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Old 14th Dec 2020, 2:49 pm   #1
Beardyman
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Default Bush VHF90a

I've been looking for one of these for a while now & one came up at a reasonable price on a well known auction site.
For the princely sum of £17 it ended up as mine, I've seen these go for a lot more so doubted I would win, such is the luck of the draw.
This forum has quite a lot of information about worthwhile mod's especially regarding the metal rectifier.
Cosmetically, this set was in fair condition, at least the case was complete if a little tatty & faded.
The paint on the front surround was flaking & falling off.
The bakelite had seen far too much sun & heat as it had blistered & faded quite badly across the top, nothing a bit of Greys Polishing paste & effort couldn't improve.
These sets, I now know, run darned hot.
That doesn't really help the case, I might look at putting some kind of heat deflector in at a later date or possibly a capacitive dropper.
For me the most interesting part of a restoration is the initial "opening up".
The thought that possibly no one has been inside the set for quite a few years I find quite exciting.
Almost like a time capsule but usually there is nothing more than dust, fluff & dead insects.
Occasionally there is a bill of sale or a sales tag glued inside.
This set does have a tag but no one bothered to fill it in, which is a shame.

The mains lead had been cut off about 6 inches from the set & was of the flat black PVC type with red/black cores.
This, oddly, gives me some confidence that the phantom fiddler hasn't been making his presence felt too much.
A couple of screws were missing from the back panel, easily replaced.
The panel was fairly straight which made a pleasant change.
The internal aerial plug was still plugged in but the wires had been ripped off, another easy fix.
The plastic tuning dial is clear but the central bright is missing, I'm sure I can find something to fill that gap.
The dial came off with the merest of pulls, sometimes these can be right so & so's to get off.
The tuning pointer was rather floppy & not gripping the shaft, again, an easy fix.
One screw was missing from the chassis mounting brackets, the rubber suspension grommets were as hard as rock & crumbling, a quick root around in the junk boxes delivered 4 replacements.
For some reason the speaker wires had been cut close to the output transformer.
With the chassis on the bench & camera at hand, many photos were taken from all angles, I find this invaluable as a reference.
First of all the valves were removed & filaments checked, all good.
No less than 3 UF89's!
And there's a lot going on in that UABC80 bottle.
Safely stowed in tissue, they were put on the shelf in a shoebox.

Out with the DMM, it was time to survey what was what.
About 75-80% of the resistors had drifted by over 50%, a few crumbling Hunts capacitors & leaky waxies were put on the list to be replaced.
The HT smoothing capacitor (3 sections) reformed very well.
Some of the PVC covered wiring near the hottest parts had suffered, insulation charred & crumbling.
This was replaced with PTFE/Teflon covered wire of the same colour but a heavier gauge, the thinking is that the extra copper will, in some small way, help move the heat away quicker.
There were a couple of resistors that needed replacing inside the cans of L8/L9 & L10/L11, they were tricky!
I have fingers like sausages, it wasn't easy!
Thank goodness for cross over tweezers!
My next concern was the metal rectifier, having read a lot of posts about these I decided it wasn't worth the risk & removed it.
My concerns were validated when it was hooked up to a current limited HV PSU.
With a load of about 10mA it was not a happy bunny, it leaked as much backwards as it conducted forwards.
It was replaced with a MUR460 diode (It was all I could lay my hands on!) with a 120R 10W metal clad resistor in series.
This was bolted to the chassis & wired in on the AC side.
Oddly, all the resistors in the tuner box were spot on in value, as were all the tubular ceramic capacitors.
I did change the one across the mains switch for an X type just to be on the safe side.
The speaker & aerial were hooked up & it was time to apply some power via the isolation transformer & variac with a meter on the HT rail.
After maybe 30-45 seconds there came signs of life!
I do like the 6V 0.5A bulb/fuse, novel but seems to work ok.
As the set warmed up the HT on the anode of the UL84 settled down to just over 238V, the trader sheet says 230V, close enough.
Sound quality is impressive, sounds far bigger than it is, it managed to pull in all the local/national stations we normally get here with just it's internal aerial.

Next up was the case & front cloth.
After a thorough degreasing with a common or garden kitchen cleaner called "Elbow Grease", the rest of the paint on the front surround fell off.
It originally had a hammered finish & a green-ish silver colour, quite nice.
I remember thinking at the time, "There is no chance of replacing that!" & was contemplating leaving it as bare bakelite.
I put that to one side & then took a look at the speaker cloth, it was very ingrained with either cooking residue or cigarette smoke, possibly both.
With the speaker board out of the case & speaker removed, the cloth was sprayed with plain warm water, just enough to dampen it.
After about 10 minutes it was possible to ease it away from the back board.
Being made from woven plastics it can withstand some fairly harsh chemicals.
I've found that mould & mildew cleaner works very well on plastics, keep it well away from fabrics as it will bleach them.
Once allowed to soak for about 30-45 minutes, it was washed off in the bath with the shower head, this brought it up looking much better & smelling somewhat sweeter.
Next was the gold coloured piping which, as seems common with these sets, had shrunk, split & warped.
As others have done I left it off, it looks much better without it.
I noted the dial bulb is a stonking 15W!
The one in mine is intact but as I had a spare 10W that would fit, I used that, it should help with the heat too.
Back to the front of the case:
We were shopping one evening & whilst perusing the middle section I happened across a single can of spray paint, the colour was said to be champagne but looked to me like a greenish-silver!
Ok, it wasn't a hammered finish but it just might work & all for the princely sum of £4.
With the case suitably masked the paint was applied, I couldn't believe my eyes, it was an almost perfect colour match.

