[Joeztech]

Jcassity;

First I looked at the plates of the two diodes of the 7C6, which are tied together. It showed simultaneously both the 455KC IF signal and the Audio signal. Then moving onto the junction of the 3.3M ohm resistor and the .06uF to the volume control you see the detected audio. From there you can trace it to the signal grid of the 7C6 and then its Plate viewing the audio signal and its amplification at its Plate. From there it can be also traced through to the Plate and Cathode of the 6J5 Phase Inverter and on to the signal grids of the two audio output tubes.

A good scope is a very valuable tool to use. It can show you both the RF signals including the local Oscillator then the signal level increases through the IF circuits. It makes it easy to spot problems along the way. I am using a Tektronix 2335 oscilloscope which is a 100mHz capable scope. Even a scope capable of say 10 or 15mHz would be fine for working on most AM/SW radios of this vintage. I also like to work on vintage AM/FM tuners and receivers, so the extra bandwidth is useful in those cases. I originally bought the scope for $80 and have had to replace some capacitors in it, but still my overall outlay is less than $100 for a very useful tool. I am not saying everyone can find a good scope for such a low price, or manage to repair it if it fails, but with good searching  and help from people here you can likely put together a very good set of equipment to help you in your repair and restoration projects.

Joe

[jcassity]

I've got a lot of time using a scope and other stuff as an AT in the navy. usually testing to component level doing tests like "check for this X freq riding on X value dc signal or check here for x value ac ripple on a particular DC level etc. Ive never really had a lot of experience using a scope dedicated to the task of signal tracing as a primary.

Im told i best have an isolation transformer for a scope if i keep tinkering with this stuff. To be honest, i know you can but never did, but you can use a scope like you would a multimeter,, it does all the things a meter can do plus more but when you have a huntron and a meter or Simpson 360,, why hook up a scope to start trouble shooting when step two is typically resistance checks, step 1 being a visual.

glad you found that problem, i was paying real close attention to see if you stumbled on the reason why i can now elimininate that big resistor i had to use.

[Joeztech]

Jcassity;

I have a nice Variac Isolation transformer that I could use, but I have a decided dislike for AC/DC type chassis radios and seldom ever work on one. And I had a couple of AC/DC Admiral chassis that I used to repair one for a friend, but as soon as it was gone, I scrounged the two donor chassis for parts and threw the rest away. I do not intend to own any AC/DC radios.

You may want to go back to page 3 of this thread and compare the AC and DC voltages I measured at the 5Y3 rectifier socket both with and without the tube installed. Compare in particular the AC voltages coming out of the power transformer to the plates of the 5Y3 to what AC voltage your unit's power transformer is delivering to the same pins 4 and 6. If you see a much higher AC voltage there that would explain why you had to use a much larger power rated resistor in your radio. Keep in mind too that if the AC voltage is the same but the current capacity of the transformer secondary is greater, you have to dissipate much more power before you can get the downstream DC voltage to the desired level. Unfortunately we do not know the full specifications of the Philco original power transformer, but since this example still has its original transformer, it does at least give a fairly accurate set of voltage readings to compare against.

After much work I got a new Loctal socket installed for the 7C6 tube only to discover that I could not plug the tube into the socket. By that time I was so irritated that I decided to take it out and install an Octal socket and a 6SQ7 tube that has the same characteristics but just a slightly higher amplification factor. As I took out the Loctal socket I saw that I had managed to get solder to wick down into a couple of the contacts, thus making installation of the tube all but impossible. In any case I made the change to the 6SQ7 and Octal socket and this works very well. The set now comes on within 15 to 20 seconds or so. I noticed that although Philco had used a center-tapped filament secondary for the 7C6 and 6J5, they had not bothered to twist the filament leads going to those two tubes. Since filament wires radiate AC energy, I decided to twist together the filament wires coming from the power transformer to help eliminate radiated 60Hz energy around the two audio tubes. After getting the radio operating again, I do believe there is less residual 60Hz hum now.

