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Old 18th Dec 2021, 11:23 pm   #1
nigelreltub
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Default Armstrong 526 Rebuild/Restoration

New Year Project, No its This Years Project, I've written this as a bit of a narrative of my journey, skip to the bottom for the issue.

This is the Armstrong 526 (fully working, allegedly) I bought to use the Z17 power supply card to get my fathers 525 up and running, now working. Well had to put a plug on the 526, not a good sign, luckily it powered up and it worked, but only on the "Tape Monitor" selector?, all the others were very noisy, like the coffee peculator when its just about finished brewing, not good. This is all before I started the 525 thread.

Well I thought it was too good to scrap, so got hold of a Z17 Power Supply Board from Jeremy (Panphonica) and a few other bits and pieces. Already had a spare set off main capacitors, so in went another order to CPC or was it RS? for the 2N3055's and a set of capacitors for the control and power amplifier boards.

Replaced the main caps and the caps on the control boards, then set about on Trevor's 2N3055 upgrade. All the AL102's were out, so set about labelling all the wires, greased up the transistors/mica and in they went, I used a 2N3614 Germanium TO3 for the Z17 board, then for the resistors and wiring (did wires all on the back of the card).

Only had the Z17 board in and no fuses, Powered it up using the Lamp Limiter, nice glow, checked the power to the fuses, 49vdc, no need to adjust, checked the main cap, about 50vdc (lamp limiter is on) full power, 69vdc and 19vdc across TR29.

In went the fuses and all the boards, powered on, nice reassuring glow from the lamp limiter, checked all the main caps, voltages across the transistors and the voltage across the fuse and lastly for any voltages at the speaker terminals, all good.

Let me just say I knew I was going to be doing this rebuild so I had been "massaging all the push button switches with "servisol" and the pots on more than one occasion.

Lets listen to some music, that's what its all about, I used a pair of RCA cables with a couple of resistors in to attenuate the signal, hooked up the laptop to the Fubar DAC, oh and the Royd Minstral's. It worked on the Tape in", selected Phono..... thunder , no turntable connected, From a thread back in Aug 2006 to quote Trevor

Default Re: Armstrong 521 noise
The 521 amplifier has self shorting contacts on the phono input this has the effect of reducing the noise level. I have had these contacts fail. Put a shorted phono plug into each phono inputs and let us know the result.
Trev

Did this, also cleaned the pickups and low and behold, what an improvement, the selector switch needs a bit more massaging but just about there.

Got to connect the turntable up and try the tuner out but looking good. Need a FM indicator bulb as I robbed this one to go in the 525, on order.

Big issue is there is a loose cable, only short in length, from the FM selector switch? I can't refer to the 525 as its a different setup I have attached a picture for comments and direction.

Big thanks to Trevor for his 2N3055 upgrade direction, Alan and Paul and everyone for all the input on 525 thread.
Nigel
ps. Paul, I just had to get this done before you finished your 400
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Old 19th Dec 2021, 12:45 pm   #2
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

With no initial intention of rebuilding 526 it wasn't a priority to document the removal of parts for the 525, anyway came across this image and I think it answers my question about the wire, its connected to + terminal on the Main 292 Capacitor.

Result, will continue with trying out the turntable and the tuner.

Nigel
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Old 19th Dec 2021, 2:17 pm   #3
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Default Re: Armstrong 526 Rebuild/Restoration

Good work. I’m Interested to see if you notice any difference in sound between modded silicon and the stock germanium.
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Old 19th Dec 2021, 3:36 pm   #4
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Default Re: Armstrong 526 Rebuild/Restoration

Isn't it nice to work on an amp where the various boards plug in!
The backplane may need some maintenance to reduce crackles, but I love the ability to swap channel boards and take boards out for repair/upgrade.
Well done - good result all round.
-Jeremy
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Old 19th Dec 2021, 6:24 pm   #5
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

Yes it is, I don't think I could have attempted this otherwise.

My favourite thing is the lamp limiter, the little glow just gives you that bit of confidence and yes to be able to swap the boards to help fault find, de-solder, re-solder, I think I would have melted more cables, I found this a real help, but not always recommended. Swapped all the capacitors on the C16 Control boards, used a 33uf/25v for the 25uf/25v, but believe 22uf/xx would have been ok?. The back plate, I shall research this.

With the turntable plugged into the MM pick ups sounds great no thunder, just the vinyl clicks (need to maybe clean them?), I thought it was more of the switch but obviously the"self shorting contacts on the phono input" causing static? crackle? in the switch.

Tuner test Next, have to lift and shift into the living room so maybe tomorrow.

