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Old 31st Jan 2006, 12:44 am   #1
Cerberos
Tetrode
 
Join Date: Apr 2005
Location: Holmfirth, West Yorkshire, UK.
Posts: 55
Default "It's been got at!"

Note from Moderators; this is the remnants of a thread which has been saved to illustrate, out of general interest, a radio which has been 'Got at' and the problems faced in trying to repair/restore such a radio.

Hi,

I've recently acquired an Ultra Coronation Twin as a non worker.

A quick look a the pictures shows why it is not working. The 2 dropper resistors r21 and r22 are totally knackered (trader service sheet reference numbers).

However the trader sheet shows r20 as a fixed value resistor. This set has a 1k pot and a fixed resistor in series.

Non of the valves are the mazda type shown on the trader sheet. They are a mixture of Brimar and mullard. I am afraid I don't know where to look to see if they are direct replacements. The 1k pot looks as if it there to set the filament current. What should that be assuming the original valve line up?

Looking at the set the resistor arrangement looks to be original with this set. Has any one else seen one like this?

The trader sheet shows R20 as filament ballast resistor at 1690 ohms, presumably the reason for the pot. 1690 does not seem to be a standard value,therfore it should be possible to set filament current with the pot.

R22 is tapped at 195, 410 and 370, how would I replace this?

R21 is 1450 ohms again I would like advise on replacement values.

It would seem I need something close to 195 ohms as a a smoothing resistor and a place to connect C24, a 50 micro farad ht smoothing C and something close to 2425 ohms ( the sum of r21 and r22 ) as a dropper resistor to generate the HT.

As a relative beginner this is all new to me, so any advice would be appreciated and if any one has seen this arrangement before again I would be gratfeul for your input.
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Last edited by Darren-UK; 23rd Jul 2007 at 10:02 pm. Reason: Ebay reference removed and forenote added.
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