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Philco 3630 motorboating - Printable Version

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RE: Philco 3630 motorboating - bridkarl - 11-03-2025

I’ve got a motorboating issue also. Arrgh.

Anyway, Caig stuff works well. I have found it best to spray some into a plastic dish and then use lint free q-tips - they make them for watch repair and salon use. Spraying from can onto switches is no bueno. Use as little as needed directly on the contacts. I also can spray a business card and work it carefully under contacts - like relays.
I don’t especially like the long black spray tube that comes with the can.
I’d read the product sheets - D5 and F5 have different applications - I think that F5 is more for fader cleaning like for pots as opposed to switches. I’ll stand corrected if I’m wrong on that.

RE: Philco 3630 motorboating - bobclausen - 11-08-2025

I dod clean the switches carefully with Deoxit but it made no difference. I then saw a Heathkit signal generator on Marketplace. I bought it from a lady whose husband had passed away. She said it worked well for him and I figured it should help me in this hobby as well as in checking my Philco.

I’m embarrassed to say it but I read the Heathkit instructions, twice, but am still confused as to how to properly connect it. I worked with my hands all my life and I learn from watching not reading. I couldn’t find a For Dummies version online on how to use the SG-8 nor could I find a youtube video.

What I did was to connect my multimeter to the voice coil, one lead from the SG-8 RF output went to ground on the chassis and the other lead with a .1 cap to pin 4 on the underside to the 6A8. It was set to 470KC. I got no difference in sound/AC/DC voltage when adjusting the IF cans.

I have no electrical background and would appreciate any advice on what I may have done wrong, connected improperly. Any suggestions on how to use this SG-8 would be greatly appreciated.

RE: Philco 3630 motorboating - KCMike - 11-08-2025

Hello, you might try this video and see if it helps you
https://www.youtube.com/watch?v=XrVS5B6i9io&t=23s

RE: Philco 3630 motorboating - RodB - 11-08-2025

The 6A8 signal grid is the tube cap. Try connecting the 0.1mfd capacitor to the grid cap. You should hear a tone if the signal generator is modulating the 470kHz carrier.

Set the Modulation to Int and the AF level to about half on the generator.

RE: Philco 3630 motorboating - bridkarl - 11-08-2025

What unit do you have? I own almost every iteration of Heathkit signal generator so I may have the manual.

RE: Philco 3630 motorboating - bobclausen - 11-08-2025

KC Mike. I did watch that and thanks for forwarding that video.

Rod. I did have a .1 cap but wasn’t sure whether I was supposed to attach it to pin 4 under the chassis or to the grid cap. I will hook it up and set up the SG-8 as you described. 

The language used in the manual appears to me to be written for people with a basic electrical background. I have trouble with all the scientific terms that are used there. The kids in the ‘50’s making these kits were a lot smarter than I am in my ‘70’s. ?   

Bridkarl. It is a Heathkit SG-8. Thanks but I don’t need a manual. I have one…I just have trouble understanding it.

Thanks again for all the help.

RE: Philco 3630 motorboating - RodB - 11-09-2025

Bob, any signal you apply to pin 4 will be bypassed to ground. Pin 4 is the screen grid which has a 0.1 mfd bypass cap to ground in addition to the power supply output filter cap.

RE: Philco 3630 motorboating - bobclausen - 11-09-2025

Thanks Rod. Should I connect my DMM to the voice coil or to the plate and cathode of the 6F6 while I’m testing the Intermediate Frequency Circuit?

Also do I take the grid cap off the 6A8 tube to do the adjustment on the IF?

RE: Philco 3630 motorboating - RodB - 11-09-2025

If you get interference from the antenna then try removing the grid cap.

You can leave the DMM on the voice coil to measure AC voltage. I usually measure the AVC voltage because it's more stable.

RE: Philco 3630 motorboating - MrFixr55 - 11-09-2025

Hi Bob,

Welcome to the Phorum and to this hobby. Please don't be afraid to ask questions; we are very happy to help!

Did it work before you disassembled the sub-chassis to replace the capacitors (aka condensers, aka "caps", not to be confused with grid caps)?

Make sure that there is continuity between the sub-chassis and the main chassis.

As said by others, the positioning of the wiring (called "lead dress) is important in all areas, but critical in the RF and IF areas.

Try this:
Remove all tubes except the detector / 1st AF, output and rectifier. Raise the volume, determine if there is excessive hum or motorboating. If so, the issue is in the audio circuit. If not, install the IF amp and repeat the test. If motorboating, troubleshoot the IF section. If not install the convertor tube, and so on and so on.

Check your work against the schematic. Unfortunately, because this is a multi-band set, it is not easy to follow the schematic. The screen grid circuits usually consist of a resistor from the common B+ circuit. There should be a cap (capacitor) between the screen grid connection on the tube to ground. Same thing for the B+ to the plate of the 1st AF tube. If these parts are bad, missing or mis-wired, motorboating will occur. On your set, it is cap # 20, a 0.1 uF cap

In addition, caps # 62 and 60 are drawn incorrectly. Ensure that the positive leads of these caps go to either side of the speaker field coil, which also acts as a filter choke for the power supply. the negative lead of C60 goes to chassis ground. Please note that the negative lead of C62 does NOT go to chassis ground but to the center tap of the secondary winding for the rectifier on the power transformer. This is common on pre-war sets, almost acting like a C- supply instead of cathode bias on post war sets. Note resistor 61, a "voltage divider. With power off, measure between chassis ground and the center tap of the HV secondary of the power transformer. You should read 245 Ohms give or take about 10 - 20%. If any part of the resistor is open than all sorts of bad stuff will occur.

