Armstrong 626 nenewal!
 

In article , Phil
Allison scribeth thus
Jim Lesurf wrote:




The main mods are that:

1) He fits a circuit to suppress the 'whoosh' which can arise if you change
the volume too soon after switch-on.


** A sure sign of electro caps charging via the track of a pot, temporarily
causing DC voltage and so noise when the wiper is moved. I see in this case 10
and 22uF electros feeding a 100kohm volume pot - so it will take around 20
seconds for the voltage to disappear, if it ever does. A couple of 0.47uF film
caps are the go there.


2) He also modifies the power amp to be more thermally stable and less
likely to develop crossover due to thermal tracking differences.



** The schem on your pages shows two ITT44 diodes for bias temp compensation
while a quasi-complementary stage normally requires three - one for each driver
and one for the upper output transistor. If both ITT44s are mounted in contact
with the heatsink, bias may be overcompensated and if only one then it will
likely be under.

A good compromise is to use three diodes, with one attached to the heatsink and
select a series resistor on test to get 20mA at idle.


I'd expected him to remove the old thermal delays and change to using
higher rated diodes in the PSU.

** So would I, seeing 1N4003s in the PSU puts my teeth on edge.

In the early 70s, I built a quite similar stereo amp for my own use - but with
an extra TO3 transistor providing a regulated B+ rail of 64VDC. There was also a
thyristor crow bar circuit that instantly shut down the B+ if the peak supply
current exceeded a safe level for the 2N3055 outputs.

Input connectors were 5 pin DIN and it drove a pair of heavily modified KEF KIT
3s (same as the Concerto) - until I discovered Quad ESL57s.


... Phil


I think your a bit of a QUAD fan Phil, was arguing with someone the
other day that such as upping the power and LS caps in a 303 from 2200
to 4700 uF was making it something else which it wasn't originally like
modifying the input LM301A chip of the 405 ..

comments?....
--
Tony Sayer

Armstrong 626 nenewal!
 

tony sayer wrote:


I think your a bit of a QUAD fan Phil, was arguing with someone the
other day that such as upping the power and LS caps in a 303 from 2200
to 4700 uF was making it something else which it wasn't originally like
modifying the input LM301A chip of the 405 ..

comments?....


** From reading published interviews, I know Peter Walker liked to get a product *right* before selling them to anyone.

From studying some of Quads famous amplifiers ( Quad II, 303, 405 & 306 ) the choice and usage of each part appears carefully considered as to suitability, necessity and reliability.

The large electros in the 303 are adequate for their job. The amp has no hum since the PSU is regulated while the output coupling electros have low enough impedance at 40Hz (ie 0.25 ohms) to effectively damp cone resonance in any 8 ohm woofer likely to be used.

Unless the electros appear to be deteriorating ( ESR heading North )I would leave them be.

The 301A op-amp in early 405s is a sore point with many enthusiasts who *feel* it is obsolete and inferior. It provides 15 times voltage gain to drive the Current Dumping power stage, which has a voltage gain of only 3.8 times.
Cleverly used in the inverting mode, it does that job very well and also provides the sub sonic filter function.

The possible replacements require some circuit modifications and do almost nothing to improve the amplifier's specs.



..... Phil

Armstrong 626 nenewal!
 

Just to let people know I've now put up a webpage

http://www.audiomisc.co.uk/Armstrong...airandmod.html

on this. Even managed to take some photos of the result. :-)

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Armstrong 626 nenewal!
 

On Mon, 10 Aug 2015 14:58:01 +0100, Jim Lesurf wrote:

Just to let people know I've now put up a webpage

http://www.audiomisc.co.uk/Armstrong...airandmod.html

on this. Even managed to take some photos of the result. :-)

Jim

An interesting quote from that web page:

"Although I'm not a very good photographer, you can see it now looks
like new. No sign of it being 40 decades old!"

I don't think any of us realised just how long Armstrong have been in
the Hi-Fi business. :-)

--
Johnny B Good

Armstrong 626 nenewal!
 

On 10/08/2015 20:22, Johnny B Good wrote:
On Mon, 10 Aug 2015 14:58:01 +0100, Jim Lesurf wrote:

Just to let people know I've now put up a webpage

http://www.audiomisc.co.uk/Armstrong...airandmod.html

on this. Even managed to take some photos of the result. :-)

Jim

Very interesting, thanks.


An interesting quote from that web page:

"Although I'm not a very good photographer, you can see it now looks
like new. No sign of it being 40 decades old!"

I don't think any of us realised just how long Armstrong have been in
the Hi-Fi business. :-)


I did notice that but didn't like to say :-)

The left hand 'Armstrong' lettering on mine is illuminated - can't quite
tell on yours, it looks to be painted, the same as the logo.

I think those are good photos by the way - reminiscent of a 70s brochure!

--
Cheers, Rob

Armstrong 626 nenewal!
 

In article , Johnny B Good
wrote:
On Mon, 10 Aug 2015 14:58:01 +0100, Jim Lesurf wrote:

Just to let people know I've now put up a webpage

http://www.audiomisc.co.uk/Armstrong...airandmod.html

on this. Even managed to take some photos of the result. :-)

Jim

An interesting quote from that web page:

"Although I'm not a very good photographer, you can see it now looks
like new. No sign of it being 40 decades old!"