As it turned out the Bozak preamp is just not usable in this radio. I tried two different magnetic cartridges and there is some sort of distortion when bass drums or bass notes are struck which makes a sputtering effect in the audio. No amount of tracking force or anti-skating adjustments with either cartridge made any difference in the distortion I was hearing. If there had been a difference between the two, one cartridge/needle assembly could have been bad, but instead both sounded exactly alike. So reluctantly I have ordered a Vaco/Varco TN4 ceramic cartridge and needle from eBay. The higher output signal will not require a preamp so the audio circuitry will be less complex. Fortunately the Bozak preamp only cost me about $15 and the Vaco/Varco cartridge is less than $18. I may eventually find a problem in the Bozak preamp, but it is not high on my project priorities. It uses two transistors in each channel. There may have been less of a chance of problems if an IC had been used. I have some 4858 Op Amp ICs I could use and may build up a preamp to take the place of the original Bozak circuitry.

Joe

[Joeztech]

Yesterday the Vaco/Varco TN4 replacement cartridge and stylus assembly arrived. I finally got around to installing it this morning. This involved removing the Bozak preamp from the circuit completely. I disconnected the 150K ohm resistor under the chassis of the radio that is the load resistor for the original Philco cartridge. I temporarily tacked a 500K ohm variable resistor in circuit for the new cartridge load and started the changer. With the record playing and both channels of the cartridge bridged together with a Y cable, I adjusted the variable control for maximum volume and best tone quality. It turned out that the best total resistance was about 312K ohms. I used a 270K ohm and a 47K ohm resistor in series to provide the load for the new Vaco cartridge. There is lower residual 60Hz hum with the ceramic cartridge and the volume level is higher with no audible distortion. The tone response is adequate throughout the tone control adjustment range.

I can now close the unit up and concentrate on cleaning up the cabinet and repairing some veneer delamination.

Joe

[Joeztech]

Over the last two days I used some GoJo waterless hand cleaner to clean the cabinet surfaces. I used cotton Q-tips in hard to reach spots. The top right area had veneer coming loose, so I may either take it off or thin some Elmer's white glue and work it up under the veneer, then apply clamps as it cures.

The right side of the cabinet has some missing pieces of veneer at the back edge. I managed to save a few pieces that came off and will put them back on and work some of the glue up under the mating edges where they are loose then apply clamps to finish the re-gluing. I have some red oak veneer that has similar wood grain that I can use to patch the areas that remain on the right side, then stain to match as closely as possible and add some clear lacquer to complete that side.

The front changer tilt-out had the top edge veneer so loose that a slight tug made the entire piece come off. I plan to use the red oak veneer package I bought to make two new pieces, in a mirrored effect if possible. Then I will apply some stain to match the vertical wooden ribs over the speaker area and apply some clear lacquer to the mirrored veneer pieces.

The vertical ribs had about 50% of their original lacquer finish flaked off. I removed the rest of the finish there and then applied some paint thinner to bring out the original stain. Then I took pictures to show what it looked like (minus the veneer on the top of the changer tilt-out).

Here are some pictures of how it looks after cleaning.
   
   
   

[Joeztech]

In the previous set of pictures the front ribs over the grill cloth have had their lacquer removed and were cleaned with some mineral spirits. They were left several days to thoroughly dry. I wanted to apply fresh lacquer to those ribs and noticed that the speaker baffle board was mounted using 6 wood screws from the back side. I wanted to get the grill cloth out of the way before applying finish. I removed the wood screws and lifted the speaker out of the way only to discover that the grill cloth is fastened to a separate thick cardboard form in front of the speaker and nailed to the wood from the back side. I have doubts that I would be able to get the nails out without damaging either the cardboard or the cloth. I have some craft paper and I think I will use some it placed in front of the grill cloth but behind the ribs from the front side. That will keep the lacquer off of the grill cloth.

The grill cloth on this radio is not an exotic type and could be replaced, but it is in good shape and it will be less time consuming to leave it in place, protected and proceed with the finish process.

I will get some more pictures soon to show the cabinet.

Joe

[Arran]

The veneer used on the sides is French walnut, not red oak, probably straight cut judging by the grain. If you have some French walnut veneer scraps those will make a good good patch material. Make the patches first, and make them larger then the areas needing repair, and irregularly shaped so that they roughly mimic the wood grain, then place the patch over the chipped area with tape, and cut around the outside of the patch into the veneer under it. New walnut veneer of any species is fairly easy to get, there is a guy on fleabay who sells lots of surplus veneer left over from fitting out yaughts and private aircraft, and there are others that will see you smaller amounts too.
Regards
Arran

[Joeztech]

Arran;

Thanks for those suggestions. I did some searches yesterday for French Walnut but came up empty at the time. I was mainly looking on Rockler's website. They do not have everything. I will check some other locations.

