New Vintage Audio Restoration HQ

[Michaels HiFi]

This is the unit I paid $100 to an EE to get running and he failed to get it running.

After I spent some time with it, poking around, and changing some things, this happened.....

 

[atmasphere]

This is the unit I paid $100 to an EE to get running and he failed to get it running.

After I spent some time with it, poking around, and changing some things, this happened.....

Most of the tube testers I've seen have had really minor problems, mostly due to age. Some of them are difficult just because of figuring out how to use them (especially older ones like this)!

 

[Michaels HiFi]

Most of the tube testers I've seen have had really minor problems, mostly due to age. Some of them are difficult just because of figuring out how to use them (especially older ones like this)!

It's interesting, starting to deal with these things I feel like I learned there are different ways of looking at this gear.

I think there is traditional electronics fixing and then what I'm calling "vintage" electronics fixing. It's almost two different ways of looking at the electronics and fixing potential problems.

For instance one of my testers I received would not read 45 tubes. I think many would open up the unit and start trouble shooting (I would have). My old tube buddy friend (he used to work on tube testers in the Navy) instead had me simply stick a pipe cleaner sprayed with QD cleaner in the 4 pin socket on the tester without opening anything.

Bingo, it worked wonders.

I bet with everything you've worked on you approach it a similar way.

 

[atmasphere]

It's interesting, starting to deal with these things I feel like I learned there are different ways of looking at this gear.

I think there is traditional electronics fixing and then what I'm calling "vintage" electronics fixing. It's almost two different ways of looking at the electronics and fixing potential problems.

For instance one of my testers I received would not read 45 tubes. I think many would open up the unit and start trouble shooting (I would have). My old tube buddy friend (he used to work on tube testers in the Navy) instead had me simply stick a pipe cleaner sprayed with QD cleaner in the 4 pin socket on the tester without opening anything.

Bingo, it worked wonders.

I bet with everything you've worked on you approach it a similar way.

Its been different over the years. It used to be that when restoring an old radio or tube amplifier all you had to do was replace filter capacitors. These days you have to go over the whole thing because so may coupling caps have rotted and resistors are miles off value.
In this amplifier

oddly, all the coupling caps were good, but nearly all the resistors had drifted off value. Its worth noting that this amplifier had sat for decades in a warehouse in Canada, unused. Allegedly was NOS and came with the paper covers for the transformers a bit rotted but still intact. So my surmise is the resistors drifted off value without any use. But the amp is 68 years old. A lot of corrosion can occur in that time...

 

[Michaels HiFi]

Making progress.

I've not got it powering up so I'm working more on the super stiff pot.

You can see it in this pic with a temp knob on it.

I decided to turn the multi-layer switch upside down and that helped me see part of the problem - the wiper on the underside of the top most layer was corroded and such.

So I hit that with some DeOxit and a pipe cleaner to scrub it clean a bit and have been turning it till my fingers are sore.

I also hit each layer where the shaft goes all the way though with a drop of Kroil and will let that sit over night.

Then I'm going to check the resistors to see if they have drifted over time.

 

[atmasphere]

Making progress.

I've not got it powering up so I'm working more on the super stiff pot.

You can see it in this pic with a temp knob on it.

I decided to turn the multi-layer switch upside down and that helped me see part of the problem - the wiper on the underside of the top most layer was corroded and such.

So I hit that with some DeOxit and a pipe cleaner to scrub it clean a bit and have been turning it till my fingers are sore.

I also hit each layer where the shaft goes all the way though with a drop of Kroil and will let that sit over night.

Then I'm going to check the resistors to see if they have drifted over time.

View attachment 35370
View attachment 35371
View attachment 35372

The switch doesn't look bad at all!

 

[Michaels HiFi]

The switch doesn't look bad at all!

It's slowly getting better thankfully.

The main wiper arm is a double wiper arm and sits about a 1/4 inch right under the black faceplate (you can see it partially in the first pic).

Hopefully after tonight's cleaning it will be good to go.

 

[Michaels HiFi]

I spent three hours on this one gauge yesterday.

The glass was up against the needle so I disassembled to fix.

All went well - up to a point.

