[Arran]

Sorry, I did not notice that the original dial was already partially wiped off. I seem to recall that there was another source of those dials other then Radio Daze, the one I have has a reproduction dial that I think came from Antique Electronic Supply. but they were not the ones who made it.
Regards
Arran

P.S I think that Mark Oppat used to supply them, maybe contact him and see if he still does as I believe he bought the equipment from the fellow whom used to make them for AES?

[eewill]

Okay. I see the replacement dial at radiodaze. I may end up ordering that at some point. I'm going to go do some more reading. still trying to figure out which caps are the most critical to replace. Is it mainly the electrolytic I need to worry about? The schematic doesn't really indicate which are electrolytic, does it?

In the meantime, I am going to continue cleaning. Every time I remove a part or shield there is more dust and dirt.

[dconant]

Hello Will, Part #67 is the electrolytic. There are two caps in there and they connect to the high voltage center tap and not ground. You will want to replace all the paper caps one at at time and test the radio as you go. I swap out the ecaps before powering up for the first. Once you replace them bring the radio up slowly on a variac watching for high current draw. You might want to check the power transformer for continuity with all tubes and pilot lights out. The 5 volt winding will be on the fat pins of the 80 tube, the high voltage winding will be the small pins of the 80 tube, the 6 volt winding will be the fat pins of the other tubes (75 or 78 will do). The high voltage center tap can be tested between the connection of the ecap that is connected to the shell of the ecap. Test from there to each of the 80 fat pins. You should read roughly half of what the reading is between the fat pins of the 80 tube. The ac winding you can test from the plug with the power switch on although the power switch might be bad. A little contact cleaner usually fixes that. You might want to test the speaker as well. On the speaker there will be the connections to the field coil and output transformer under that metal box. The two big wires are the field coil and the output trans connections will be coming directly off the trans. The field coil and trans will share a connection. The top wires of the trans is the primary. The secondary connections are at the bottom. When you read the secondary you will be reading the voice coil as well so might want to isolate one of he wires going to the voice coil. The schematic shows all the resistance readings I just mentioned. One more thing most of the capacitors are in those bakelite blocks.

I'm sure others will chime in.

Good luck and keep us posted.

Dan

[morzh]

Radiodaze seems to have 625, 630 and 640 dial glasses.
Which one fits the 620?

[RodB]

Hi Will, the schematic has a parts list. All capacitors on the list that are electrolytic and tubular should be replaced. The tubulars are paper capacitors; 80 year-old paper deteriorates.

Mike- Radio Daze has a dial for the 620.

[eewill]

Lots of good information. Thanks, guys. I'm just about to the limit of what I can clean without fully removing things.

Looking forward to the weekend to spend some time on it. It sounds like my best bet should be to walk through the schematic and find the actual components in the radio. Make a list of electrolytic or paper tubular capacitors to order replacements. It sounds like some some of you try to stuff the old components where possible to keep the original look. I like that idea.

I noticed several of the metal "cans" on top have a couple of screws plus three or four spring clips that push through the chassis. Is there an easy way to remove those? Not sure if they will need to come off, but I tried to remove one for cleaning and I couldn't get clips to push through one at a time.

[Arran]

I had a look, online, of photos of the underside of other 620 chassis, and they seem to have a mix of tubular and Bakelite block caps. The latter are a good idea to restuff as the terminals on top do double duty as terminal strips for the resistors, and other wiring, what is good about this example in particular is that it looks like they were all left in place by previous repairmen, like whomever added the Olson brand caps in there.
As I mentioned I have a model 620 myself, and whilst I haven't used it in a long time I can recall that it was a good performing radio, likely due to the tuned RF amplifier stage. I can't remember what the difference was between the 620 and the 630, I believe that the latter had a shadow meter above the dial, the 640 had a shadow meter and a push pull output stage I think, but it also had a bigger chassis.
What I would not mind getting is a late version of a 116B, it had a different cabinet then the early version, my late uncle had one years ago. The early version looked like the 620 but with a larger cabinet, and a fancier front panel, the rest had the same dark lacquered poplar covered arch, with shoulders, just wider, and deeper.
Regards
Arran

[MrFixr55]

Hi eewill,

Welcome to the Philco Phorum,

As grungy as the top pf the chassis is, the underside looks good. If you have knowledge of analog solid state electronics, you are 3/4 of the way there.

