AR 3 serial numbers

[rwalton46]

I'm a newbie member, but I've been monitoring this site for several years.

I have a pair of AR 3's that I found at an estate sale (for ridiculously cheap)five or so years ago. I knew what they were when I got them, and was most pleasantly surprised when everything worked. Well, the pots were typically intermittent.

Now I've discovered that the tweeter and mid in one of the cabinets aren't working and I'll soon be opening both cabinets to clean up the pots and maybe re-cap the crossovers, depending on what I find inside. That brings up the serial numbers.

The cabinets are numbered C 6634, and C 08232. The label with the 4-digit number has "SPECIAL" stamped on it, and has slightly different wording and a slightly different format than the label with the 5-digit number. These two cabinets look almost identical. So I'm curious: what is the difference that makes the earlier cabinet "special?" When did AR start using a zero in front of the other digits? When did the label change? So many questions!

I also own two sets of AR 2ax's, one set of fairly early vintage, the other of later vintage.

Thanks,

Rick

[JKent]

Hi Rick and welcome as an "active" member of CSP

I'm working on an AR3 restoration right now. Just taking a break. Something you should find interesting is the paper on AR3 crossovers, in the library here:

http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_schematicss/thoughts_on_ar-3_schematics/thoughts_on_ar-3_schematics.pdf

C6634 and 08232 both seem to be from what authors John O'Hanlon and Tom Tyson identified as the first xo change, in 1960. So your two speakers should match. Mine had 2 different crossovers, so I've rebuilt them to match yours. Like you, I also own 2ax's (and 2a's).

Don't know what "special" is. Maybe one of the AR3 experts will know. Be sure to follow the AR3a restoration booklet. Much of it applies to the 3. Are you sure the mid and tweet are dead? The pots are probably bad, and bad pots will cause a lack of sound from the mid and/or tweet. I'm using Ohmite pots as replacements, but L-pads would have been MUCH easier and just as good.

Attached is a photo of the new xo [edit: removed photo but see post #6]. I used Clarity PX caps (25uF & 6uF). Only one speaker had the 0.06uH inductor as shown in the schematic, example "B". So I used 0.05 18ga Jantzen inductors from PE in both. The Ohmite pots are in a plastic project box. It gets an aluminum cover. The one thing I'm waiting to find out is the "white dot" position for the pots. Once I have that info, I'll drill 1/8" holes for the index tabs on the pots. If you use L-Pads you can forego that hassle (see pages 10 to 15 of the restoration guide).

There are a couple of AR3 threads active now, so you probably will want to check them all.

Good luck and keep us posted on your progress.

Kent

[dynaco_dan]

Hi Rick and welcome as an "active" member of CSP

Don't know what "special" is. Maybe one of the AR3 experts will know. Be sure to follow the AR3a restoration booklet. Much of it applies to the 3. Are you sure the mid and tweet are dead? The pots are probably bad, and bad pots will cause a lack of sound from the mid and/or tweet. I'm using Ohmite pots as replacements, but L-pads would have been MUCH easier and just as good.

Attached is a photo of the new xo. I used Clarity PX caps (25uF & 6uF). Only one speaker had the 0.06uH inductor as shown in the schematic, example "B". So I used 0.05 18ga Jantzen inductors from PE in both. The Ohmite pots are in a plastic project box. It gets an aluminum cover. The one thing I'm waiting to find out is the "white dot" position for the pots. Once I have that info, I'll drill 1/8" holes for the index tabs on the pots. If you use L-Pads you can forego that hassle (see pages 10 to 15 of the restoration guide).

There are a couple of AR3 threads active now, so you probably will want to check them all.

Good luck and keep us posted on your progress.

Kent

Hi Kent

I see your solution to the past concern that I had with the exposed pot wipers and fiberglass.

A very neat and creative idea.

Very well done, Kent

[JKent]

Thanks Vern

It's a little snug, and not finished yet, but it should work. Bought the box at my local electronic parts store but it seems to be identical to this:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=320-420

Kent

[ADVENTAGIOUS]

Kent, are you going to connect the wires to the pots through the switch cover plate or through the side of the box (individual holes)? Great idea!!

[JKent]

Here's an update. I used the white dot values for the 3a, which resulted in an awkward placement of the pots with regard to the lugs. Lug 2 on the Hi pot is precariously close to the windings on the Mid pot. I may change that.

