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Old 30th Nov 2021, 5:46 pm   #21
PaulR
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Personally I would go for the higher value ones but I doubt you would hear any difference. The tolerance for electrolytics is 20% so the value isn't critical.

Al's advice about mounting the new caps in the original cases is good. It is often called "re-stuffing" them. I tend to cut off the end of the old cap with a small hack saw so that the cut will be covered by the clip. You can drill very small holes through the original insulated end close to the original connector tags, push the new wires through and solder them to the tags. The whole thing can then be taped back up with the clip covering the tape. Either method makes the job a lot neater and preserves originality.

Your spare set of caps will come in very useful for your next restoration!

I would leave the suppressor cap off.
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Old 30th Nov 2021, 7:31 pm   #22
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Thanks Paul,

Capacitors ordered, going to be busy this weekend. Already thinking about the 526 I have sat in the corner but that will mean trying to source another power board, which could mean another broken Armstrong, the never ending story
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Old 1st Dec 2021, 9:56 am   #23
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Yes that's a very slippery slope!
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Old 4th Dec 2021, 1:16 am   #24
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Evening,

Lamp limiter is up and running and have been taking some measurements. Well......

236VAC the coming from the fuse to the voltage selector.
Not sure which contacts to check coming out of the voltage selector so left well alone.
The are 3 leads coming from the transformer Red - 29.8vac, Black - 14.4vac, Yellow - 5.17vac.

The Power board/supply has the 50vdc on both outputs through the 1amp fuse.

Capacitors DC Readings (Ch - Chassis / + terminal on cap / - negative cap terminals

Cap 273A 273B 286A 286B 292 300
Ch to + 24.46 24.61 23.58 0.07 0 0 vdc
Ch to - 40 45.49 24.46 24.64 35.15 50.48 vdc
+ to - 15.92 20.89 1.06 24.63 35.29 50.51 vdc

I imagine there is something wrong as the reading don't seem to be any consistancy? Apologies for the attempt at a table but I hope the colour coding works?

I will be re-stuffing the old capacitiors tomorrow and will do the same readings again, hopfully will clear the 25vdc of the CH A speaker terminals.

Wait out
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Old 4th Dec 2021, 11:17 pm   #25
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Default Re: Armstrong 525 Motorboating/Thudding Channel

All the capacitors swapped out but still 25vdc on CH A?

The "Lamp Limiter" has a dim glow, thats one good thing, right.

Have done all the readings across the capcitors and the are as follows:

Cap____273A 273B 286A 286A 292 300
Ch to +__23.97 24.57 24.51 -0.17 0 0 vdc
Ch to -__40.85 45.31 23.43 24___35.35 50.98 vdc
+ to -____17.54 20.84__0__24.35 35.41 50.97 vdc

The "Ch to - (Neg)" Terminal" on the capacitor are all Negative readings, as keeping the Common probe on the chassis and the Pos probe to the neg terminal.

I am at a total loss now? Any suggestions please
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Old 5th Dec 2021, 10:00 am   #26
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Default Re: Armstrong 525 Motorboating/Thudding Channel

In one picture it shows a thick black wire going to the + (positive) connection of a cap, and to - (negative) on the next picture. You need to check and double check that you have got all the connections correct on all the bits you've replaced.
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Old 5th Dec 2021, 12:01 pm   #27
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Yes, spotted this in my final comparison of visual checks with the original pictures and reversed it so the +pos (red dot) is to the bare wire. So the second picture of this view is correct.
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Old 5th Dec 2021, 1:12 pm   #28
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Not making a lot of sense is it?
What voltage do you measure at the output terminals if you disconnect the Negative lead from the output cap (286) cap? Take care Not to short the free end of the (blue?) wire doing the test.

Confirm that swapping the A15 driver boards round does not change the problem?

Wondering if there is a break in the feedback wire that goes to resistor 1290. That and 1261 would normally 'pull' the 25 volts from the output cap down to ground, ie 0 volts?

PS have a good look at the connector forks that the A15 boards plug into, any thing bent or a foreign body dropped in?
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Old 5th Dec 2021, 7:53 pm   #29
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Alan, your a star, skip to the bottom

Readings with the Neg lead disconnected from capacitor, did both A & B for comparison? Marked the Resisters.

1. + to - on capacitor.
2. + to chassis.
3. - to chassis.
(Corrosponding DMM probes to output terminals, ie + to +)
286A
1. 0.38
2. -27 decreasing
3. 26 decreasing
286B
1. 0.01
2.-0.06
3. -0.08
Boards swapped over
286A
1. 0.11
2. -25 decreasing
3. 26 decreasing
286B
1. 0.12
2. -0.06
3. 0.17
All the boards look ok and the connector forks too, but I am no expert.

