Thanks for the info. I have a wealth of info about the original tuner will get back to it in a bit. It's similar to what you describe but continuous tuning.
Next, let's take a look at the massive power supply. Easily 100 pounds.
This is a sign of the times. Electrolytic caps were still a fairly new thing. Only four in the whole set and three are in parallel!
Most of the filtering is done by massive filter chokes - even the high voltage.
This chassis is mostly original. Just one major repair.
The original HV transformer has been replaced with one from a later TRK-12 model.
Not exactly a perfect fit. They added a support bracket on one side. The other side is held down by some twisted wire.
The original was held down by metal tabs fitted through slots in the chassis and bent over as was RCAs construction technique at that time.
The original also had all the wires coming out the bottom while the HV leads comes out the side of this one.
A bit ugly for sure, but I'm unlikely to find anything better anytime soon.
This also led to another issue. This set uses two HV rectifiers. One for focus and one for the main HV supply. That means we need two independent, insulated 2.5 VAC secondaries. The TRK-12 only uses one and a voltage divider for the focus voltage.
Well, that means they had to add a dedicated filament transformer.
That's the open frame transformer we see here surrounded by capacitors.
Speaking of caps. These are the four electrolytics I mentioned. Three 18uF connected in parallel for the main B+ filter and a 10uF for the push-pull 2A3s plate supply.
The two at the top are originals while the others are replacements. It would be nice someday to replace them with period correct caps so they all match.
The gnawed box to the left also contains caps. Two 10uF and a 50uF but they are not electrolytics.
They are foil, paper and wax encased in tar. The are a couple more blocks like this on the upper chassis.
That's good for me as they are easy to restuff.
I will be using high quality polypropylene film caps to replace them all.
The HV supplies are brute force half-wave rectifiers on the 60Hz transformer secondaries.
That's why they needed so much filtering. PI filters - two caps with a choke between them.
I've been told the HV caps are oil filled and likely fine so I'll leave them alone for now.
It uses and 878 and 879 rectifier tubes.
Not many parts down below. Mostly some bleeder resistors in the HV supply.
Six 1M resistors in series right across the 6kV supply.
1kV on each is pushing them hard as 2W resistors are typically spec'd at 750v.
I'll upgrade them when I build replica replacement dogbones.
The phenolic board is warped and cracked. I may attempt to repair or replacement might be a better option.
Some rewiring will also be required.
This set uses a mix of brittle failing rubber wire and cloth covered.
I'll try to match them as best I can with new wire.
