Russian K75-10 cap quick review

Hey folks - I know many of us spend a good bit of time tinkering with crossover networks for our high efficiency systems.

I’ve typically run PIO GE Dielektrol motor run caps - mainly because they’re cheap enough to have tons of them around for tinkering and sound good enough.

I’ve always told myself when I got a network/ system in place I liked well enough to keep around for a long time, I’d cough up the scratch for really good caps and be ‘done’ (lol).

Anyhow, I wanted to try something different for less money than ‘destination caps‘ might cost, and rolled the dice on a bunch of Russian K75-10 so-called hybrid PIOs, so called because they are reputed to use a dialectric consisting of paper and polyethelene terephthalate (mylar) in oil.

I just got a new pair of Markwart networks installed using (mostly) K75-10s, and can report they sound fantastic. Outstanding texture and timbral definition... colorful, dramatic, juicy mids, authoritative lows and nicely extended, if not quite as extended as modern polys might be. Nice delicate highs though.

Still breaking in, but they really complement the Altec sound for me.

They’re quite unlike anything I’ve ever heard - they kinda sound like if a modem company were going to design a vintage-vibe cap, and succeeded wildly. They kill the motor run caps for me.

Anyway, if you’re into having contests to see if friends can identify which model reverb processor is being used on a given recording based on decay texture, then looking up the correct answer in back issues of Tape Op (Eventide SP2016!) these are the caps for you.

Oh yes, they’re HUGE.
 

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Fran604g

Just Call Me Junior
Hey folks - I know many of us spend a good bit of time tinkering with crossover networks for our high efficiency systems.

I’ve typically run PIO GE Dielektrol motor run caps - mainly because they’re cheap enough to have tons of them around for tinkering and sound good enough.

I’ve always told myself when I got a network/ system in place I liked well enough to keep around for a long time, I’d cough up the scratch for really good caps and be ‘done’ (lol).

Anyhow, I wanted to try something different for less money than ‘destination caps‘ might cost, and rolled the dice on a bunch of Russian K75-10 so-called hybrid PIOs, so called because they are reputed to use a dialectric consisting of paper and polyethelene terephthalate (mylar) in oil.

I just got a new pair of Markwart networks installed using (mostly) K75-10s, and can report they sound fantastic. Outstanding texture and timbral definition... colorful, dramatic, juicy mids, authoritative lows and nicely extended, if not quite as extended as modern polys might be. Nice delicate highs though.

Still breaking in, but they really complement the Altec sound for me.

They’re quite unlike anything I’ve ever heard - they kinda sound like if a modem company were going to design a vintage-vibe cap, and succeeded wildly. They kill the motor run caps for me.

Anyway, if you’re into having contests to see if friends can identify which model reverb processor is being used on a given recording based on decay texture, then looking up the correct answer in back issues of Tape Op (Eventide SP2016!) these are the caps for you.

Oh yes, they’re HUGE.
So, what Altec drivers are you using?
 

John Frum

Secret Society Member
So those GE polypropylene-in-oil caps were, in their later incarnations, made by Genteq in Mexico, first under license by GE, and later having bought out GE’s cap manufacturing with the perk of getting to continue to use the GE name. To the best of my knowledge, the currently available Genteq caps are the same product.

Which is to say that I’m sitting on a pile of them for my Markwart 604-8G build! 😂
 
Anyone use as coupling caps?
I have actually - in a few vintage restorations. I’ve used them in a few spots in my Scott 299b and Mcintosh mx-110z.

They sound more similar to a good quality PIO than to say, a Mundorf Supreme or others higher up the Mundorf line. They don’t have that kind of Mundorf slippery modern sheen. Nor do they have any of the toppiness I associate with a lot of hifi film caps.

They are a more colorful than vintage sounding PIOs. Not more colored nessicarily, just more fun to listen to. Wetter. More pop and drama. More lively. But not by virtue of top end emphasis - more by virtue of an unusually juicy and finely textured midband. I guess I’ve never really heard anything quite like them.

A critic would probably say they’re midrange heavy, but like, so is music. I don’t find them lacking on the top end at all and I really dig what they do for the LF.

The big (ha) issue using them as coupling caps is that their size can be prohibitive.
 

Fran604g

Just Call Me Junior
Hey folks - I know many of us spend a good bit of time tinkering with crossover networks for our high efficiency systems.

I’ve typically run PIO GE Dielektrol motor run caps - mainly because they’re cheap enough to have tons of them around for tinkering and sound good enough.

