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Old 19th Jan 2020, 9:40 pm   #1
dinplug
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Smile Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Hi there,
I bought this radio for !0 pounds off a market trader 2 days ago, sold as seen.
On initial inspection, the FM aerial plug was missing, I assume the two pin connector are 2mm diameter approx.The IF transformer L17/18 has been replaced at some stage with a non-standard replacement, one of it's 4 pins was short to chassis,preventing LW/MW reception,VHF was OK, once the short was removed the radio worked on all 3 bands.
One strange thing I note is after warm up, is if I switch off and on at the mains socket quickly, the volume and sensitivity increases on all bands.
I downloaded trader sheet 174, and replaced C60 0.01UFWAX,C42 0.04UF HUNTS,C54 0.01WAX,C63 0.04UF HUNTS.
C53 5UF checked out OK value and ESR wise.
C59 0.01UF grid coupler cap to UL84 had already been changed as had C44 0.01UF, both these caps were RS components brand in a grey plastic tubular case. I also replaced R21 100K as it was badly dis-coloured.The mains input filter cap went bang early on test so was changed for an X2 type 0.1uf/250 volt AC.So far so good and no more more bangs yet!

Does anyone have a spare L17/18 IF transformer to help maintain originality.
Tips on other components to check,together with an explanation of the increase in volume and sensitivity by rapid ON/OFF mains socket switching would be welcome.
There was a bad attempt at retouching the gold paint finish on the case.
I have removed all the paint and am trying out brush painting with a fine paintbrush and using plasti-kote fast dry enamel, (gold leaf 31 code), just happened to have this in stock.Could a better finish be achieved with a spray can? Oh yes, had to restring the dial cord, a bit of a pain, it was badly binding, so after lubricating the pulleys, used some strong thread.This same thread has also worked in a Cossor 470ac and a Codar cr70a radios,which I serviced in earlier years.
Look forward to some feedback.
Cheers.Steve
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Old 19th Jan 2020, 10:45 pm   #2
Northyorks1
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

I got a very nice finish on a bush VHF70 using Humbrol Acrylic spray, colour is Brass 54 metallic. Goes on great cost 5. Then used Rust-oleum matt finish clear laquer both bought from boyes. Apply very fine coats of laquer as it orange peels if you put to much on at once as I found out.

Ian.
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Old 19th Jan 2020, 11:19 pm   #3
ajgriff
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Very impressive job by Ian. I'd opt for spraying too. Also worth using modellers masking tape if you need to mask. Avoids broken edges when the tape's removed.

Alan
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Old 19th Jan 2020, 11:48 pm   #4
cathoderay57
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Hi Steve, when you switch off and on you say the volume and sensitivity increase. Do they stay that way, or does the sound fade back down to the previous level after a second or two? Rapidly re-applying power will cause a surge that can sometimes have strange effects, sometimes harmful particularly to a possibly tired old rectifier valve or HT smoothing capacitor and so I recommend you don't demonstrate it too often. It would be helpful to measure dc voltages on the cathode of the rectifier and the anodes and screen grids (Grid 2) of the valves in the steady-state condition. You should be able to compare these with the values quoted in the Trader sheet. If you are using a digital voltmeter then expect your measurements to read higher than the Trader. Cheers, Jerry
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Old 20th Jan 2020, 1:59 pm   #5
dinplug
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Hi,
thanks for the replies so far..
Yes I think spray can is the way forward, is the casing made out of bakelite or plastic?

As to the strange on/off extra gain fault, the increased volume and sensitivity remain on, for as long as the radio is powered up.
Will check voltages on UY85 and the rest of the line up according to the data sheet Trader 1474, in nominal state first then compare after a quick switch on off.
The main smoothing HT cap is original, so will check values and ESR.
Steve.
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Old 20th Jan 2020, 3:21 pm   #6
cathoderay57
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Hi Steve, another thought is that the surge on re-applying power could possibly be overcoming a dry joint somewhere, or a dirty switch contact. The radio's mains switch is a possibility although unlikely. Possibly wavechange switch, or speaker leads especially the "tinsels" braided leads where they join the solder tags on the speaker (especially if the tags have aluminium rivets) and on the cone where they connect to fine wires to the speech coil. Also perhaps most likely are dirty valve pins and/or sockets. Good luck
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Old 21st Jan 2020, 12:25 am   #7
dinplug
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Smile Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

A few things done,including switch cleaner on v2 (uf89) valve base and cleaned the valve pins.Replaced the grid cap on the UL85 just to be ultra sure.Here are some voltages taken.
UY85 cathode 225 on fm and 230 on am, anode 210 on fm and 212 on am both these being ac. UL84 anode 200 on both fm/am, screen grid 80 on fm and 90 on am, cathode 7 on fm and 6.5 on am.The intermittent fault seems to have cleared but will do a cold test in the morning.
Other valves to be measured but the UABC80 giving 50 volts on the anodes.
The 5.6k resistor across the main HT smoothing block reads 7.1k, any idea what the resistor is rated at Watts wise? Gave the selector switches a dose of Servisol as well.
Comments invited.
Cheers
Steve
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Old 21st Jan 2020, 12:53 pm   #8
ajgriff
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Quote:
Originally Posted by dinplug View Post
Yes I think spray can is the way forward, is the casing made out of bakelite or plastic?
Have never owned a VHF80 but from the ones I've seen I always assumed that the cases were plastic which would tie in with an early sixties production date. However, on-line references generally seem to describe the case as bakelite, so no definitive answer it would appear. Someone out there might know or be able to suggest a technique for distinguishing between the two.

