Armstrong 525 Motorboating/Thudding Channel

[Ted Kendall]

Originally Posted by snowman_al

Stereo FM was not generally available until 1973 earlier in the south east on R3 I believe?

Scheduled multiplex stereo transmissions on the Third Programme from Wrotham began in 1966. Holme Moss and Sutton Coldfield had stereo via analogue links in the late 60s, but more widespread stereo services had to wait for the PCM distribution network and upgraded studio facilities. The launch was announced as part of the 50th anniversary celebrations in 1972, but it took most of the rest of the decade for every transmitter to receive a PCM feed.

[nigelreltub]

Yes you guys are right, I spoke to my father, he did confirmed the card was for the stereo radio transmissions, and it was around 1972. He added, "It was from some chat in Wolverhampton", but can't remember the name of the shop? I was a bit puzzled when he originally just said "Stereo card".

Still waiting for a few bits to finish of the 525, should be here Wednesday.

I will be starting a new thread soon as I have started a few bits on the 526, as I imagine it will have different issues

Thanks as always
Nigel

ps. Very festive Alan

[nigelreltub]

Well the bits and pieces came this afternoon from CPC, so,
-all caps replaced on the A15 Power Amplifier Boards, will attempt the C16 Control cards at a later date, there's a lot of caps on them.
-all power transistors greased up.
-did all the voltage checks and....... 24vdc on one of the speaker channels, went straight to the connector forks, looked ok, swapped cards and the fault moved with the card, one of the silver runs looked almost bare, added some solder to it and it solved the problem, phew.
-All other measurements were good

So gentlemen, this has brought the journey with the 525 to a successful end but really a new beginning. Listening to it right now, sounds great. The Wall.

Thank you for all the help, advice and support and no doubt I will hear from you on the "Armstrong 526 Restoration Thread" Coming soon.

Nigel

[Whaam68]

Looks great. I did a 521 and it had a really punchy bass. There were a lot of caps to change as I recall but it was a nice sounding amp. Must dig mine back out.

[Trevor]

Just a word of caution re swapping driver boards about you have to be very carful (especially with germanium output devices ) it is possible to damage them if you move a faulty board over I know this from personal experience and you can end up with both channels damaged
did this some 50 years ago as an 18 year old
Trev

[nigelreltub]

These germanium transistors are a real nightmare, the 526 will have your 2N3055 upgrade, hope these a bit more forgiving and I expect at some point I will upgrade the 525 to these.

[nigelreltub]

Its all good news, the tuner works great had to lift and shift into the living room to use the aerial there as I knew it had a good stereo signal to test the tuner properly. Only small issue is the stereo indicator bulb isn't working, have found a thread back from 2009 by Jetsonz, so this should help resolve this issue (saved in my favourites along with all the others).

Have made up a pair of RCA cables fitted with resistors to attenuate the signal from the small DAC and now gives me more control over the volume, thanks to Paul for pointing me in the direction of "Geoff the Grey Geeks" calculator. Maybe a small attenuation box could be on the horizon?

The Armstrong 525 is in a lot better place, working wise, any last comments otherwise I think this thread can be closed.

Thank you to all that have contributed.
Nigel
ps. 526 thread coming sooner than I expected

[Trevor]

Another thing to look at in these Armstrong,s is the dreaded AF transistor disease Tin Whiskers!
These Germanium AF 117\6 etc are well known to create shorts in the RF and IF stages
Trev

[nigelreltub]

Hi Trevor,
Tuner sounds good...... at the moment, just read a thread, (21st Feb 2015, 8:16pm Goldieoldie) the AF125's as a replacement but might be some loss of gain? Had a quick look in the 526 and counted 8 of them (AF10X/AF11X). There not cheap, Cricklewood have some on their website(£11), or there's zapping, but I will leave that well alone. Sounds like you have had experience of this issue?

Is there a tuner schematic about?
Nigel

[nigelreltub]

Originally Posted by Whaam68

Looks great. I did a 521 and it had a really punchy bass. There were a lot of caps to change as I recall but it was a nice sounding amp. Must dig mine back out.

Definitely dig it out, I am so impressed with it, could well take prime position in the hifi rack. Yes lot of caps aaannd transistors but its worth it

[nigelreltub]

It has been a while. I couldn't wait for the Russian GT transistors as I'm off to my fathers next weekend so I wanted to get this sorted, so I went ahead and ordered some AF178's, checked them all on the DMM and were good, the AF116's were all shot, so worth changing and the results proved it.

The AF178's have short legs but was able to position them in a way that needed no extra insulation. Checked all the connector forks and gave a couple a tweaks.

Boom, what a difference, a lot loader, stereo light working and picking up a lot more channels than previously, and you could tell it was stereo. When I put it back in its prime position in the "back room" it was still picking up stations, not very clearly though and a lot of mush.

The 526 will get the GT322B treatment, don't think they will be as easy to get in but we'll see.

It's most probably cost a few quid to get the 525 back in order but I have thoroughly enjoyed it and it's been worth penny. Can't wait to show it off next weekend.

All that is left to say is thanks again to Trevor, Alan, Paul and all contributors on the 525 journey.

P.S. 526 finale coming as soon as the GT transistors turn up and then a showdown between the 525 (AL102) and the 526 (Trevor's silicon mod).

[nigelreltub]

Thought would add this in as information for anyone considering swapping out the transistors in the tuner section.