I’ve always told myself when I got a network/ system in place I liked well enough to keep around for a long time, I’d cough up the scratch for really good caps and be ‘done’ (lol).

Anyhow, I wanted to try something different for less money than ‘destination caps‘ might cost, and rolled the dice on a bunch of Russian K75-10 so-called hybrid PIOs, so called because they are reputed to use a dialectric consisting of paper and polyethelene terephthalate (mylar) in oil.

I just got a new pair of Markwart networks installed using (mostly) K75-10s, and can report they sound fantastic. Outstanding texture and timbral definition... colorful, dramatic, juicy mids, authoritative lows and nicely extended, if not quite as extended as modern polys might be. Nice delicate highs though.

Still breaking in, but they really complement the Altec sound for me.

They’re quite unlike anything I’ve ever heard - they kinda sound like if a modem company were going to design a vintage-vibe cap, and succeeded wildly. They kill the motor run caps for me.

Anyway, if you’re into having contests to see if friends can identify which model reverb processor is being used on a given recording based on decay texture, then looking up the correct answer in back issues of Tape Op (Eventide SP2016!) these are the caps for you.

Oh yes, they’re HUGE.
@Baaronj Would/could you be kind enough to label your photo with the combinations of values you used to arrive at the proper specs? I may build this version at some point just for fun.
 
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I bought a box of 2.2uF K75-24's ( the 400 volt version ) back when I was in my late 40's ( I'm now in my mid to late 60's ).
- Maybe worth pointing out is that back in 2002 these were not sold as PIO caps ( they were described as just straight PETP or Mylar ).
- It actually makes sense that they aren't just the standard Mylar as we know it >> since they have none of the 'milky opacity" description that poly-ester/mylar caps normally get associated with.

At the time of purchase my ears were definitely more wideband and acute than they are now and I thought the K75-24's were the most distinctly dramatic caps that I had heard . I never put them to use since they were just "too much" .

The "problem" was they sounded to me like they had a built in Aphex Aural Exciter hiding within them with the "frequency select knob" adjusted for too low a frequency ( + if Baaronj is in the biz then he'll know what I'm talking about ).

I've always liked a bit of Aphex in my live mixes ( especially after tweeters in PA systems became somewhat passe due to the adoption of Meyers Sound products >> this was back in the 1980 + 90s's ).

Some might find the 400V version too euphonic and/or etched ( I know I did back then ) but now some 18 years later I don't have that same opinion.
- For some reference I've also added a Fostex 945 tweeter to my Altec 288 / Emilar EH500 setup to add some more "air" ( I think mostly due to age related HF hearing loss ) .

Early this year I also added a few K75's into fulltime use within my horn circuit.



@billfort , if you want to borrow a hand-full for use in your HF circuit, simply message me ( + I'll drive them up to you from Richmond Hill ) for a Covid-Free hand-off .

:)
 
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@Baaronj Would/could you be kind enough to label your photo with the combinations of values you used to arrive at the proper specs? I may build this version at some point just for fun.
Sure thing...I think I can actually do it from memory:

Posting the pic again for reference:
047CD36E-2B92-4A7D-83DE-A26F6371900C.jpeg
Starting at the bottom left, and moving up through the HF signal path:

1) 6uf value comprised of:

3.3uf x 1 (big one on the bottom)
1 uf x 2 (the two outermost caps
.3 uf x 2 (the two smallest caps)

2) 12uf value comprised of:

10uf x 1 aka ‘smoke grenade’
1uf x 2 (it’s hard to see in the pic, but there are two)

3) 6uf value comprised of:

10uf x 1 motor run cap
in series with:
10uf x 1 K75-10
the two caps above in parallel with:
1uf x 1 K75-10

I ran out of large value K75-10s and had to get creative for the final cap in the HF path.

There is surely a better way to build these networks with K75-10s than I did. I didn’t actually acquire these caps with the explicit intention of building the Markwart networks with them....I was just going for flexibility in the neighborhood of usual 8ohm Altec network values of 2-12uf. There is, eg, a 4.7uf commonly available I didn’t have on hand.

The lone black cap is the 25uf value in the LF section....I happened to have it from a previous Markwart build and couldn’t stomach the thought of how many 4uf motor run caps I’d have to parallel to get to 25uf. I’m in the process of sourcing 2x 10uf, 1x 4.7uf, and 1x .3uf K75-10s for that spot. I got all the K75-10s on the auction site.... I’ve never come across a North American source for these caps, so they all came from Eastern Europe.