This experience has given me some "insight" that I'll share. If you decide to use Ohmite pots,

1. don't
   
2. use L-pads
   
3. don't use Ohmites
   

There's no way the Ohmites are worth the hassle. What a PITA!

Anyway, here are shots, with cover on & off.

Kent

[rwalton46]

I'm adding a couple of photos of the speaker labels as a follow-on to my original post. I don't know if that will help.

I've just barely launched myself into the restoration project by managing to remove one grill cloth without breaking the plastic frame. The cloth didn't pull away from the front of the frame, but did release on the sides. I'll have to find some way to make it adhere to the sides so that the frayed edges of the cloth don't stick out. I'm trying to imagine the fun the AR manufacturing employees had when assembling the speakers initially.

I'll take pictures as I progress and post the ones that seem relevant.

Rick

[dynaco_dan]

Here's an update. I used the white dot values for the 3a, which resulted in an awkward placement of the pots with regard to the lugs. Lug 2 on the Hi pot is precariously close to the windings on the Mid pot. I may change that.

This experience has given me some "insight" that I'll share. If you decide to use Ohmite pots,

1. don't
   
2. use L-pads
   
3. don't use Ohmites
   

There's no way the Ohmites are worth the hassle. What a PITA!

Anyway, here are shots, with cover on & off.

Kent

Hi Kent,

Great photos but I am unable to save them for some reason.

Both of these do not save to a known file name and will not open for me.

Or should I put on my glasses? LOL

[JKent]

Hey Rick

I have the same problem with my grilles--the vinyl "fabric" has pulled away from the plastic frames on the long edges. Tried Aleene's 7800, available in craft stores like Michael's. It is a sort of Goop or contact cement and it seems to work wrll. The only caution: DO NOT use too much. You apply it to both surfaces. I applied it to the plastic frame then mooshed the vinyl into it, then pulled it apart. You let it dry 5 minutes, then stick the pieces together. I clamped it. One side came out perfect. The other, where I used too much glue, ended up with some glue oozing through the vinyl mesh. When it dried, it had a reddish color. Don't know why it's that color. It's not "too" bad but it can't be undone so if you use the 7800 use just enough--no blobs.

Kent

[rwalton46]

Hey Rick

I have the same problem with my grilles--the vinyl "fabric" has pulled away from the plastic frames on the long edges. Tried Aleene's 7800, available in craft stores like Michael's. It is a sort of Goop or contact cement and it seems to work wrll. The only caution: DO NOT use too much. You apply it to both surfaces. I applied it to the plastic frame then mooshed the vinyl into it, then pulled it apart. You let it dry 5 minutes, then stick the pieces together. I clamped it. One side came out perfect. The other, where I used too much glue, ended up with some glue oozing through the vinyl mesh. When it dried, it had a reddish color. Don't know why it's that color. It's not "too" bad but it can't be undone so if you use the 7800 use just enough--no blobs.

Kent

Thanks for the excellent tip. I will use it.

I noticed that all the existing glue is a dark reddish color. Maybe some of that dissolved into the new glue you applied. Just a thought.

Rick

[rwalton46]

By the time I quit fooling with the 3's last night, I had managed to successfully remove both grilles without breaking them or detaching the cloth.

When I started this thread, I was asking about the differences in the speakers based on the serial numbers, especially because of the difference in the formatting of the numbers. After I got the grilles off, I found one major difference in the two cabinets: the woofers. The speaker with serial number C6634 has what must be an older style woofer. It has no damping rings and a smooth cone. The C08232 woofer has the big damping ring near the center, a narrow damping ring near the edge, and concentric ridges in the cone material.

Interestingly, the C6434 mid has written on it in red grease pencil "35X 10-11-60". I don't know what the 35X means, but I'm guessing that the 10-11-60 is the date of assembly. The C6434 tweeter has the number 728 written across the dome. The C6434 woofer has 17 written on the cone, and another number that I haven't been able to clearly make out. It could be 27, but I think it is 2-C.

I've attached a couple of photos of the speakers sans grilles. I'm most curious to find what other differences in these cabinets might be waiting inside.

