Powering Up Heathkit Model GR64 Shortwave Receiver After 55 Years - Page 1
Forum section: electronics / repair

author: electromotivetrains
author_rank: Newbie
timestamp: November 12, 2024, 02:25:34 am
content: Hello all: I built this Heathkit Model GR64 shortwave receiver and Q-Multiplier (model GD-125) 55 years ago. It hasn't been powered up for at least 53 years. It worked fine when last used. Been sitting in my basement. My question is this. What process should I use to power this thing up gently. Not sure if the capacitors are still good etc. I have a FLUKE digital voltmeter and a RCA Isotap II (model WP-27A) isolation transformer that has multiple secondary output voltages that can be selected ranging from 25 vac to 150vac in 25 volt increments. I have all the original assembly manuals and schematics. Any advice would be greatly appreciated. Some pictures are attached as well...Thanks (11/11/2024 9:20 pm EST (New York)

author: MathWizard
author_rank: Super Contributor
timestamp: November 12, 2024, 04:50:29 am
content: Hi, yeah it must be cool to be looking at something you made that long ago. Probably the easiest way would be to power it up with a series limiting light bulb, and an auto-transformer. With the auto-transformer, you can dial the AC voltage up and down, and slowly turn it up, and let parts like capacitors, get used to all the voltage again. How long all that takes, and at what voltages, IDK tho.And the series lightbulb, like 100W or more, helps when the DUT doesn't use that much current, so maybe a few hundred milli-amps. But if for some reason, the DUT becomes a short, like a cap blows up and short circuit, or if you accidentally short the hot side of the DUT to GND, then all that happens is the light bulb can use as much current as it wants, and just lights up.The DUT and the light bulb form a voltage divider, and if the DUT is low impedance and can use a lot of current, a lot of voltage can be dropped across the light bulb. So sometimes thats good too, as a way to limit the voltage to the DUT. Other times you need a higher power, lower resistance light bulb, if you want the DUT to fully run.But without a big heavy expensive auto-transformer, you could apply some low DC voltage after the rectifier tube or diode, but 12V or 24V won't get far in a circuit meant for hundreds of volts.If I really wanted some higher DC voltage, I might tap off the 170V after some rectifier, in say a computer PSU, And then if I only wanted a few milliamps max, to charge up some caps, I'd use some series resistor. I would not try pulling any amount of current that way. But yeah I wouldn't try that, I have an auto-transformer anyways.Ok and you have an isolation transformer with taps. Yeah just start at 25AC, and leave it for a few minutes, maybe more, IDK. And them move up to the next level, and repeat. But yeah if you add a series light bulb, that should save your radio, if some something goes short to GND.I'd also say go on youtube, and watch some old VT radio repair video's. Mr.Carlson does lots of nice restorations, and there's some old guy Shangoo ?? that will get some 60yo TV working, that he finds out in a desert landfill.Also, I'd check as much unpowered as I could, even if it meant unsoldering some caps.

author: electromotivetrains
author_rank: Newbie
timestamp: November 12, 2024, 04:00:11 pm
content: Thanks "MathWizard" for your quick reply. At 70 years old I'm just now getting back into electronics from my younger days so I'll apologize in advance for some of my questions and clarifications. My question is: When you say to place a 100 watt light bulb in series (to act as a current limiter) should the set-up look like this? Please see attached drawing/diagram. Thanks...11/12/2024 11 am EST (New York)

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 12, 2024, 05:00:32 pm
content: I do this sort of thing frequently.Most of the time these things just power up.If you wish to be careful, put the radio in the garage and put it on your RCA Isotap and start at 25 volts and increase to 120 volts over about couple hours. .Take the cover off and watch it from time to time. I have had caps go poof and it is easier to clean up the garage than the house.....I do not think the Heathkit has the type of caps that have caused me trouble.You might just want to check the Isotap first with your meter...

author: electromotivetrains
author_rank: Newbie
timestamp: November 12, 2024, 10:30:31 pm
content: Thanks all for the help and suggestions. Firing this up in the garage is a good idea! I'll probably start on it this weekend. Need to get my test equipment set up first ...Thanks all. (11/12/2024 5:30 pm EST, New York)

author: MathWizard
author_rank: Super Contributor
timestamp: November 12, 2024, 11:59:15 pm
content: Yeah in series like that. I screwed an old lightbulb socket, and light switch, and a wall plug, onto a piece of 2x4.And I even added a fuse. With the socket, I also have a dummy bulb, that just has 2 wires coming out of it, twisted together, so I can still use it when testing other AC power stuff, and have a nice solid, safe switch, and plug.I usually put my isolation transformer 1st, then the series bulb and SW/plug.Are VT prone to burning out on power up like light bulbs ?? I guess it's good to give them a gentle start too.

author: electromotivetrains
author_rank: Newbie
timestamp: November 14, 2024, 03:18:16 pm
content: Thanks again "MathWizard" and "Wallace G".Doing the gentle power-up per your directions worked like a charm!Over an 8 hour period I ramped up the line voltage to the receiver (DUT) [via the RCA Isotap II (model WP-27A) isolation transformer] in 25 vac increments. Started at 25 vac. I let each voltage increment increase soak for 2-3 hours each.All is well.Threw a 30 ft. temporary antenna on it and was able to pick up stations in the 550 KC to 30 MC range.Next step is to get a real antenna on it. Thanks again (11/14/2024 10:15 am EST New York)

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 14, 2024, 04:37:12 pm
content: You said this is your build so you might remember aligning the rig.....Nice that it powered up smoothly. But in cases like yours, it is my experience that almost always that the realignment will help considerably after so many years of hibernation.