I’m probably going to sell the Iconic super crossovers I was using previously on the classifieds. I noticed they were doing something weird right at the crossover region and eventually dug up an old post from one of the designers of those networks stating they were explicitly designed for the 604-8H’s Mantaray horns and thus have the crossover centered about 100hz below the unloading point of the G.
 
I bought a box of 2.2uF K75-24's ( the 400 volt version ) back when I was in my late 40's ( I'm now in my mid to late 60's ).
- Maybe worth pointing out is that back in 2002 these were not sold as PIO caps ( they were described as just straight PETP or Mylar ).
- It actually makes sense that they aren't just the standard Mylar as we know it >> since they have none of the 'milky opacity" description that poly-ester/mylar caps normally get associated with.

At the time of purchase my ears were definitely more wideband and acute than they are now and I thought the K75-24's were the most distinctly dramatic caps that I had heard . I never put them to use since they were just "too much" .

The "problem" was they sounded to me like they had a built in Aphex Aural Exciter hiding within them with the "frequency select knob" adjusted for too low a frequency ( + if Baaronj is in the biz then he'll know what I'm talking about ).

I've always liked a bit of Aphex in my live mixes ( especially after tweeters in PA systems became somewhat passe due to the adoption of Meyers Sound products >> this was back in the 1980 + 90s's ).

Some might find the 400V version too euphonic and/or etched ( I know I did back then ) but now some 18 years later I don't have that same opinion.
- For some reference I've also added a Fostex 945 tweeter to my Altec 288 / Emilar EH500 setup to add some more "air" ( I think mostly due to age related HF hearing loss ) .

Early this year I also added a few K75's into fulltime use within my horn circuit.



@billfort , if you want to borrow a hand-full for use in your HF circuit, simply message me ( + I'll drive them up to you from Richmond Hill ) for a Covid-Free hand-off .

:)
HA. I know the Aphex well. And I know exactly what you mean....pure speculation here, and I’m assuming you don’t mix live now as much as you did then, but I wonder if some part of your being more comfortable with the sound now has to do with how accustomed you were in the 80s/90s to hearing (presumably) RTA’d/flattened room curves in a live setting, and that your ears were very sensitive to the departure from it these caps caused. My brother is a recovering FOH guy, and I find the less he does sound, the more accepting he tends to be of the, err, lack of uniformity in domestic audio.

Regardless, this is fascinating. All the caps in my networks here are the 250V. As I mentioned in the previous post, I ran out of K75s on this build and went with a Dayton I had on hand for the LF section. I wonder now of I should stick with the networks as is.

They really do have a big dramatic sound, but I don’t find them to be etched. I had my hearing checked a year or so ago by an audiologist and she was surprised at the HF perception I still had given my age (40s). The main thing I’ve found that has changed with my hearing is that I’ve become more sensitive to MF and lower HF.... it seems like it takes less energy for mids and highs to sound too hot for me than it used to.

What’s interesting about these caps to me is that, while they have this big dramatic rendering of the MF, they sound less edgy in the MF range than motor run caps tend to. Maybe that’s the LF emphasis you mentioned? The absence of anything grating is probably what I’m liking best about these caps so far.
 

Fran604g

Just Call Me Junior
Sure thing...I think I can actually do it from memory:

Posting the pic again for reference:
View attachment 28782
Starting at the bottom left, and moving up through the HF signal path:

1) 6uf value comprised of:

3.3uf x 1 (big one on the bottom)
1 uf x 2 (the two outermost caps
.3 uf x 2 (the two smallest caps)

2) 12uf value comprised of:

10uf x 1 aka ‘smoke grenade’
1uf x 2 (it’s hard to see in the pic, but there are two)

3) 6uf value comprised of:

10uf x 1 motor run cap
in series with:
10uf x 1 K75-10
the two caps above in parallel with:
1uf x 1 K75-10

I ran out of large value K75-10s and had to get creative for the final cap in the HF path.

There is surely a better way to build these networks with K75-10s than I did. I didn’t actually acquire these caps with the explicit intention of building the Markwart networks with them....I was just going for flexibility in the neighborhood of usual 8ohm Altec network values of 2-12uf. There is, eg, a 4.7uf commonly available I didn’t have on hand.

The lone black cap is the 25uf value in the LF section....I happened to have it from a previous Markwart build and couldn’t stomach the thought of how many 4uf motor run caps I’d have to parallel to get to 25uf. I’m in the process of sourcing 2x 10uf, 1x 4.7uf, and 1x .3uf K75-10s for that spot. I got all the K75-10s on the auction site.... I’ve never come across a North American source for these caps, so they all came from Eastern Europe.

