Quad II

[Paul Barker]

If it wasn’t for Morgan’s Valve Amplifiers 4th Edition I would have insufficient Knowledge of the Quad II.

Thank you Morgan for you’re comprehensive explanation?

Anyone considering tackling a Quad II I recommend Morgan’s 4th edition.

I’m hoping to win a salvage pair. Not considered cheap though so may have to keep waiting patiently.

Might be just what I need for my Quad 57’s.

Sadly I can’t find the edition Morgan signed. Must have been 2nd from the year we all met in Vry’s flat.

It’ll turn up….

One day it’ll be on The Antiques Road Show.

[pre65]

I've got a fourth edition that Morgan gave me at Owston a few years ago, and signed with an inscription, but it is a Chinese print.

I do still have my pair of Quad 11 amps, my first valve amps bought many years ago from a hi-fi shop in Bury st Edmunds.

I modified them using data sheets supplied by Russ Abbott (or was it Andrews ?) using Holco resistors and an assortment of capacitors. They came with GEC Kt66 valves but they were worn out.

To be honest the sound was not (to my ears) brilliant, but certainly not offensive.

They did work OK when I had a pair of ESL57 (now in Nicks ownership) but that's to be expected ?

I might still have the Russ data sheets somewhere if you want a copy.

PS. I would consider selling them minus the KT66 and rectifiers, I won't want "silly" money.

[Paul Barker]

Im your Man then Phil. Let me know youre thoughts on price of the monoblocks.

Yes please on the Russ Andrews sheet. I dont follow him but I bought his lowest priced speaker cables.

I’d be buying the lowest priced Russian KT66’s. Langrex probably have them. I have some gec but I’ll have to restore my poor man’s avo before I dare plug it in its probably 20 years since I last used it.

So in short I may have four GE equipment pulls which may be ok. But if not, 4 Russian matched from Langrex. Not exorbitant.

Out of interest I have two tl12’s the el84 version with all transformers and a stereo 20 with only one opt and the power transformer. So I have plenty of projects already. Not to forget the cinema monoblocks. Though I plan to use EL36’s in those.

[shane]

Be interesting to see if the Quads and Leaks sound any better than the KEL84.

[Paul Barker]

Interesting thought. I took the liberty of ripping all the measures to make square waves look better for the printed word, and it began sounding better. I converted the pentode input valve to triode, took out the global feedback and it sounded better still. I played to to my friend a non audiofile in a flat we were working on. He said it sounded really good. But I set it up again at home and he moaned, so I took my EL38 single ended amp with an excessive “bench supply” controlled by a variac with 500mA power transformer a choke as large and 30henry two potato Mashers two Black Gates. He preferred my EL38 single ended amp, and so do I. I was getting carried away with the improvement in sound of the kel84 when I made it pure triode from start to finish and then the SE amp blew it away. But pure triode kel84 is better than uL with global feedback and square waves cheats.

I had been reading about the “perfect amplifier” I think it was named, just prior to the Williamson amp. It was full triode and no global feedback either. Thats inspired me to go radical with kel84.

Now Im getting my sights on the Quad II after carefully following Morgans wisdom surrounding it. I’m too simple to comprehend completely but it seems Quad II is a thing that as a whole comes out better against the odds and serves a specific purpose; driving 57’s. I wouldnt dare mess with its complexity. I have to restore it, give the power transformer an easier life by not sending power to the preamp of filament supply. Make my own preamp wth its own power supply. Oh and uprate the 3 watt dissipation resistor Morgan points out they used a < 3 watt resistor from the factory.

