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39-30 Refurb - Printable Version

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39-30 Refurb - Nick3092 - 05-13-2015

I just finished refurbishing (all new caps and all new resistors) my 39-30 last night.  Thought I'd post a few findings here in case anyone else is looking for info on doing the same (and one question/issue I'm having).  The radio was pretty much all stock electrically except for the first filter cap which had been removed and replaced under the chassis.  The remaining two lytic cans were still connected, but leaked a white crumbly material out the top.  I didn't power the radio (as I never do before a refurb), but the previous owner did and said it just "screeched".  So I had no idea what to expect to find, or if it would work when I was done.


Like most 39 Philco radios, it was loaded with rubber wiring - half of which was crumbling.  And only a matter of time before the other half started.  That includes the PT, OT, and both IF cans.  There were only like 4 cloth covered wires going to the tuning condenser and 2 grid caps.  I replaced all of the rubber wire, even the stuff that still seemed pliable.

Someone had poured some kind of black tar/caulk material over the wires coming out of the PT.  I had to cut that all away to take the shell apart.  Once apart I had each wire marked and crumbled one, re sleeved it with the proper color heat shrink, and moved on to the next.  Pretty much same thing for the OT, crumbled and re-sleeved the two wires 1 by 1.

I removed the preset buttons, coils, and trimmers completely to make it easier to work on the chassis.  I had 2 push buttons that were sticky.  Once it was out of the chassis, I laid it on some paper towel and shot some D5 into the 2 or 3 holes for each switch and worked them back and forth.  I flipped the whole thing over and repeated the process.  I replace all micas by default (personal choice - I only want to work on a chassis once and people have started seeing mica's failing more frequently in the past couple years and I lack the gear to test them) and from what i read these 370pF ceramic ones fail quite frequently anyway.  I put a 360 and 10 in parallel to replace each one.  I noticed the one attached to the coils was grounded to the bracket, while the one attached to the push button was grounded inconveniently to the radio chassis itself.  To make it easier to reinstall (or remove again if I ever have to), I found a point to ground it to on the push button assembly that gets screwed to the chassis.  Now removing the push button assembly would only require removing the black wire on top and the red wire on the bottom of the push buttons.

The bias resistor 45 (280 ohms) was a Micamold domino resistor.  The package was bulged and looked heat distressed.  Surprisingly it still measured correctly.  I suspect it was either underrated to begin with, or just marginally rated at original line voltages and couldn't handle today's higher line voltages.  I probably went a bit overboard here, I replaced it with a 100 and 180 ohm 5w 1% wirewound in series.  That should more than cover any wattage/heat issues going forward.  The 70 ohm was a regular carbon resistor in good condition, but read high (and I replace all resistors anyway - again I only want to work on a chassis once).  So I replaced it with a 68 1w that was conveniently reading a little high at about 69.5.

The band selector was mounted in the most inconvenient way possible.  And it had _a lot_ of rubber wires on it.  I decided the easiest thing to do was to take it out.  Before doing so I marked each wire with a letter or number sticker, and also place a matching sticker to where it terminated in the chassis.  I then cut the wire as close as possible to the termination point in the chassis.  I also took lots of pictures both before and after marking them and cutting them.  Then I could work on the band switch mounted in a small portable vice on my work bench.  I could cut new wires to pretty much exact lengths and even pre-bend them to match the path of the original, so when I put it back in they would be right where they needed to be.  I replaced them one by one on the band switch along with the .05uf C3.  I remounted the switch and reconnected all the new wires.  I had removed the old wire stubs on the chassis ends except on the antenna coils.  They are not mounted very securely and moved around too much when I tried to desolder and bend off the old leads.  So I just added the new wires to the terminals with the old stubs still soldered on.

I came across what appear to be 3 deviations/run changes not documented in the info I got from Chuck.  The documents noted two minor capacitor changes in run 1-1 (neither of the changes were present in this radio).  The back was stamped "3-3", so maybe this was run 3-3?