In practice, whether it's plastic or bakelite, I'd take the same approach to spraying. Well worth stripping all the old paint using an appropriate solvent. Meths might a good one to try to start with and then follow all the usual rules for paint spraying. I'd certainly recommend using modellers masking tape as mentioned previously.

Alan
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Old 21st Jan 2020, 1:14 pm   #9
trott3r
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

regarding model masking tape, is there a brand that I can look out for.
then i can avoid cheap tape that had been misdescribed?
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Old 21st Jan 2020, 1:41 pm   #10
ajgriff
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

I use this as the supplier happens to be based near where I live:

https://www.ebay.co.uk/itm/Precision...fgpReViUk7roUA

Lots of modelling supply outlets sell the same thing but I've always had good results with it. It's more expensive than ordinary decorators tape but is well worth the extra cost. It generally comes in narrower widths but is only needed at the edges of the area to be painted. Decorators tape and newspaper can then be used to mask the rest of the piece.

Alan
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Old 21st Jan 2020, 1:57 pm   #11
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

The attached photo of a re-painted Roberts grille is an example of what can be achieved with modellers tape. When I tried this with strips of ordinary masking tape the result was disastrous.

Alan
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Old 21st Jan 2020, 2:00 pm   #12
Lloyd 1985
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

The VHF80 is Bakelite, very thin Bakelite at that! I repaired a VHF80C many years ago, it’s on the forum somewhere. I had to repair the cabinet after postal damage, and I also resprayed the front, on the 80C the front is white/cream, while the 80 is gold, or on the 2 that I have it’s gone sort of green! I used bog standard masking tape when painting mine, and it wasn’t very good! The model masking tape will be much better.

Regards
Lloyd
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Old 21st Jan 2020, 2:01 pm   #13
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Nice job on the Roberts! I had to do one of those and I ended up using a roll of insulation tape! Yours looks much better.

Regards
Lloyd
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Old 21st Jan 2020, 8:31 pm   #14
trott3r
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Quote:
Originally Posted by ajgriff View Post
I use this as the supplier happens to be based near where I live:

https://www.ebay.co.uk/itm/Precision...fgpReViUk7roUA
Thanks for that link i have ordered.
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Old 21st Jan 2020, 10:35 pm   #15
cathoderay57
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Hi Steve. Re: voltage measurements: UY85 rectifier looks OK; UABC80 should have 50v or so on the triode anode only, I assume when you said anodes it was a typo. UL84 screen grid is a tad low probably because R28, the 5.6k you mentioned, has gone high. Annoyingly Trader 1474 doesn't show the valve currents in the table, only the voltages (whereas the older sheets did). So looking up typical currents in the data book we have, passing through R28:
UL84 screen 5mA; UABC80 anode 1mA; UCH81 screen 8.1mA; UF89 anode 12mA and screen 3.9mA giving a total current of 30mA. That's worst case as with reduced emission for ageing valves the currents will generally be less. Therefore 30mA through a 5.6k resistor dissipates 5W. If you used a 5W it would run extremely hot so I would recommend sticking a 10W resistor in. Alternatively use two 5W 2.7k in series or two 5W 12k in parallel. Cheers, Jerry
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Old 22nd Jan 2020, 12:42 pm   #16
dinplug
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Hi,
yes thanks, useful info there.I replaced the 5.6k resistor with a 5 watt RS ceramic bodied NOS 5.6K resistor and soak tested for 2 hours,resistor runs warm to very warm.That jacked up the HT a bit.The strange fault remains.Only affects MW.When present the local radio station on 200 metres, Radio Stoke, is to be found at 550 metres on the tuning scale, together with reduced sensitivity.The fault can be cleared by manipulating the band selector buttons, or quick power on/off/on.It's now reassembled for now with the casing refurbished.I used gold enamel paint,2 coats applied to give an undercoat for the gold spray can and the 2 coats of gold and finally 2 coats of clear laquer.I used sellotape to mask the edges together with A4 sheets of paper.Found 4 equal sized washers for the rear cover screws.
I coloured in the 4 BUSH logo letters at the bottom of the casing with a black sharpie pen, I was tempted to scrape off the gold paint,but one mistake or slip, would mean another re-spray, ouch !
Except for a minor ding on the top of the casing LHS, it's in fair shape.Will soak test today and investigate the intermittent fault when I am in the mood. I did give the wafer contacts on the selector buttons a good dose of Servisol Super 10 on both sides of the wafer assembly.
Cheers
Steve
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Old 22nd Jan 2020, 2:02 pm   #17
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Looks good. Well done.


Alan
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Old 22nd Jan 2020, 3:39 pm   #18
julie_m
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Default Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

Quote:
Originally Posted by dinplug View Post
When present the local radio station on 200 metres, Radio Stoke, is to be found at 550 metres on the tuning scale, together with reduced sensitivity.
200 metres = 1499kHz
550 metres = 545kHz
Difference = 954kHz
This is close enough to 2 * 470kHz to be just the expected image frequency. Ordinarily, the aerial tuned circuit would block the image; but a very strong local station might break through anyway.
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Old 27th Jan 2020, 11:39 pm   #19
dinplug
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Smile Re: Bush VHF80, Recaps,Case Paint,IFT and strange fault.

I finally went through my valve collection and rooted out some spares for the Bush VHF80.
Then tested a few on my Taylor 45b valve tester.
V4 = UF89, third I.F. amplifier valve would not allow setup for mutual conductance test so swopped it out for a spare one from my stock that tested fair to good.Mutual conductance should be 3 but the best I had was 1.8.
Am hoping it might sort the weird low gain fault on MW, which can be cleared by rapid switching between MW and VHF, or interrupting the mains supply briefly.

I know its off topic but is it possible to convert my 45b into a 45c valve tester?
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