Rick

[rwalton46]

Don't know what "special" is. Maybe one of the AR3 experts will know. Be sure to follow the AR3a restoration booklet. Much of it applies to the 3. Are you sure the mid and tweet are dead? The pots are probably bad, and bad pots will cause a lack of sound from the mid and/or tweet. I'm using Ohmite pots as replacements, but L-pads would have been MUCH easier and just as good.

Attached is a photo of the new xo [edit: removed photo but see post #6]. I used Clarity PX caps (25uF & 6uF). Only one speaker had the 0.06uH inductor as shown in the schematic, example "B". So I used 0.05 18ga Jantzen inductors from PE in both. The Ohmite pots are in a plastic project box. It gets an aluminum cover. The one thing I'm waiting to find out is the "white dot" position for the pots. Once I have that info, I'll drill 1/8" holes for the index tabs on the pots. If you use L-Pads you can forego that hassle (see pages 10 to 15 of the restoration guide).

Kent

Hi Kent,

Yesterday I opened up the C6634 cabinet, the one marked "special", and was met with a surprise. Instead of the usual AR pots, I discovered the Ohmites shown in the picture. They were totally unenclosed. Upon close inspection, I realized they are the same Model H Ohmites that you just used in your AR-3 restoration. I'm also intrigued by the signature on the crossover board.

Did AR ever use the Ohmite pots in production units? This cabinet showed no signs of having been previously opened. The grille was glued down with no signs of being re-glued. The paint around the woofer was undisturbed. Could the "Special" stamp on the labels be about the pots?

The next question is, how do you clean these? I'm pretty sure they are the reason the tweeter and mid aren't functioning. Before opening the cabinet, I listened carefully, and I could hear the tweeter when the pot was rotated to the extreme max position. I couldn't get anything out of the mid, though.

Rick

[JKent]

Hey Rick. AFAIK, AR never used Ohmites, and those blue hookup wires add to my suspicion. You tease us! What are the caps? That may be the real giveaway. As far as cleaning the Ohmites, maybe just use a vacuum. I would not recommend dis-assembly of the pot. There is a hex nut that secures the indexing tab in place. You can loosen it, but I would not remove it.

After installing Ohmites in the plastic project boxes, I'm not a fan. L-Pads work fine and they're easy to work with (and cheap).

Had a disappointment with my 3s. Got one all back together, stuffed with 3 small bags of Johns Manville white fiberglass from Lowes, replaced the ratty Kimpac with some tulle fabric (like a bridal veil). Hooked it up to my receiver and at first it sounded good. That 12" woofer rocks! But when I turned up the volume and let it play a while, it became clear that the midrange was toast (or on its way to toastdom). Very ragged sounding, some static-like sound, and inconsistent volume. Drat! So at least one mid is no good. Hope yours has not suffered the same fate. First thing would be to test it with an ohmmeter. There should be a green wire from the + side of the mid running to the middle lug on the "Mid" pot. Then there should be a yellow wire from the mid - to lug #2 on the pot. Looks right in your photo. Disconnect one lead and check resistance between the green and yellow wires. Reading should be "about" 2 ohms.

If you don't have an ohm meter, you "could" hook up your source (receiver) to the mid directly. A mid is essentially a full-range speaker and should work fine if powered at LOW LOW power. Don't crank it up, just make it listenable and see if the sound is equivalent to a good table radio.

Good luck

Kent

[rwalton46]

Hey Rick. AFAIK, AR never used Ohmites, and those blue hookup wires add to my suspicion. You tease us! What are the caps? That may be the real giveaway. As far as cleaning the Ohmites, maybe just use a vacuum. I would not recommend dis-assembly of the pot. There is a hex nut that secures the indexing tab in place. You can loosen it, but I would not remove it.

After installing Ohmites in the plastic project boxes, I'm not a fan. L-Pads work fine and they're easy to work with (and cheap).

Had a disappointment with my 3s. Got one all back together, stuffed with 3 small bags of Johns Manville white fiberglass from Lowes, replaced the ratty Kimpac with some tulle fabric (like a bridal veil). Hooked it up to my receiver and at first it sounded good. That 12" woofer rocks! But when I turned up the volume and let it play a while, it became clear that the midrange was toast (or on its way to toastdom). Very ragged sounding, some static-like sound, and inconsistent volume. Drat! So at least one mid is no good. Hope yours has not suffered the same fate. First thing would be to test it with an ohmmeter. There should be a green wire from the + side of the mid running to the middle lug on the "Mid" pot. Then there should be a yellow wire from the mid - to lug #2 on the pot. Looks right in your photo. Disconnect one lead and check resistance between the green and yellow wires. Reading should be "about" 2 ohms.