So far so good - the veneer I added on the tilt-out looks good. I had a few pieces of the French Walnut that had cracked off of the side and have already managed to glue those back on as well as regluing some areas that were loose.

Joe

[462ron]

Joe, try Constantines Wood Center for veneer!

Ron

[Joeztech]

This one appears about right:
http://www.constantines.com/walnut-frenchstripe.aspx
I may let the customer know about this and allow them to pursue replacing the veneer using a local cabinet refinisher.
Thanks.
Joe

[DavidHTO]

Is the schematic in the attached for Code 122?  It was a photostat I made many years ago from the archives of the Boston Public Library (l...o...n...g... before the Internet) and I note it shows the 7AF7 which is NOT in the Code 121 version. If this is the 122, where do I find the three updates that I need to complete the schematic for a 125?

Thanks

David

[jcassity]

wow,, i think,,, i really think i might be the only one here who has the exact answer.

your diagram seems to be a code 122 print... yes the 7AF7 superseded the prior codes which was 7F7.

There was never a print made for the 46-1226 code 125 period,,, noda!!!
what you do is use the code 122 prints but you integrate all the changes manually in your minds eye or physically with parts to meet the "typed out only" changes provided for code 125 run 1,, run 2 and Run 3.

the philco workbench can get you the prints.
I can get you copies
either way go to our resources page and order them up ,,, they come from a member here and it was really cheap.

what this boils down to is "how you ask for prints".

you say,,,,
"i want prints for a philco 46-1226 code 125 which consisted of 3 run numbers.  run 1, run2 and run 3.
You wont really know very well which run number you have until you get a print of code 122 in front of you.  Still you will need the typed out text documents that integrates all the changes pertaining to code 125 run 1,2 & 3.

I can help any time at 304 772 3411

also,, here is the link to my 46-1226 code 125
I think i have come a long way since this resto but i still got a lot to learn.
to save you a lot of reading time,, i took all my lessons learned and put them into post #1
http://philcoradio.com/phorum/showthread...ht=46-1226



>>>>
here is the meat of it below but please look over my thread because if i recall correctly,,, towards the middle i finally was posting pics of all the stuff i needed to resto this set.

edit update to this post 1- date of 25 april 2017
For the subject line of this thread, during the restoration i found out i would need to be using the 46-1226 code 122 prints.
Code 121 is close, but code 122 are a match BUT,, there are updates to to the code 122 such as some filter cap changes, PM speaker mod and power supply secondary re-wire tasks.  THERE IS NO KNOWN print to specifically match code 125,, dont even ask.  in order to restore a 46-1226 code 125, you must combine code 122 prints and the updates which will then equal code 125.  

5may2017 update= lessons learned- If you obtained a set of prints from Chuck at the philco work bench **and** you are restoring a code 125, ****USE ONLY*** the fold out schematic for rewiring as this iwll accuratly represent the changes pertaining to the V1 7AF7 tube socket updates.
You will recieve a technican repair guide pamplet and that represets the component layouts for an *earlier* radio version.,,, use the pamplet as a guide only but revert to the fold out schematic to work through your troubleshooting or repair.
if questions call scott at 304 772 3411, thats me.

[jcassity]

oh,, and by the way,,

it went like this...
code 121
code 122
code 125
there was never any codes 123, or 124

[jcassity]

the major 2 things of many on code 125 was you have a PM speaker and your transformer became wired differnently than the previous code 122... just sayin'
so be careful... i stayed confused for a long while till i got my head around one single concept..........
only use the fold out schematic for code 122 **and** the typed out text pertaining to code 125 runs 1>3.

the philco workbench sent me a good bunch of info but...
they provided a booklet that broke up the radio into sections on individual pages.

there was an insert fold out schematic that also had dark lines around "sections".

i have no idea why but ignore the booklet !!!!!!!!!!!!!!!!!!!!!!!!!!!!
Just use the fold out schematic.

i suspect the booklet is early code 122 and the fold out schematic (what you want) is later run 3 code 122.

[DavidHTO]

Okay, yes, I was aware of the PM speaker.  Where can I obtain the "fold out schematic for code 122 **and** the typed out text pertaining to code 125 runs 1>3"

Thanks

David