Check Cap #18, which is the filter cap for the screen circuits and 1st AV B+, and cap # 20, the bypass cap for this circuit.

An important cap is the AVC filter cap. IN this set, there are two; #15 for the convertor and #5 for the RF. Also check cap # 35, the IF cathode bypass cap. Note that these caps connect to the AVC through the band switch. If the band switch is dirty, this can happen. Caig DeOxit D5 is the correct stuff to use.

Hope all of this helps. Keep us posted!

Another important "cap" is #54 which decouples the bias voltage for the 1st Audio Amp.

RE: Philco 3630 motorboating - bobclausen - 11-09-2025

MrFixr

Thanks for all the help. I will get to it as soon as I can. We’re actually just getting our first snowfall and my wife is reminding me that I should have gotten the yard ready for winter.

I will report back in a couple of days.

Yes the radio was working. I took it apart to do the caps and resistors and then had to do it again to install the chassis supports from Renovated Radio.

RE: Philco 3630 motorboating - bobclausen - 11-10-2025

MRFixr

I was re-reading your notes this morning and am a bit confused.

You said to remove the output and rectifier tubes, no problem there but I’m confused as to your reference to “detector / 1st IF”. The 6Q7 is referenced to on the schematic as the 2nd detector but 1st Audio, whereas the 6A8 is referred to as Detector/ Oscillator.

I just want to do that test properly so I don’t post incorrect information.
Thanks

RE: Philco 3630 motorboating - bobclausen - 11-11-2025

I left the 6F6, 5Y4 and 6Q7 in, took all the other tubes out, as MrFixR suggested, and still got motorboating on all bands. I do receive the two local AM stations but when I turn the volume up it starts. The volume does increase slightly when I touch the 6A8 cap.

My electrolytic’s are wired correctly and cap 20, 54, 15, 5 and 35 all measure properly. I took the chassis apart again to access a couple of those caps and to recheck #6 resistor which measures correct.

My bias resistor measures right on at 245 ohms from the chassis to center tap.

It was D5 that I used to clean the switches. I ordered both but I had already read that the F5 was for pots only.

I had replaced almost all of the resistors on the 8 lug terminal board on the side of the chassis since I had to disconnect one side to measure them anyways. The 2 side by side 1 megs, #44 and #50, were ok. That was done when I initially did the paper caps.

Should I order new terminal strips to replace that existing 8 lug terminal board? The soldering looks decent but I don’t have any issue with doing that if that could be the issue.

Again I want to thank all you gentlemen for your assistance!

RE: Philco 3630 motorboating - MrFixr55 - 11-11-2025

Hi Bob,

With only the audio tubes and rectifier in, if it motorboats, then that eliminates most of the rest of the radio. Concentrate on the audio section. Measure between the 6Q7 grid cap and chassis ground. It should be about 1.5MOhm. Does the motorboating change with the position of the tone control switch?

RE: Philco 3630 motorboating - MrFixr55 - 11-12-2025

Another thought, rare but possible that the 6Q7 may be gassy.

Re the DeOxIt, yes, F5 is for "pots" (potentiometers like volume and tone controls), but would not be tragic if used on switches. However, using D5 on pots can destroy them.

Re the snow and the wife reminding you that you did not get the yard ready, I hear you. I had always wanted a generator in case of a storm and had weathered quite a few, not often but enough to pay for the generator in lost food. Ms. Fixr thought it was an extravagant big boy's toy. Then Storm Sandy threatened to hit, and Ms. Fixr suggested 2 days before the storm that I consider buying a generator when the big box stores were all sold out and any small vendors who actually had some no-name Chinese 3500 Watt generators for sale were selling them under a huge markup.

We were without power for 4 days. Since I worked from home as a tech support help desk specialist, I had to take vacation days. (Amazingly Verizon Internet was back up a day after the storm, but I had no power. When we got power back, we were giving power to neighbors whose backyard abutted us because their phone pole and transformer fell. They were without power for 10 days. A few days later, Lowes had a sale on generators that were returned unused or when a big shipment finally arrived. So, closing the barn door after the horse escaped, Ms. Fixr urged me to buy one.

I bought what I thought was a US made 5500 Watt unit. (You can tell by the cardboard, and that it did state on the box country of origin USA.) Well, the Chinese motor, Chinese generator and Chinese outlet box was installed in a cradle in the USA. Needless to say, I was )!$$ed, because If I had to buy a Chinese generator, I could have gotten a 6KW electric start one for the same price. (I am now 70 years old, have arthritis, and pull-starting a 420 CC 11 HP motor with an alternator rotor permanently attached in freezing weather is not fun. I guess that is why the Good Lord gave us ether starting fluid.