Ohmite Rheostat replacement?

[xmas111]

Think I might buy some of these and see if they'll work in place of the Ohmite rheostat.

Good price.....delivery time not so good.

Maybe we could find a place that sells them. The guy on ebay only has a couple.

http://www.ebay.com/itm/25W-15-OhM-CERAMIC-WIREWOUND-POTENTIOMETER-PPB-25G-SOVIET-MADE-ORIGINAL-BOX-/161006083683?pt=LH_DefaultDomain_0&hash=item257cb5de63

What do you guys think?

John

[ra.ra]

I'll let the electronics wizards chime in, but it sure looks like a heavy duty little bugger. The control shaft is a bit long, but with your tool kit that can be reasonably modified. I like the wiring terminals, but I'm curious why the ceramic shaft might be so deep? This device (from Bulgaria) looks almost identical, quantity limited.

http://www.ebay.com/itm/PPB-25G-15ohm-22ohm-15-22-ohm-25W-25-Watt-Ceramic-Wire-Potentiometer-Rheostat-/370734006167?pt=LH_DefaultDomain_0&hash=item565177ff97

[JKent]

They're both from Bulgaria and undoubtedly identical. One caveat: These have open backs like the Ohmites so will require some sort of cover.

Kent

[xmas111]

I just bought the five units the two sellers had.

Not sure when I'll receive them but I'll report back when I do.

John

[xmas111]

In case any of you guys are interested there's 5 more of these Russian made pots up for sale on ebay.

http://www.ebay.com/itm/25W-15-OhM-CERAMIC-WIREWOUND-POTENTIOMETER-PPB-25G-SOVIET-MADE-ORIGINAL-BOX-/151126528520?pt=LH_DefaultDomain_0&hash=item232fd7d208

I haven't received mine yet, hopefully this week sometime.

John

[xmas111]

Received the Russian pots the other day. Not to bad for delivery time....12 days from Bulgaria to Plymouth, MA.

They look pretty well made, very solid. They measure exactly 0-15 ohms. Other than dimensional differences the Russian pot as has less contact between the wiper and the wire. Almost point contact.

I haven't decided if I'm going to use them in the 2ax's or not. I also have the Ohmite pots. Guess I'll flip and coin to see what way I go.

Here's a few pic of the two pots together.

John

[Mafia1976]

Hey guys I found these & wondered if they are similar to what AR use?

25 Ohm Wire Wound Potentiometer, standard shaft. Body Diameter 22mm.

[Carlspeak]

Hey guys I found these & wondered if they are similar to what AR use?

25 Ohm Wire Wound Potentiometer, standard shaft. Body Diameter 22mm.

Exactly what are "THESE"?? (i.e. brand, model #, etc.)

[Mafia1976]

Hope the link works. http://www.falconacoustics.co.uk/resistors-ceramic-wire-wound-metal-oxide-loudspeaker-crossover-network/wire-wound-pots-switches/wire-wound-25-ohm-potentiometer-variable-resistor.html

[JKent]

Ohmites (and A_P) pots are 15 ohm, 25w and not 25 ohm.

I have not tried them yet but I am tempted to try the stepped attenuators http://www.classicspeakerpages.net/library/acoustic_research/special_sections/mods_and_tweaks/sa-16-ar_stepped_attenuator.pdf

Of course plain ol' cheap L-pads work well.

Kent

[RoyC]

Hope the link works. http://www.falconacoustics.co.uk/resistors-ceramic-wire-wound-metal-oxide-loudspeaker-crossover-network/wire-wound-pots-switches/wire-wound-25-ohm-potentiometer-variable-resistor.html

Wrong resistance...and no power rating is specified.

Roy

[JKent]

How 'bout these?

http://www.aliexpress.com/item/15-Ohm-25W-Watt-Ceramic-Power-Rheostat-Variable-Resistor/930027165.html

$23.18 for a pair ($11.59 each) with free shipping from China. Don't know a thing about the quality. They have open backs like the Ohmites.

Kent

[RoyC]

How 'bout these?

http://www.aliexpress.com/item/15-Ohm-25W-Watt-Ceramic-Power-Rheostat-Variable-Resistor/930027165.html

$23.18 for a pair ($11.59 each) with free shipping from China. Don't know a thing about the quality. They have open backs like the Ohmites.