You can see in the photo I choose to put tape around the outside of the metal ring that then slides up against the glass to keep it secure which made the fit tight again within the metal gauge cylinder.

I also took the time to clean the glass. Needed to use super fine car polish to get the glass clean as no glass cleaner was strong enough to remove 90 years of grime.

I choose not to use glue to secure the ring in case I ever broke the glass and needed to disassemble it, glue would have prevented that.

The issue?

That little piece that is about 1/8th on an inch wide that sticks out to be able to adjust the gauge needle didn't want to go back. Evidently this one was plastic (unlike my other one that was metal) so it was deformed.

I finally got it back together and not sure if I'll be able to use the set screw to zero the needle.

Solution?

I ordered an entire gauge off Ebay for $14. It's not the right needle reading but it's the exact same unit so I'll simply use the little pin off the replacement if need be. Now I also have spare tiny gauge screws and glass for the future.

First pic is when I started and last pic is finished gauge.

 

[Michaels HiFi]

Well, I spent 4 hours on this yesterday going through the resistors, caps and checking all the wiring connections.

Believe it or not, some of the resistors (all mil-spec) were still within tolerances!

Regardless, I made a list and ordered all new ones today to replace anyway. Even the ones supposedly still in spec are getting changed out.

When the resistors only cost 50 cents each, it doesn't make sense to not replace them. Plus by the time I de -older one end out of circuit to test it I may as well simply do both and install a new part. The wire wound resistors were the most expensive at a couple of bucks each and I needed a handful of them.

I used AI to help me review the manuals for the TV-10, Supreme 85, Supreme 89, NRI 70 and Weston OQ-2 and make sure I ordered all the right parts and upgraded most of them to even tighter tolerances than was factory.

By the time I ordered parts for all 4 testers, new fuses and more, and paid shipping and tax it only came to $90.

Every one on the TV-10 tested in spec but I am still replacing all the parts in the primary critical path and leaving the resistors that tested in spec in the harder to reach places alone.

Am also upgrading the cap on the meter movement to make sure that is protected and accurate.

Pictured is the Weston OQ-2 from 1939. I enjoy the older testers as they are usually a bit more simple and easier for me to learn on. After 7 hours I got the potentiometer seemingly working and I rebuilt the meter as shown in pics above.

 

[atmasphere]

I spent three hours on this one gauge yesterday.

The glass was up against the needle so I disassembled to fix.

All went well - up to a point.

You can see in the photo I choose to put tape around the outside of the metal ring that then slides up against the glass to keep it secure which made the fit tight again within the metal gauge cylinder.

I also took the time to clean the glass. Needed to use super fine car polish to get the glass clean as no glass cleaner was strong enough to remove 90 years of grime.

I choose not to use glue to secure the ring in case I ever broke the glass and needed to disassemble it, glue would have prevented that.

The issue?

That little piece that is about 1/8th on an inch wide that sticks out to be able to adjust the gauge needle didn't want to go back. Evidently this one was plastic (unlike my other one that was metal) so it was deformed.

I finally got it back together and not sure if I'll be able to use the set screw to zero the needle.

Solution?

I ordered an entire gauge off Ebay for $14. It's not the right needle reading but it's the exact same unit so I'll simply use the little pin off the replacement if need be. Now I also have spare tiny gauge screws and glass for the future.

FWIW the glass on meters like that is usually glued in.

 

[Michaels HiFi]

FWIW the glass on meters like that is usually glued in.

Yeah - I think all the glue is long dried up decades ago. The glass has been loose on all the ones I've received.

I know Murphy's law - the minute I glue it back it will break.

 

[atmasphere]

the minute I glue it back it will break.

Unless it doesn't! Glue it carefully and treat the meter with respect and it will be fine.

 

[Michaels HiFi]

Made in interesting discovery on the "switch from hell" I've been dealing with.

It just seemed like it still wasn't where it needed to be - like there was still something a bit stuck.

After taking some Deoxit and a pipe cleaner to gently scrub it a bit more (I still wanted to get it more free turning), and my magnifying glass I realized what I thought was a simple fixed nub on the wiper arm (the part that turns with the metal on metal contact) , is actually a wheel!

So I took a bit more carefully applied deoxit sprayed on the pipe cleaner and kept lightly brushing both sides of the two wheels (there is one also at 180 to this one).

