Topics

Moreton Cheney Amplifier


Michael O'Beirne
 

Allan
 
How are you getting on with rebuilding your ancient amp? 
 
I ask because while clearing out my garage over the weekend I came across a few old HiFi mags.  HiFi News of June 1996 describes the impending issue of the “Celebration Quad II” amp.  This uses the same KT66s as your amp -  well not quite because it says “proper KT66s are about as common as Bugatti camshafts, Rolex Bubbleback winding  crowns or Leica 5cm viewfinders”.  These Quads were using the 7581A.  I can’t find it.  The mag says that the only alternative is the Chinese-made Edicron KT66-2, which is hideously expensive. 
 
My old Illife Valve Data says the KT66 equivalent is the 6L6G, which I suspect was a lot cheaper.
 
Only 600 numbered pairs of Quad IIs were to be made.  And the price of the amps – “expect a pair .... to sell for something not unadjacent to £6,000”.  Ouch.
 
73s
Michael
G8MOB
 
 


Chris_Suslowicz
 

Michael (G8MOB) wrote:

Allan
 
How are you getting on with rebuilding your ancient amp? 
 
I ask because while clearing out my garage over the weekend I came across a few old HiFi mags.  HiFi News of June 1996 describes the impending issue of the ???Celebration Quad II??? amp.  This uses the same KT66s as your amp -  well not quite because it says ???proper KT66s are about as common as Bugatti camshafts, Rolex Bubbleback winding  crowns or Leica 5cm viewfinders???.  These Quads were using the 7581A.  I can???t find it.

7581A is/was a military spec 6L6 apparently.
 The mag says that the only alternative is the Chinese-made Edicron KT66-2, which is hideously expensive. 
 
My old Illife Valve Data says the KT66 equivalent is the 6L6G, which I suspect was a lot cheaper.

Ha!

The KT66 was an improved 6L6 where GEC managed to straighten out the 'kink' in the valve characteristic - which is why they were prized by the HiFi fraternity of the day.
Only 600 numbered pairs of Quad IIs were to be made.  And the price of the amps ??? ???expect a pair .... to sell for something not unadjacent to ??6,000???.  Ouch.

A collectors piece aimed squarely at the Audiophool market (IMAO).

Best regards,
Chris. (G8KGS)


Andy_G8JAC
 

 

>>The KT66 was an improved 6L6 where GEC managed to straighten out the 'kink' in the valve characteristic

 

 

Hence KT  =  Kinkless Tetrode.

 

Andy  G8JAC


greenboxmaven
 

Replacing KT66s with  6L6s should be done with care.  A plain  metal 6L6 or 6L6G  has a lower rating than a KT-66.  The 6L6GC  is usually acceptable, but it's anode dissipation is still a bit lower than a KT-66.  There are plenty tales and lore about RCA obtaining the patent license of the KT-66 and using it to develop the 6L6.   Supposedly, the 6L6 was deliberately designed to have greater distortion in certain ways than KT-66s.  There is also the comparison between the 6550 and KT-88.  Sixty years ago, audiophiles would argue the virtues of each,  KT66s and 88s were  more expensive so  many people bought them for prestige even if they did not notice a real difference in sound.  The aesthetics of four  Genelex "Gold Lion" KT88s in a McIntosh 60 or 75 watt amplifier glowing in subdued room lighting, however, was quite pleasant and the KTs of all sizes seemed to last longer in heavy use. One valve that more closely resembles the KT-66 is the Western Electric 350B,  but it was expensive in the day and is ghastly expensive today. 

           Bruce Gentry, KA2IVY


On 9/9/20 7:44 AM, Michael O'Beirne via groups.io wrote:
Allan
 
How are you getting on with rebuilding your ancient amp? 
 
I ask because while clearing out my garage over the weekend I came across a few old HiFi mags.  HiFi News of June 1996 describes the impending issue of the “Celebration Quad II” amp.  This uses the same KT66s as your amp -  well not quite because it says “proper KT66s are about as common as Bugatti camshafts, Rolex Bubbleback winding  crowns or Leica 5cm viewfinders”.  These Quads were using the 7581A.  I can’t find it.  The mag says that the only alternative is the Chinese-made Edicron KT66-2, which is hideously expensive. 
 