Well that's 2, almost, looking for a third, what about a Bryan 900, Trevor has a liking for these (https://www.vintage-radio.net/forum/...ad.php?t=65335) read his thread back in Feb 11.

Well will update once tuner is tested.
Thanks
Nigel

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Old 19th Dec 2021, 6:32 pm   #6
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Default Re: Armstrong 526 Rebuild/Restoration

Bryan a cracking amplifier good choice to restore !!
They have a certain magic
Trev
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Old 20th Dec 2021, 10:51 am   #7
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Default Re: Armstrong 526 Rebuild/Restoration

That's an excellent job, Nigel. It just goes to prove what I say about what appears impossible can be achieved with the help of the experts on here and a willingness to have a go.

I haven't got my son's 400 series to look at yet. It will probably be in the new year now.
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Old 20th Dec 2021, 11:59 am   #8
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

Quote:
Originally Posted by Trevor View Post
Bryan a cracking amplifier good choice to restore !!
They have a certain magic
Trev
Missed out on the Bryan, was going for a bargin as well, I expect another member picked it up. I think I've got the bug.

Paul, yes I really wouldn't of had a clue where to start otherwise but I think I'm on that slippery slope you spoke about. I have a spare set of 2N3055's, possibly for the 525? Possible something else? I'm looking for a new New Year's project now.

Nigel
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Old 20th Dec 2021, 12:15 pm   #9
Trevor
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Default Re: Armstrong 526 Rebuild/Restoration

about 10 years ago I went to the original Bryan works Sale near Manchester just to get a sense of the works
Very boutique manufacturer in their time highly advanced For me the earlier Germanium are the ones to go for I think I have 6 or so in my collection
Better than any other transistor amplifier I met my first 0ne as a 15 year old now 69
Trev
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Old 20th Dec 2021, 11:44 pm   #10
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

I saw the amp up for sale and did a search on the forum and found your thread on the Bryan, very interesting, I will keep my eye out for another.

Well have had the tuner hooked up, not good,
-no meter dial light
-meter does't move/work
-no stereo indicator bulb, taken for the 525
-a lot of noise interference during tuning and when it picked up a channel

It's these Cats whiskers I thought, "Tap or Zap", so I tapped the first AL116 in the top right corner and ........ now not working at all, oh dear. So it's the transistors??

In a thread back in Nov 2014, its recommended that a BC214 will do to replace all the AF11x transistors, would this be a straight swap or would it require biasing as I have read in the "Transistor Faults, Testing and Replacement - AF117 series transistors" section of hints and tips.

It also mentions the AF125 , ouch £10 each, also in another that the Russian GT322B is an equivalent to the AF125, well they are expensive as well, there is the GT322A on eBay(20 @ £13 incl P+P), which I didn't think was too bad?, just need to learn Russian But the BC214 would be good?

BC214 link
https://www.switchelectronics.co.uk/.../pdf/BC214.pdf

GT322A link
https://www.ebay.co.uk/itm/164453449...gAAOSwFk1gTF6~

Any thoughts, suggestions.

I think the 525 could do with a new set, not as good as I first thought
Thanks
Nigel
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Old 21st Dec 2021, 10:00 am   #11
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

More digging on the AF transistors, found this good thread/links detailing quite a few options and also Mark Henessy's article, also very informative aannnnnd Heral1360's link to the RadioMuseum pages with lots of variations,

Oldelectronic's thread (Jul 17)- https://www.vintage-radio.net/forum/...d.php?t=138127
Mark Hennessy's article- https://www.markhennessy.co.uk/artic...ransistors.htm
GT322 pinout - http://www.radiomuseum.org/tubes/tube_gt322.html no need to learn Russian now
AF124 - http://www.radiomuseum.org/tubes/tube_af124.html

Is there bias fix for the BC214? Not quite the right look but if it gets it working.

Decisions decisions, OK I guess I'm going to spend the day on Google.
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Old 21st Dec 2021, 8:40 pm   #12
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

Well have gone with the GT322's from Russia bit of a wait till they come.

The M8 board however has different transistors than the board in the 525 (AF116's), no real markings so don't know what type, they are missing the shield pin, may have already been modified?. I'll not replace these when the time comes as they shouldn't have any issues??

So for the moment the rebuild/restoration has come to a halt, however the the music hasn't
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Old 21st Dec 2021, 9:40 pm   #13
Trevor
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Default Re: Armstrong 526 Rebuild/Restoration

Ah yes the M8 board the transistors will be a general purpose PNP silicon device some thing like a bc212 and possibly fitted by Armstrong
I noted that the board has not been fully loaded these never were
I used to order and fit these as stereo broadcasts were extended

best of luck and happy new year
Trev
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Old 23rd Dec 2021, 7:24 pm   #14
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

As I'm waiting for the Transistors to come I'd thought I'd give the 526 a good clean, removed the knobs and the front panel, gave the panel indicator lamps a clean and one has broken , is there any way to drop a 24vdc supply of one of the main capacitors to 12vdc (maybe with resistors??) to power a couple of LED's for the panel lights? if its a straight no that's that, Google/ebay for some replacements it is.

