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Old 20th Aug 2008, 11:22 am   #1
Nickthedentist
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Default Bush VHF90A: a few queries

Hello everyone,

I've decided to tackle a Bush VHF90A radio which I bought at a very good price in Paul Stenning's big sell-off here a few years ago.

It's never going to be perfect, and is suffering from most of the minor cosmetic problems that these sets usually have, but luckily the scale has not been damaged by its lamp

First question... Has anyone found a non-destructive way of removing the hardboard baffle which the speaker and scale are mounted on? This would allow me to re-attach the loose grille cloth, do something with the shrunken plastic piping and polish the brass dial surround properly.

It's held in by screws and brackets at the bottom and at the sides, but the top edge is attached by no less than 4 Spire clips () which not only touch each other but also rest against the top of the cabinet. So, they can't be rotated, nor can Mike Phelan's sewing machine needle trick be used because of their small dimensions.

I presume the DAC70 is the same in this respect.

Any ideas, please?

Nick.
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Old 20th Aug 2008, 3:18 pm   #2
Aerodyne
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Default Re: Bush VHF90A: a few queries

Hi Nick
Tricky problem. I managed to extract the panel on a DAC70 a few years ago and I'm sure you are right, the fixing method is the same. I guess I'd have used one of a range of jeweller's screwdrivers to 'persuade' those dreaded clips to release their grip. If you plan to replace the fabric you may be able to provide an alternative fixing method (perhaps something like countersunk 4BA/3.5mm screws?).
Maybe someone else on the forum can be more helpful.
-Tony
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Old 20th Aug 2008, 4:25 pm   #3
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Post Re: Bush VHF90A: a few queries

Quote:
Originally Posted by Nickthedentist View Post
It's held in by screws and brackets at the bottom and at the sides, but the top edge is attached by no less than 4 Spire clips () which not only touch each other but also rest against the top of the cabinet.
Well Nick if a dentist can't remove them what hope is there for the rest of us A pic would be useful as I am not familiar with this set, but it might be a case of sacrificing the fixings by pulling the clips to bend one side free though I am not sure what the Spire clips look like.

Geof
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Old 20th Aug 2008, 5:06 pm   #4
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Default Re: Bush VHF90A: a few queries

Can you cut the clips off with a Dremel?

I really need to do this with my DAC70, but things aren't too bad so I've left well alone.

Paul
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Old 20th Aug 2008, 7:20 pm   #5
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Default Re: Bush VHF90A: a few queries

Hi Nick, a bh of a job! i did one a couple of years ago & broke two
of the clips trying to remove the baffle. you will also have fun with the piping,
it had gone very hard at the top of my set, probably due to the heat from
the 15w bulb

Mark
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Old 21st Aug 2008, 6:47 pm   #6
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Default Re: Bush VHF90A: a few queries

Thanks everyone, I'm going to look into all your suggestions when I'm feeling a bit more patient and less tired.

In the meantime, I've reformed the electrolytics, bypassed the rectifier with an 1N4007 + series resistor, and powered up via a limiter then directly... and it works, albeit in a rather feeble fashion. Next, I will replace the wax caps, of course.

Second question... Should the MES "fuse" lamp glow slightly in use? Mine does, and it would be nice to know if this were nornal.

Nick.
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Old 21st Aug 2008, 7:43 pm   #7
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Default Re: Bush VHF90A: a few queries

More help needed please...

Q3: What are these components not shown on the service sheet?

First, is a large metal-cased device which was bolted to the chassis, with both terminals connected together and to chassis (!). It's presumably a cap, as it's marked SOLAR .1MFD. 1000W.V.D.C. Should I just bin it?

Next is a Sprage 10nF 1000V axial cap on some tagstrip connected so as to mains-isolate a Belling-Lee coax socket mounted on the rear panel. From the tagstrip runs a length of co-ax which then passes through a grommet to the other side of the chassis, where it is double-insulated. It's connected to the junction of R15/C26/C28 (manufacturer's sheet), so presumably it's a tape output/gram input. Very neatly done, not the work of a bodger.

Finally, there's a huge 1K resistor connected between the dial lamp and chassis, presumably to reduce the risk of melting the dial. Again, this is neatly installed (much more so than the pic suggests), and I can see no reason to remove it.

Thanks,
Nick.
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Old 21st Aug 2008, 8:34 pm   #8
Rob Lines
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Default Re: Bush VHF90A: a few queries

Hi Nick
I though a variation on Mike Phelan's sewing machine needle might be to use something with a small but strong hook on the end of a stalk, like 2 crochet hooks for instance. I havent had a chance to try this yet, but hope it helps.
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Old 21st Aug 2008, 9:55 pm   #9
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Default Re: Bush VHF90A: a few queries

The Sprague capacitor can't, under any circumstances, work at all with both tags shorted to earth so presumably whatever purpose it originally had is not being fulfilled. It definitely doesn't look original. I'd bin it, for sure.
The wirewound in series with the lamp will limit current and keep the lamp temperature lower than it would be were the resistor not in place: extended running test will tell if the resistor generates excessive heat.
The double-insulated socket would be something I'd remove, personally; I know others may disagree but in my book there's no place for gram connections in live-chassis sets, no matter how effectively fitted and its non-standard, of course (but then, so is the limiter wirewound, though that is at least credible as a mod).
Good luck with the spires.
-Tony
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Old 21st Aug 2008, 10:04 pm   #10
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Default Re: Bush VHF90A: a few queries

Sorry, missed the question about the MES 'fuse'. Yes, its in series with the HT rectifier so I'd expect a glow caused by the passage of current on every half cycle, limited by the high resistance of the HT+ line, especially as the rectifier is of the contact-cooled metal type and some leakage is typical with these rather inefficient devices (worse with age). However, if the lamp blows, you've a short on the HT line!
-Tony
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Old 25th Aug 2008, 10:37 pm   #11
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Default Re: Bush VHF90A: a few queries

Thanks for the help and encouragement re. the clips, Tony, Paul, Geof, Mark and Rob.

