The Fine Things are Always Hand Made
went to power up the Philharmonic today and encountered a problem. It performed badly: poor sensitivity and poor signal to noise ratio. It was as if it had a very poor aerial. Tried obvious things with no luck. So got it out on the bench to test the valves. The oscillator tested bad though fitting a new one made no difference! Then I noticed a small amount of smoke from the left front of the chassis (looking at it). Check under chassis for burnt component but nothing visible. Cautiously connected to mains again and no smoke or smell. My guess is that a resistor has burnt out. I know it's impossible to diagnose at a distance but if you Seasoned Scott enthusiasts have any suggestions as to where to start, I'd be most grateful!
Did you replace the filter caps and the smaller wax/paper/foil caps ?
A shorted cap can allow voltage in unintended circuits and cook resistors and .burn out coils ...
Having done that, then start looking for inappropriate voltages in the major circuits - perhaps with the radio on a Variac with just enough voltage to allow aome B+.to form.
Thanks David. The set had a partial though competent restoration by a previous owner but not all the caps were replaced. Am I right in thinking there are caps concealed inside the coil cans? Jonathan
Jonathan - On the Philharmonic - location of less obvious caps to replace-
-some positioned half way through the chassis with half below and the other end inside some large coil cans.
-rectangular soldered box (part 74) riveted to the inside chassis left side with seven caps inside (all .05). I cut it open with Dremmil tool, pulled out the tar potted guts, replaced with 630 volt film caps inside.
-the bass choke assembly (chrome plated, back left - part 9- has 4 caps inside) ) located topside between the p-p 3rd audio 6J5's and the Expander p-p 6L7's - a must, as a short may seriously degrade sound quality and destroy the dual bass control).
-may be one or two inside (unsure about this) the cover over the tuning condenser.
- also - note that one of the power supply B+ filter caps is isolated from the amp chassis - it is the first filter, ahead of the two filter chokes - originally mounted on a fiber mounting with the negative end connected to the below ground center tap of the high voltage winding. Grounding it will spoil the sound, etc.
If you don't have all the Rider's Vol 14 Philharmonic pages, print them from the archive/set folder on this site.
Yours being an older partial restoration - be especially leery of any Sprague Black Beauties or "bumblebee" caps. Indeed, I would replace any caps that aren't modern film/polyeaster type caps.
Thank you David, that's hugely helpful. The metal box of caps has already been done, thankfully, but I need to check everything else you mention here. Hopefully I can escape the festivities for a few hours to do so...
all best, Jonathan