Hickock 539A Tube Tester Maintenance

[nevetslab]

I dragged out the aging Hickock 539A Tube Tester, that's been sitting under my bench since I moved up here in 2009. Bought it used in Sept 1977 from Industrial Liquidators (Hawthorne, CA) for $47.50. Didn't use it much back then, as I wasn't really doing much tube work. I opened it up today, it missing half the screws that mount the control panel to the suitcase, where the wood had stripped out, so have that to tackle. Type 83 and 5Y3GT Rectifier tubes inside. I see a 0.1uF/400V Paper capacitor and a cobbled electrolytic capacitor that was made using a couple parts series connected to replace the original 8uF/150V in series with a 470 ohm resistor across the bias meter. That looks like some of my handiwork from the 90's. I see there's another electrolytic cap that's supposed to be across another meter, which I've yet to find.

The Mains Fuse is a Type 1133 Automotive Bulb, BA15S Bayonet Lamp base, which has become so worn, you can't twist it out. I did carefully grip the base with my vintage large gas pliers to hold the base and got the bulb out. Working bulb. After spending a bunch of time trying to determine WHAT the lamp base type was, then finding various websites trying to sell you something that obviously was NOT that size, I finally pulled out the JB Weld, mixed up a batch of that and after spending a little time with the brass bristle brush, and did solder one of the solder lugs back to the outside housing, I then liberally applied the thick gooey stuff all around to cure and left it sitting in the small vise to dry overnight.

The Pilot lamp is the same Fender Pilot Light assy on their Twin Reverb amps, with a Type 47 bulb installed.

All of the rotary switches, of which comprise the majority of the activity of this instrument look to be in good condition. Not sure about the push button switches as the panel is out and face down on the housing for the moment.

I'll know more when I get the Mains Fuse/Lamp assy re-installed and wired back in.

Found the date code on the larger of the two power transformers: DEC 1952. Definitely looks to be that vintage. OAK Rotary and Push Button switches.

[g1]

The fuse/lamp should be # 81 bulb. 1133 is much higher wattage. Manual with schematic attached.

[TomCarlos]

And if you ever need help on this project, visit the Antique Radio Forums site. There are plenty of threads and guys who can help you.

Start here - Hickok 539A Tube Tester Restoration

[nevetslab]

The fuse/lamp should be # 81 bulb. 1133 is much higher wattage. Manual with schematic attached.

Thanks for that heads-up. I thought that huge lamp in that socket seemed out of place!

[nevetslab]

And if you ever need help on this project, visit the Antique Radio Forums site. There are plenty of threads and guys who can help you.

Start here - Hickok 539A Tube Tester Restoration

Good link....Thanks, Tom. Spool Resistors. So THAT's what those cute little collections of 'sewing thread spool's are. Onward with the adventure....

[mozz]

Coffee didn't kick in yet. Something about not spraying the switches with cleaner? Alcohol only?

[TomCarlos]

Mozz- There are several YouTube videos on Tube Tester Repair / Restoration where guys are saying to be careful when using cleaners on Wafer switches, as the liquid soaks into the wafer and causes a resistive path. Here is one of those videos - Wafer switch repair

One of my testers is a B&K 707. There is a switch that is not your typical SPST or DPDT. It looks like two small circuit boards that has multiple switch points. This type of switch is what makes old tester restoration challenging - knowing how these work. I believe the Hickok does not have that type of switch.

Nevets - yes the spool resistors are not common, but now you know. I would spend some time looking for threads on the Antique Radio site, for this particular tester and other Hickok (which have parts in common). I have also seen some restoration videos on YouTube. So do some research first then make your checklist for this project.

Good luck !!

[nevetslab]

Mozz- There are several YouTube videos on Tube Tester Repair / Restoration where guys are saying to be careful when using cleaners on Wafer switches, as the liquid soaks into the wafer and causes a resistive path. Here is one of those videos - Wafer switch repair

One of my testers is a B&K 707. There is a switch that is not your typical SPST or DPDT. It looks like two small circuit boards that has multiple switch points. This type of switch is what makes old tester restoration challenging - knowing how these work. I believe the Hickok does not have that type of switch.

Nevets - yes the spool resistors are not common, but now you know. I would spend some time looking for threads on the Antique Radio site, for this particular tester and other Hickok (which have parts in common). I have also seen some restoration videos on YouTube. So do some research first then make your checklist for this project.

Good luck !!

I just watched the first You Tube video on cleaning/restoring wafer switches, which was very informative....once one has removed all of the wiring to a multideck switch. Looking at that result, and then pondering the insane complexity of all the wires that would have to be desoldered to even remove the switch from the panel.........absolutely freightening. Hope this unit isn't going to need that depth of work.

I'll stop off at an automotive parts store on the way in to see if I can pick up the Type 81 lamp, then see how the glue-up of the holder came out from curing overnight.

Thanks, Tom!