The first was one of the tone caps (C39 .006uF) was .008uF.  Probably not a huge difference.  I recognized a similar circuit from my 38-10 (.008 and a .03 in series with the tone switch shunting the .008), so I kept it .008 since it came from the factory that way.

The second deviation was the fact they shielded the 37 tube.  It has the trademark square base riveted to the socket.  The drawing of the chassis in the service notes only show that around the 75, and Bob Andersen's chassis also lacked that base.

The third deviation caught me off guard at first.  It's similar to what Bob noticed in his, but a different resistor value was used.  In the schematic, the brown lead form the secondary of the primary IF goes to the AVC line with C3 to ground (assuming I'm understanding the circuit correctly). In the radio however, the brown lead is going to a 490k resistor and a .05uF cap. The other end of the cap goes to ground (this is not C3, that is buried under the band switch). The 490k then goes to the tap between the 280 and 70 ohm voltage divider off the CT of the transformer. Bob's was a similar change, except his had a 2M resistor instead of roughly .5M.  When looking at other 39 chassis in my Riders scans, I happened to notice that this exact change is how they designed the 39-36.  So for whatever reason, Philco must have been playing around with the 1st IF in this chassis and wound up mimicking what they did in the 39-36.

39-30 Schematic:
http://www.nostalgiaair.org/PagesByModel/289/M0013289.pdf

39-36 Schematic:
http://www.nostalgiaair.org/PagesByModel/295/M0013295.pdf

Other than that, no major surprises.  A couple tubes tested weak, but I figured I'd fire up the radio first to see how it worked.  Fired it up slowly on the variac watching the ammeter and B+ voltage, everything was fine.  Radio came to life.  Like Bob, I noticed that without a ground from the chassis to my house's electrical system the radio tended to pick up some extra noise.  Not nearly as much as I heard in his YouTube video, but still noticeable.  This radio over all seems to be more succeptable to noise than most of my others.

One of the weak tubes was the 6A8.  With the weak one, I was seeing AVC voltages of -2 (no station) to about -6 (strong local).  After I popped in the new one, I was seeing AVC all the way to -14vdc on a strong local, and about -10 on my SSTRAN.  After replacing the 6A8 I did an alignment and was able to peak up the IF's quite a bit.  Now the dial is tracking well, and the radio is working except for one small thing.

This radio has three tone settings.  Basically the 1st setting is no bass (short out C26), 2nd is some bass (nothing shorted out), and 3rd is full bass (C39 shorted out).  Any time on the setting is on 2 or 3, some distortion is introduced along with the bass.  You don't hear it as much on talk radio.  But on the music playing through my SSTRAN it's pretty apparent.  The speaker cone is in good shape.  There was just one little hole in the middle, but I patched it with a bit of fabric glue a couple days ago.  I've checked the rest of the cone, everything else looks good.  I would also assume if it were a cone issue, I would hear at least some distortion even on the no bass setting.

Any ideas on this issue?  Everything else seems good on the radio.

Thanks!

-Nick

RE: 39-30 Refurb - Radioroslyn - 05-14-2015

I'd check for overloading in the rf or if stages. Detune them a bit and see if it clears up. May have a weak avc diode.
Terry

RE: 39-30 Refurb - Nick3092 - 05-14-2015

If there was an issue with overloading, wouldn't I hear some distortion on the lowest bass setting as well? Not arguing, just curious. As a clarification as well, the distortion is mainly when the bass-y parts of the songs play. So it's not distorting the entire signal. I do have a signal tracer. I guess I could put that on the plate of the 41 and see if it experiences it as well to clear the speaker itself.

All of the tubes (except rectifier and OP) tested weak originally. As I had to get some new tubes, I ordered these as well. Plus since I have a 39-6 which also uses the 75/78 and a 38-10 that uses the 6A8, they would be good spares to have on hand. Right now all the NOS tubes are in. As I recall (my notes are at home right now), my Hickok 533A said the diodes were good on the original 75. But my Weston 981-1 (which somehow tested the diodes together, as opposed to the 533 that tested them individually) showed them as being weak/bad.