The fully balanced Webster monoblocks I have to commission in this jorney all triode no global feedback. I’ve ordered two more EL36’s from Langrex at £30 each to join the two I already bought all new boxed Mullard valves. Its almost a 2a3. A poor mans 2a3. But I shall in time buy enough Russian 2a3’s match them and see what the Webster may have sounded in the movie theatre. But I cant get my head round the field coil element of fixed biasing the valves. Right Naively I thought use my Graets field coils and by magic it will work. But it wont because it doesnt have to current draw of the field coils and bymotors the Webster amp was designed to match. Either I draw the current with combination of resistance and chokes and maybe too my Graetz field coils motors. I recall when I read about techniques in rado anuals of making a bias voltage on the negative rail, but it wasnt seen then as a hifi thing by any means. I’m yearning, knowing the power transformer must have in it that additional voltage, and it is so easy to pluck it out on the evolved method audiofiles use ; auto bias. But the 2a3 data sheet gives more power using fixed biass and half the distortion. Likewise some of the things Morgan says about the Quad II sumarise similar stories. Nothing is simple each product has more behind it than from its era than we can know unless we try it.

Who knows, having criticised Lyn Olson I may like the fully balanced Webster. Up to now I have a good sounding kel84 better than it sounded on arrival. But its no matched from a beven better sounding valve than the amaising EL84 in single ended topology, still my favourite sound. Confirmed by my builder mate.

Its a bit like Stephies comments in his website “I took it to work and they liked it”. But there is no compromise in my se amps power supply. All these commercial push pull profucts are compromised , webster its opt, Quad II its power transformer and cathode resistor. Leack, though the transformers are seen as an upgrade by kel84 fans it doesnt have the Mackintosh feedback winding. In the days Dave Slagle was experimenting using a fillament current winding opposite to the se dc current it wasnt simple and Im not shure he publish a successful summary at the end. I think my transformer winding days are over, I’m a passenger there now. But as a passenger I want to hear that element of Quad II.

[Paul Barker]

The pre Wilkinson Wireless World “Quality Amplifier”.

[Paul Barker]

Went to see Alan who owns victors vinyl and vintage. One of his Quad II’s is blowing fuses. So I said I’ll give you a low price for it. He said you can have it just give me the valves. Mint. Hope its not the power transformer that’ll be two Quad 2 transformers I’ll be short of. Anyway going under general anaestgetic tomorrow for biopsy so nothing done til next week. Diana is home but doolally. Sam is going for surgery Thursday I’m going to give my house keyto Fire Man Jo up the street who is taking me in for my procedure he can make sure Diana is OK, and I'll tell him if shes left her key in and locked door he can use his firemans axe . Will only cost a double glazing panel.

So Ive got bigger fish to fry than tracing this fault.

Funny that the other quad II which is in the post was Haydon Boardmans who said in an article the power transformer isnt rated enough. Welll now I know why he knew that. Because his was blown, and its taken him all these years to finally sell it and the bidding only went to £99.


https://ibb.co/JRXnjtV0

Well if this one is the transformer aswel. There will be someone winding if they dont go in a case idntical to what Quad used, a bare transformer will do. I shall never sell them anyway.

[Paul Barker]

In the background of the picture is Mo’s kel84 converted to completely triode. One of his jjel84’s has blown. I put one of my 6n3n ones in. He can decide whether to buy a matched quad from Derek Rocco at Watford Valves or just buy a single.

[Paul Barker]

The choke in q2 is 40h, i was impressed. I’m working on the one from Victors Vintage and Vinyl. It was blowing 1 amp fuses. Tested the original q2 square electrolytic capacitor one side is 20uF other 13uF. Not lighting led. But Ive ordered two 16uF polypropylene caps. They shall fit where the square electrolytic was. Ive also ordered 20uF pio for the cathode bypass. A 160v should just fit. So that will be no electrolytic caps remaining. Next I’ll change the coupling caps to pio. I’ll test all resistors and leave them alone if adequate for each of their role’s. They are original.

I don’t think the transformer is faulty. Alan kept his valves. May have had a faulty valve, or could it have been the 20uF cap in first position combined with hhe may not of had the correct rectifier and a quick blow fuse?

[Paul Barker]

I’ve ordered matched quad of kT66 from Derek Roko. If anyone has ef86 Im interested.

