well, we'd have to spend a while crawling over the landscape painting those mountains a bit more lurid, and the same for the trees adn the grass sward in the foreground. We'd need to hire a bonnie prince charlie look alike in full highland fig to stand in the bottom left corner and plant a stuffed stag somewhere about the place. We'd get the photo, but get crucified for vandalism and polluting the landscape. BUT we'd keep the photographic accuracy people happy, and produce a properly lurid photo of just the hackneyed sort expected on biscuits.

In other words, all the distortions and effects that people like done as part of the performance, and recorded and replayed with unimpeachable fidelity.

****** expensive!

So along came photoshop and its ilk. Mov some sliders around and you can exaggerate colours, you can restrict it to some areas, or the whole thing. You can paint out that pile of sheep muck in the foreground, you can add in one or more bonnie prince charlies afterwards and rotate them to suit. If you can imagine it, you can do it. Instant vandalism with no pollution. It turns the whole world into a cartoon or a caricature of itself IF YOU WANT. Crazy uncle Ned can also be discreetly edited out of that wedding photo once his crimes come to light. BUT it can also be used subtly to repair errors and failures.

I don't have a copy. I object to the way it is sold. Some firms seem to treat their customers as involuntary blood-donors. So I use Affinity and GIMP.

What does this mean in hifi terms?

Well, I have no objection to people changing sounds to fit their tastes. I do object when claims of accuracy and rightness are made. I'll defend their right to having their own preferences. I may disagree or agree with those preferences. I will attack dishonest claims though.

LIke a picture, sound can be sexed up and made to pop. It can be fun and enjoyable. I don't suppose most people would enjoy this all the time, contrast would be lost and you'd acclimatise, so the pop would be lost and boy would reality, the things you see and hear directly, seem dreary by comparison.

Trying to recreate the performance also has validity to see or hear what the artist had in mind during the phase of creation. What was heard in the concert hall, what was heard in the mix-down suite. These things also have legitimacy.

Recording a landscape accurately is also interesting. A record of how things actually were for the curious.

I have in mind taking an accurate photo of a classic shortbread tin scene with a stuffed stag blown over just to one side and a rather drunk prince charlie waving a bottle at the other. Fun and humour. I'd put it in a few photo competitions. Just for fun.

Dishonest claims get me going. Feel free to have your own preferences, but own up to them and I'll support your right to have them.

Pseudo-science is a hoot.

The prices of cult hifi are hilarious. I just hope the victim's families don't suffer hardships to pay for the addiction. Ideally, it's a victimless crime, but it may not always be ideal or victimless.

So, you're having fun, Andy, and that's what it's all about. You also know what you're doing to the sound and you have a sense of proportion in terms of how much is being done and where the thresholds of perception of it lie. You're not being led along by anyone peddling twaddle. All is fine in your world, to my thinking.

David

I need to save up for a stuffed stag, now. A cheap one with bad taxidermy, a silly smile and a leer in its eye would actually be best. Drunken teuchters are generally available. An empty Drambuie bottle in his hand would add a joke.

[GrimJosef]

Originally Posted by Radio Wrangler

... Trying to recreate the performance also has validity to see or hear what the artist had in mind during the phase of creation. What was heard in the concert hall, what was heard in the mix-down suite. These things also have legitimacy ...

This is true. But I've also heard listeners argue that while they like the way Simon Rattle gets all his musicians to play in tune and come in at the same time, they would prefer it if his performances had a bit more warmth. Furthermore since stereo is only creating an illusion of the original sound field, they need their brain's help to reconstruct that illusion, and in their case it steadfastly refuses to ignore the fact that they're in their living room, not the Barbican. So they need the sound to be match their environment more convincingly.

The bottom line is that since they're paying for the kit they feel they're entitled to have it deliver the kind of music they like, perhaps over and above the wishes of the artists. I have to say I have some sympathy with that point of view, although I don't hold it myself.

Cheers,

GJ

[Radio Wrangler]

Originally Posted by GrimJosef

Simon Rattle gets all his musicians to play in tune and come in at the same time, they would prefer it if his performances had a bit more warmth.

