Working on Another VHF90

[Bushbaby]

Hi All,
I've recapped a VHF90 and this one wiring isnt too bad so this will soon roll off the production line.

I need some guidance though regarding R35 (trader sheet) which is a 160R 3 watt resistor. Does it need to be changed (I was lead to believe that they did?) and if so, the nearest value I have is 200R which does appear to be near enough tolerance wise.

Any thoughts?

Thanks

Rob

[Joe]

I can't see any earthly reason to change that one any more than any other. If the value is OK leave well alone.

- Joe

[Steve_P]

It does get hot!

Measure it and if it's risen unduly (i.e, more than 10%), change it. The one you put in it's place must be at least 3 Watts, 5 Watts if possible.

If it's OK, then there's no reason to change it.

Cheers,

Steve P.

[Bushbaby]

Steve,
I changed all of the power resistors in the previous VHF90 that I restored and I was amazed that it wasn't throwing out a terrific amount of heat in operation. Have read nearly all of the restoration threads/stories, I thought that I would replace these on sight (yes I know what you are going to say Mr R!).

However, in this instance I don't have suitable value resistor to replace it with directly although I do have some ERG resistors of 100R and 50R value which I could run in series??

Whats your thoughts?

Thanks

Rob

[AlanBeckett]

http://www.ebay.co.uk/itm/2x-WELWYN-W22-...upplies_ET&hash=item5d376a6342

Alan

[Bushbaby]

Thanks Alan,
Duly purchased

Rob

[Yorkie]

Hi All,
I've recapped a VHF90 and this one wiring isnt too bad so this will soon roll off the production line.

I need some guidance though regarding R35 (trader sheet) which is a 160R 3 watt resistor. Does it need to be changed (I was lead to believe that they did?) and if so, the nearest value I have is 200R which does appear to be near enough tolerance wise.

Any thoughts?

Thanks

Rob

I don't personally change resistors unless they're at least 10% out of tolerance, so I wouldn't have changed that resistor or any other just for the sake of it, especially if it's within its 5% tolerance. It's no bad thing if resistors drift a bit high in value as it's kinder to the valves and other components to be a bit under-run. I do generally change paper caps as experience has shown that they are often leaky (in the electrical sense) so may put DC where you don't want it, though the older the set, (eg, pre-war), the more that 'conservation' rather than 'restoration' comes into play.

As to Trader Sheets, though they're are better than nothing, they're usually a poor substitute for the Maker's data sheets where such sheets are available. In the case of Bush radios, the maker's sheets are very comprehensive - ten pages in the case of the VHF90 compared to the Trader Sheet's 4 pages. (8 pages in the case of the DAC90A compared to 2 on the Trader Sheet). Trader Sheets often have untidy printing, only sparse info about alignment and voltage readings, and don't often specify the wattage of resistors. Confusingly, they also use different numberings from the makers.

The Bush data sheet for the VHF90 specifies the resistor that the Trader Sheet calls 'R35' as being 160R, 4 Watts, 5% tolerance.

Every success with the restoration Rob.

For anyone who doesn't have Paul Stenning's Radio Service Data DVD, his Christmas offer will soon end. Makes a great stocking filler, (though it doesn't fill a stocking quite as nicely as Kylie)