I have completed full re-cap on a customers Philco 47-1230. I cleaned the Push Button section, and phono switch, & all is working great.
Today, after playing the radio over 20 hrs since restoration working great on all bands, something weird happened. I attached the phono a.c. plug 2-pin connector to see if phono motor would turn, and let the old phono motor run for a short amt of time. After some help by hand, the old motor started turning. In the process of doing that, the radio quit working. I had the old phono mono input rca attached, but the tonearm not connected thru the old hi-imp transformer mounted in fnt bottom of cabinet.
Anyways, the radio receiver shut down, but still had some audio on higher volume. After tapping on the tubes, I found the n.o.s. 7R7 tube I just purchased and played over 20 hrs testing from AES was very microphonic. I replaced the 7R7 tube, and the Radio receiver started working again.
My question is this, did the turntable motor pass some AC current via orig input wire back into the chassis to take out the nos 7R7 tube? Since I replaced the tube, everythings working fine in the radio again. I have unplugged the phono ac line output plug from chassis, and when I engage the phono pushbutton , everything is fine with just the phono RCA input still connected. Now I can engage & release the phono button without any harm to the radio. I really dont think the prob is in the phono ac switch. For now, I will leave the phono ac connector disconnected altogether. Without pulling out the schematic again, this doesnt compute for me right now? Anyone ever had this prob happen before? Thanks for your thoughts, Im overlooking something simple here on the Philco 47-1230 chassis. Randal
well,.... after some minor head-scratchin, realizing there was no way a Philco turntable could ever take-out the 7R7 tube anyhow,( I really didnt want to have to remove that chassis again!!, not again!!),... I broke down and pulled the chassis out again. I found the 7R7 tube socket had a internal broken tube-pin contact inside the socket wafer. Just wiggling the tube, found the prob with my continuity tester. I replaced the socket, alls good now! Just tryin to start some good-conversation here at the B&G, in the 1st place! Where is everybody these days? I see lots of "lurkers" here, but not many Philco techs that can "splain" why a Philco turntable can blow a 7R7 tube? I was Just-Kiddin!!
You see, when you get to be my age, there needs to be a " Pfilco Pfamily oversight committee" here, to deal with such ol-farts tech questions like these!?? Reckon? Perhaps not. Just checkin.
Sorry, Randal...I pop in here on a fairly regular basis but have not had much time of late to post many replies.
That was a very odd problem indeed with your 47-1230. Good to know the problem was a bad tube socket. I didn't think there was any way the phono input would fry a tube!
Don't you just love loctal tubes and sockets!
Loctals to octals. If you have a bad loctal tube, and can't find another one right away, here's a trick. If you hammer the loctal just right, you will still have the tube base. Now cut away all the superstructure until you just have the pins and file away any jagged edges. We are now ready to attach an octal socket to the loctal base. The Loctal pins on top will be hard to solder to, so file away the oxidation first. Solder short pieces of wires to all the pins you need, then solder them to the appropriate ones on the Octal socket. Now get one of your plastic prescription bottles that fits around the loctal base and octal socket and tape the whole thing together. I hope you have enough vertical height to make this fit inside the cabinet, but mostly it works. Took me about 45 minutes to make this one up. I didn't have a 14A7, but I did have a 12sk7, and I wanted to finish the repair. To my utter astonishment this works; alignment was not even off that far. I would have no concerns about subbing, say, a 50L6 for a 50A5, and so on. Now when I get a 14A7, I will merely remove the contraption and plug in the replacement. Kludge? yes. Works? yes.
One cute way to cut the top off of the tube is to wind one turn of nichrome wire around the glass envelope of the tube. Apply a current through it enough to make it glow a good red heat. The concentration in the glass will cause the glass to crack in the line of the heater wire, and you have it "cut". They do this on cathode ray tubes when they cut off the old electron gun, preparatory to welding on a new one.
I'm a little amused by this thread. It's really the reverse of what we did during WW II. One "for instance" was the total unavailability of the 12SA7 for the duration of the war. Somewhere along the way, someone discovered that the 14Q7 is a Loktal 12SA7. It was the practice to make an adapter out of a discarded octal tube base, make the connections to a Loktal socket, and plug the loktal tube into the adapter, and the old base into the socket.
I've found that Loktal tubes have been easy to find, to the extent that I've found boxes full of them at swap meets. Nobody seems to want them, and often, they go begging.
The service shops never did like Loktals, because of the hazard of breaking sockets. Indeed, I once found a nice 42-1010 Philco in a furniture store, with all the tubes gone, and a few broken Loktal sockets. I bought it for 5 bucks, and the dealer almost kissed my feet for buying it. Sure, the replacement of sockets will some day be a bt of a job, but it will get me a nice radio. I have plenty of tubes for it, too.
One thing about Loktal tubes. Their construction was new and innovative, and it was soon discovered that they performed far better at high frequencies than Octal based tubes. Loktals would logically be just the ticket for television tuners in the 1939 sets, but for RCA to use Loktal tubes (a Sylvania development), would be like a Rabbi having a ham sandwich. The RCA 12 inch prewar set I have uses a 6J5 oscillator in the front end, but a 7A4 would surely have made a better choice. (An XXL, even?)
Isn't the XXL and the 7A4 pretty much the same? I've probably got more XXL's than I'll ever use, (Thanks, Brian!).
The XXL is a 14AF7. It is a loctal 12SN7. There was also a 7AF7 which is roughly equal to a 6SN7. The ubiquitous dual medium mu triodes, they behave as a "modern" 12AU7. This is a re-post, as my original message did not go through. Is this what you were interested in?
codefox, I think you are thinking of the XXD which is equivalent to the 14AF7.
I stand corrected. The XXL is a 7A4. I need new (eye) glasses.
Thanks.
Hey Ron,
Thanks for answering our quesitons. Here are the photos you requested regarding the switch above the turn table. Hope you can figure it out.