If you don't have an ohm meter, you "could" hook up your source (receiver) to the mid directly. A mid is essentially a full-range speaker and should work fine if powered at LOW LOW power. Don't crank it up, just make it listenable and see if the sound is equivalent to a good table radio.

Good luck

Kent

Thanks for the tips. I do have an ohmmeter, and will test that way. The caps in this cabinet are the big oil-filled cans. Compared to modern polys, these look like total overkill. From what I've read, though, they are probably OK and I should leave them alone. I don't think I have a capacitor tester, and even if I do, it is buried away in storage and I would spend an inordinate amount of time trying to find it.

I will also try the hook-up test method. That might be the easiest.

I have other photos of the xover and the caps. I'll post them later today.

Rick

[JKent]

Interesting. I just opened a pair of AR2a's yesterday--had planned to steal their tweeters for my AR3 project but there's been a change of plans there. Ended up putting the 2a's back together--totally stock. Didn't even clean the pots. Then did a listening test. I REALLY like them so far (with a live jazz recording). They may be better-sounding than my restored 2ax's. We'll see. FYI, here's what AR guru johnieo said about the caps:

Keep them!

[These have] MIL SPEC construction.

* all metal can

* all soldered or welded joints

* Alumina ceramic electrical feed through insulators

* inside wire soldered to inside of steel terminal wire

* outside lead soldered to outside if steel terminal wire

* feedthrough wire braised to the ceramic

* outside of the ceramic brazed to the can.

What does this mean? It mean a couple-of-hundred-year hermetic seal!

It means that the OIL in these cans has absorbed zero moisture.

If yours are anything like the ones in the picture, keep them.

btw--judging by the photos of the fronts of your 3s they look like the mahogany veneer. Are they?

Kent

[rwalton46]

Interesting. I just opened a pair of AR2a's yesterday--had planned to steal their tweeters for my AR3 project but there's been a change of plans there. Ended up putting the 2a's back together--totally stock. Didn't even clean the pots. Then did a listening test. I REALLY like them so far (with a live jazz recording). They may be better-sounding than my restored 2ax's. We'll see. FYI, here's what AR guru johnieo said about the caps:

Keep them!

[These have] MIL SPEC construction.

* all metal can

* all soldered or welded joints

* Alumina ceramic electrical feed through insulators

* inside wire soldered to inside of steel terminal wire

* outside lead soldered to outside if steel terminal wire

* feedthrough wire braised to the ceramic

* outside of the ceramic brazed to the can.

What does this mean? It mean a couple-of-hundred-year hermetic seal!

It means that the OIL in these cans has absorbed zero moisture.

If yours are anything like the ones in the picture, keep them.

btw--judging by the photos of the fronts of your 3s they look like the mahogany veneer. Are they?

Kent

Yes, the caps in the C6634 cabinet do resemble the ones in your picture. I think the small one is identical, but the large one is unpainted, that is, it has a silvery finish with the info printed on it, and it has four (I think - I don't have the speakers or the pictures in front of me)large ceramic insulated terminals. I do plan to keep them.

I'll probably open the other cabinet this evening, so I'll be able to report on what differences I find beyond the woofers.

As for the cabinets, I think they probably are mahogany veneer. They have a glossy, lacquered finish, with minor dents and scratches appropriate for their age.

Rick

[rwalton46]

OK, here is the info on the caps. The large can is a triple-8, strapped to get 24. The small one is actually two 2X2's strapped in parallel to get another 8.

I checked continuity on the mid, and it isn't open. But when I put a signal to it, I get nothing. I do get sound from the tweeter, although my ancient ears seem to think it is weak.

I decided to draw out a schematic, and by doing so I see that if I disconnect the common to the mid and tweeter, I'll be able to check continuity with no worries of anything else affecting it. I'm a little baffled that I get continuity on the mid, but no sound. I expected to get at least a click or something.

I'm still really curious about the presence of the Ohmite pots, and the "Special" stamp on the label.

Rick

[Carlspeak]

Now that's one pair of caps I wouldn't want to get caught with going thru airport security....