After re-assembling the case & the chassis put back in, it was time to "give it a go".
The dial light is, in my opinion, still far too bright, I will have to have a think about that.
I did read a post on this forum that putting a series resistor with the lamp could help but my thinking says this would add to the heat issues.
Maybe a capacitive dropper just for the lamp? I shall see.

The now familiar smell of hot dust & long un-powered wire wound resistors drying out, came forth.
After about an hour the top of the case can still be touched so I would say it was at perhaps 30-35C, not at all bad.
Hardly any drifting off station & a very good audio tone, quite rounded as some would say!
Not one of the most challenging restorations I've done but definitely worthwhile.
I'll upload some more photos later.
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Old 24th Dec 2020, 8:46 am   #2
MurphyNut
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Default Re: Bush VHF90a

Enjoyable write up, this is a set on my "want list." Saying that some years ago I picked up "parts" set, not working at a car boot in appalling condition for next to nothing. It was worth it just for the plastic scale completely undamaged from the usual lamp heat.
You've confirmed what I've read about these sets in them sounding very nice, must get one!
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Old 24th Dec 2020, 12:59 pm   #3
Beardyman
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Default Re: Bush VHF90a

They are quite easy to work on, the only tricky bit being near the volume control, it's a bit congested there. And those awful spring clips that hold the speaker board in! Six of those to contend with but a pair of needle nosed pliers will, when applied in a gentle twisting motion away from the post to each tang in turn, allow them to be taken off with little or no damage to the case. The case on mine seems to have bubbled (3-5mm diameter) all over the top, probably heat in general caused it. They do seem to suffer from heat though, as you say, to get one with the dial intact & legible is an exception rather than the rule. Best of luck as & when you decide to take the plunge!
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Old 27th Dec 2020, 10:53 am   #4
mark pirate
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Default Re: Bush VHF90a

Quote:
The dial light is, in my opinion, still far too bright, I will have to have a think about that.
I have seen these with a melted dial due to the 15W bulb, I think this is a design problem with these sets, my own example is using a 5W bulb, which is just the right brightness & the heat is way less & saves 10W in power consumption.


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Old 27th Dec 2020, 2:59 pm   #5
Lloyd 1985
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Default Re: Bush VHF90a

Very nice restoration! I’ve got a few of the MW/LW versions of these, and they are quite good too. The blistering could be due to the Bakelite having been damp at some point, I have an Ekco A22 that was probably submerged for most of its life, and the cabinet on that had quite bad bubbles and blisters! Came up ok though. Just a thought, but could the bulbs on these be replaced with a modern LED one? It might produce less heat!

Regards
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Old 31st Dec 2020, 12:23 pm   #6
Beardyman
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Default Re: Bush VHF90a

I had thought about the LED option but all the ones I've tried (so far) have all caused interference of some kind, probably due to the "cheap & cheerful" internal switchers used. Some where better than others. It is possible to run LED's straight from the mains, I've been looking at LED filaments from RS, they need 70VDC per filament, they even have the right colour temperature (2700K) to look "vintage". My thinking is three in series would need 210VDC thus minimising dissipation in a resistive dropper. It's something I'll need to look into further but it does at least show promise. The maximum current is 15mA but at that level they are too bright, I've had them running down to 3-4mA so it may be possible to run them from the HT? Again, I need to look into it further. Many thanks for all your comments, much appreciated, and a happy new year to all.
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Old 31st Dec 2020, 3:15 pm   #7
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Default Re: Bush VHF90a

A great write up, appreciate the detail.

The 550 Ohm dropper could be replaced by 2uF to 2.2uF HV poly cap saving 5W dissipation.
If you remove the 10...15W filament dial lamp then R27 and R28 would be passing less current (approx. 50mA less) and therefore dropping less volts.. you would need to increase R27, R28 resistances accordingly.

The separate capacitive dropper for your LED option seems to be a good and efficient solution

Best Regards
Chris
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Old 9th Feb 2021, 10:07 pm   #8
vinrads
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Default Re: Bush VHF90a

Thanks for a most enjoyable read , well done with the restoration , I am with you in thinking the lamp is a touch to bright on these , but gives a nice glow sitting in the corner of the room . Mick.
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