I’m probably going to sell the Iconic super crossovers I was using previously on the classifieds. I noticed they were doing something weird right at the crossover region and eventually dug up an old post from one of the designers of those networks stating they were explicitly designed for the 604-8H’s Mantaray horns and thus have the crossover centered about 100hz below the unloading point of the G.
Thank you! I'm intrigued, and if there was a US source I think I'd build another set of xovers to play with. I still own the N604-8K's Bill @GPA sold me years ago, and it would be fun to swap and play with their useful components.
 

billfort

Administrator
Staff member
- For some reference I've also added a Fostex 945 tweeter to my Altec 288 / Emilar EH500 setup to add some more "air" ( I think mostly due to age related HF hearing loss ) .

Early this year I also added a few K75's into fulltime use within my horn circuit.



@billfort , if you want to borrow a hand-full for use in your HF circuit, simply message me ( + I'll drive them up to you from Richmond Hill ) for a Covid-Free hand-off .

:)

Hi Earl, nice to see you here and Welcome! I think we have crossed path before and it's great to hear from someone who is so close to me that may have ended up on the same audio path. I'd love to hear more about your system; I have a pair of 299 re-diaphragmed and tuned up by Great Plains into 288 sitting on the shelf for a 'someday' system, and would love to hear your impression of them on Emilars.

When I get back to messing with my system, these caps really seem like something I want to try, I might take you up on your offer and would love to have a chat - thank you!

I don't know what part the GE motor runs play in my Markwart crossover's performance - I started and ended with them in every position other than a single 1uF Solen, but I love the way this crossover works on the 604-8G. I liked these drivers (a lot!) when I first got them using the stock Altec crossover but I found them a little dark on top and the midrange too in-your-face and grating at times. The Markwart just nailed it to my ears though, so I never second-guessed the GEs, hell, I still have 'temporary' sand-cast resistors and a dreaded level pot in the circuit!



What you all are saying on the how these K75s sound though, has me wanting to give these whirl. I really want to replace those resistors, take the pot out of the circuit and re-think the binding posts too (maybe no posts, solder everything direct) so it'll be a round of changes and don't want to throw in too many variables at once.
 
Thanks muchos for the welcome Bill.

I think the great thing about these K75's is they are such a dramatic departure from so many caps > meaning they should offer a pretty cheap aural education ( all things considered ).

re; the Emilars.

The EH500/Altec 288 combo works very well within an MTM configuration ( which is how I use them ).

It's probably best to simply borrow mine at some point ( with adapters ) to form your own impressions ( since I'm not about to wax-on eloquently just to convince someone to pursue a pair of almost unobtanium horns ) .

They do "image" quite well // which is one reason I keep them in the system ( I do wish they were a smidge bigger and made of wood ) .

Anyways, bigger horn drivers ( on much larger horns > compared to the 604's ) are a completely different rabbit hole to jump down ( I'm sure you realize ).

IMHO, one still wants to build up a ( virtual ) point-source system to create a fair comparison to what you already enjoy and experience.
- This means upscaling to an MTM build of some sort.

That translates to you needing to buildup at least another pair boxes to house some top "M" speakers ( while using the 604's woofer ) as the bottom of the MTM ( new crossovers + more amps, not-with-standing ).
- Oddly enough, I've found "asymmetrical" MTM's ( iow; a 12 over a 15 ) can work ( imaging wise ) just as well as dual 15's ( maybe better in some aspects ).
- The top box can even be a couple of db down ( compared to the bottom box ) and still be an important contributor to the point source effect.
- Think of some 8-16 ohm Altec 414 working over an 8-ohm, 93-95db efficient, JBL woofer model ( both, mostly covering the same range ).

The Focal Grand Utopia is one such example ( I do believe ) of an asymmetrical MTM .



Just replace the "cone+dome" middle section with a radial horn ( to get the vision ).


:)
 
The EH500/Altec 288 combo works very well within an MTM configuration ( which is how I use them ).


Hey Earl - where did you come by 1.4”—->2” adapters for this setup? I’ve wanted to try 288s on my EH500s but hadn’t yet gotten around to searching for adapters.

Agree the EH500s image very well.
 
Baaronj,

They were made by Selenium.

I've had these adapters for a good 20 years now ( they're much like an upgraded JBL 2330 adapter but with nicer casting ( they are definitely NLA as a new product ).

Currently Eminence offers a 1.4" to 2" adapter ( they just need to be drilled out to accept the Altec 3-bolt pattern ) .
- They are the most economical solution that I know about.

It's called the Eminence HA14-2 . It's also a nice casting .



:)
 
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