EL84, Balanced Input, Push-Pull Amplifier

What people are working on at the moment
Andrew
Eternally single
Posts: 4206
Joined: Thu May 24, 2007 2:18 pm

#76

Post by Andrew »

JamesD wrote:

Boy, do you do things right!

James
Abso...effing..lutey :!:

Couldn't agree more....
Analogue, the lost world that lies between 0 and 1.
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#77

Post by Cressy Snr »

After those ghastly 6463s I was keen to return to the 5687 in the driving position, but looking at the solder-splattered, tired old interior of the amp I couldn't face doing the heater wiring to the sockets.....again.

Instead I changed out the anode resistors for a couple of 47K two watters which were soldered to the bus bars (no need to touch the socket) and cut out two of my parallel cathode resistors, to give 500R.

You see all this talk of distortion manipulation and harmonic equalisers, got me thinking, always a dangerous thing, but what the hell, it's a hobby after all
and one I'm enjoying again.

So I tried an ECC82 driving the output stage. OK, so these are not the flavour of the month and are much mocked among serious valve afficionados, but their distortion pattern like the ECC81, is reputed to be a nice match with EL84s , so say the old guys.

Well whaddya know those old guys were right on the money. The combination of ECC82 and EL84 gives a lovely, sweet presentation that you can just relax into and let the sun pour down like honey.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#78

Post by Cressy Snr »

What I need now is some good NOS ECC82. I'm using Electro Harmonix gold pin ones at the moment.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8864
Joined: Mon May 21, 2007 9:42 pm

#79

Post by Paul Barker »

I have some of these but they aren't for sale. If I find them at the lockup in time I'll bring them to Owsten so you can hear them.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#80

Post by Cressy Snr »

Paul Barker wrote:I have some of these but they aren't for sale. If I find them at the lockup in time I'll bring them to Owsten so you can hear them.
I couldn't afford them if they were for sale :D
Valve prices are getting stupid these days.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
User avatar
Ali Tait
Eternally single
Posts: 4373
Joined: Fri Jun 08, 2007 8:10 pm
Location: Galashiels

#81

Post by Ali Tait »

Have some nice Amperex and Telefunken I could bring too.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8864
Joined: Mon May 21, 2007 9:42 pm

#82

Post by Paul Barker »

SteveTheShadow wrote:
Paul Barker wrote:I have some of these but they aren't for sale. If I find them at the lockup in time I'll bring them to Owsten so you can hear them.
I couldn't afford them if they were for sale :D
Valve prices are getting stupid these days.
Yes that is why I can't afford to sell them I have no private pension and not many years paid up for state pension with few years of work left. So I have to think about food and clothing during meagre retirement.

I paid Derek Rocco £7.50 each when it was a small fortune to pay that much for an ECC82. We had a conversation about the loss of the Mullard ECC83 and he said the next to go will be the ECC82 I have these if you want some. He was right. The ECC81's then were awash but now those have joined the rarity procession.

My biggest mistake was sending about 50 Mullard ECC83's to an American guy in 1998 for £1 each. Over here they hadn't hit the giddy levels yet, he knew that over there they had, but he found a mug across the pond. That was before eBay opened up to the Bits and we began to see values across the world. For a very brief period before the UK dealers became conversant with what had just awoken me to the world market, you could buy 6sn7's from Derek and double your money on eBay. Very quickly everybody found out! Then the pendulum swung the other way, and those people you used to get valves cheap from, used mythical heresay statements to boost their value. It was all over.

Last time I spoke to a British dealer I asked "what do you think will happen to our old valves? " What was in my mind was will they always go up in value or will the bubble burst. His response surprised but also woke me up. "we will run out of them". That I think is the truth. The future is no more stock of what we once took for granted.

What I am not sure of is whether after that time the few rag tag valves we have left will become worthless. With everyone using new production Chinese. They have acording to what I read from you lot here, improved.

Prices seem to have had a recent upturn. I discovered this while looking for valves myself, and decided not to buy any. Just look harder for what I have.

Found the 1619's thankfully. They have gone up, but fortunately mine were from the era others hadn't caught on to them.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#83

Post by Mike H »

Paul Barker wrote:Last time I spoke to a British dealer I asked "what do you think will happen to our old valves? " What was in my mind was will they always go up in value or will the bubble burst. His response surprised but also woke me up. "we will run out of them". That I think is the truth. The future is no more stock of what we once took for granted.

I think so too.

Steve I might have some NOS ECC82's but need to have a search
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#84

Post by Cressy Snr »

Cheers chaps!

Isn't it odd how things turn out?
I go all round the houses with a simple PP circuit and then end up, apart from the balanced, phase splitterless operation, with what is near enough a classic design. Those old engineers had it right in the 50s and 60s; of course they did. They forgot more about valve amp design that I'll ever know in my lifetime.

It was probably the demand for ever-increasing power because of decreasing speaker efficiency, ever more impressive distortion specs from the marketing department, plus the cost-cutting demands from the bean counters that crippled these old designs.

Put in the beefed up dual power supplies and use balanced operation or transformer phase splitting, triode strapped output pairs and you have a classic design brought bang up to date, with superb sound.

The ECC82 differential driver stage/splitter is a staple of old-fashioned EL84 PP amp design. It is not difficult to see the reasons.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#85

Post by Cressy Snr »

Right, that's it!
There ya go :)

Image
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#86

Post by Cressy Snr »

That's the curtain down on this one.
Now I know I can do push-pull and make a good sound, I can start on some more projects.
It would be an absolute scandal to let that quad of KT120s go to waste.
What to drive them with will be the thing to think about.


Then there is the idea of an all Brit push pull amp.
Two pairs of ML6 as diff drivers into two pairs of 6P25.

I can't make my mind up.
Despite the indecision, my interest in this hobby has been revitalised no end :)
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#87

Post by Cressy Snr »

I've also got four globe meshplate UX227s that could work as pairs
in a differential driver stage for 6P25s, and three 2.5V centre tapped heater transformers, and four UX5 sockets :wink:

Decisions decisions :lol: :lol:
Sgt. Baker started talkin’ with a Bullhorn in his hand.
User avatar
Greg
Social outcast
Posts: 3198
Joined: Wed May 23, 2007 11:14 am
Location: Bristol, UK

#88

Post by Greg »

You've mentioned KT120's again. Just incase you've forgotten, look at
http://www.world-designs.co.uk/forum/sh ... php?t=6788
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#89

Post by Cressy Snr »

Thanks for that Greg.
after looking at that thread, I'm going to have to do KT120s.
It would be dumb of me in the extreme not to, now wouldn't it :)

You've made up my mind for me.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8864
Joined: Mon May 21, 2007 9:42 pm

#90

Post by Paul Barker »

Image
:D :D :D :D

Just playing with ya.

I ordered myself four because they are so cheap.

From JACMUSIC

"compared to GU50, KT88 is only a consumer tube. GU50 is extremely strong and very low distortion. Amazing quality Russian military old stock."
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
Post Reply