My old Illife Valve Data says the KT66 equivalent is the 6L6G, which I suspect was a lot cheaper.
 
Only 600 numbered pairs of Quad IIs were to be made.  And the price of the amps – “expect a pair .... to sell for something not unadjacent to £6,000”.  Ouch.
 
73s
Michael
G8MOB
 
 


Michael O'Beirne
 

Chris
 
Thanks for your input. 
 
Yes, those Quads were clearly aimed at the audiophool market with deep pockets.  I reckoned that the price would get you into about 200 concerts at the Royal Festival Hall (maybe not atm!).
 
I had a quick look at the McIntosh 275 mkVII amp with its four KT88s going new for £7,100.  It does look immaculately built and weighs 67 lbs but what a price.   I suppose we should recall Proverbs 21:20 that a fool and his money are soon parted – but that will just open a can of worms. 
 
73s
Michael
G8MOB

From: Chris_Suslowicz
Sent: Wednesday, September 9, 2020 1:53 PM
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] Moreton Cheney Amplifier
 
Michael (G8MOB) wrote:
 
 
Only 600 numbered pairs of Quad IIs were to be made.  And the price of the amps ??? ???expect a pair .... to sell for something not unadjacent to ??6,000???.  Ouch.
 
A collectors piece aimed squarely at the Audiophool market (IMAO).
 
Best regards,
Chris. (G8KGS)
_._,_._,_


Jacques_VE2JFE
 

The KT66 was made as a substitute for the 6L6, maybe, but use a completely different internal elements configuration.

The KT66 do not use a “shadowed screen grid” construction.

So it is not equal to the 6L6 family of valves in every application.

One example is the output stage of the MC30 McIntosh amplifiers: using KT66s there at full power output, the KT66 screen grid can be seen glowing dangerously, which is not happening with the 6L6GC or 7581A.

 

The other differences are a filament current of 1.3A for the KT66 vs 900mA for the 6L6 family and:

19W maximum plate dissipation for 6L6, 6L6G, 6L6GA, 6L6GB,

21W for the 1614,

23W for the 5881

30W for the 6L6GC and KT66

35W for the 7581A

 

And do not forget the 807 family, which are basically 6L6s with a plate cap…

 

73, Jacques, VE2JFE


AllanIsaacs
 

The amplifier is on hold for a spell Michael. It’s now a Williamson.

http://www.radiomuseum.co.uk/MCamplifier.html

It’s now fully operational but waiting for the odd connector to be fitted. The built in PSU with original transformer and chokes turned out to be 100%.  Not even a sign of (acoustic) hum from them… completely silent (despite looking like they’d been underwater when first received).

Surprisingly, over the years, I’ve amassed dozens of original KT66 valves, most new in GEC boxes because those are the ones that didn’t get chucked out from collections. Goes some way to explaining why they’re so rare.. I’ve probably got them (all). J

Numerous people donated them and it’s the first time I’ve actually used any.

I was given an HP141 Spectrum Analyser complete with a set of plug-ins including the audio one with tracking generator and I’m intending to check the performance of the Williamson amp with that. Something new to learn. Presumably linearity and harmonics can be checked out.

Maybe fiddle with the feedback resistor and coupling capacitors etc. also the original Williamson had some HF responses that needed to be damped out in the Mk2.

I’m going through a busy spell (lifts keep breaking down) so things are going slowly on the radio front.

73 Allan G3PIY

 

Re

Allan

 

How are you getting on with rebuilding your ancient amp? 

 

I ask because while clearing out my garage over the weekend I came across a few old HiFi mags.  HiFi News of June 1996 describes the impending issue of the “Celebration Quad II” amp.  This uses the same KT66s as your amp -  well not quite because it says “proper KT66s are about as common as Bugatti camshafts, Rolex Bubbleback winding  crowns or Leica 5cm viewfinders”.  These Quads were using the 7581A.  I can’t find it.  The mag says that the only alternative is the Chinese-made Edicron KT66-2, which is hideously expensive. 

