questions about restoring old tube receiver

[towerdog]

made a lucky find today, and old 1950s vintage Heathkit receiver for $20.
I know the caps have got to be dried out, hopefully not all but the larger paper electrolytic have got to be.

I powered it up about 3 hours ago and just now found out you are supposed to slowly increase voltage with variac.

It almost works, at first nothing and very little audio output but now its actually picking up several shortwave stations, but nothing but static and pops on AM broadcast.

This radio looks all original, would replacing the caps with modern equivalent help or hurt the value, or should I try to find reproduction caps, perhaps stuff a modern cap in the old cap's shell?

What would hooking it straight up to 110v AC do to it, I figure when they use a variac to ramp up the voltage it helps the old caps expand or set somehow so would it have ruined what was left of the caps. Would what I have done hurt the tubes as well?

The radio is still running, should I let it run overnight or pull the plug now and hit self in head for messing things up worse by not ramping up the voltage?

Harbor freight or somebody made a cheap multimeter that measured capacitance, would such a thing be useful for this or are they junk?

 

[towerdog]

I think it is a Heathkit AR-3 kit receiver professionally built into a nice wooden cabinet, or sure looks like whoever built it did a good job.

 

[fodendaf]

leave it set upside down for a few days. I've heard it helps the liquid move in the caps.

 

[BJ radionut]

TD: Ramping her up slowly was wise, if she had not been on for a good while. When that was made most electric service drops were 110/220v...today however most service drops are 120/240, with this in mind is why a good bunch of the old receiver gurus look for those small 5 to 10 amp table top variac transformers. The original receiver transformers were rated for 110v primaries. So with the increased service voltage the secondary filament and tube plate voltages came out to high for rated specs.
You can check many sites for suggestions in regards to the caps, but the purest restorers rebuild the old cases. You can check some of the RL Drake restoration pages an some good suggestions are there. I however have never gone that way. I guess it depends if this is something you want to keep for yourself or is this an "investment" restoration. Most collector grade buyers would want the original case, knobs, same as new throughout. The refitted version would not be something "those" type of collectors would not want unless they would use it for a parts rig. The chassis has been in a damp or salt water environment to rust so completely. The cleaning may be coming to late...However the Drake sites can offer some excellent tips also for cleaning and sealing the chassis to prevent further damage as many of their early tube chassis were copper clad and very prone to rust over time.
A good run across the tube checker comes to mind also, if you have one or can borrow one for a spell.
If the caps are original or even slightly newer(waxed paper tubes) they are not long for this world...they will need to go. A look around the web should yield a schematic once you identify the actual model or brand of chassis...
Looks like fun, but take your time and be careful...that old chassis can pack a "Punch" if you get in the wrong place working her "HOT"!
I had my old Silvertone floor model SW/AM/FM radio cross my eyes once and that was only the speaker voltage! However anyone that ever works on those old girls has more than "one" story...Yep I do!
All the Best
BJ

 

[unit_399]

TOWER -

BJ is absolutely correct. You have two choices: restore it to original, or make it operational. For max bucks ($), original is best. For best fun, operational in your rec room is solid. If it were mine, I would upgrade whatever is necessary, and run it everyday.

- 399

 

[towerdog]

I am thinking at this point to go "operational". I can find no record of Heathkit making a wooden cabinet for the AR-3, although it could maybe have been another manufacture using the AR-3 chassis for their own radio.
It could have also been a cabinet from another radio with an AR-3 chassis mounted inside it, as its all notched wood, precise screws, and that pegboard looking crap that old electronics have.

I want to do some more research, anyone know of another forum or group that specializes in the Heathkit AR-3. If it is, a manufactured radio and is worth alot of $$$ I will just leave it alone and sell it, let the pros do a proper restoration.

If it aint, and is just someone's custom project, might as well fix it best I can, it looks very nice in my living room.

This radio is more than just decoration, or a collectors item, its an awesome radio.
Heathkit AR-3 Receiver - YouTube
0.5-30mhz in 4 bands, fine tuning, a BFO for SSB, with all the amateur bands and WWV stations marked on the dial.

I may have most of what I need to get it operational, I have a small box full of old caps with high voltage ratings, they're old, my school was cleaning out their junk and I ended up with a trunk full of semiconductors and various components. I also have a box of caps and tubes out an old tube TV that my grandparents had at a vacation home, used to set the new tv on top of.

So I guess my question is, are cheap multifunction multimeters, the ones with every function you can think of, the little socket for transistors, capacitance, etc. Can they be trusted to check the caps both on radio and in my junkboxes? If not what should I use?

