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Old 7th Dec 2021, 7:04 pm   #41
nigelreltub
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Hi Alan,

Don't know what happened to the new 300 cap? Yes the voltage at the fuses is just below 50vdc, so the all good and the TR29 reads right. I have the end caps, might see if I can get a bit of blue heat shrink and pop them on, it would look better.

I searched for the AL102 and Cricklewood Electronics came up with the AL102 but not available. Lower down the page it said, "AL102 PNP TO3 Germanium. Please go to equivalent 2N3614".

Followed the link and its specifies the 2N3614 as PNP TO3 Germanium 60V 15A 77W. Very low saturation 250mV. hFE 60-120 @ 3A. Urrrm maybe should have screwed down into the finer detail a bit more.

Had a look at the 2N3055 silicone transistors (2N3055 - NPN TO3 60V 15A 117W. Complement to MJ2955), they are cheap, I think I paid £12 for these 2N3614's

Are the mod's on the boards because they are NPN transistors? Is this the Trevor Latala Upgrade? If I can get hold of a Z17 Power Board I might try the 2N3614 in the 526 Amp I have sat in the corner or try the silicone upgrade.

The 525 is running sweet, had it running for a couple of hours and no issues, only got to rig an antenna to try the tuner.

Thanks Alan
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Old 7th Dec 2021, 7:38 pm   #42
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Yes I use the same changes that Trevor has noted, I just do the wiring and track cutting slightly differently. The result is the same.
Yes the mods allow you to use NPN silicon transistors in place of the PNP Germanium originals.

If you have not found it here is another method using the MJ2955 output devices; https://studyres.com/doc/5387319/arm...or-replacement there is more general info if you scroll down.

Just remember, you must keep the modified boards with the specific transistors, fitting an un-modified A15 in a modded amp will destroy it and vice versa...

If it were me, I would keep the 2N3614s for TR29 regulator duties, it will only see 20 volts emitter to collector and will be fine there.

Good luck finding a spare regulator board and you are welcome, Alan
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Old 8th Dec 2021, 12:01 am   #43
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Default Re: Armstrong 525 Motorboating/Thudding Channel

I am delighted that you have remembered the 2N3055 conversion that I did some 12 years ago I also did a simple PNP conversion that required a change of a few resistor values If you look at the original thread you will find the resistors values stated
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Old 8th Dec 2021, 3:54 pm   #44
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Hi Trevor,
I'll say this first but I will look at possibly doing this early in the new year on the 526 first, but I know this has a lot of problems, crackly, only the tape monitor worked and that's just for starters, sounds like it'll be fun.
But, yes just read the original thread about the conversion, I think I saw this and thought was well over my head but having you guys at hand and my hands in the 525 it all sounds do'able. I like the sound of the Silicone PNP change though, only changing a couple of resisters (will mine be the same value?) and the Transistors fit in as normal, I think that's it, Then it gets a bit technical, having to do measurements, etc, etc

These are the couple of directions I would need some help on but will most probably make sense when I have a good look at it....... I hope.
I would also change the series regulator at the same time .You have to adjust the bias by adjusting the voltage regulator for about 20 ma this can be measured across the emitter resistor of the output device.

As ever always turn down the supply volts and then adjust the bias by monitoring the voltage drop across the emitter resistor.

I am going to put a post in the "Wanted" section to see if I can get hold of a Z17 Power board.

Got to sort those horrible looking capacitor tops out, oh and an antenna to check the tuner.

Nigel

PS Google'd the 2N2955 PNP Power Transistor couldn't find anywhere selling them but one site mentions suitable equivalents.

Last edited by nigelreltub; 8th Dec 2021 at 4:01 pm. Reason: Add a PS comment
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Old 8th Dec 2021, 10:31 pm   #45
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Update, had a bit more time, yes lots of the "MJ2955", Alan even mentioned it in his last post, I presume its the same as the 2N2955? bare with me.
Still thinking about both variants of the upgrade?
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Old 9th Dec 2021, 3:57 pm   #46
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Hi Trevor,

Putting a shopping list together and looking at the resistors, for either PNP/NPN Silicone conversion/upgrade. What would the "watts" rating be, I understand the calc (AXV=W) but not knowing the values I'm a bit lost. I understand getting the watts wrong could cause them to burn out and the bigger the watts the more expensive and larger they are.

Thanks in advance
Nigel
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Old 9th Dec 2021, 5:04 pm   #47
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Default Re: proposed upgrade to armstrong 521
Sorry its taken so long re the silicon PnP output transistors
The value of the resistors to be changed are take out the origional 18k to 13.9k this was done with a 10k and 3,9k in series in my case !
As ever always turn down the supply volts and then adjust the bias by monitoring the voltage drop across the emitter resistor
regards Trev
Picked this from the archive they can be 1/4 watt
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Old 9th Dec 2021, 5:31 pm   #48
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Default Re: Armstrong 525 Motorboating/Thudding Channel

No worries Trevor, Thanks
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Old 9th Dec 2021, 5:33 pm   #49
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Default Re: Armstrong 525 Motorboating/Thudding Channel

nb these are for the pnp/pnp upgrade
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Old 9th Dec 2021, 5:37 pm   #50
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Default Re: Armstrong 525 Motorboating/Thudding Channel

https://www.vintage-radio.net/forum/...ong+521&page=2

go here for the complete story npn and pnp
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Old 11th Dec 2021, 11:18 am   #51
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Hi Trevor/Alan,
Have picked up a Z17 Board courtesy of Pamphonica (Jeremy) and a few other bits to help tidy the 525 and to start on the 526.