 

My old Illife Valve Data says the KT66 equivalent is the 6L6G, which I suspect was a lot cheaper.

 

Only 600 numbered pairs of Quad IIs were to be made.  And the price of the amps – “expect a pair .... to sell for something not unadjacent to £6,000”.  Ouch.

 

73s

Michael

G8MOB

 


Michael O'Beirne
 

Allan
 
I have had a quick skim through your notes.  Have you thought of becoming a professional technical writer!! 
 
The Williamson circuit seems a far better bet than the old clunky Moreton Cheney design.
 
That HP141 with the LF plug in looks like a valuable instrument and will be a lot more revealing than a standard distortion meter such as the old TF2331 (all of £10) which only gives total distortion.  It’s good enough for me and goes down reliably to about 0.01% THD.
 
73s
Michael
G8MOB
 
 

From: AllanIsaacs
Sent: Wednesday, September 9, 2020 3:39 PM
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] Moreton Cheney Amplifier
 

The amplifier is on hold for a spell Michael. It’s now a Williamson.

http://www.radiomuseum.co.uk/MCamplifier.html

It’s now fully operational but waiting for the odd connector to be fitted. The built in PSU with original transformer and chokes turned out to be 100%.  Not even a sign of (acoustic) hum from them… completely silent (despite looking like they’d been underwater when first received).

Surprisingly, over the years, I’ve amassed dozens of original KT66 valves, most new in GEC boxes because those are the ones that didn’t get chucked out from collections. Goes some way to explaining why they’re so rare.. I’ve probably got them (all). J

Numerous people donated them and it’s the first time I’ve actually used any.

I was given an HP141 Spectrum Analyser complete with a set of plug-ins including the audio one with tracking generator and I’m intending to check the performance of the Williamson amp with that. Something new to learn. Presumably linearity and harmonics can be checked out.

Maybe fiddle with the feedback resistor and coupling capacitors etc. also the original Williamson had some HF responses that needed to be damped out in the Mk2.

I’m going through a busy spell (lifts keep breaking down) so things are going slowly on the radio front.

73 Allan G3PIY

 


Pete_G4GJL
 

If the KT66 was developed in 1937 and the 6L6 in 1936, as stated on the Valve museum site, http://www.r-type.org/exhib/aaa0101.htm ,   why would RCA obtain the patent licence of the KT66, if they had already developed the 6L6?

Pete
G4GJL

On Wed, Sep 9, 2020 at 3:40 PM greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io> wrote:

Replacing KT66s with  6L6s should be done with care.  A plain  metal 6L6 or 6L6G  has a lower rating than a KT-66.  The 6L6GC  is usually acceptable, but it's anode dissipation is still a bit lower than a KT-66.  There are plenty tales and lore about RCA obtaining the patent license of the KT-66 and using it to develop the 6L6.   Supposedly, the 6L6 was deliberately designed to have greater distortion in certain ways than KT-66s.  There is also the comparison between the 6550 and KT-88.  Sixty years ago, audiophiles would argue the virtues of each,  KT66s and 88s were  more expensive so  many people bought them for prestige even if they did not notice a real difference in sound.  The aesthetics of four  Genelex "Gold Lion" KT88s in a McIntosh 60 or 75 watt amplifier glowing in subdued room lighting, however, was quite pleasant and the KTs of all sizes seemed to last longer in heavy use. One valve that more closely resembles the KT-66 is the Western Electric 350B,  but it was expensive in the day and is ghastly expensive today. 

           Bruce Gentry, KA2IVY


On 9/9/20 7:44 AM, Michael O'Beirne via groups.io wrote:
Allan
 
How are you getting on with rebuilding your ancient amp? 
 
