UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Success Stories

Notices

Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

Closed Thread
 
Thread Tools
Old 20th Aug 2021, 11:54 am   #1
Gabe001
Octode
 
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
Default My first Marconi: restoration of the 571

Browsing facebook marketplace for bargains, as one does, led me to an advert of a lonely and unloved radio which was so tatty that it was being given out for free. Eagle eyed colleagues on this forum identified it as a Marconi 571 (thank you) from 1937. Some preliminary research identified it as a live chassis set – I generally dislike them due to the lack of Gram input, general safety considerations and propensity to hum a bit more than their AC only counterparts - but hey-ho, it was being given away from free. I collected it the next day.


Upon collection, the set was left outside for me. It actually looked worse in person than it did in the picture. The seller told me that they had bought it because they liked the look of it ?!? but they no longer had the space for it. It lacked a mains plug. It looked big (huge), and felt incredibly sturdy. It was also incredibly heavy. I cant imagine how much the version with a transformer weighs!


The varnish was flaking off everywhere, the veneer glue was failing around the edges and was detaching, and the inside was probably the dirtiest I’ve ever seen, complete with cobwebs, live spiders and a thick layer of dust. It had probably been stored in a shed or garage. Luckily there was no woodworm.


Some before pictures of the case can be seen attached.


Contrary to my usual approach, I decided to restore the case first. After dismantling the set and giving it a good clean, inside and out, and reguing the veneer (lots of clamps), a coat of polycell varnish remover was applied. This dissolved the varnish, which was scraped off with a plastic putty knife. Stain was applied where required (Fiddes naphtha stain). I keep the lightest and darkest shade and mix them accordingly to obtain the closest matching colour. Unfortunately there was no way to save the marconi logo on the top and a waterslide transfer wouldn’t have been sufficiently opaque. I used danish oil to varnish, in multiple layers, applied with a cloth and carefully wiping off the excess to avoid ending up with a sticky mess. The results were very satisfactory, with a close match to the original. The grille needed no work apart from a clean. Picture of the finished case below.


The back panel was warped. This was easily sorted by spraying it with water and letting it dry flat using some weights. Multiple applications were required. There were 2 leather “hinges” holding the back to the cabinet – one was torn so I replaced that using an old belt. This completed the cosmetic restoration
Attached Thumbnails
Click image for larger version

Name:	IMG_20210725_105206.jpg
Views:	190
Size:	41.8 KB
ID:	239706   Click image for larger version

Name:	IMG_20210725_105201.jpg
Views:	192
Size:	62.3 KB
ID:	239707   Click image for larger version

Name:	IMG_20210820_111825.jpg
Views:	196
Size:	83.1 KB
ID:	239708   Click image for larger version

Name:	IMG_20210815_070042.jpg
Views:	191
Size:	51.4 KB
ID:	239709   Click image for larger version

Name:	IMG_20210725_175625.jpg
Views:	211
Size:	122.1 KB
ID:	239710  

Gabe001 is offline  
Old 20th Aug 2021, 11:59 am   #2
Gabe001
Octode
 
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
Default Re: My first Marconi: restoration of the 571

Next, it was time to tackle the electrics.

For those unfamiliar with this set, it is slightly quirky. It has a working range down to 110V. HT from the rectifier for this set is quoted as a measly 138V DC. It has a mains dropper that drops the mains voltage for the whole set in excess of 100V. The mains dropper is a separate unit that looks like a toaster/electric heater – its not a simple resistor. There is excess ventilation on the back panel. The bulbs are almost at HT potential. There is additional ventilation below the dropper, on the back panel and a metal heat shield above the dropper.

There is also a earthing arrangement, using an isolating capacitor and an earth socket – the usual pole in the ground type. The dropper resistor case, grille and speaker were all connected to this earth. There is a separate power lead, similar to the DAC90a, that can be connected either way round. Unlike the DAC90a however, this is screwed to the back panel so that its impossible to touch the chassis with the lead attached.

Before I was to do any work, the chassis would need a good clean. Years of heat had baked the dirt onto the metalwork, and it needed a good scrub with any solvent I could get hold of – or a mix of all of them. Although still not perfect, it is now no longer a tetanus risk! Luckily the underside was reasonably, apart from some dust.