Below is a link to the World Radio History website that has many very cool documents. The link is specifically to a PDF copy of the 1937 RCA Receiving Tube Manual, version RC13 which will have the specifications and "pinouts" for all tubes used in your radio:

https://www.worldradiohistory.com/BOOKSH...13-OCR.pdf

The first chapter discusses vacuum tube theory. Funny, this chapter was first written in 1930 or before and was in every version of the RCA Receiving Tube Manual until the 1975 RC30 version and is essentially unchanged except for the addition of Beam Power tubes and CRTs. There are sections that describe the individual vacuum tube circuits as well as example buildable circuits, such as amplifiers, TRF and Superheterodyne radios, etc, whose theory is well described.

A great book, if you can find it is the US Navy training manual "Basic Electronics", by VanValkenberg etal, published by John Rider. Here is a link to Internet Archive where the book is available as a PDF
https://ia801405.us.archive.org/29/items...955%29.pdf

As a "Baby Boom" child, one of 6 children in our 1960s middle class Irish - German Catholic family, I was the weird kid on the block, not good at socialization or sports (I was eventually diagnosed as autistic) but had a great interest in "how things work", and fortunately, I was smart. I taught myself electronics by reading books from the library and those that Dad and Mom gave me for Christmas, and from radios and TVs given by neighbors or obtained from those boutique stores Offenderstrasse and offthestreetini. I learned mechanics the same way from discarded bicycles, lawn mowers, etc. Funny, as kids my age found out my skills, I was more accepted. In addition, y skills at plumbing, electrical and auto mechanics exceeded my father's skills. Rather than being insulted, he was rather proud. Of course, by the age of 12 my level of chores increased from cutting the lawn to repairing the family cars, (including replacing transmissions, clutches, rear ends, rebuilding engines, etc.) Household plumbing and electrical work (including replacing the water heater, repairing leaking pipes, etc., and keeping our ancient TV functioning.

Bachelor's Degree is in Clinical Lab Technology, but I "morphed" my education and lab experience and my hobbies into a 41 year career a Field Service Engineer, then a Technical Support Specialist for a bio-medical corporation, from which I recently retired.

Hope this helps.

[eewill]

Definitely a resounding yes on the restore. A lot of experience here if I have questions!

I have a computer engineering degree (EEC). The only courses that degree lacked from a standard EE is power and thermodynamics. I graduated from LSU and went to work for AMD (Advanced Micro Devices) in a division that made ICs for Telephony (both central office and house side boxes). I started out as a test engineer and eventually moved into an analog design position at Motorola working on mixed-signal ICs. This is early 2000's so everything on chip used MOSFETs as much as possible. I went through a couple of mass layoffs as the tech bubble burst and companies struggled to stay in business for a while. Eventually, I decided to look for something more stable and changed to doing data analytics and reporting in the healthcare industry. I get to work with my other interests, programming and math.

While a lot of those skills are a bit rusty, I still take on personal projects from time to time to get my engineering kicks. I have built my own quadcopter (drone) and 3D printer from scratch using online plans. All-in-all, the only daunting part of this restore is getting started and keeping track of all the components. While I've done some breadboarding that looks similar to what's underneath the chassis, that's a whole other level! There will also be a bit of a learning curve as I figure out how the thing works.

Looking forward to getting started. If I had one request to make it easier, it would be a part order list to get started. That may remove some of the fun of the project though. I don't have any components on hand at the moment.

If I'm understanding you guys correctly, my first order is to deal with the capacitors. I can see how the early construction methods would degrade over time. I am looking to catalog electrolytics, paper, and bakelite caps for replacement? correct?

[eewill]

@MrFixr55 - oh man. What a great background and quite a journey. I will definitely be checking out those books. You guys are a fount of knowledge.

[radiorich]

Hello eewill,
Making a list of parts that you will need is fairly simple and I will try to make time today to post one for you consisting of Electrolytic and film capacitors that you will need .
Sincerely Richard

[radiorich]

Hello eewill,
First thing we will need to do is to figure out if it's the late or early run chassis .
They made some different parts changes.

Also There these little bakelite blocks held in with one screw with wires tied to them those consist of capacitors and tar they will need to be gutted and new capacitors installed .

Sincerely Richard

[eewill]

@radiorich - I noticed there were two schematics for early and late versions. Is there an easy way to tell between the two?

[Arran]

I think that the most critical components to replace, before a power up, aside from the electrolytics, are the audio coupling caps between the #75 1st audio tube, and the #42 power output tube. I would also see if there is anything between B+ and ground such as bypass caps, the tone correction caps can be clipped out of circuit temporarily for testing, and in the case of the tone control switched out of circuit. Did anyone link to this before, it has both early, and later 620 diagrams, an under chassis part placement diagram, and two parts lists?
https://philcoradio.com/library/download...l.%201.pdf
Regards
Arran

[radiorich]

Hello Arran,
I link the schematic in the first post I did .
Sincerely Richard