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Old 22nd Sep 2017, 7:38 pm   #1
high_vacuum_house
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Smile Bush VHF81 restoration

This is a bit more of a repair than a full restoration as the cabinet is not too bad with a couple of small knocks but more than presentable.

This came from the recent Radiophile Cowbit event for 6. It looked complete and no signs of any damp. It was also full of dust. In fact it was well crammed with dust and took a lot of hovering with a paintbrush to get rid of it all leaving a very clean chassis.

The UY85 rectifier was very wobbly and loose so the valveholder pins were tightened with a jewellers screwdriver. It is much more firm in its holder now.

The tuning dial would not move. This was down to the small plastic pulleys all being gunged up. They were cleaned and given a very small drop of clock oil. The tuning drive works correctly now.

I decided to cut out the distressed mains filter capacitor and run the set up on the variac. There was no dial lights and only the slightest rustle from the speaker. I decided to tackle the dial lights. One bulb had blown but was rusted solid in the holder. About an hour trying to remove it in pieces failed so I decided to replace the holder. This was no so easy as the MES bulbholder is at near mains potential relative to chassis and therefore a conventional clip on one could not be used. I found an old Maplin plastic surface mounting holder which would suffice and managed to get it to fit with a 4BA nut and bolt. This got the dial lamps working but still not much from the speaker.

I changed out all of the wax capacitors and hunts mouldseals all of which were tested and found very bad. This still did nothing much but was able to pick up 5 live on MW very weakly but with a healthy hum with a finger on the AF triode grid which showed that the AF section was ok.

After checking all of the anode and screen grid resistances were ok I decided to see what the anode and screen voltages were doing when on. I soon found at V2 which is the 2nd IF amplifier a UF89 that there was no voltage drop across the anode load or screen feed resistor. Cleaning the pins did not help and so another UF89 was pinched out of a Ferguson set and immediately the set sprang to life with good volume on all wavebands. The original UF89 had zero emission!! The correct voltages were then observed on the anode and screen pins.

The sound was good but VHF quality was poor. I decided to replace the 5uF capacitor in the ratio detector and the sound is now very good. The original had gone down to 0.1uF!!

Other than a good clean I am very happy with the result and it is a good sounding set. I have been listening to radio 3 all evening at a decent volume and have hardly heard a crackle.
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Old 22nd Sep 2017, 8:17 pm   #2
Boater Sam
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Default Re: Bush VHF81 restoration

Not common for UF89s to go no emission. I like these sets, a bit later than I usually go for but they do work well and there are not too many Hunts Mouldseals compared with say VHF61s.
Good sized speaker for the cabinet size. Nice job Christopher.
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Old 22nd Sep 2017, 8:20 pm   #3
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Default Re: Bush VHF81 restoration

Nice work and an example of a lovely, undervalued set.

I still have a couple - one from you(!) and the other from Howard. They don't see much use currently but they work ever so well and are really reliable and easy to service. Also very compact and will sit on a very shallow shelf.
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Old 22nd Sep 2017, 10:07 pm   #4
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Default Re: Bush VHF81 restoration

Lovely job! I haven't had one of these in the "Batcave" yet, but I gather they sound good when going.
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Old 23rd Sep 2017, 11:32 am   #5
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Default Re: Bush VHF81 restoration

Nice! I have a bit of a soft-spot for these: a relative had one as her kitchen-radio back in the sixties (always tuned to Radio 2, alas...)

I must get round to working on my VHF81 again over the winter; it had the same 'scale lamps corroded irretrievably into the holders' issue as yours - I was able to get some small white plastic MES holders [4 for 1] from the Frome radio rally and they fitted perfectly. Replaced the Mouldseals and it now works fine on FM (though lacking HF response - might be the capacitor you mentioned!) but it also has *something* shorting the HT when on MW or LW, which needs detailed investigation.
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Old 23rd Sep 2017, 8:53 pm   #6
high_vacuum_house
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Default Re: Bush VHF81 restoration

Many thanks for your comments. It is a very undervalued set that doesn't go for that much. It isn't going to upset the neighbours easily but it does give a very good quality of sound at a decent volume. The UL84 output valve is a full size pentode in its own bottle (power dissipation 12W) compared with say a UCL82 (power dissipation 7W) which it needs to share the pentode with a triode and therefore is smaller.

I find these VHF sets quite appealing as LW/MW only sets I find there is very little of interest to listen to on AM and R4 isn't really a sit down to listen for a long period station and R5 is an instant turn off. R3 and classic FM are good stations to listen to bar the adverts on Classic FM.

Christopher Capener
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Old 27th Sep 2017, 8:55 am   #7
Phil G4SPZ
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Default Re: Bush VHF81 restoration

Good job, Christopher. I also have one of these sets and it gives very good performance on its internal aerial on FM.
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Old 30th Sep 2017, 10:18 am   #8
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Default Re: Bush VHF81 restoration

I also have one of these, it's on permanently whenever I'm home, and apart from a noisy volume pot works superbly. Unfortunately I seem incapable of putting the drive cord back correctly, my last two attempts resulting in a reversed drive to the pointer!

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Old 30th Sep 2017, 11:28 am   #9
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Default Re: Bush VHF81 restoration

Re-string it left handed?
You have simply wrapped the spindle in the wrong direction, easily done.
You need a few Philips sets to practice on!
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Old 30th Sep 2017, 9:33 pm   #10
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Default Re: Bush VHF81 restoration

Great little sets that give a very good account of themselves mainly due to the extra IF stage on FM that doubles as an RF amp on AM. Audio quality is good and the small amount of negative feedback makes a big difference.
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