I've just had another look when feeling a bit less tired, and removed them in a couple of minutes! A bit of a cheat really. Here's how...

The first pic shows one of the three pairs of clips in situ. Nasty.

But have a look at the second, which shows the hardboard baffle: it turned out that it has slots rather than holes for the Bakelite posts to which the clips attach. So, if the lower (non-Spire) retaining clips are all unscrewed and the plastic trim teased out, the baffle can be slid downwards and backwards and out of cabinet, leaving the Spire clips still attached to their posts.

Finally, the clips can be released by giving them a gentle squeeze with long-nosed pliers. This is only possible because there's now 1/8" space in front of them where the baffle used to be. And yes, I do think they have to come off, as re-assmebly would be almost impossible without.

Nick.
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Old 25th Aug 2008, 11:51 pm   #12
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Default Re: Bush VHF90A: a few queries

Well done nick, i have the am version of this set in my 'winter to do' pile.
Keep us informed how you deal with the plastic piping!
Cheers
Mark
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Old 26th Aug 2008, 7:27 pm   #13
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Default Re: Bush VHF90A: a few queries

Slots. The fiends. At least you've solved the assembly method!
-Tony
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Old 31st Aug 2008, 9:20 pm   #14
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Default Re: Bush VHF90A: a few queries

Thanks Mark & Tony

Back to the chassis... I've now changed all the wax/paper caps and it's working well, though there is some persistant smoking from R29 (550 ohms, the resistor between the thermistor and the heater chain). Not loads, just a steady little wisp. And yes, it's set for 250V operation

Using a true RMS meter, I measure 54.5V across it when the set's warm, equating to some 5.4W. It's apparently rated at 6W. Do people feel that it's safe to leave it smoking gently away to itself?

Nick.
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Old 31st Aug 2008, 9:55 pm   #15
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Default Re: Bush VHF90A: a few queries

Well I wouldn't. Put a more powerful one in IF you're sure the rest of the set is working OK.

Cheers,

Steve P.
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Old 1st Sep 2008, 2:30 pm   #16
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Default Re: Bush VHF90A: a few queries

I couldn't agree more with Steve. Uprate it. Smoking can't be right in any situation, if it is continuous i.e. not caused by damp being driven out. From your measurements it is too near the limit of its rated capacity.
-Tony
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Old 1st Sep 2008, 2:46 pm   #17
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Default Re: Bush VHF90A: a few queries

Thanks Steve and Tony!

I agree too, but haven't dared leave it on for more than a minute so maybe it will imporve once moisture and surface contamination have gone.

Quote:
Originally Posted by Aerodyne View Post
From your measurements it is too near the limit of its rated capacity.
...or maybe something's drawing excessive current?

On the other hand, assuming my Fluke true RMS meter's telling the truth, the current through it equates to 99.1mA which sounds correct for a U-series valve heater chain.

I will leave it on for longer, closely supervised, and report back. It seems a shame to change it as it's the original.

Nick.
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Old 1st Sep 2008, 3:27 pm   #18
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Default Re: Bush VHF90A: a few queries

Hi Nick

One thing you could do is carefully disconnect one end and put your meter in series with it and confirm that the current is 100mA or whatever it's supposed to be.

However, these resistors did used to smoke lightly after disturbance and through handling etc. When I were t' tellyman I used to renew mains droppers fairly routinely and they always smoked. I used to talk to the customer to keep her attention while the new dropper smoked off. When she commented on the smell I would tell her (quite honestly) that the smell was caused by the new part warming up and that it would soon disappear. By the time I had packed my case and done the paperwork and demonstrated that the set was now working correctly, the dropper had stopped smoking; generally about twenty minutes.

TimR
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Old 1st Sep 2008, 3:47 pm   #19
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Post Re: Bush VHF90A: a few queries

Quote:
Originally Posted by Nickthedentist View Post
I will leave it on for longer, closely supervised, and report back. It seems a shame to change it as it's the original.

Nick.
Well done with those clips, I am sure they didn't feel a thing But the resistor won't be original for long, might be ok for indians to send smoke signals but not resistors, why not unhook it and put a ten Watt ceramic fireproof one beside it.

Geof
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Old 1st Sep 2008, 6:57 pm   #20
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Default Re: Bush VHF90A: a few queries

Hi Nick, I have the other version of this set, the VHF90C with chrome rather than brass trim, and that has a factory-fitted gram socket, though obviously I agree with Tony when he says that really it's not the best idea to have such a thing on a universal chassis.

Mine had loads of Hunts caps, but only one wax device, the tone correction cap.

I broke one of the bakelite studs in mine when trying to remove the spire clip, so glued it back on and left well alone since the slightly wavy chrome-on-something with the consistency of perished rubber trim strip doesn't bother me as the set isn't to be sold so doesn't need to be perfect.

I can also confirm that the lamp inside the back cover glows dimly on mine too, that with all voltages correct around the place and one last thing, don't forget to swap the candle lamp for a microwave oven cavity one as the smaller envelope will prevent that fragile, backlit dial from becoming damaged as some of them have with age and use.

Have fun, these are pleasant-sounding little things when the caps are all good, I was pleased about just how simply laid out their chassis are since some of my Bush sets with equally ancient Hunts caps inside have proved reluctant to let my clumsy fingers get anywhere near some of the things due to their being buried under at least half a dozen other components at the same tags.

RE the smoking resistor, the same one was smoking on mine after I'd rebuilt the set and everything checked out fine, replacing that with a handy 12Watt one did the trick.
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