I don't think any of us realised just how long Armstrong have been in
the Hi-Fi business. :-)

Apologies. Someone else pointed out the error this morning. Now fixed.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Armstrong 626 nenewal!
 

In article , RJH
wrote:


The left hand 'Armstrong' lettering on mine is illuminated - can't quite
tell on yours, it looks to be painted, the same as the logo.

It is illuminated, but may not show up clearly. Limitations of my skill
sic as a photographer. cf below.

I think those are good photos by the way - reminiscent of a 70s brochure!

Inc. our 1970s furniture. 8-]

I was trying to get images that approach the ones in the old 600 range
publicity shots, etc. The process gave me a *lot* of respect for the
photographers back then! I'm a lousy photographer, alas.

A snag was that my camera is very 'automatic' so gives you *no* option to
manually focus. At low light levels it tends not to focus well. So I have
to take many shots, then some are fuzzy, some are better. Fortunately,
digital cameras mean it is cheap and easy to take lots of photos, then
discard most of them.

I spend about two days experimenting with lighting conditions, etc, to try
and get photos that appeared as close to "what you see" as possible. The
main difficulty was getting the light level 'just right' so you can see the
tuning scale illumination without the rest of the scene being too dark.

A second problem was reflections in the glass of the tuning display. I
ended up with a black jersey over the back of the chair to which I'd fixed
the camera. This blacked out the area being reflected.

The stereo LED is also 'burned out' in the photos. i.e. it looks like a
small white light surrounded by red. But to the human eye is is just bright
red, however it saturates the camera.

BTW one of the pix showing the whole 626 is actually two joined photos.
That allowed me to zoom in and get more detail to start with. Then played
with GIMP to fiddle the results together. If you look you can see the join,
but it seems minor enough to pass muster.

The zoomed in pic of the tuning scale, etc, is one of the paired images.
Didn't put the other on the page, but can do if it seems worthwhile.

One trick which was suggested to me was to take one photo with no added
light, so only the lighting of the 626 itself would show. Then take another
with reasonably high lighting to make the set sharp and clear. Then
'PhotoShop' (GIMP in my case) the tuning scale and meters from the first
over the second. Apparently the magazines do this routinely. But I found
when I tried it the result looked obviously like a composite. So seemed
un-natural, and might make people think I'd "fiddled the images" to make
the unit look better than it really now is.

The truth is that it looks better than the photos I could take! And sadly
you can't hear what it sounds like from the photos... I'm currently
listening to a string quartet on R3 FM via 626 + LS3/5A's. Really nice. :-)

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Armstrong 626 nenewal!
 

On Tue, 11 Aug 2015 11:21:39 +0100, Jim Lesurf wrote:

In article , Johnny B Good
wrote:
On Mon, 10 Aug 2015 14:58:01 +0100, Jim Lesurf wrote:

Just to let people know I've now put up a webpage

http://www.audiomisc.co.uk/Armstrong...airandmod.html

on this. Even managed to take some photos of the result. :-)

Jim

An interesting quote from that web page:

"Although I'm not a very good photographer, you can see it now looks
like new. No sign of it being 40 decades old!"

I don't think any of us realised just how long Armstrong have been in
the Hi-Fi business. :-)

Apologies. Someone else pointed out the error this morning. Now fixed.


I realised what had happened (I've done the same myself). It's a case of
"Changing Horses In Mid-stream" where you intended to type 40 years and
then decided the phrase 4 decades would be better, forgetting to remove
the now unneeded zero.

I bet you proof read it and *still* managed to miss it, eh?[1] :-)

[1] I often spot such errors (and ommissions) when proof reading but I'm
all too often dismayed by the number of such Es & Os that *still* manage
to appear in the final 'publication'.

--
Johnny B Good

Armstrong 626 nenewal!
 

In article , Johnny B Good
wrote:

I realised what had happened (I've done the same myself). It's a case
of "Changing Horses In Mid-stream" where you intended to type 40 years
and then decided the phrase 4 decades would be better, forgetting to
remove the now unneeded zero.

Yes. As I wrote I was dithering between "for four decades" and "for about
40 years" and ended up writing a mashup of the two. 8-]

I bet you proof read it and *still* managed to miss it, eh? :-)

Sadly, yes. I followed my usual practice of leaving the draft for a day or
two for my brain to clear, then going though it two or three times looking
for mistakes, tweaking the phrasing, etc. Managed to miss it. I also missed
another error that Mike Solomons noticed immediately I'd put up the page
and told him.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Armstrong 626 nenewal!
 

On 12/08/2015 09:22, Jim Lesurf wrote:
In article , Johnny B Good
wrote:

I realised what had happened (I've done the same myself). It's a case
of "Changing Horses In Mid-stream" where you intended to type 40 years
and then decided the phrase 4 decades would be better, forgetting to
remove the now unneeded zero.

Yes. As I wrote I was dithering between "for four decades" and "for about
40 years" and ended up writing a mashup of the two. 8-]

I bet you proof read it and *still* managed to miss it, eh? :-)

Sadly, yes. I followed my usual practice of leaving the draft for a day or
two for my brain to clear, then going though it two or three times looking
for mistakes, tweaking the phrasing, etc. Managed to miss it. I also missed
another error that Mike Solomons noticed immediately I'd put up the page
and told him.


IME one of the worst people to proof is the author. I often miss things
that on hindsight would have been howlers. You could do worse than post
final drafts here?

--
Cheers, Rob