Armstrong 600 series tuners and receivers

[stevehertz]

I realise that it's not 'intelligent' fault finding, but I've ordered replacement electrolytic caps for both the diode switching and AM boards. At least those - which are always suspect - will then eliminated. I'll report back. Thanks for the input so far everyone.

[stevehertz]

Originally Posted by PaulR

Are there separate switches for AM & FM? If not it would suggest that the AM only fault is further back

Tuner selection is not conventional. There is a switch marked 'tuner' that initially selects FM. To select AM , you then also depress another switch that is identified by a small 'square' character (not marked AM). So...?

[Trevor]

I am not so sure its been a long time since i used the AM/FM version
Having said that it should be in the full service sheet But I can remember the AM Fm square button I think
You can always use the amp as a tracer just look at the output from the AM board
good luck
Trev

[PaulR]

I was thinking that if the FM comes through when the key switch is pressed then the diode switching arrangement must be working and the problem must be with the AM board. In practice I think the approach of simply replacing caps is not a bad one. I have gone down the "intelligent" route of diagnosing faults and replacing only the associated components only to have more faults to appear one after another.

[Trevor]

From memory both the Am tuner and the Fm tuner come through different ports on the diode logic I will have a look on the schematic tomorrow ! do you have any signal tracer or scope ?
Trev

[stevehertz]

I have a scope yes Trevor.

[Trevor]

Please look at this you will find a detailed description of the 600 am tuner here

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

Trev

[stevehertz]

Thanks Trevor. Although I thought I'd picked the bones from that web site, I'd missed that in depth explanation of the AM tuner. Not so sure if it will help me, a 'dry joint/switch cleaning/cap changing' radio repairer, but we'll see. Hopefully changing all those potentially faulty electrolytics will help. They should be arriving any day now.

[Trevor]

Using your scope it should not be difficult ! To be honest I never was and still am not a big AM fan
After Fm it seamed to defeat the object of quality amp and speakers Having said that the FM tuner was superb rates with anything made since at the price
What you also need is an Am oscillator also should be able to pick one up from the wlell known site
You have pulled the ferrite rod away from the unit Have you ytried a piece of wire in the arial socket
Trev

[stevehertz]

Originally Posted by Trevor

Using your scope it should not be difficult ! To be honest I never was and still am not a big AM fan
After Fm it seamed to defeat the object of quality amp and speakers Having said that the FM tuner was superb rates with anything made since at the price
What you also need is an Am oscillator also should be able to pick one up from the wlell known site
You have pulled the ferrite rod away from the unit Have you ytried a piece of wire in the arial socket
Trev

I've done loads of AM alignments, I've got an Advance B4B sig gen. I'm just not that good at 'higher level' fault finding, RF signal tracing etc. Hopefully with your help..

Out of interest, until my caps arrive and we get technical again, what was your selling experience of these at Stoke? What shop etc etc? I'm interested as a local.

[Trevor]

I worked for about 20 years in the trade a very small company called high fidelity stoke on trent
The business was originally a one man band A mr Earnest Beard his real love was film and film music He did a lot of reviews for radio Stoke
We had Dual Leak Sugden Armstrong Wharfedale Kef Castle Morden short Trio Harmon Kardon and so on
This was replaced by Hk Bowen
It went on for a no of iterations before closing down due to poor management the hi fi side did well enough but all profits seems to go into badly thought out schemes
I did shop sales and service before going into industry trying to make some proper money
Quad /Armstong B+W Kef Castle were real quality to deal with true gentlemen
I have in my time spoken with most of the early icons in the trade
Trev

[stevehertz]

Thanks Trevor, very interesting.

[vidjoman]

I presume you have the external ferite rod aerial still attached. I've seen them where it's been removed/broken off as MW wasn't wanted.

[stevehertz]

Yes the aerial is in place. I've also connected an external aerial and switched between the two.

[thermionic]

As I understand it, the Armstrong tuners were generally well thought of.

The designer, Ted Rule was an active radio amateur, so one can only imagine that he had a passion for getting the best performance out of his designs providing the accountants would let him!

Regarding the 600 series amplifier, I remember having several problems on the early versions with the thermal delay switch not operating, and the shunt resistor (47R)? Overheating.



SimonT.

[stevehertz]

Originally Posted by thermionic

As I understand it, the Armstrong tuners were generally well thought of.

The designer, Ted Rule was an active radio amateur, so one can only imagine that he had a passion for getting the best performance out of his designs providing the accountants would let him!

Regarding the 600 series amplifier, I remember having several problems on the early versions with the thermal delay switch not operating, and the shunt resistor (47R)? Overheating.



SimonT.

Hi Simon, thanks for your info and input. Yes, I'm aware of the thermal switch and fortunately mine has been well behaved. As I understand it, it was not present in the very first models, then it was introduced and there were a lot of problems so it was dropped again in later models. The general view now is that if you have one (thermal switch) that is working then all is well as the iffy ones have been weeded out years ago.

[PaulR]

Mine had an iffy delay switch which had been shorted out but it turned out that the contact points were dirty. Cleaning them restored it to working order. The cover slides off it if you are careful.

[stevehertz]

I've changed the electrolytics on the AM tuner board and the diode switching board, no difference, no AM. Whilst in that mode I'm also changing electrolytics on other boards so if I discover anything else meanwhile I'll report back.

[PaulR]

If you haven't done so or are about to do it I would change the pots that control the quiescent current whilst you have the soldering iron out. The emitter resistors are very tightly soldered to the circuit board and I replaced mine with tubular ones to make it easier to measure the quiescent current.

[stevehertz]

Thanks Paul. What should the quiescent current be? I've seen 5mA and 20mA stated in Armstrong documents and on a schematic.