[genek]

You wouldn't want to get any of the oil on you if they ever leak, either. Caps of that period were filled with PCB.

[tysontom]

OK, here is the info on the caps. The large can is a triple-8, strapped to get 24. The small one is actually two 2X2's strapped in parallel to get another 8.

I checked continuity on the mid, and it isn't open. But when I put a signal to it, I get nothing. I do get sound from the tweeter, although my ancient ears seem to think it is weak.

I decided to draw out a schematic, and by doing so I see that if I disconnect the common to the mid and tweeter, I'll be able to check continuity with no worries of anything else affecting it. I'm a little baffled that I get continuity on the mid, but no sound. I expected to get at least a click or something.

I'm still really curious about the presence of the Ohmite pots, and the "Special" stamp on the label.

Rick

Rick,

The presence of the Ohmite level controls is correct; AR used this type of control on the early AR-1s (this replaced the early AR-1 shorting straps), AR-2s, AR-2as and AR-3s up until 1961 or so. Also, mil-spec, oil-filled capacitors were the rule rather than the exception for all AR speakers built up until this 1961-1962 period as well -- perhaps a bit earlier. AR, as well as KLH, used a lot of war-surplus parts for the crossovers, and the oil-filled capacitors were used in these cases. KLH used these capacitors on the early model Fours, Sixes and Sevens, with a change to a cheap-O paper capacitor somewhat later, causing a huge service nightmare for KLH return service for some of the later KLH models with the epoxy woofers and paper caps. But as Kent points out, these oil-filled capacitors will probably last for an eternity without changing values, and the possibility of "leaking" oil from one of these sealed cans is extremely unlikely. You would have to shoot a hole in the can to get it to leak. Also, I don't believe that these relatively low-voltage mil-spec capacitors were filled with PCB, since this non-flammable dielectric oil was primarily used in high-voltage, high-temperature transformers and some capacitors in power stations and so forth where there was a risk of fire, etc.

The "signature" on the Masonite crossover board was simply a worker's QC signoff; the crossovers were built on a subassembly line on another floor of the 24 Thorndike Street Cambridge plant.

The AR-3 woofer without the ribs and damping rings was the AR-1-type woofer that was used in every AR-1 from around 1957 on up, and it was used in every one of the early AR-3s. In 1959 Roy Allison joined AR as an assistant to Edgar Villchur, and one of his first projects was to work on continuing improvement of the already impressive performance of the AR-3. One of the things he did around 1961 or 1962 was to update the cone with the annular ribs and damping rings to absorb any energy going up the cone on the higher end of its range, since the AR-3 had a 1 kHz crossover. The damping rings made a slight, but measureable, improvement in the smoothness of the high end of the woofer's response, but I don't think the improvement was even audible. Otherwise, the woofers were pretty much identical, with the early version without damping rings having one of the lowest free-air-resonance numbers for any of the AR woofers.

The word "special" probably denotes a finish variation, but I'm not sure. I've seen it before. AR speakers themselves were all the same for a given production run, and there were no consecutive-number pairs, special-speaker variations or special parts used or that sort of thing. Hope this helps.

--Tom Tyson

[dynaco_dan]

Here's an update. I used the white dot values for the 3a, which resulted in an awkward placement of the pots with regard to the lugs. Lug 2 on the Hi pot is precariously close to the windings on the Mid pot. I may change that.

This experience has given me some "insight" that I'll share. If you decide to use Ohmite pots,

1. don't
   
2. use L-pads
   
3. don't use Ohmites
   

There's no way the Ohmites are worth the hassle. What a PITA!

Anyway, here are shots, with cover on & off.

Kent

Hi Kent

If you have enough room, try an electrical 4" x 4" plastic box.

They may even come extra deep as well.

Just a thought for tonight.