[TomCarlos]

Nevets: There is a guy on the east coast, Bob Putnak. His company is called "Tube Sound." He is in PA. Check out his website and videos. One thing he recommends for the B&K is that all lamps should be solderd into place, both ends. This is because the lamps we part of the control circuitry and not just "On/Off" indicators. I will let you look into that. I don't think it is the same for Hickok testers. But Bob has lots of info on Hickok units.

[mozz]

Also try and find a old 81 lamp, i read the new ones do not have the same resistance or current draw since it is also a fuse besides a lamp. I second the reading in "antique radio forum" a lot of very knowledgeable people there

[TomCarlos]

Mozz.... Bob Putak of Tube Sound made the same claim about the lamps, that new ones do not have the same resistance. So I guess this depends on how a lamp is used in the Tester. For the Hickok, I believe it might be less of an issue.

[nevetslab]

Nevets: There is a guy on the east coast, Bob Putnak. His company is called "Tube Sound." He is in PA. Check out his website and videos. One thing he recommends for the B&K is that all lamps should be soldered into place, both ends. This is because the lamps we part of the control circuitry and not just "On/Off" indicators. I will let you look into that. I don't think it is the same for Hickok testers. But Bob has lots of info on Hickok units.

Good advice. Though the form factor of the Type 81 lamp isn't exactly made for soldering. No doubt one could solder to the brass base, but the leaded contact that mates with the spring-loaded plunger....uncharted territory for me there. On the way in this morning, I stopped off at two different auto parts stores, not finding the Type 81 bulb.

Mozz, interesting tip...didn't know current lamps differ in filament resistance from the older one. More digging to do on this front.

Meanwhile, after a little work with my can of Bestine and an old X-Acto 1/2" wide straight 'chisel' blade (favorite tool for peeling off old labels from panels) to get aged adhesive tape placed on the panel for 'temporary markings' of tube settings, I got a first quick clean-up of the top panel for photos. The glue-up of the lamp/fuse holder for that CM81 6.5V1A Fuse Lamp, G-6 Bayonet Base (from my CML catalog) came out strong, and I got it mounted before anything else when I came in.





From my initial inspection of the wafer switches, they look remarkably clean for being 71 years old! There is corrosion on them, but not like I've seen on other older gear. The small AC Mains rheostat looks like I need to un-solder it and clean it up. I haven't looked close at the OAK Pushbutton Switch contacts. The collection of tube sockets look a bit on the crusty side. I'll have to do some contact scrubbing inside no doubt.

I can't recall if I was the one who installed the power cord, or it was that way when I bought it. I knew better back then not to install the Ground lead the way I see it done here....attempted soldering it to the mounting screw shaft of that AC Mains Panel Meter at the upper left corner of the unit.

I had loaned this instrument to Kim Hoffman, who at the time was BGW System's Purchasing Agent (late 80's, early 90's I think). Can't recall if it was he or his brother that started Hoffman Amplifiers. He tracked down my Instruction Manual for the instrument, also a fresh paper scroll and I think was the one who installed that type 1133 automotive lamp.



The black Tolex-covered Suitcase & removable lid are in great shape, no doubt responsible for keeping this in good condition inside, plus Los Angeles County isn't really a humid environment, though Rust grows anywhere. There is a lot of crusty metal parts in the assembly.

So onward.........

[TomCarlos]

Thanks for the photos.

Ok, one last thing I will leave you with (and sorry if I am making this more complex than it needs to be)....

For the Tube Rectifier, there are solid state replacements available. Some guys just go for two diodes and a couple resistors. Again, and this comes from Bob @ Tube Sound, some testers do not behave properly when the original tube is replaced with a Solid State replacement. I will let you research that. Here is just one opinion, but do some research on this: SOLID STATE REPLACEMENTS FOR HICKOK TUBE TESTER'S Cutting Alnico Magnets? RECTIFIER TUBE?

I have other links for discussions on this topic. Just ask if you want them.

[nevetslab]

Thanks for the photos.

Ok, one last thing I will leave you with (and sorry if I am making this more complex than it needs to be)....

For the Cutting Alnico Magnets? Tube Rectifier, there are solid state replacements available. Some guys just go for two diodes and a couple resistors. Again, and this comes from Bob @ Tube Sound, some testers do not behave properly when the original tube is replaced with a Solid State replacement. I will let you research that. Here is just one opinion, but do some research on this: SOLID STATE REPLACEMENTS FOR HICKOK TUBE TESTER'S Cutting Alnico Magnets? RECTIFIER TUBE?

I have other links for discussions on this topic. Just ask if you want them.

I do like that! Interesting package & details. I'll start with what I have, of course, but once I get this up and running, that looks like a viable solution. I've no idea what the demand for Type 83 tubes are these days, though most everything in Vacuum tubes is going up in price.

Complex? One quick glance at the innards of this already is enough to scare most folks away. Of course, I'm just at the starting point, beginning with the simple tasks....next is correcting the power cord ground wiring. Then remove that small 'variac' to see what I can do with it.

[Enzo]

Oh man, no pc board, no pick and place machine. Can you imagine building these all day for a living?