Kent

Hi Kent,

They look OK....and at a much better price than Ohmites. I still prefer a $3 Erse L-pad and a 50 cent 25 ohm resistor. It is a reliable arrangement with no open backs to deal with.

Btw, I recently worked on a person's AR-3's who had begun the work himself a couple of years ago, and who had installed Ohmites. I found they were not measuring properly. They were not corroded, but had developed a tarnish. I had to remove his protective barrier/sub-enclosure to get to them. Deoxit did the trick. I share this story, so people thinking Ohmites are the answer to the AR control problem are not lulled into a false sense of security. They are expensive, require a protective back to be installed, and will still need cleaning at some point. Better make sure that protective sub-enclosure can easily be removed.

Roy

[DDGP1027]

Hi guys,

I'm currently in touch with www.uraltone.com located in Finland who can furnish a 16ohm/25 watt pot. The person I'm in contact with, a certain Mikko who is extremely helpful and who has refurbished his own AR5, AR6 and AR2 with these pots has explained that they are open-backed and of course need to be sealed tp prevent the ingress of the rockwool. I'm awaitng a reply to see exactly how he "sealed" these pots.

[JKent]

Hi Roy (et. al.) and welcome DDGP1027!

Having installed Ohmites in my AR-3a's I can say it was a real hassle. Your finding that these "built-like-a-tank" pots corrode and go out of spec, like the reviled A-P pots is disconcerting but just underscores your point: L-pads (+ resistors) are the ideal replacements. Good to know Erse also sells them (besides PE and Madisound).

I would be interested to hear more about the stepped attenuators but let's face it: For most of us the level controls on the backs of our speakers are a "set it and forget it" thing. I doubt there is a lot of fine-tuning with these things. If people really did adjust the mid and tweeter levels for every recording more speakers would have those dials on the front baffle, like Avid.

Kent

[Mafia1976]

My apologies all of my AR speakers have the switch on the rear & 9's have the switches on the front.

But if anyone in the UK requires caps etc they are very helpful & fast to deliver.

[ra.ra]

Good discussion here, and two things I like to keep in mind. JKent's comment that we "set it and forget it" is probably very true for most of us - - - once I set things up to my liking, the control usually stays there. Also, sometimes I hear many voices advocate bypassing the pot altogether, but I've learned here on CSP that it is important to keep the resistance in the circuit. Regarding the older AR two-way speakers at least, my preference normally tends toward the maximum tweeter output, and that works best with my inclination to have some absorptive surfaces in my listening rooms.

So, our options are:

1. Restore original A-P pots - many of you hate these buggers, but I will probably continue to tear these apart and try to re-use, if possible. This process has worked for me, even tho' I agree that it is a somewhat flawed component.

2. Ohmite replacements - very robust build, far too expensive, and now Roy has documented long-term performance issues.

3. Bulgarian pots - I really liked this alternative discovery, much better price, but alas, they seem to be extinct now.

4. Chinese pots - good find, JKent, looks like a similar product.

5. L-pads - although I still have not tried this approach, I plan to get some in my personal parts box, along with req'd resistors.

Looking at Erse site, I found only two L-pads: 100W/8ohm and 15w/8 ohm. Aren't we looking for 25w/15 ohm?

[RoyC]

.

Looking at Erse site, I found only two L-pads: 100W/8ohm and 15w/8 ohm. Aren't we looking for 25w/15 ohm?

The 15 watt version is the one to use...Vintage AR and AB Tech have sold boatloads of these with absolutely no problems with power handling (and adding a 10 watt, 25 ohm parallel resistor increases the power handling somewhat). The series and parallel resistance of an "8 ohm" L-pad acts differently than a 15 ohm pot...apples and oranges, so disregard this spec. The "8 ohm" spec of an L-pad refers to the control maintaining a theoretical 8 ohm driver's impedance near 8 ohms at all settings. This is not what the "15 ohm" spec of a pot is referring to.

Roy

[ra.ra]

Thanks for clarification, Roy, as always.

[xmas111]

I wonder if putting dielectric grease on the Ohmite or Russian pots would prevent any tarnishing.

Of course it would then be imperative to make sure any enclosure used would keep any stuffing from getting in.

John

[JKent]

Those Russian pots from Bulgaria are back:

eBay item number:151216470866

$16 each ($8 + $8 shipping with no combined shipping discount).

The listing shows 8 available.

