On 31/07/2015 11:14, Jim Lesurf wrote:
I've just been going though the process of having one of my old Armstrong
626 recievers serviced/modified by Mike Solomons of London Sound. I
actually sent him both the examples I owned and he then worked on the one
judged the 'best' for service and improvement.

I understand from the courier 'tracking' that it should arrive soon. All
being well, it is promised today. So I have the relevant home-made
adaptors, etc, and eagery await delivery so I can give it a go. :-)

Feel anxious in case the carriers manage to damage it on the last leg of
its trip away from me.

OK, the 626 - even with mods - isn't the technical peak of audio
perfection. But they do look nice and can sound good. Still feel it is a
shame no-one makes anything that looks like them today. But no doubt they'd
fail all the modern 'elf and safty' rules. Wooden lid that is easily
removed without tools. Plastic tray lower section, similar. etc.

Fingers crossed.


I have one of those - very nice too, and still works perfectly. It
hasn't been in daily use for some time now, though.The only slightly
annoying thing for me is the DIN speaker sockets.

What are the mods you're having done?

--
Cheers, Rob

In article , RJH
wrote:
On 31/07/2015 11:14, Jim Lesurf wrote:


I have one of those - very nice too, and still works perfectly. It
hasn't been in daily use for some time now, though.The only slightly
annoying thing for me is the DIN speaker sockets.

What are the mods you're having done?

I plan to write something about this in detail for my website. However I
should say up front that Mike was happy to give me full details of the mods
he makes *on condition* that I don't disclose all the details because they
are his ideas and his bread and butter. That seems fair enough to me, so I
agreed happily. Journalists have to respect their sources, particularly
when they are very helpful.

All that said...

The standard changes are simply to restore and repair. e.g. what I sent to
him had meters that didn't work properly and lamps that had failed. Some
switches/sockets were intermittent. All the predictable signs of a long
life of use for such old kit.

The returned set I now have here has all the meters, lights, etc, working
'as new'. (If I can manage I'll take some photos for when I write about
this, but I'm a lousy photographer.)

He also checked things like the IF/RF alignments, but since the set had
been owned by Ted Rule, then me, found these were spot on OK.

I think he also installed new heatsink compound, etc, for the output
devices to ensure the thermal sinking. And old electrolytics may get
replaced.

Essentially where possible he fixes/replaces what has gone wrong or seems
likely to go wrong soon. The main area where this is limited is if there is
physical external damage and he doesn't have a suitable replacement lid, or
whatever. Meters can be a problem. For my set he actually had to shave a
small bit of plastic and slightly bend the meter 'hand' as it had been
sticking because the plastic had slowly warped with time from the heat of
the pea bulbs. This perhaps gives you some idea of the detailed work he is
prepared to do when needed, and that it all depends on the specific set and
the wishes of the owner.

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. This tends to occur eventually with
the earlier sets with the carbon based tracks. FWIW I used conductive
plastic pots in a later version and these are less likely to get the
problem. So if a set is one of the later versions you may not experience
the problem. But earlier sets are very prone to it. This mod also tends to
reduce the switch-on thump I found.

2) He also modifies the power amp to be more thermally stable and less
likely to develop crossover due to thermal tracking differences. The result
seems to be more consistent and lowered distortion in normal use. This
change means he can set a higher bias current safely, so get smoother
results.

3) Along with (2) he tends to fit better drivers and splitter transistors.
So the amp should finding driving low loads easier, etc.

I'd expected him to remove the old thermal delays and change to using
higher rated diodes in the PSU. However he feels that this isn't necessary
if the delay still works. On reflection I ended up agreeing with him. I
changed the sets to lose the thermal delay because these were causing most
of the set returns under guarantee. However talking to Mike I realised this
was because some delays were dud. Once they've worked for a few years
they'll last forever. So by this stage they are unlikely to become a
problem as the survivors are the good ones! :-)

He may make other changes depending on the state of the set and the precise
details of the version. Bear in mind that the actual production circuit was
changed in detail many times as it 'evolved'. Alas, no-one now has any
clear record of them. [1] All minor, but each designed to tweak an aspect
of performance. e.g. The output caps and reservour cap values were
increased more than once to get more power at LF and into low loads - once
the drivers, etc, could cope!