And now that I got the little tiny wheels turning the switch feels like it is turning without the feeling I was fighting something.

What was happening before is the wheel would go into each indent you can see in the pic, but then because it was frozen from oxidation the wheel would not turn to allow the switch to be turned out of that indent and onto the next. That's why it was still tight. I was in essence trying to drive the car with the E-brake still on.

You can also see I labeled the back of the panel "D". I do that on the back of the panel for each switch so I know where I am relative to the front panel switches - am I working on switch A, B, C, or D because sometimes from the back I loose my bearing.

 

[atmasphere]

Those wheels are supposed to have a spot of grease on them, as should the track itself. It should be something that doesn't flow easily, like automotive bearing grease. I would not use a lithium grease. Not only will the grease make things work even better but it will protect the part from oxidation.

 

[Michaels HiFi]

Those wheels are supposed to have a spot of grease on them, as should the track itself. It should be something that doesn't flow easily, like automotive bearing grease. I would not use a lithium grease. Not only will the grease make things work even better but it will protect the part from oxidation.

I've got the perfect grease I use on firearms. I LOVE this stuff: Brownells grease

 

[atmasphere]

I LOVE this stuff: Brownells grease

Thanks for the tip!

 

[Michaels HiFi]

I received all my parts yesterday. Today I'm going to be replacing all the resistors, caps and the big yellow wire wound resistors.

90% of them still tested in spec!

Regardless I'm going to be replacing them all.

 

[Michaels HiFi]

Very excited about this.

Thanks to a generous person, I've received my first real piece of test gear: an oscilloscope!

 

[atmasphere]

Very excited about this.

Thanks to a generous person, I've received my first real piece of test gear: an oscilloscope!


View attachment 35409

You have tube testers and a DVM- those are real bits of test equipment too!

Most of my repair work is done with the DVM. The 'scope helps see if I did a good job; also useful for troubleshooting more complex situations. I recently used it to align an FM multiplex circuit.

 

[Michaels HiFi]

Picture of the latest addition - a fully restored Western Electric 15750-L2 tube tester.

What is a WE tester?

Most people assume the Hickok 539C and the Western Electric 15750 are basically the same tube tester. Same DNA, different label — right?

Not quite.

I find the differences very interesting. But then I'm a total tube geek.

The 539C is a fantastic all-around tester. Flexible, easy to use, and capable of testing a huge range of tube types. If you're building a general-purpose bench, it's hard to beat.

But the 15750 wasn't designed for general purpose. It was built specifically for Western Electric — not the consumer market — and it was engineered around one particularly demanding family of tubes: DHTs. Direct Heated Triodes. Think 45, 2A3, and 300B.

Why does that matter?

DHT tubes are unusually sensitive to test conditions. They don't just need a voltage applied and a reading taken. They're highly dependent on three things:

- Filament stability — the heated cathode must reach a consistent operating temperature
- Bias consistency — the grid voltage must be precise and stable
- Operating point — the combination of voltages must reflect real-world conditions

Most testers approximate these conditions. The 15750 was designed to control them.

Here's how it does that technically:

The 539C uses AC-derived bias — meaning the bias voltage shares a common source with other voltages in the circuit. That creates subtle interactions that can affect readings, especially on sensitive tubes.

The 15750 uses filtered DC bias — a cleaner, more isolated source that produces more stable operating points during the test. Less interaction between voltages means more consistent, repeatable results from tube to tube.

On top of that, Western Electric specified hand-trimmed resistances and individually calibrated values during production. This wasn't off-the-shelf assembly. Each unit was built to hit specific electrical targets — something that simply wasn't done on consumer-grade Hickok builds.

So what does all this mean practically?

If you're testing a mixed bag of receiving tubes — 12AX7s, 6L6s, EL34s — the 539C is the better tool. It's faster, more versatile, and perfectly accurate for the job.

But if you're dealing with 45's, 2A3;, 300B's like I often am and where consistency really matters, the 15750 gives you something the 539C simply can't: repeatable, system-level results under controlled conditions.

It's not that one is universally better than the other. It's that they were built for different jobs — and knowing the difference helps you use both correctly.

Right tool. Right context. Better results.