I ask because while clearing out my garage over the weekend I came across a few old HiFi mags.  HiFi News of June 1996 describes the impending issue of the “Celebration Quad II” amp.  This uses the same KT66s as your amp -  well not quite because it says “proper KT66s are about as common as Bugatti camshafts, Rolex Bubbleback winding  crowns or Leica 5cm viewfinders”.  These Quads were using the 7581A.  I can’t find it.  The mag says that the only alternative is the Chinese-made Edicron KT66-2, which is hideously expensive. 
 
My old Illife Valve Data says the KT66 equivalent is the 6L6G, which I suspect was a lot cheaper.
 
Only 600 numbered pairs of Quad IIs were to be made.  And the price of the amps – “expect a pair .... to sell for something not unadjacent to £6,000”.  Ouch.
 
73s
Michael
G8MOB
 
 


Jacques_VE2JFE
 

Allan wrote : Surprisingly, over the years, I’ve amassed dozens of original KT66 valves, most new in GEC boxes because those are the ones that didn’t get chucked out from collections. Goes some way to explaining why they’re so rare.. I’ve probably got them (all). J

 

Not really all: four dozen NIB GEC here…

And a dozen of KT88s too !

 

About the (original) Quad II: very good amp, once all the res and caps are changed for modern components (metal film resistors, polypropylene caps).

They belies their 15W rating, but they really sound best with the original KT66s.

The Russian/Chinese copies did not come to their heels…

The Williamsons sound surprisingly good too !

I still have a rare Hallicrafters A-84.

 

73, Jacques, VE2JFE


Jacques_VE2JFE
 

Hello Pete,

This is right and relates to what I wrote before: the KT66 is not a shadowed screen grid tube !

 

73, Jacques, VE2JFE


cwlathes
 

Jaques,

Do you have , or have you rebuilt a pair of Quad II’s , and if so are you aware of the impact of the small capacitance introduced in the coupling capacitors to the KT66 grids  by the original metal can caps ?

Apologies if I am taking coals to Newcastle
😊

Regards,

Carvel

ZR6APX

 

From: wireless-set-no19@groups.io [mailto:wireless-set-no19@groups.io] On Behalf Of Jacques_VE2JFE
Sent: Wednesday, September 9, 2020 6:24 PM
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] Moreton Cheney Amplifier

 

Allan wrote : Surprisingly, over the years, I’ve amassed dozens of original KT66 valves, most new in GEC boxes because those are the ones that didn’t get chucked out from collections. Goes some way to explaining why they’re so rare.. I’ve probably got them (all). J

 

Not really all: four dozen NIB GEC here…

And a dozen of KT88s too !

 

About the (original) Quad II: very good amp, once all the res and caps are changed for modern components (metal film resistors, polypropylene caps).

They belies their 15W rating, but they really sound best with the original KT66s.

The Russian/Chinese copies did not come to their heels…

The Williamsons sound surprisingly good too !

I still have a rare Hallicrafters A-84.

 

73, Jacques, VE2JFE

_._,_._,_


Jacques_VE2JFE
 

Hello Carvel,

 

Yes I am: we should have read the same warning on the Keith Snook site about that.

However, I have “rebuilt” four pairs of Quad II in the last 20 years and never see any effect related to not “emulating” the coupling capacitors to ground original capacitances.

No oscillations, no ringing, everything was fine (and still is, as far as I know).

 

73, Jacques, VE2JFE


cwlathes
 

Mmm . . .  I have a pair which were rebuilt using WIMA caps for coupling without any ‘emulation’ of that capacitance , and I also can’t measure anything amiss . . . 

I am about to tackle a second pair , so was just interested in your experience . . 

Many thanks

Carvel

 

ZR6APX

 

From: wireless-set-no19@groups.io [mailto:wireless-set-no19@groups.io] On Behalf Of Jacques_VE2JFE
Sent: Wednesday, September 9, 2020 8:40 PM
To: wireless-set-no19@groups.io
Cc: 'cwlathes'
Subject: Re: [wireless-set-no19] Moreton Cheney Amplifier

 

Hello Carvel,

 

Yes I am: we should have read the same warning on the Keith Snook site about that.