I am no expert, I was wrong, back tracked the to the specific connecter forks and the set for the 1261 resistor looked a little more open than the rest, sqeezed them together, replaced the board and now we have 0.13vdc across channel A and 0.07vdc across ch B, is this acceptable?
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Old 6th Dec 2021, 10:04 am   #30
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Default Re: Armstrong 525 Motorboating/Thudding Channel

How does it sound now?
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Old 6th Dec 2021, 10:51 am   #31
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Morning Paul,
Thought about this after asking the question, Is that vdc on the terminals ok?, think I was just looking for reassurance.
So, there was 0.18vdc on Ch B originally, and that sounded good. So on the basis that there is 0.13vdc on Ch A, I got it all connected up this morning and I am sat here with warm coffee listening to a few tunes.

"How does it sound?", in one word, FANTASTIC. Been running for a hour now, no issues. I'll be getting the turntable out of the loft and connecting that up this afternoon and going to rig up an FM antenna of sorts.

All I can say is big thanks to you guys getting me this far, but bare with me a bit longer, a few more things to check with the turntable and tuner.

Only problem is I have the spare 526 sat there without a power board
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Old 6th Dec 2021, 11:19 am   #32
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Others will be able to answer the question about the residual voltage on the terminals with authority but it sounds pretty negligible to me.

That is the problem with buying anything for spares. You think it is too good to break up and get another for spares ... !

The tuner is probably ok as it is, but power it up gently with the lamp limiter. If it is trying to work like that, just leave it for 1/2 hour or so for any reforming of the electrolytics then give it full power

What turntable/cartridge do you have?

PS - if it was mine I would replace all the electrolytic caps in the amp. Others may disagree; it is a matter of choice and personal preference. You do run the risk of introducing faults into a working amp if you disturb it further.
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Old 6th Dec 2021, 2:57 pm   #33
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Default Re: Armstrong 525 Motorboating/Thudding Channel

It's an MM cartridge on the turntable (Pro-Ject Debut III) I believe the 525 has an MM stage? Yes the lamp limiter is still next to the 525 so will definitley power it up with the lamp limiter before trying out the tuner.

Already replaced all the main electrolytic Capcitors, that was fun cleaning out all the old ones, Alan recomended this, not going to attempt any others on the boards.
What I have noticed is it seems loud even on the lower settings, I did read something about attenuation/bias and CD players having a higher output, I'm actually using, dare I say, a Media player through a small DAC?? But still sounds great. I've got to hook some Kef Concerto's up to it yet, so that will be a treet.

Turntable has had time to climatise so...........
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Old 6th Dec 2021, 3:09 pm   #34
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Yes, the output from a CD player can be loud. I made a little attenuator box for mine once but then inherited a deck that had a variable output that it "remembered" when switched off. That attenuator consisted of two resistors for each channel to make a voltage divider housed in a small project box with phono sockets as the input and output.

The deck sounds good. Yes the amp will have a MM input. Have you got lots of vinyl to play on it - maybe Father Christmas could help there!
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Old 6th Dec 2021, 4:35 pm   #35
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Hi Paul, Will look into an attenuator box, will it do any damaged in the meantime?

Turntable up and running, some quiet fuzz on the speakers( no grounding lug on the 525, connected to another earth lug and the fuzz got higher pitched, so it's off for the moment) but when it's playing can't notice or hear a thing and sounds as good as it did 40 years ago. Maybe not your taste but The Wall (Pink Floyd) on vinyl sounds so much better than CD, don't think I'll have time for the tuner today.

Record collection, I did have from my youth but sadly not as many, not sure what happened to them but managed to keep hold of a few. Most probably crank up the turntable up when the wife and I are feeling nostalgic thinking back to our youth with a glass of wine, still got a lot off 45's, will be fun with the grandkids.........maybe!! Maybe inspire them?

Tuner tomorrow
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Old 6th Dec 2021, 4:49 pm   #36
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Default Re: Armstrong 525 Motorboating/Thudding Channel

No, you won't do any damage overloading the input like that.

I usually replace the two core mains lead with a three core one and earth the chassis. Never on AC/DC radios though, but that is another story. Lots of fun to be had trying to eliminate hums on peripherals, especially turntables with a magnetic cartridge.

I never really got into "The Floyd" I have to say but I do indulge the occasional vinyl purchase.

I have loads of 78s and my granddaughter quite likes them. Not many 4 year olds can sing along to Boogie Woogie Bugle Boy of Company B!!
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Old 6th Dec 2021, 7:01 pm   #37
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Default Re: Armstrong 525 Motorboating/Thudding Channel

@ Nigel,
Very pleased the amp part is working. Though there is an anomaly in your voltage readings for the big cap (300). It should be about 70 volts DC across the cap terminals. The Z17 regulator board then is set to 50ish volts, ie at the 2 fuses. So there should be about 20 volts across TR29 emitter to collector. Or maybe the lamp limiter was still in circuit when you took the measurements.