I guess I can try swapping in the originals 1 by 1 tonight to see if that makes a difference. I can also try the ones from my 39-6 and 38-10 to see if they change anything before moving on to detuning sections.

RE: 39-30 Refurb - morzh - 05-14-2015

How's your speaker spider and/or the cone glueing job?

The best way to exclude the speaker is to use another speaker.
Base is close to resonant frequencies of cones and so if there are things wrong with damping structures, this is where it might show up.

I would start with another speaker first.

RE: 39-30 Refurb - Nick3092 - 05-14-2015

The speaker looks good overall. I don't have another speaker handy. I may have a small 4" PM from a car somewhere I might be able to dig up and connect to the voice coil. The signal tracer I know is handy, which is why I was going to put that on the OP plate.

RE: 39-30 Refurb - Nick3092 - 05-14-2015

I swapped out the 6A8, 75, 78, and 37 all one at a time, and none really made a difference. Except for the 6A8, but I think that is because it was weak. It cut down on the signal strength all around. I grabbed the 6A8 out of my 38-10 and it acted the same as the other NOS 6A8. So I think that is just confirming when my tester said, the original 6A8 is on it's way out the door.

So I broke out the signal tracer. I checked the plate on the 41, and it sounds like the distortion is still there. Went to the grid on the 41, and it sounds like it was gone. So I grabbed the 41 out of my 39-6 (which was an NOS tube with very low usage on it in my 39-6) and put it in. The behavior was the same. Now, I'm not sure if that's just becasue the signal tracer was amplifying an already amplified signal off the plate. I was pretty sure I had the signal tracer volume low though. I can always check again later. Voltages look good on the 41 - actual (schematic) - plate is 198 (205), Screen 208 (215), Grid -14.5 (not listed, data sheet says -13.5 with 180v plate/screen, so this seems reasonable).

So, any other ideas?

RE: 39-30 Refurb - Nick3092 - 05-14-2015

I went over the whole circuit from the 78 IF to the voice coil with my sig tracer. Sometimes I think I hear it, some times I think i don't. I guess I'll just need to dig up a PM speaker and try that. I'm assuming I just need to desolder the two voice coil wires and lift them and then jumper them to the PM, correct?

RE: 39-30 Refurb - Nick3092 - 05-15-2015

Also, what are the odds I could try the speaker in my 40-180? This morning I just remembered it has the same shape connector. Assuming the field coil is on the same pins, would that work? It looks like the field coil on it has less resistance though (1100 in the 40-180 vs 2000 in the 39-30) and the voice coil grounds to the speaker frame in the 40-180, which it doesn't in the 30-39. That way I don't have to try and find a PM speaker probably burred somewhere in my parents basement and mess around desoldering anything.

40-180 schematic:
http://www.nostalgiaair.org/PagesByModel/336/M0013336.pdf

RE: 39-30 Refurb - morzh - 05-15-2015

You have to watch the pins, I do not know. I never go by "what are the odds", I ptake the documentation or measure it with a meter.

As for the field, I would add 1K 3-5W resistor in series not to stress the output.

RE: 39-30 Refurb - Nick3092 - 05-24-2015

I finally got around to hooking up a PM speaker. I lifted the 2 voice coil wires off the original speaker and jumpered them to a PM speaker I picked up in my last DK order (easier than digging one out of my parents basement). This is the speaker, if it matters: http://www.digikey.com/product-detail/en/GF1004/GF1004-ND/304447

Anyway, still sounds distorted on the mid and full bass settings. Not sure if that speaker is just too small to handle it, or if that means I do have an issue else where.

RE: 39-30 Refurb - Nick3092 - 07-30-2015

I finally got around to wiring up a 3.5mm jack using 2-100 ohm resistors to tie L and R together, and then coupled it using a .1uf film cap to the high side volume pot and another .1uf to chassis ground. I disconnected the audio feed from the 2nd IF from the high side of the pot as well. I had the original radio speaker hooked up.

