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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! |
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20th Mar 2016, 6:54 pm | #1 |
Pentode
Join Date: Jun 2006
Location: Crawley Down, West Sussex, UK.
Posts: 151
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Hacker Mayflower RV14 singing again.
The story starts with me winning an ebay lot from a local seller nearby.
Initially I thought he was is South London, about 25 miles from my home, but in fact he turned out to be living just up the road! This Hacker came with some history which is always nice to have. Bought by his parents back in the early 1960's this radio was in use almost every day until last year. It spend its last few years in his brothers garage where the sound slowly became weaker until it faded away to just a distorted whisper. The cabinet had a few scratches to the veneer but otherwise was in good shape. On initial power up I was greeted with some mains hum and a dim magic eye that grew dimmer as the set warmed up. This suggested to me a leaky grid cap biasing on a valve hard or a bad smoothing capacitor. So I started by replacing C31 C32 in the output stage that were very leaky and no doubt causing the distorted sound, Then came the smoothing capacitors. C24 and 36 are double can type and the underside of this capacitor showed a blow hole had vented at some time. Both these capacitors were changed with 47uF 450 volt types soldered under the chassis to keep the set looking original. I then proceeded to change 4 smaller electrolytic's used in the cathode bypass stage. Surprisingly these capacitors were OK, probably due to the low voltage across them. The last caps changed were C8 and C25. C8 is the discriminator damper and C25 Audio amplifier decoupling. I then checked through the resistors and as expected found that the higher value components were over 20% of their rated tolerance. At this point I decided to do a power up to see how my replacement parts had helped. Mains hum had all but gone the set was working fairly well but seemed to be low in sensitivity and touchy to FM tuning, The magic eye was dim and I started to suspect low emission from the valves. At this point I checked all the valves but found they were all close to 100% emission. The only other thing apart from the resistors being out of spec is the set needed alignment. Hacker are very specific about their alignment procedures So I spent a bit of time reading the instructions before getting the core twiddler's out. First off is Discriminator alignment with seep generator and marker fed into the final IF grid, This produced a slightly unbalanced response from the discriminator but only needed a light tweak to get the S curve looking symmetrical and the 10.7 marker central. The other IF stages were all aligned one at a time and these were all quite a way off. The previous owner did ask me why the set might have lost audio in the first place, I wonder if his brother was a Phantom dabbler? Once the IF was done the RF section was aligned. This is very simple and takes a few minutes. Sound was now far cleaner and stations come into tune without the "Off tune distortion" they had before, At this point I checked the HV voltage now the caps were all good and found there to be around only 170V instead of 250V! This turned out to be the selenium rectifier running hot and failing probably due to excess load from failing capacitors. A silicon bridge was fitted with a series dropper resistor and bingo 255V The radio now really worked well, sensitivity was great and the magic eye was far brighter. I have covered most of the repairs on my YouTube channel for those interested I hope they will be interesting to you. I also checked the frequency response and distortion of the amplifier with some impressive results. THD 0.6% at 1 watt from a 55 year old radio? |
20th Mar 2016, 8:03 pm | #2 |
Hexode
Join Date: Dec 2015
Location: Walsall, West Midlands, UK.
Posts: 327
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Re: Hacker Mayflower RV14 singing again.
Do you have a youtube handle or a link please?
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20th Mar 2016, 9:32 pm | #3 |
Pentode
Join Date: Oct 2008
Location: Downham Market, Norfolk, UK.
Posts: 143
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Re: Hacker Mayflower RV14 singing again.
__________________
Regards, John. |
21st Mar 2016, 6:50 pm | #4 |
Pentode
Join Date: Jun 2006
Location: Crawley Down, West Sussex, UK.
Posts: 151
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Re: Hacker Mayflower RV14 singing again.
Whoops sorry yes that's me.
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21st Mar 2016, 10:24 pm | #5 |
Hexode
Join Date: Dec 2013
Location: Torrington, Devon UK.
Posts: 446
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Re: Hacker Mayflower RV14 singing again.
Great work as usual Simon
Keep em coming Graham |
14th May 2016, 7:34 am | #6 |
Heptode
Join Date: Apr 2016
Location: Croxley Green, Hertfordshire, UK.
Posts: 979
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Re: Hacker Mayflower RV14 singing again.
Lovely high quality radios, I hope to own one some day I'd enjoy listening to Radio 3 on one. I've noticed they seem to go for quite high prices now.
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