Another question, whats the cheapest way to bring 120 down to 110, coulnt I just construct a voltage divider, or maybe a dimmer or is not that big of an issue. (cant afford a triac and know little about them)

 

[unit_399]

If you have a good feeling about the test equip you have then I would say, "go for it".

 

[office888]

Harbor freight or somebody made a cheap multimeter that measured capacitance, would such a thing be useful for this or are they junk?

Just measure the voltage.

On my DX40 with dried out caps, a cap that was supposed to be 400v, was bouncing between 200v to 500v or so.

After replacement with modern equivalents, it now stays steady at about 402-405v.

 

[BJ radionut]

A few pics...Looks like production 1959-1961...came with fabric covered fiber board cabinet
All the Best
BJ

 

[BJ radionut]

Looks like the transformer has a 117v primary winding so line voltage in today's world not an issue.
The main power supply "can" cap should be available but expect it will cost more than you paid for the rig. Not sure if I may have one here used or new but should be easy to find a usable sub.
The looks of the mounting in the homebrew cabinet may be a challenge to get her out to work on it...but it may come out by removing the top and it may slide out.
The circuit grounding points should also be cleaned and retacked and she may come back to life on all bands. The tubes are common and should not set you back a bunch if they need replaced.
Enjoy
All the Best
BJ

 

[towerdog]

So how much voltage should the replacement caps be marked for.

Can they be marked for a significantly higher voltage, say use a 600v cap in place of a 200v cap, or is the capacitance voltage dependent?

I found a Heathkit assembly manual and schematic, it has a parts list of all components used, however the list does not give me voltage ratings on the caps. The only mention of operating voltage is on the schematic, 250v on the transformer secondary times 2 going into the tube diode, but I dont know if its using both or how it works, so I either got 250 or 500v circut, maybe I break out the multimeter tomorrow, just hope i dont burn up the multimeter.

Honestly, I know very little as to how tubes work, plates, grids, etc is all new to me but I am learning. Also found out that cheap capicator testing multimeter will not work, I need a high voltage capacitance test rig I am told, or make one and time the discharge and convert with formulas.

 

[RatsoW8]

Unless you're a collector or just want to learn, why bother?. Decide why you want to restore it and go from there. Heathkit didn't make the best receivers by the way so your not going to get back any money spent restoring it.

 

[towerdog]

I think I want to keep it, it looks nice in my living room and my wife can put up with its presence (when its turned off). I also like that sense of accomplishment that I fixed something, that I turned next to worthless junk into something thats worth more than it was, provided I didnt have to put much money into it.

I cant replace the caps this weekend, the caps I have are only rated to 100v, i need 230v for this, not to mention they are from the 1970s, likely same deal.

I have some more paper caps, look very much like whats inside it, I think 70s also but, knowing what I know now they're no good.

I have a handful of electrolytic caps I salvaged from an old copier that was dumped in the woods at a cellsite I was working at, rated at 300v I think, I am hoping I have the right ones for the power supply, I suspect that will make alot of difference.

I learned something else, firsthand, that old caps have a way of somewhat healing themselves. The tubes are not glowing red, its not smoking so I didnt see much harm in leaving it on. After leaving it on most of the day now I have 3 out of 4 bands working, with one of the bands working very well. Even the BFO is trying to work tonight, with audio barely coming in, compared to just a loud hum that didnt change with tuning different frequencies or volume levels.

 

[BJ radionut]

TD: Do you have have a call sign? Just curious...but anyway your now officially a SWL'er!
I have another little tip to try....Only when the old girl is cool(been turned off)....Reach in the cabinet and wiggle each tube around in it's socket. This will help remove some tarnish or corrosion on the pins of the socket. Then remove each tube wipe off the glass and the pins and reinstall and wiggle it back in the socket "Gently".
If you have some "canned" air you can blow out the junk and cobb webbs with the little tube directed in the sockets and switches may help.
The front plate can be cleaned with mild dish soap diluted with water on an old T-shirt....rub gently and make sure your not rubbing off the letters...Do not use Windex/409 or anything like that!...Liquid Gold for the cabinet or Pledge is ok
All the Best
BJ

 

[Kamikaze]

The easiest way to reduce the voltage in that radio is replace the tube rectifier with solid state diodes and use the original rectifier filament winding to buck the primary. That is hook it up in series with the winding in opposite phase. Those 2 tricks will lower the load on the power transformer and put the radio closer to voltages it was designed to make in the supply.