I queued up the same song (Sing, Sing, Sing by Benny Goodman) on both my ipod and my SSTRAN. First I played the ipod. I had the volume control all the way up on the iPod, and adjusted it via the volume pot on the radio. I rotated through all 3 tone settings with no notable distortion out of the speaker. The tone controls affected the sound exactly as they should.

I then disconnect the jack and put the line from the 2nd IF back on the high side of the pot and played back the same song via my SSTRAN. I got the distortion again on med and high bass settings.

So, I think that means I can say for sure the audio stage, tone controls, and speaker are not causing the issue. So now I'm left trying to figure out what in the earlier stages is causing some kind of distortion that is being filtered out on the "no bass" setting, but comes through on the other 2 settings.

This type of problem is new territory to me, so I'm wide open to suggestions.

RE: 39-30 Refurb - Radioroslyn - 07-30-2015

Hi Nick,

<So, I think that means I can say for sure the audio stage, tone controls, and speaker are not causing the issue. So now I'm left trying to figure out what in the earlier stages is causing some kind of distortion that is being filtered out on the "no bass" setting, but comes through on the other 2 settings.

If I'm reading your previous paragraph correctly your issue could be in the 1st audio stage. So you know the drill check plate,grid, and cathode voltage for anything that seem hi or low.
Check 31 to see if it is open, 32 gone high, replace 34 for the heck of it.

GL
Terry

RE: 39-30 Refurb - Warren - 07-30-2015

Nick. Sing sing sing.... you have good taste. I have the original record of that song, very rare. Worth about 150.00. Great song.    ; D

RE: 39-30 Refurb - Nick3092 - 07-31-2015

Warren - That is a nice record to have!  i started getting into the big bands and early jazz once I started working on/collecting tube radios.  I wanted to hear what they would have sounded like playing the music from that era.  And suddenly i found my self enjoying it.  10 years ago i would have called myself crazy...

Terry - I replaced all resistors when I refurbed the radio.  R31 is reading 3.98M and R32 is 69.7k.  Both spot on.  I also replaced all mica's, so C34 is brand new.  I did check voltages way back when i first powered it on, but can't find the numbers.  But i do recall them all looking fairly good.  But I rechecked them.

Below is what I read, and in parentheses is what the schematic/service notes say (a few are hard to read, those have ? marks).  I had the variac on 115 to start, but it drifted down to 114 by the time I was done.  Radio was on BC and tuned to my SSTRAN (the service notes didn't say if it should be tuned to a station or not), but with the volume all the way down.  All readings VDC and to chassis, except where noted.

C43 - First filter
Pos to CT: 318.2 (325)
CT to Chassis: 14.88 (15)

C18 - Second filter
209.8 (215?)

C17
184.6 (190?)

84 Rectifier
Cathode: 303.9 (310)

6A8 Det/Osc
3 Plate: 209.8 (215)
4 Screen: 77.8 (80)
5 Osc Grid: -26.6 (n/a)
6 Osc Anode: 161.9 (175)

78 IF
2 Plate: 210.7 (215)
3 Screen: 78.0 (80)
4 Suppressor: -2.88 (n/a)


37 2nd Det/AVC
2 Plate: -5.11 (n/a)
3 Grid: -4.38 (n/a)

75 1st Audio
2 Plate: 143.1 (135?)
3 &4 Diodes (tied together): -5.69 (n/a)

41 Output
2 Plate: 203.8 (205)
3 Screen: 213.9 (215)
4 Grid: -14.02 (n/a)

Over all, nothing is jumping out at me as blatantly wrong.  B+ is a touch low - about 5 to 6v, but that shouldn't matter much.  The 75 plate is a little high, but I suspect that is because the DMM isn't loading the circuit.  The only other reading that is off is the osc. anode/"plate" that is about 13v low.