Bush VHF90

[Joe]

Today I received a VHF90. The seller said it had been in regular use until recently when it had just stopped.

When I tried it its was dead with no continuity through the plug. The wires in that were OK as was the fuse - 5A.

I started checking valve heaters but then some instinct directed me towards the dial lights. One had blown and after changing that it not only worked but is fantastic; I can get Radio 2 on a four inch bit of wire.

Obviously it should work sans light so that's something to investigate. I'm not going to take it to bits until I've put a Philips set I'm working on back together but can see it's been partly re-capped at some point. I have also noticed a damned great hole in the board with the high power resistors on.

- Joe

[Steve_P]

There's a resistor across the dial lights. It's 50 Ohms on a VHF90 - R37 on the Bush Sheet, R38 on the trader.

Cheers,

Steve P.

[Joe]

Thanks, Steve. That's top of the list to check, along with what else has been 'repaired' in the past.

All the best

Joe

[Tedzed1]

Hi Joe, I also had one of these until recently, same problem, had also been 'repaired' in the past, the 50 Ohhm resistor blew on mine, so removed it and had to keep replacing the dial bulbs to use it, which would blow quite frequently, also had good burn up on the board, so never bothered with it further,

Could it possibly be the same radio?

(PS, mine had blown a dial light bulb again before i sold it)

[Joe]

Mine's the white version, though I may have to look out for a brown one to keep it company.

I'll have a proper look at it soon so I can get any bits it needs ordered.

Cheers

Joe

[Joe]

This is curious as the Bush data sheet I downloaded says the lamp shunt resistor is 30Ω. I'll be interested to see what's actually fitted.

- Joe

[Yorkie]

This is curious as the Bush data sheet I downloaded says the lamp shunt resistor is 30Ω. I'll be interested to see what's actually fitted.

- Joe

Of course the lower the value of the shunt resistor, the more current that will flow through it. and the less current will flow though the bulbs, thus conserving their life. Maybe Bush realised this at some stage, so lowered the value of the shunt to 30R? If you check the voltage dropped across the shunt, when you check the actual resistance you'll be able to discover the current flowing though the resistor (I = V/R), and from that, the correct wattage (W = I x V).

If a shunt resistor goes high due to aging, that will mean that less current will flow through the resistor, and more will flow though the bulbs, putting them at risk. If for the sake of example, a 30R shunt resistor drops 10V, (I'm not saying it does drop 10V in the VHF90), the current flowing through the resistor would be 333mA. If that resistor went high - say 50R, it would then only pass 200mA, so that would place a higher load on the bulbs.

Best of luck with it Joe - do keep us posted!

David

[Joe]

It's currently o/c so the lamps are copping for the lot and popping.

I'll get both 30 and 50 ohm ones and have a play.

I'm trying to be disciplined and not take it to bits until I've got some other jobs tidied away.

- Joe

[Bluebottle]

I'm trying to be disciplined and not take it to bits until I've got some other jobs tidied away.

- Joe

Silly boy, next you'll be telling us about flying porkers !!

[Joe]

I couldn't fully resist and took the chassis out.

The resistor in question is an RS 10W 25Ω wire-wound and has clearly blown at one end.

It looks like the audio section has been re-capped already as as it performs so well (until a lamp blows!) I'm inclined to leave well alone, though will obviously have a poke around with a meter first.

- Joe