But use L-pads

-Kent

[xmas111]

But use L-pads

-Kent

just kidding....sorry, could resist Kent!

[ra.ra]

Hot properties indeed, those Iron Curtain pots - - - here today (yesterday), gone tomorrow (today). All sold, as of this post.

Curiously, I began to follow stupidhead's parallel post on AK about his 4x restoration, and stumbled upon this comment from Roy (1.19.14, post #50) about AR-4x tweeter controls (in blue, below). These things look just like the vaunted L-pads I've not yet used, but apparently they have different characteristics. Oddly, just a few days ago. I found something very similar (altho' mine were 15 ohm, not 16 ohm, see pics) in a pair of very dilapidated AR-3 cabinets I am considering trying to revive. I have read much about the original Aetna-Pollaks; followed trials and tribulations about the robust Ohmite replacements; same for newly-found Russian-Bugarian versions; embraced the option for 3-position Euro switches (per 4xa resto); but this is the first I've heard about legitimate 16 (or 15?) ohm Japanese replacement pots which are yet another viable option for tweeter control.

My two pots shown are completely frozen up, so are probably headed for the scrap pile. If anyone wants one for dissection, lemme know.

Early replacement controls like yours (made in Japan) are actually legitimate 16 ohm replacement pots. They are no longer available! Today's new "AR replacements" being sold on Ebay and elsewhere look exactly the same, BUT are actually 8 ohm (15 watt) L-pads. They will work, but have different electrical and sonic characteristics. They are also available from websites such as Parts Express, Madisound, and Erse for $4 to $7 each.

Mr. Head's AK thread:

http://www.audiokarma.org/forums/showthread.php?t=568900&page=4

[RoyC]

Curiously, I began to follow stupidhead's parallel post on AK about his 4x restoration, and stumbled upon this comment from Roy (1.19.14, post #50) about AR-4x tweeter controls (in blue, below). These things look just like the vaunted L-pads I've not yet used, but apparently they have different characteristics. Oddly, just a few days ago. I found something very similar (altho' mine were 15 ohm, not 16 ohm, see pics) in a pair of very dilapidated AR-3 cabinets I am considering trying to revive. I have read much about the original Aetna-Pollaks; followed trials and tribulations about the robust Ohmite replacements; same for newly-found Russian-Bugarian versions; embraced the option for 3-position Euro switches (per 4xa resto); but this is the first I've heard about legitimate 16 (or 15?) ohm Japanese replacement pots which are yet another viable option for tweeter control.

Hi ra.ra,

The 15 ohm pots in your photo (I may have have been mistaken about the 16 ohm value) were excellent AR replacement potentiometers, which were sold into the mid 90's by the "authorized" AR parts source, AB Tech. They are usually stamped with the resistance value on one side, and many (not all) are stamped "Japan" on the other side. As I mentioned in my AK post, although they are virtually identical in appearance to the common (Chinese) 8 ohm L-pads available today, they are no longer available....and have not been for quite some time.

It should be noted that AB Tech (and others) have not changed the description of the generic 8 ohm replacement L-pads they sell at rather high prices today as AR replacements. In fact, in some cases the "8 ohm" stamp is being removed to deceive folks into paying more for them as "AR replacement controls". ABT still uses the term "potentiometer" on their website. These are readily available from a number of speaker parts dealers for much less.

As I've mentioned before, all variable controls (Ohmite, Russian, to the Chinese 8 ohm L-pads described above) will require servicing at some point. Those of you boxing in your open-back replacement controls should build in easy access for the future.

Roy

[stupidhead]

Hi guys,

I am thrilled that my 4x restore project is getting action here as well. Thanks to all for the interest and input to date. It has really been an eye opening experience, and I am now thirsting for more info on this topic in general, and I am certain I will be looking for another set of AR's to do a restore on, from what I can tell probably a set of AR 3's. As for the technical aspect commented on here, I will get a pic of the side of the pot (referred here foreward as the mongrel) to verify the rating referred to by Roy. I am including a pic here (a CSP exclusive) of the pre restore bottom corner of one of the speakers, and am here to tell you the end result will be quite different! The badges have shined up nicely, Mrs. Stupidhead is working on the grille cloth, and I have put the first coat of oil on the prepared walnut surfaces.

I will post the other pic(s) later, and thanx again to all, but particularly Roy.