Just a few things to do on the 525:
- a bit of thermal grease for the main transistors
- clean the fuse contacts on the Z17 Board and re-check the voltages
- tweak and clean all the connector forks
- change the capacitors on the A15 Power Amp boards, maybe even the C16 Control Unit board
- tidy those awful main caps
- I'd Like to put a longer power cable/lead on, don't know why my had cut it?
- give the case a polish and enjoy
I think that's it?

I'll post a few pictures.
Nigel

PS anything else worth looking at within my limited capability?

Last edited by nigelreltub; 11th Dec 2021 at 11:20 am. Reason: PS
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Old 11th Dec 2021, 1:10 pm   #52
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Default Re: Armstrong 525 Motorboating/Thudding Channel

It sounds as though you have done a great job. The help and support from the experts on here (I don't include myself in that) goes a long way. The thread together with Trevor's from 2008 will be a great knowledge resource.

You have inspired me to look at my son's 400 series receiver which is reported to be dead on one channel. It has the earlier A14 power amp boards though.
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Old 11th Dec 2021, 2:03 pm   #53
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Default Re: Armstrong 525 Motorboating/Thudding Channel

To quote Trevor from a thread (Mar 18) he posted in "I ask why would you use the much rarer 400 parts as spares for the common 500 models"

It would be a shame to let it fall by the way side

With what ever you don't know someone else will, so I am sure you will succeed


PS. My 525 is common BUT is sounds darn good
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Old 11th Dec 2021, 2:47 pm   #54
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Default Re: Armstrong 525 Motorboating/Thudding Channel

I have always had a soft spot Armstrong products from the days when, as a teenager, I saved up my summer job earnings to buy a 621 amp. Ironically I never got it as the shop had returned their stock to Armstrong due to various manufacturing faults. I bought a Rotel RX400A receiver for the same price.

I have since bought a 621, 624 tuner and a 625 receiver. All silicon of course!
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Old 11th Dec 2021, 4:21 pm   #55
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Default Re: Armstrong 525 Motorboating/Thudding Channel

No offence intended the 521 was a great sounding amplifier I actually preferred it to the later 600 series
I used to sell the 600 units never ever had to return a faulty one to Armstrong
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Old 11th Dec 2021, 6:15 pm   #56
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Of course I don't know how big their "entire stock" would have been, maybe only 2 units. I was very disappointed as it was right at the limit of what I could afford and I had done loads of research in hi-fi mags. I went along clutching my £10 notes (eighty odd pounds?) only to be told they didn't have any and didn't know when they would get any. The return of stock story might have been just that so that the salesman could make a sale there and then! It must have been late summer 1973 I think

I would have preferred the receiver but that was well beyond my resources. As it was I then had to save for some speakers so I could give back the home made ones I borrowed from a friend.
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Old 11th Dec 2021, 11:52 pm   #57
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Default Re: Armstrong 525 Motorboating/Thudding Channel

Trevor, no offence taken, it was meant a bit tongue in cheek. When my Dad bought his 525 he took out a loan and he said it was a mono amp and then he had to buy a stereo card later to upgrade it?? Have you heard that one? He made some speakers cabinets to take some Wharfedale 12" bass drivers, quite a sound, don't know where they ended up?

Been busy this evening, main capacitors tidied, tried some heat shrink (blue of course) but didn't work, ended up with some blue electrical tape, it was the right shade until you stretch it a little.

Alan, not quite as good as your caps but a whole lot better than my first attempt.

Then moved on to cleaning the Z17 fuse holders, they were black. I had to come up with an easier way of doing it as I was getting a bit fed up of sitting there with my bit of emery paper, thinking there's got to be an easier way.
Bit of wire wool spun round a drill bit and hey presto job done, seconds, finished off with a bit of servisol.

Connector forks and maybe the power cable tomorrow?
Nigel
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Old 12th Dec 2021, 10:48 am   #58
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Default Re: Armstrong 525 Motorboating/Thudding Channel

I wonder whether it was a stereo decoder card for the tuner?
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Old 12th Dec 2021, 11:58 am   #59
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Default Re: Armstrong 525 Motorboating/Thudding Channel

^^^^ This.
The amp of course has always been stereo, but you could add the FM radio stereo decoder (if not already fitted to your 525/26) once stereo FM was available in your area. Do not forget Stereo FM was not generally available until 1973 earlier in the south east on R3 I believe?

A tip for the future: To clean up badly tarnished or blackened terminals or contacts, silver polish (the pad type or liquid on a cotton bud) is best. Just clean with contact cleaner after use.

And a note of caution about using wire wool. Be very careful not to loose any wire strands in the surrounding components, it will play havoc. Best not to use it or if you do, do it as far away from the rest of the electronics as possible...
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Old 13th Dec 2021, 1:56 pm   #60
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Default Re: Armstrong 525 Motorboating/Thudding Channel

I can remember in the 1970 selling and fitting the decoders into the 500 series
They were often sold with out a decoder as stereo radio was not generally broadcast
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