Michael Flanders: "...And they practice beforehand, which ruins the fun!"

I wouldn't dare sing that song here, North of the border, sufficient would fail to see the ironic nature and before you know it, we'd have a wee stooshie.

David

[AdrianH]

I have been reading this thread for a little while, (not been on the forum that long) and some of the tales of the snake oil being passed as truth and being sold, are to my mind criminal.

As GJ alluded to in his post, for me when listening to music I do not wish to hear the fidgeting of some audience member in the chair two rows down, If I do not like the response and would like a bit more bass or treble, I would move to the amp and turn the relevant knob to satisfy.

And as Andy a few posts up is playing with amps, that is part of the fun and I would like to guess when listening music on his amp it will sound more pleasing to him then a basic store bought device.

Beauty is in the ear of the beholder, probably from my limited experience with HI-Fi semi to decent speakers can help a lot.

Even my crappy amp with badly wound transformers is sounding good to me!

Then again my last hearing test said I was loosing it over 6KHz so what the hell, no snake oil here.

Adrian

[AdrianH]

I'm getting a bit mixed up between threads, duh sorry, they are merging into one.

Adrian

[Steve_Bell]

I posted the answer to my original query on page 1. Mods, please feel free to close this post.

[Trevor]

I remember as a young lad of 17 working on a Vox AC100 in the basement workshop did the repair was starting to slide the chassis back into its enclosure touched the ht capacitor with my hand as it slid in The resulting shock caused me to throw the chassis in the air smashing the output valves on the ceiling took me a good few moments to get over that one
Trev

[Aub]

We knocked over a pint glass full of bitter shandy into the grill above the EL34s on one or our AC100 amps 😄. We had to use the Baker Major 100 standby amp that night. What a sticky mess it was cleaning up the AC100, not to mention the new EL34s we had to buy.

Cheers

Aub

[Valvepower]

Originally Posted by Aub

Hi Terry,

Hard to believe but my mates and me used two AC100 amps for stereo, when we had our disco in the seventies. I wonder where they are now.

Cheers

Aub

Oh, that puts to shame the 50 watt Sound City 6 channel mixer amp with Northcourt Fifty used as a slave used for Social Club and PTA disco's in the seventies.

The Northcourt was latterly modified to fixed bias operation when I got 'pukka' 3.5K a-to-a 50 watt output transformer from the guys at Roost amplifiers, Southend.....

Regards
Terry

[Radio Wrangler]

R&D at HP used to have a christmas night at the social club in the main hall. Catered buffet etc. Bill Miller organised it one year and got some friends of his in to do the disco... Linn Products. Wall-to-wall Isobarik speakers etc etc.

Once upon a time the electrical eng lab at uni had a doo... would you believe with a 1/2 inch B&K capacitor mike for announcements.

David

[m0cemdave]

Originally Posted by Radio Wrangler

Once upon a time the electrical eng lab at uni had a doo... would you believe with a 1/2 inch B&K capacitor mike for announcements.
David

Ah yes, I've done that too just for a laugh. Despite their being omnidirectional you can get a surprising amount of GBF in that application, due to the amazingly flat frequency response.

In the late 1980's, after a few studio engineers found out how good they were, B&K started manufacturing versions fitted with ultra low noise preamps for the pro-audio market. The department was spun off as Danish Pro Audio (DPA), still making some of the best mics in the world.

And another thing. Ever wondered how the Grateful Dead managed to sing with a giant PA system just a few yards behind them, without it all feeding back? Differential pairs of closely spaced B&K half-inch measuring mics!

[Hartley118]

Originally Posted by m0cemdave

Ah yes, I've done that too just for a laugh. Despite their being omnidirectional you can get a surprising amount of GBF in that application, due to the amazingly flat frequency response.

In the late 1980's, after a few studio engineers found out how good they were, B&K started manufacturing versions fitted with ultra low noise preamps for the pro-audio market. The department was spun off as Danish Pro Audio (DPA), still making some of the best mics in the world.

And another thing. Ever wondered how the Grateful Dead managed to sing with a giant PA system just a few yards behind them, without it all feeding back? Differential pairs of closely spaced B&K half-inch measuring mics!