No issue with a few milli-volts at the output, an 8 ohm speaker will bring it down to nothing.

Unfortunately the plug in boards are the Armstrong 5xx series Achilles heel. Then they added solder to the board connectors for good measure, not a good idea. Be prepared to polish the solder pads and tension the forks from time to time.

The other common failure mode is the AL102 transistors, as you have found. Transistor testing readings from these can be a nonsense... It might be better to replace future failures with silicon transistors and re-work the driver boards. There are several well documented ways on the web.

You may have to gently exercise the push buttons too, these get dirty with non use. Use Servisol switch cleaner very sparingly if you have to.

Do not expect the phono section to be quiet, the transistors are a bit noisy by todays standards. By the way if you have not already found out - use the no.2 pick up sockets for MM cartridges. (The no.1s are for ceramic cartridges.)

You might want to consider replacing the remaining 4 electrolytic (blue Daly) caps on the two A15 driver boards to protect against future failure. Some measure fine others go low, but if you are taking them out to test, easier to replace them anyway. The same for the C16 control boards too at some stage?

I've repaired quite a few of these in the past, they used to be disliked due to the common problems and were often on ebay 'spares or repairs' for £10-15 BIN. How things change. They do sound good when fully restored. Picture of the last one I did added.
Enjoy, Alan
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Old 6th Dec 2021, 8:45 pm   #38
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Hi Paul, I will be taking the amp and turntable down to my dad's towards the end of the month so we can play a few of his albums, Glen Miller, Frank Sinatra and some of the classical composers, dare say I will bring a few albums back along with the 525 and I'm sure he has got some 78's as well?

Hi Alan,
Yes the lamp limiter was on during all the readings, so this could account for it? Will re-check. Its good to know about the millivolts I can stop worrying about the speakers, phew.

I got hold of some "2N3614 Case TO3 Vishay Dale" Transisters, Cricklewood's website say the are an equivalent to the AL102, when I did take some measurements of the AL102's they didn't measure as expected, all have reading across every which way you connect the DMM in diode mode, did the same on the new ones and they measured as expected, so they may have deteriated but Yes I have seen some of the threads on changing them for silicone ones, this is a possibility....later. Might do the the other electrolytic caps on the boards when the power transistors get done, I think this will be my New Years project.

It's funny you say about the pick ups, I moved it from No1 straight to No2, much better.

Why don't my main caps look this that, lovely job, do you still do the restorations? My wife's sister lives in Mid-Wales

All the best and thanks again, moving into the child minding (grandchildren) part of the week, will keep up updated, on the 525 that is
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Old 7th Dec 2021, 2:13 pm   #39
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Morning Alan,
The TR29 did read low across the emitter to collector, 15v. Swapped it over and now reads 17.5v, not a big difference, Lamp Limiter by-passed. Any thoughts on getting it to the 20v?

Was having a moment (de-soldered the neg terminal?? should have just read across it) and I couldn't get any reading, so totally de-soldered the 300 cap and it read OL all the way up to the 60M setting, can over heating them with soldering iron damage them? This could have been the problem.

Any way out came the spare, popped it in and now the reading across the 300 Cap is 68v.

Readings across the speaker terminals 0.06v and 0.08v, so they seem to have improved.

Any thoughts on these "2N3614 Case TO3 Vishay Dale" Transisters?

https://www.cricklewoodelectronics.com/2N3614.html

I think I cut the wrong end of the caps off numpty
Nigel
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Old 7th Dec 2021, 4:21 pm   #40
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Okay,
Without the lamp limiter, all you want is close to 70 volts across the big (300) cap. A few volts above or below will not matter and will change with your mains voltage anyway. So 68 volts is spot on.
Then adjust the voltage at the 2 fuses (F1/2) on the Z17 board to about 50 Volts, do not go over that. (The voltage across TR29 is simply the difference between the voltage on cap 300 and the output from the fuses.) If you can do that all is well with the supply and regulator. Very unlikely to damage a capacitor with soldering.

Re. the 2N3614 transistor. Where do you read that is equivalent to the AL102? A quick search does not get me any results to their equivalency.
The AL102 has much higher Emitter-Collector voltage spec at 60 volts, the 2N3614 is only 35 volts so may be a bit of a risk in the Armstrong? Has some one has tried it with success?

Personally, I have always swapped the AL102 outputs with 2N3055 silicon devices and modified the A15 drivers to suit. (Some people use MJ2955, but they used to be more expensive and the A15 still needs modification.) Any 'good' AL102s were used for TR29 regulator duties.
I did this simply for long term reliability as I either gifted the repaired units to friends or moved them on, on an auction site. As yours is staying in the family, I would leave well alone it might be fine for another 40 years!

Yes, I drilled out the rubber seal and removed the old cap all from the bottom. No cutting involved. Can you not find some plastic caps to pop on if the open top bothers you - or glue the original 'tops' back in place?

Alan
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