Careful inspection revealed a few potential issues:

1. it had some work done in the 60s or so – as evidenced by a number of electrolytic capacitor replacements. The large can originally containing about 6 of them had gone. It was replaced by a dual can that was leaking electrolyte. Most of the other electrolytics had been replaced at some point.

2. the tuning capacitor was wobbly. I applied some plumbers silicon grease to the rubber washers to refresh them, which helped somewhat. It still wobbles, but only about a mm or so

3. The fact that the chassis and mains dropper were separate parts combined made turning on the set outside the case a bit awkward.

4. Its contained an extraordinary number of paper capacitors that needed replacement, luckily they all seemed very accessible (unlike in the ferranti 145)
Attached Thumbnails
Click image for larger version

Name:	IMG_20210807_151649.jpg
Views:	167
Size:	59.5 KB
ID:	239711   Click image for larger version

Name:	IMG_20210724_183835.jpg
Views:	159
Size:	47.2 KB
ID:	239712  
Gabe001 is offline  
Old 20th Aug 2021, 12:04 pm   #3
Gabe001
Octode
 
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
Default Re: My first Marconi: restoration of the 571

Following some preliminary checks (thank you Jerry), including checking the dropper for continuity (it was, surprisingly), ensuring the chassis was connected to neutral, and checking the double pole switch, the first job was to remove that leaky dual can, which was straightforward process. A spare can was fitted instead – not original I know but better than leaving an empty hole.

All the electrolytics were replaced using the rubycon capacitors. They’re not the cheapest but they've served me well in the past and have suitable ratings. The only change I did was up the reservoir capacitor from 16uf to 32uf (maximum rated for the rectifier valve) which helped with the hum. I had to add a few tag strips as mounting points – due to the number of capacitors.

The grid coupling cap was next, followed by mains filter capacitors c36/37 and c34/35 attached to the anode of the rectifier. Suitably rated components were used. One of the mains filter caps had blown. The two 1.25A fuses were replaced with new 1.25A fast blow fuses. The mains dropper paper heat shield had started to tear in areas, so I gave it a touch of epoxy putty (JB extreme heat – rated for 230C continuous heat). Similarly one of the fuse holders was a bit wobbly and I used the same putty to give it some support.

After all this, it was time for first switch on. There was some life as I could hear the dropper warming up and the filaments starting to glow. It transpires that there were two open circuit resistors that needed replacement, R27 and R28. Most other resistors, except one, were within range. In fact, surprisingly, most were pretty much spot on. One of the 3 scale lamps was blown, which I replaced. The remaining paper caps were replaced, of which there were quite a few. The moving parts were lubricated and this got them going again, and the waveband switch was cleaned.

This got the set going quite well. A quick test with the signal generator indicated reception on all 3 bands. The magic eye was dim, as expected, and I’m not planning to replace it. The volume and tone control were smooth and crackle free. The double pole on and off switch was fine too. Volume was good. Some stations could be heard on MW without an aerial. There were no additional sounds other that the usual mains interference, which I'm well used to.

The only issue I noticed was with the LW band, where the tuning scale was shifted to the left. BBC radio 4 was being picked up at 1200m instead of 1500m. LW overall reception was not great but reasonably good. An attempt at alignment as per manufacturers instructions only shifted the scale by 50m or so, and I was reluctant to twiddle too much. This fault is probably down to the storage conditions and moisture affecting the coil inductance or causing capacitor drift, and addressing this is beyond my capabilities at the moment. It really is nothing that I cannot live with.

In conclusion, this set is excellent on short wave and medium wave, and so-so on LW. The latter is probably due to a fault condition. Sound quality is superb. It actually sound better than my pilot u650, or the defiant m234. Volume is excellent and the large case gives the bass a nice resonant timbre. Listening to it through the Minimod makes for a very enjoyable experience.


Enhancements


I find myself using sets with bluetooth or AM transmitter (minimod) almost exclusively nowadays, and I expect that most here do the same

As such, I thought it would be a good idea to fit this set with an internal bluetooth module. Without going into too much detail, the principles applied are the ones Donald discussed in his BT thread on the dac90a. You can see my BT module attached to the back of the chassis using a custom 3d printed mount.

In a nutshell, the KRC-86b module had its 4 resistors removed to allow for radio muting when BT is connected (it mutes the radio about 95% in practice). It is powered by a 230v-9v encapsulated transformer, half wave rectified using a schottky diode, smoothed by a 2200uf cap, regulated down to 5v, and further smoothed. The audio output is connected to the volume control. A small resistor dampens the initial current surge and reduces the voltage load on the regulator. It works very well and has been going for hours without issue.

