I'm looking at this Philco 59, and man is everything crammed in there. I have two 6C6 tubes instead of two 77 tubes. They look to pin out the same (or am I wrong?). Was the 6C6 a common substitute for a 77? They seem to be as old and dusty as everything else in this set. The PT ohms out as good, so I guess I will dive in. Cabinet is in great shape, the dials are in great shape, too.
I was just wondering if anyone had any advice about the 6C6 tubes...but any advice about working on this midget set in particular will be welcome.
The 6C6 is supposed to be a rough equivalent to the 77...but I wouldn't use them. In my experience, 6C6 tubes worked poorly or sometimes not at all in Philco receivers designed for 77 tubes. YMMV.
I think that I may have found the answer, these two tubes are NOT really substitutes for each other, at least according to the RCA specs I found.
http://frank.pocnet.net/sheets/021/6/6C6.pdf
http://frank.pocnet.net/sheets/021/7/77.pdf
The interelectrode capacities are different Whilst the input capacitances are close, 5 mmf to 4.7 mmf, the output capacities are way off, 6 mmf to 11 mmf. However it looks like a 6C6 is interchangeable with a 6D6, but that doesn't really help here, I wonder if a type #78 might work though?
Regards
Arran
6C6 interchangeable with 6D6? A sharp cutoff pentode with a remote cutoff pentode?
My comments in post #2 also apply to trying to use a 6D6 in place of a 78. Where Philco calls for 77 and 78 tubes, that is what should be used. Not 6C6 or 6D6. Again, my opinion, YMMV.
Oh, I looked on my favorite online tube site - nj7p.org - and it lists 77 as a preferred sub for a 6C6; 78 as a preferred sub for a 6D6; 6C6 for 77 and 6D6 for 78. But again...in my experience, 6C6 for 77 and 6D6 for 78 in Philco sets will work poorly or not at all. Arran, you raise a good point here.
Maybe I'll look for some 77s. I would have to assume the 6C6 tubes worked at some point or they wouldn't be in there, but getting some 77s makes more sense.
I also see that the Ryder's has a mistake on it for the filter circuit hookup to the field coil and output transformer.
Never have had good luck swapping 6C6 or 6D6's for 77 or 78's. Yes the pin out is the same but they seem hard to tame, getting them to work without oscillating has been a problem for me. I think the 77-78's where more popular haven't seen many 6C orD6's used in broadcasts set with the exception of low end TRF sets. They do turn up in communications receivers.
(11-05-2016, 09:29 AM)Ron Ramirez Wrote: [ -> ]6C6 interchangeable with 6D6? A sharp cutoff pentode with a remote cutoff pentode?
My comments in post #2 also apply to trying to use a 6D6 in place of a 78. Where Philco calls for 77 and 78 tubes, that is what should be used. Not 6C6 or 6D6. Again, my opinion, YMMV.
Oh, I looked on my favorite online tube site - nj7p.org - and it lists 77 as a preferred sub for a 6C6; 78 as a preferred sub for a 6D6; 6C6 for 77 and 6D6 for 78. But again...in my experience, 6C6 for 77 and 6D6 for 78 in Philco sets will work poorly or not at all. Arran, you raise a good point here.
Ron;
It was kind of late when I posted that, I was looking at interelectrode input and output capacities and not the biasing of the tube. None of these tubes are particularly hard to find, I looked up #77 tube on Duck Duck Go and a fleabay page full of them came up, everything from overpriced single NOS ones to very cheap used but good testing ones sold by the dozen. I haven't run into very many #77s in the stuff I own, mostly #78s and #58s. Another thing that may cause problems is that the spec sheets mention a 6C6 having an internal shield connected to the cathode, which the #77 does not. I don't know the reason for the substitution, perhaps tube shortages during war time. However IF amplifier tubes seem to last for a long time, many of the sets I run into still have the originals in place, RF amplifier tubes are somewhat shorter lived but they last a long while as well.
Regards
Arran
I thought I'd check back in on this one. I'm waiting on parts for the other two sets right now, so I returned to the 59. I had a bad power transformer it turned out. I got a replacement power transformer and have installed it. It went well...much easier than I thought it would be, and I learned a good bit about Its doing it. Putting it in, though, I decided to remove the two transformers under the chassis to make room (good idea...it really helped), BUT it turns out the antenna transformer has a bad secondary. The coil itself is dead simple: two windings that share a common ground lug. The one that is bad is the shorter winding on the outside of the primary. The other coil measures out about what it should, so I'm OK there.
I've read here before about rewinding (something else I've never done before), and I remember Ron and others saying that baking the form is a mandatory step. Does that apply to forms that still have the primaries on them? I have some enameled 34 gauge wire here. Will that be thin enough for my purposes?
In my experience antenna coils need not any baking. In fact even the winding direction, if it is simple antenna coil, matters not.
Baking is, I think, a good idea for oscillator coils where moisture screws up coupling enough for oscillation not to occur.
If however you see lots of green stuf not just where the wire solders to lugs, but under and inside the winding, the wure veing corroded along the length of it, then do bake the coil.
(11-25-2016, 10:11 AM)ccomer1955 Wrote: [ -> ]I thought I'd check back in on this one. I'm waiting on parts for the other two sets right now, so I returned to the 59. I had a bad power transformer it turned out. I got a replacement power transformer and have installed it. It went well...much easier than I thought it would be, and I learned a good bit about Its doing it. Putting it in, though, I decided to remove the two transformers under the chassis to make room (good idea...it really helped), BUT it turns out the antenna transformer has a bad secondary. The coil itself is dead simple: two windings that share a common ground lug. The one that is bad is the shorter winding on the outside of the primary. The other coil measures out about what it should, so I'm OK there.
I've read here before about rewinding (something else I've never done before), and I remember Ron and others saying that baking the form is a mandatory step. Does that apply to forms that still have the primaries on them? I have some enameled 34 gauge wire here. Will that be thin enough for my purposes?
Hi Charlie,
Methinks you have it a bit backwards. Generally the winding on the left of a transformer is the primary and right side is the secondary on the schematic diagram. Today is your lucky day! The primary is the open one and it's the easier/smaller one to rewind. There is no particular phase relationship to the two winding so direction is not all that critical. Also it's not a tuned circuit so the # of turns are super critical. The secondary is.
> Does that apply to forms that still have the secondaries on them?
Yes, If you are of that mindset. The idea is to evaporate any moisture absorbed in the coil form, the moisture can have an effect on the efficiency of rf transformer. I would think that it is more critical for the osc transformer. This efficiency is known this the "Q" of the coil or transformer
> I have some enameled 34 gauge wire here. Will that be thin enough for my purposes?
Yup your good. But don't use the original resistance as a gauge to determine # of turns. The larger wire will have a lower resistance hence you would be prone to more turns to achieve to "correct resistance". Here if you count the turns that is the best if not just wind enough turns to fill the original space and add a few more for good luck.
PT's aren't difficult to replace if you can find a replacement that meets the physical and electrical requirements. Most have a known color code for the wires which save alot of guesswork. Some of the oem units don't conform to the RMA standard color code.
Mike types much faster than I!!!