OK, The output ckt is indeed unique, only the grounded grid cross-cathode coupled phase inversion is shared with the Philips Uranus. Otherwise it's UltraLinear-like with a cathode coupling back thru the OPT which is a very special item for this radio. Measure the larger speaker's resistance and connect the lower resistance one to the tap and the higher to the end. If same, connect woofer to upper and mid to tap and see if it sounds reasonably well tone-balanced at neutral tone settings once working. Phasing matters between the cone drivers, there will be a 'hole' in the mid-bass response if wrong. Drivers are polarized, brown common wire probably low/ground and other sides to xformer tap and high end.
The tweeter ckts are always problematical with age, I'd assume the tweeters may be shorted and disconnect the network at C601/EL84 plate and ignore it and the tweeters for now. If it continues to squeal there may be stability issues related to working tweeters not HF-loading the lower output tube's plate. We'll deal with that later if necessary. Otherwise it may be a mis-wire in the tone ckts. Fortunately for us the tone ckts in this radio are relatively simple compared to other examples. Use the schematic to get the volume/tone ckts back to design, resistance test the volume control end-to-end and to the center wiper while turning the volume knob from both ends. If all good, we go onward with next stage of diagnosis if necessary.
Trying to digest all this info...
Anyway, it'll be simpler for me to show pics and how it is connected now.
Below, the green and yellow wires coming from underside were initially connected to the biggest speaker (I didn't touched and let it this way):
As you could see below, they're tied on one side (green) to the socket ground lug (this lug is also tied to the one of the external speaker terminal). I assume it goes to the negative side of the woofer. Yellow side is tied to a green wire coming from the OPT. Someone worked here as I guess the colors were inverted:
On the preceding pic, you could also see the "other" connection, a shielded wire of some sort. The red end is tied just after a 200k resistor. Looking at the schematic, it should go to the tweeter positive I guess? The shield is tied right at a yellow wire also coming directly form the opt. Where should it go? Below, a pic of the tweeters, soldered together on the positive side I guess, with the red end soldered right there. It was disconnected when I got the receiver:
Weirdly, connecting the "shield" to the neg. side of the tweeters, there's sound. Connecting the red end and the shield together to the pos. side of the tweeters, there's sound also...:scratch2:
Connecting the negative side of the woofer to the neg. side of the tweeters, there's sound...:scratch2::scratch2:
I'm lost!
Following, a pic of an unused orange wire coming form the OPT. I don't know what's the purpose (maybe to connect to the mid?):
Do you think someone messed up the connections?
About the squeal, it does it even if the tweeters aren't connected and it even kind of oscillate with a certain amount of volume and treble...
The 295v I should have right after the rectifier is not there too. I got 277v instead. :scratch2:
All tubes tested in the "good" range on my (calibrated) Jackson 648 tester for the record.
Thanks for any help.
Patrice
) and it emits a big hum. No doubt, the caps needs an overhaul.