[rwalton46]

Rick,

The presence of the Ohmite level controls is correct; AR used this type of control on the early AR-1s (this replaced the early AR-1 shorting straps), AR-2s, AR-2as and AR-3s up until 1961 or so. Also, mil-spec, oil-filled capacitors were the rule rather than the exception for all AR speakers built up until this 1961-1962 period as well -- perhaps a bit earlier. AR, as well as KLH, used a lot of war-surplus parts for the crossovers, and the oil-filled capacitors were used in these cases. KLH used these capacitors on the early model Fours, Sixes and Sevens, with a change to a cheap-O paper capacitor somewhat later, causing a huge service nightmare for KLH return service for some of the later KLH models with the epoxy woofers and paper caps. But as Kent points out, these oil-filled capacitors will probably last for an eternity without changing values, and the possibility of "leaking" oil from one of these sealed cans is extremely unlikely. You would have to shoot a hole in the can to get it to leak. Also, I don't believe that these relatively low-voltage mil-spec capacitors were filled with PCB, since this non-flammable dielectric oil was primarily used in high-voltage, high-temperature transformers and some capacitors in power stations and so forth where there was a risk of fire, etc.

The "signature" on the Masonite crossover board was simply a worker's QC signoff; the crossovers were built on a subassembly line on another floor of the 24 Thorndike Street Cambridge plant.

The AR-3 woofer without the ribs and damping rings was the AR-1-type woofer that was used in every AR-1 from around 1957 on up, and it was used in every one of the early AR-3s. In 1959 Roy Allison joined AR as an assistant to Edgar Villchur, and one of his first projects was to work on continuing improvement of the already impressive performance of the AR-3. One of the things he did around 1961 or 1962 was to update the cone with the annular ribs and damping rings to absorb any energy going up the cone on the higher end of its range, since the AR-3 had a 1 kHz crossover. The damping rings made a slight, but measureable, improvement in the smoothness of the high end of the woofer's response, but I don't think the improvement was even audible. Otherwise, the woofers were pretty much identical, with the early version without damping rings having one of the lowest free-air-resonance numbers for any of the AR woofers.

The word "special" probably denotes a finish variation, but I'm not sure. I've seen it before. AR speakers themselves were all the same for a given production run, and there were no consecutive-number pairs, special-speaker variations or special parts used or that sort of thing. Hope this helps.

--Tom Tyson

Hi Tom,

Thanks for the information. It all makes sense because the speaker showed no signs of having been entered before I did. I haven't opened my second speaker yet. I rather expect to find the usual pots in the crossover. The good news with the second cabinet is that the tweeter and mid are both working, quite nicely in fact. The pots, though, have the usual affliction. I expect once I open that cabinet, I'll have a pot restoration job to do, and maybe a cap replacement unless it has the same oil-filled caps that I've already encountered.

Are the Ohmite pots subject to the same corrosion problems as the more common pots in AR speakers? The ones that I discovered look like they could be new -- no signs of corrosion or wear. Would their direct contact with the fiberglass cause problems that might not be obvious to the naked eye?

Again, thanks.

Rick

[genek]

Also, I don't believe that these relatively low-voltage mil-spec capacitors were filled with PCB, since this non-flammable dielectric oil was primarily used in high-voltage, high-temperature transformers and some capacitors in power stations and so forth where there was a risk of fire, etc.

Nonflammable dielectrics would have been the standard for all MIL-SPEC condensors, regardless of the design voltage. In an application where people may be shooting at you, internal electrical faults are not the only potential risk of fire.

[tysontom]

Hi Tom,

Thanks for the information. It all makes sense because the speaker showed no signs of having been entered before I did. I haven't opened my second speaker yet. I rather expect to find the usual pots in the crossover. The good news with the second cabinet is that the tweeter and mid are both working, quite nicely in fact. The pots, though, have the usual affliction. I expect once I open that cabinet, I'll have a pot restoration job to do, and maybe a cap replacement unless it has the same oil-filled caps that I've already encountered.

Are the Ohmite pots subject to the same corrosion problems as the more common pots in AR speakers? The ones that I discovered look like they could be new -- no signs of corrosion or wear. Would their direct contact with the fiberglass cause problems that might not be obvious to the naked eye?

Again, thanks.

Rick

Rick,

The Ohmite controls are subject to corrosion and the usual "drop-outs," but to a lesser degree than the newer Pollock controls. Unless the speakers were in an unusually damp environment or the speakers were filled with rock wool instead of fiberglass, the controls usually continued to work pretty well. I believe my old AR-1s and AR-2s with the early controls have held up okay, but admittedly I haven't checked lately.

--Tom Tyson

[tysontom]

Nonflammable dielectrics would have been the standard for all MIL-SPEC condensors, regardless of the design voltage.

Possibly, but are you assuming this or do you know this for fact? Mineral oil, used as a dielectric, is non-flammable at room temperature.