Something pretty like this perhaps, though I guess with longer cables. Costly if you drop them though.

Martin

[Radio Wrangler]

Ooh, and that shade of green says that the box at the far ends of the goosenecks is a B&K job too. Dual polariser? but how handy for a pair of mikes, if money is unlimited!

Gorgeous stuff.

Back in the days of doing my batchelor's the head of department put his head round the door of the small lab where I was working on my project and asked If I could help out for a moment as they were short-handed.

A first year student was doing a basic lab experiment... one of a pair of Goodmans Magister speakers the lab kept on a trolley, B&K 70W amp, BFO sweeper, plotter, mike polariser/preamp. He was trying to plot a speaker response. Lab acoustics weren't suitable, but the learning exercise would be useful.

Problem: No sound. No B&K Wooooooop!

So grab a scope, signal from BFO OK, signal from power amp OK. Signal OK at speaker terminals. Look for a fuse! No problem there.

Took grille off speaker. Some begger had stolen the drive units! other speaker the same. Quick trip for H of D's office.... "You won't believe this...."

Heard later that it had been a lab tech who was leaving... hence the short-handedness.

I like B&K tackle.

David

[Hartley118]

Indeed David, that’s a B&K 2807 microphone power supply. My collection of B&K kit lies at the masochistic end of my hobby because its mechanical packaging was designed on the assumption that no servicing would ever be required. My first 2807 caught me out because I had assumed that the only significant voltages would be the 200V mic polarising supply. It was only after being reminded by a sharp ‘belt’ that I realised that the solid state amplifier used a similarly high voltage as it’s ‘HT’. I guess that tends to happen when a bunch of valve instrument designers turn to solid state and rejoice that high voltage transistors permit use of familiar circuit voltages.

We could discuss much further, but that would lead this thread even further OT!

Martin

[cmjones01]

Originally Posted by Radio Wrangler

Problem: No sound. No B&K Wooooooop!

So grab a scope, signal from BFO OK, signal from power amp OK. Signal OK at speaker terminals. Look for a fuse! No problem there.

Took grille off speaker. Some begger had stolen the drive units! other speaker the same. Quick trip for H of D's office.... "You won't believe this...."

Some years ago I had a worried phone call from a friend who works in acoustics. He was making some measurements in an anechoic chamber, also using B&K gear I think, but all results had ceased. There was no sound any more. Cutting a long story short, we traced the reason back to a 'funny burning smell' which had been passed off as incidental. The speaker drive units were there, but they no longer conducted electricity. Lesson learned. It's surprisingly easy to burn out speakers when you can't hear them!

Chris

[Radio Wrangler]

All of the B&K gear was a bit other worldly in terms of electronic design.

Getting a wide-frequency-range oscillator by beating two low RF oscillators together (Beat Frequency Oscillator so their naming was honest) seems rather olde worlde but it could be swept without bouncing, which Wien Bridge oscillators would have done.

There's a lot of 'if only they were valves' design done even today. Pat Hawker's column was full of it, but now we have the reverse direction of people with a solid state background trying to design with valves as if they were transistors.

We have quite a few people on the forum having some fun learning about an alien world with thermionic things in it, but I've not seen much curiosity about one side-effect of the valve era on circuit design. Active devices used to cost an average man's weekly wage, so they were used very very sparingly and every trick in the book was used to get the greatest gain from the fewest devices.

Later on, the prices fell to merely being a bit expensive, but the ethos of minimising bottle count remained. I suppose bottle count taxation cemented the attitude in place in pre-history.

So valve audio is strongly tied to ultra-simplistic circuitry where the imperfections of devices show pretty clearly in the end result.

Few have shown any interest in designs with as many devices as necessary to do the job well, of avoiding the need for output transformers and having the gain.bandwidth needed to make performance controlled by passive components. It can be done. I once did it. It proved a point and then got dismantled. Heater power alone put it in Krell class-A territory. No use as a finished product for daily use, lots of fun and quite educational. Reinforces the shame that there is no 'PNP' complementary valve. Maybe Asimov knew a thing ot two?

David