However, I have “rebuilt” four pairs of Quad II in the last 20 years and never see any effect related to not “emulating” the coupling capacitors to ground original capacitances.

No oscillations, no ringing, everything was fine (and still is, as far as I know).

 

73, Jacques, VE2JFE

_._,_._,_


greenboxmaven
 

As I said before, there is a lot of lore and legend about the 6L6 and KT-66.  Your source seems to dispel any doubts.  RCA was not always the most ethical and truthful company, and released a lot of self serving research.  Add to this a bit of mystique, and legends are born.

     Bruce Gentry, KA2IVY


On 9/9/20 12:06 PM, Pete_G4GJL wrote:
If the KT66 was developed in 1937 and the 6L6 in 1936, as stated on the Valve museum site, http://www.r-type.org/exhib/aaa0101.htm ,   why would RCA obtain the patent licence of the KT66, if they had already developed the 6L6?

Pete
G4GJL

On Wed, Sep 9, 2020 at 3:40 PM greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io> wrote:

Replacing KT66s with  6L6s should be done with care.  A plain  metal 6L6 or 6L6G  has a lower rating than a KT-66.  The 6L6GC  is usually acceptable, but it's anode dissipation is still a bit lower than a KT-66.  There are plenty tales and lore about RCA obtaining the patent license of the KT-66 and using it to develop the 6L6.   Supposedly, the 6L6 was deliberately designed to have greater distortion in certain ways than KT-66s.  There is also the comparison between the 6550 and KT-88.  Sixty years ago, audiophiles would argue the virtues of each,  KT66s and 88s were  more expensive so  many people bought them for prestige even if they did not notice a real difference in sound.  The aesthetics of four  Genelex "Gold Lion" KT88s in a McIntosh 60 or 75 watt amplifier glowing in subdued room lighting, however, was quite pleasant and the KTs of all sizes seemed to last longer in heavy use. One valve that more closely resembles the KT-66 is the Western Electric 350B,  but it was expensive in the day and is ghastly expensive today. 

           Bruce Gentry, KA2IVY


On 9/9/20 7:44 AM, Michael O'Beirne via groups.io wrote:
Allan
 
How are you getting on with rebuilding your ancient amp? 
 
I ask because while clearing out my garage over the weekend I came across a few old HiFi mags.  HiFi News of June 1996 describes the impending issue of the “Celebration Quad II” amp.  This uses the same KT66s as your amp -  well not quite because it says “proper KT66s are about as common as Bugatti camshafts, Rolex Bubbleback winding  crowns or Leica 5cm viewfinders”.  These Quads were using the 7581A.  I can’t find it.  The mag says that the only alternative is the Chinese-made Edicron KT66-2, which is hideously expensive. 
 
My old Illife Valve Data says the KT66 equivalent is the 6L6G, which I suspect was a lot cheaper.
 
Only 600 numbered pairs of Quad IIs were to be made.  And the price of the amps – “expect a pair .... to sell for something not unadjacent to £6,000”.  Ouch.
 
73s
Michael
G8MOB
 
 



Pete_G4GJL
 

Yes I guess there was skulduggery of all sorts and at all levels even then (!)
 
Ill go back to my shack and to listening to Radio China on my AR88D (Camden Factory of course).
 
Pete

On Wed, Sep 9, 2020 at 9:36 PM greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io> wrote:

As I said before, there is a lot of lore and legend about the 6L6 and KT-66.  Your source seems to dispel any doubts.  RCA was not always the most ethical and truthful company, and released a lot of self serving research.  Add to this a bit of mystique, and legends are born.

     Bruce Gentry, KA2IVY


On 9/9/20 12:06 PM, Pete_G4GJL wrote:
If the KT66 was developed in 1937 and the 6L6 in 1936, as stated on the Valve museum site, http://www.r-type.org/exhib/aaa0101.htm ,   why would RCA obtain the patent licence of the KT66, if they had already developed the 6L6?
 
Pete
G4GJL

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