[Paul Barker]

Phil let me know what you want in a pm. Youre answer isn’t a pair of Tribute output Transformers though.

[Paul Barker]

While Im alive the Tributes remain here.

[Paul Barker]

I’m scared to put a trim pot on the QII’s.

So I’m following the late Patrick Turner’s advice 390 ohm cathode resistors bypassed 470uF Nichicon Muse terminating one phase w and other phase u. Old bias resistor shorted.

Hayden Boarman’s amp without a power transformer he had used inequal bias resistors 350 ohm and 365 ohm with 100uF cheap as scraps thrown on youre fish and chips take away.

Im also using white coffins but I’ll balance the lower value up with small resistor/s

Why Im scared to go with the manual trim pot is the wierdness of the inverting EF86 circuit, which Morgan has explained by my cognitive mind consists of leaky blotting paper which looses blood a small amount at a time. So I cant fathom clever stuff.

Ive ordered a power transformers for Hadon’s old amp. But cost a lot of money. The amp only cost £99 though so I’ve done OK.

Ive also ordered two plugs for the Two Jones 6 pin plugs which I could solder a pair of interconnects to for an active preamp or passive like my existing preamp. I shant take the ht or the 6.3v from the Jones. I’ll put an earthed fused switched IEC input on both Quad’s, and earth the chassis of both. Why Patrick biased with 195 ohm is something he took to his grave. But I don’t think he made a misprint, he was a lot cleverer than I am.

[Paul Barker]

Just got off the phone to Derek Rocco who is selling me the valves I need. He mention a Quad II EXPERT who increase the bias to give the power transformer less stress. Cant recall the man’s name but it’s written down at home where I took the call.

[Paul Barker]

Didnt find where I wrote it. Anyway I’m perfectly capable of biasing my own q2’s @ less current.

After talking to Derek, who uses same amps for music at home, he is a big fan of the single cathode resistor. He is also a big fan of his croft preamp.

Hence why I’ve decided to build my 6em7 preamp.

Now then, I am planning in my head a hybrid way to balance the push pull output valves.

So Derek already said bigger cathode resistor value. The late Patrick Turner also increased the bias resistors and split them by puting them on the other end of the opt cathode feedback coils. I’m like “I just dont like electrolytic caps”

Actually I dont understand why the effectively long tailed pair resistor as standard should be bypassed. But anyway in case its all a part of the synergy the designer built into the Q2 design, I’m prepared to bypass that resistor with a paper in Oil cap that I can just fit in.

Ive found that I can just fit polypropylene main b+ supply instead of electrolytics.Derek has ez32’s from Russia for £15 plus vat plus carriage. So Im trusting the designers choice of 16+16, after all its a pp design and the choke is 40henry. And I like valve rectification. Derek said put gz34’s and put bigger caps in. I said “I cant afford gz34’s these days.”

Atm cant find the ef 86’s I know I bought years ago. Theyve gone up enormously . So I’ll find mine in the end.

To finally get to the point. Adding the bias resistance can be a hybrid. Original 180 on the long tailed bypassed with pio. The additional resistance between each cathode and other end of feedback winding. Plus a dual gang linear pot wired heach gang opposite way. Start with it middle for diddle, bypass it with 10 ohm resistor so 10 ohm is max resistance. Plus one 10ohm fixed resistor from the cathode of each valve for current indicating. Balance adjusted by the two gang linear pot. Non of this resistance bypassed. Effectively its only 15 ohm per valve so the 180 is only raised effectively by 7.5 ohm as a starting point when the valves are new matched and the trim pot is middle for diddle.

The new matched quad from Derek cost almost £200 in the end. russian made Marshal TAD. Sadly clear glass. I think I have a few grey glass ge’s so if I sell the product I can balance those as above and charge more money. I dont think I bought enough grey kt66’s back in the day, now that they are premium priced. Ho hum. The counter that though I seem to have quite a few Mullard ecc83’s I could sell.
Have I made sense?