FWIW As per an earier posting I'm using a set of DIN speaker adaptors I
made, based on some 'new old stock' plugs Dave kindly found and sent to me.
(Again, thanks Dave for those! :-) )

Currently listening to Radio 3 using the 626's FM tuner. Even though I've
not yet sorted out a sensible VHF antenna it sounds very good to me.
(Currently I'm using a set-top UHF TV antenna in the loft as the VHF
antenna! Need to get into the loft. 8-] )

Cheers,

Jim

[1] You may have noticed that there are two different Armstrong circuit
diagrams that were released with the 600 range sets. The change that
confuses most people is the change to the output bias current from 5 to 20
mA. But there are other changes that people miss. And in reality there were
many more 'versions' than two! One of my biggest regrets now is that all
the production paperwork was discarded and so I can't tell now how many
sets were made, and which changes were made, when! If I'd realised in time
I'd have tried to rescue the info. But it was too late by the time I
started writing the Armstrong webpages and asked others about this, and
other details now lost. :-/

With that in mind I wonder if it is worth asking people who have a 600 set
what serial number it is and when they bought it. Might be possible to
recover some details if enough sets are about. Should ask Mike as well as
he might have worked it out...

--
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

On 01/08/2015 12:44, Jim Lesurf wrote:
In article , RJH
wrote:
On 31/07/2015 11:14, Jim Lesurf wrote:


I have one of those - very nice too, and still works perfectly. It
hasn't been in daily use for some time now, though.The only slightly
annoying thing for me is the DIN speaker sockets.

What are the mods you're having done?

I plan to write something about this in detail for my website. However I
should say up front that Mike was happy to give me full details of the mods
he makes *on condition* that I don't disclose all the details because they
are his ideas and his bread and butter. That seems fair enough to me, so I
agreed happily. Journalists have to respect their sources, particularly
when they are very helpful.


Very well worth knowing about London Sound. FWIW I had some repairs and
mods done to a Beard valve amplifier by Chris Found - involved going
round to his home somewhere in/around central London. Can't speak highly
enough.

Also loosely intrigued that you would let somebody else loose on a
design you must know more about that most (anyone?!). Is that because
he's maybe more up to date? Better at say soldering? And/or you have
better things to do?

All that said...

The standard changes are simply to restore and repair. e.g. what I sent to
him had meters that didn't work properly and lamps that had failed. Some
switches/sockets were intermittent. All the predictable signs of a long
life of use for such old kit.

The returned set I now have here has all the meters, lights, etc, working
'as new'. (If I can manage I'll take some photos for when I write about
this, but I'm a lousy photographer.)

He also checked things like the IF/RF alignments, but since the set had
been owned by Ted Rule, then me, found these were spot on OK.

I think he also installed new heatsink compound, etc, for the output
devices to ensure the thermal sinking. And old electrolytics may get
replaced.

Essentially where possible he fixes/replaces what has gone wrong or seems
likely to go wrong soon. The main area where this is limited is if there is
physical external damage and he doesn't have a suitable replacement lid, or
whatever. Meters can be a problem. For my set he actually had to shave a
small bit of plastic and slightly bend the meter 'hand' as it had been
sticking because the plastic had slowly warped with time from the heat of
the pea bulbs. This perhaps gives you some idea of the detailed work he is
prepared to do when needed, and that it all depends on the specific set and
the wishes of the owner.

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. This tends to occur eventually with
the earlier sets with the carbon based tracks. FWIW I used conductive
plastic pots in a later version and these are less likely to get the
problem. So if a set is one of the later versions you may not experience
the problem. But earlier sets are very prone to it. This mod also tends to
reduce the switch-on thump I found.

2) He also modifies the power amp to be more thermally stable and less
likely to develop crossover due to thermal tracking differences. The result
seems to be more consistent and lowered distortion in normal use. This
change means he can set a higher bias current safely, so get smoother
results.