Thanks
nigel

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Old 23rd Dec 2021, 7:57 pm   #15
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Default Re: Armstrong 526 Rebuild/Restoration

LEDs need say 10ma and drop 1.4v each. So you need to lose 21.2v at 10mA. Ohms law says that will take roughly a 2.2k resistor in series, rated at 1/4 watt or more.
Does that help?
-Jeremy
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Old 23rd Dec 2021, 8:13 pm   #16
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

This is all the info I have, but they are pre-wired with an inline resistor already fitted.

Requires 9-14VDC
DC forward current: 20mA (typical)
nothing about drop in voltage?

When connected up in series, would I take a lead from the 24vdc main cap feed and then to the chassis? If its possible with there spec?

Thanks
nigel
ps I'm looking at your shopping list

Last edited by nigelreltub; 23rd Dec 2021 at 8:13 pm. Reason: ps
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Old 27th Dec 2021, 6:32 pm   #17
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

LED UPDATE: After a message from Jeremy, a bit more reading, and testing with 9v battery, they are working, bit white! and the panel could do with another good clean as its a bit discoloured, makes it look worse. All the original wiring has been left in place for changing back to original bulbs at some point...... maybe?

Took + from main chassis with 2 resistors in series to half the voltage to the LED's and then back the connector fork on Ch B power amp board. See picture.
Doesn't seen to affect the sound quality.

Any comments or issues with the chosen points will be appreciated or a better solution than using the Power Amp board?

Picture of the 525 (original lamps) and the 526 to compare.

Thanks
nigel
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Old 27th Dec 2021, 6:55 pm   #18
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Default Re: Armstrong 526 Rebuild/Restoration

I feel that new lamps would be best. I’ll check mine and see what the rating is. Then I’ll check “stocks”.
The led arrangement does not look right. The two resistors do form a potential divider, but the centre voltage will droop when the led load from mid-point to earth is applied. A simple single series resistor, calculated to drop the relevant voltage is best. Ohms law will help you. Voltage drop equals resistance times current. So for instance, to drop 12v at 10mA you need a 1.2K resistor.
Let’s talk in the New Year! Meanwhile I’ll check bulbs and that meter you need.
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Old 27th Dec 2021, 7:14 pm   #19
nigelreltub
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Default Re: Armstrong 526 Rebuild/Restoration

Thanks Jeremy,

Can you add a 526 panel scale as well please if you have one. Mine is nice and clean but has no scale
Yes I think the new lamps would be best too.
nigel
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Old 14th Jan 2022, 12:47 pm   #20
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Default Re: Armstrong 526 Rebuild/Restoration

Russian GT322B Transistors are all in replacing all the AF series transistors and the tuner section is back up and running.

By now I have put a dipole antenna in the back room. So cleaned the PCB contacts and the connector forks on the M8 board and in it went for its first run, no indicator light to start, moved the tuner needle down the scale and next thing stereo indicator lamp was on permanently with lots of interference and hiss/crackle but it did pick up stations but not great.

Out came the M8 board, had read that the 2 transistors could be at fault, the ME4102 and the BSV44a. ME4102(PNP) seemed ok, the BSV NPN) was showing one of the junctions open.

Replaced it with a BC109, no loud interference or hiss, tuned into stations ok but no stereo indicator lamp but it was stereo (yes 100%).

The pin out for the ME4102 had the Base at the bottom where the BC109 had it in the middle of the 3. Checked the MJ again taking the centre pin as Base, this now seemed OK using the "Diode" setting on the DMM. Put it back in, still not right I don't think, there is an underlying high tone while tuning and again the stereo indicator light flickers, get a good tune though but no light.

Put the BC109 back in the M8 board with the pins in the correct place, no underlying high tone, overall sounds better but the stereo indicator comes on just before you get a nice clear tune on a station and then goes off?

Could the frequency pots need resetting? I have read about this but it involved a Computer and a test frequency. Can anyone elaborate on this or is there an easier way, or am I looking totally in the wrong place.

Pictures show from the left the original AF transistor , AF178 and then the GT322B (tiny).

Pin outs for the MJ4104 which look like they conflict with another spec sheet.

Getting so close, Advice and thoughts.

Thanks in advance
nigel
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