Philco Mystery Control Receiver

[ghjkl67]

Yes, I did see the tech info page. Some of it makes sense to me, but some of it doesn't. It's hard for me to understand the thyratron operation, such as, what is the proper bias for the grid? Also, what should the grid waveforms look like during activation and during steady operation? It looks like there should be AC and DC there, but the grid vs. plate graph doesn't specify. Anyway, I was trying to scope it out. It looks like the negative portion of the AC cycle is cut off at the grid during activation. When the thyratron gets stuck, the negative portion comes back very gradually. Because of this, I thought that the control grid circuit was sticking, causing the thyratron to be stuck. Then, I tried pulling the thyratron. Instantly, the grid waveform returned to a normal AC cycle. So, it looks like the grid is being controlled rather than controlling.

These are just some testing methods I came up with off the top of my head. I don't know if there is any logic to them. I'll try any other testing methods suggested on this thread. I only have a digital meter, analog meter, and a scope. If any signal generators are needed, I can try to find or borrow some.

Phil, when you talk about the styling of receivers, do you mean the cabinet style? If so, I'll have to agree. The only reason I bought the set was for the mystery control. That's why I'm trying to so hard to get it working. Without it, the set looks like a dishwasher cluttering up space. However, as far as performance and reception goes, this is one of the best sets I have.