I currently giving still testing the set, and am currently listening to a two cellos rendition of Queen’s “show must go on” via bluetooth, and it sounds fantastic. I think Marconi would be pleased to know that his set is still capable of delivering musical enjoyment almost 85 years after it was made.

I hope you found this enjoyable. Ill try to upload some videos if the set working. Please don’t be too critical of my electrical work (this is a hobby for me), but I'm happy to accept constructive criticism.

regards

Gabriel
Attached Thumbnails
Click image for larger version

Name:	IMG_20210820_111859.jpg
Views:	194
Size:	72.8 KB
ID:	239713   Click image for larger version

Name:	IMG_20210819_205612.jpg
Views:	184
Size:	81.3 KB
ID:	239714   Click image for larger version

Name:	IMG_20210814_170154.jpg
Views:	197
Size:	80.3 KB
ID:	239715   Click image for larger version

Name:	IMG_20210819_103630.jpg
Views:	183
Size:	58.9 KB
ID:	239716   Click image for larger version

Name:	IMG_20210820_121357.jpg
Views:	175
Size:	57.2 KB
ID:	239717  


Last edited by Gabe001; 20th Aug 2021 at 12:15 pm.
Gabe001 is offline  
Old 20th Aug 2021, 12:18 pm   #4
Gabe001
Octode
 
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
Default Re: My first Marconi: restoration of the 571

And a few videos:
LW - https://youtube.com/shorts/NWD0RiASkuc?feature=share

MW (note lots of RF interference in my house, this is fairly typical): https://youtube.com/shorts/hU_MSoa4byQ?feature=share

SW: https://youtube.com/shorts/6nN3Z-FMQG4?feature=share

And the final one to show switching between MW and BT
https://youtube.com/shorts/_7d_GgB-W88?feature=share
Gabe001 is offline  
Old 20th Aug 2021, 1:29 pm   #5
cathoderay57
Nonode
 
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,358
Default Re: My first Marconi: restoration of the 571

Hi Gabriel, you've rescued a very nice receiver and made a fine job of it. Keep up the good work (SWMBO permitting!) Cheers, Jerry
cathoderay57 is offline  
Old 20th Aug 2021, 3:27 pm   #6
stevehertz
Dekatron
 
stevehertz's Avatar
 
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
Default Re: My first Marconi: restoration of the 571

Great job there, well done.
__________________
A digital radio is the latest thing, but a vintage wireless is forever..
stevehertz is offline  
Old 20th Aug 2021, 7:45 pm   #7
ColinB
Heptode
 
ColinB's Avatar
 
Join Date: Apr 2003
Location: Newton Abbot, Devon, UK.
Posts: 759
Default Re: My first Marconi: restoration of the 571

Very nice!
ColinB is offline  
Old 21st Aug 2021, 12:40 pm   #8
MurphyNut
Heptode
 
MurphyNut's Avatar
 
Join Date: Apr 2016
Location: Croxley Green, Hertfordshire, UK.
Posts: 979
Default Re: My first Marconi: restoration of the 571

Very enjoyable write-up and pictures, always great to see pre-war radio fall into the right hands and brought back to life again!
__________________
Clive
MurphyNut is offline  
Old 21st Aug 2021, 1:25 pm   #9
Guest
Guest
 
Posts: n/a
Default Re: My first Marconi: restoration of the 571

Its cherished possession status has been reinstated, wonderful job. When I see such a good job I imagine the joy of the first owners listening to the magic (and content!) of radio. "Dad, dad, it's time for Dick Tracey...", I will now be shot down for getting the favorite kids programme of choice at the time wrong.
 
Old 21st Aug 2021, 9:27 pm   #10
Gabe001
Octode
 
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,611
Default Re: My first Marconi: restoration of the 571

Thank you for the kind comments. It was an interesting set to work on, and I found the set's quirks quite fascinating. It has, for example, a chain between the waveband switch and the frequency indicator. Clearly a cord wasn't good enough. It was definately built to last and I'm sure it would have been quite an expensive luxury item at the time.

I have developed a liking to pre-war woodies, despite the restoration challenge. They are nice decorative items of furniture too. I wonder why they aren't more popular.
Gabe001 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:51 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.