3) Along with (2) he tends to fit better drivers and splitter transistors.
So the amp should finding driving low loads easier, etc.

I'd expected him to remove the old thermal delays and change to using
higher rated diodes in the PSU. However he feels that this isn't necessary
if the delay still works. On reflection I ended up agreeing with him. I
changed the sets to lose the thermal delay because these were causing most
of the set returns under guarantee. However talking to Mike I realised this
was because some delays were dud. Once they've worked for a few years
they'll last forever. So by this stage they are unlikely to become a
problem as the survivors are the good ones! :-)

He may make other changes depending on the state of the set and the precise
details of the version. Bear in mind that the actual production circuit was
changed in detail many times as it 'evolved'. Alas, no-one now has any
clear record of them. [1] All minor, but each designed to tweak an aspect
of performance. e.g. The output caps and reservour cap values were
increased more than once to get more power at LF and into low loads - once
the drivers, etc, could cope!

FWIW As per an earier posting I'm using a set of DIN speaker adaptors I
made, based on some 'new old stock' plugs Dave kindly found and sent to me.
(Again, thanks Dave for those! :-) )


(I did get a few DIN plug screw-type cheapies - fine for my purposes)

Currently listening to Radio 3 using the 626's FM tuner. Even though I've
not yet sorted out a sensible VHF antenna it sounds very good to me.
(Currently I'm using a set-top UHF TV antenna in the loft as the VHF
antenna! Need to get into the loft. 8-] )

Cheers,

Jim

Very good! Sounds interesting, and look forward to the write-up.



[1] You may have noticed that there are two different Armstrong circuit
diagrams that were released with the 600 range sets. The change that
confuses most people is the change to the output bias current from 5 to 20
mA. But there are other changes that people miss. And in reality there were
many more 'versions' than two! One of my biggest regrets now is that all
the production paperwork was discarded and so I can't tell now how many
sets were made, and which changes were made, when! If I'd realised in time
I'd have tried to rescue the info. But it was too late by the time I
started writing the Armstrong webpages and asked others about this, and
other details now lost. :-/


Well, I hadn't noticed ;-) It's testimony to something that you still
see them popping up on ebay.

With that in mind I wonder if it is worth asking people who have a 600 set
what serial number it is and when they bought it. Might be possible to
recover some details if enough sets are about. Should ask Mike as well as
he might have worked it out...


Quite happy to supply photos etc of mine if it helps. SN 610455



--
Cheers, Rob

In article , RJH
wrote:

Also loosely intrigued that you would let somebody else loose on a
design you must know more about that most (anyone?!). Is that because
he's maybe more up to date? Better at say soldering? And/or you have
better things to do?

Well, we probably discussed the changes/fixes in more detail than most of
his customers. :-)

Alas, I don't trust my eyes/fingers/judgement as much as I used to. Afraid
I've developed a tendency to clumsiness and muddle. I'm still happy to work
on simple circuits and ones I don't mind trashing and having to redo. But I
didn't want to end up doing more harm than good to my 626s. Particularly
for the set Ted owned before me, which was the 'best' in many ways despite
being an early version.

In addition both sets had problems with failing meters, etc. So really also
needed some mechanical TLC and parts I lacked. I've never been any good at
mechanical issues.

Mike also could offer doing his mods which I decided to try because they
seemed like the kind of thing I'd have done at the time if things had gone
differently back in the days when the sets were being made. I was curious
to hear the results. Now pleased I did. :-)

And in the end I decided it might help others if I had Mike do this and I
could write about it. That might help others in a similar situation. Having
been though the process I'd now happily recommend it on the basis of
experience.

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

On 03 Aug, wrote:
And in the end I decided it might help others if I had Mike do this and
I could write about it. That might help others in a similar situation.
Having been though the process I'd now happily recommend it on the basis
of experience.

Should have also added:

For years people have been contacting me to ask if I can repair/check their
old Armstrong sets. I've always then had to explain I don't do this, and
suggested they try Mike or AHVS as the best places to go.

Having done that so often it seemed a good idea to finally practice what
I'd preached. :-)

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

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

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

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

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

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