Farnsworth restoration

http://www.nostalgiaair.org/Resources/941/M0005941.htm

Bewildered…..so I purchased a Farnworth ET-066 as is, not working, no cord. The schematic tube line-up is 50L6, 12sa7, (2) 6ss7, 12sq7, 35z5. I purchased it no tubes. So replaced all the caps a couple of out of spec resistor, plug it up, no sound. AC checked really close on all tube pins but I have almost no DC. Long story short , I read a blog about replacing the 50L6 with a 35L6 and the (2) 6ss7 with 12sk7. Gave it try…..lo and behold it plays music and the DC voltage was back. What the heck is that all about? Is the schematic wrong?

First, 6sc7 is nothing like a 12SK7 either electrically, or, otherwise.
So, somebody messed up somewhere.
Secondly, Go back to the 50L6. The original intention was to make the tube line up to work on 115 volts ac.
Your tubes are running hot on today's line voltage. Put the fifty volt tube back in, and, you should be fine, that is, unless there is a ressistor in siries.
Bill Cahill

There is no 6cs7 in the tube line-up. There are (2) 6SS7 tubes but either way the that explains the "why". Thanks

How did the 35z5 test out on a tube checker? The first number on the tube generally is the voltage if I am not totally brain dead this morning. I added up the schematic tubes and it comes to 121. By putting in the substitutions if I added correctly it adds to 130. So it shouldn't add more voltage to the tubes, in fact they each get a little less. One thing I am wondering is how the original tubes for it tested you installed? Could some be weak. I didn't see any added resistors to the series of the filiment circuit. This is a interesting situation. On the Nostalgia air site did you know the guy who puts it out was at the Nashville Meet? I remember seeing him at a few of them. We talked at the meet this time and he told me he was the one who put it out. He gave me his card. I need to email him. He doesn't live to far from me and sounds like he has a huge collection. Maybe he will invite me to see his radio stuff and a road trip will be in order. Anyway it will be interesting to see what caused this. I am wondering if some of the tubes may be weak.

willy3486 wrote:
How did the 35z5 test out on a tube checker? The first number on the tube generally is the voltage if I am not totally brain dead this morning. I added up the schematic tubes and it comes to 121. By putting in the substitutions if I added correctly it adds to 130. So it shouldn't add more voltage to the tubes, in fact they each get a little less. One thing I am wondering is how the original tubes for it tested you installed? Could some be weak. I didn't see any added resistors to the series of the filiment circuit.

Good morning Willy. Your math is correct. The radio had no tubse when I received it. I pulled the tube line-up from Nostalgia which listed 50L6, 35Z5, 12SQ7, 12SA7 and (2) 6SS7. I didn't have any 6SS7 tubes so I ordered a couple. All the tube tested better than
70% with most above that. The 50L6 was at 90%. The 35Z5 was 75%. All resistors were listed in the schematic, no additions. The 50L6 socket did have (2) 470k resistors that were reading high and I did not have them (on order now) so I replaced with 500k. The 35L6 is running hot so I'll put the 50L6 back in tonight and see how that affects it.

Ben

Drop the 50L6 back in last night. Running much cooler so all is well, now time to refinish the cabinet. Updates later.

The Farnsworth ET-066 is complete. Not sure if this was an off brand or just rare but I haven't seen a lot of info or talk about it and few pictures so here is what I think is a nice looking, well playing radio.

Looks great! You do good work Ben!

Thanks Doug...........Did you ever get around to putting on the grill cloth I sent you?

Not yet. Life keeps getting in the way of me doing the things I really want to be doing...Ce la ve...(laughing)

Ben, Farnsworth was the paremt companny of Capehart. They weren't as well known, but, in one form, or, another had been around since the 30's.
Nice job.
Bill Cahill

Thanks for the kudos guys. This radio stood out when I was looking for new project. Most radio of its age are boxy and we have all seen hundreds with the "waterfall" fronts but this radio
just had a bit more design and character, that is for my taste.
Any-who, I liked it, I purchased it, I rebuilt it and it now going into my collection.

For a interesting read look up Philo Farnsworth. Of all the early electronics pioneers he to me is most like Armstrong. Farnsworth is a interesting and brilliant character to me.

Interesting guy for sure.