KLH Model Thirty-Three speaker

[jessiAV]

JessiAV wrote previously:

"It might be helpful to know where the wire from the speaker's positive terminal connects to this crossover. I'm guessing it attaches to some of the open cap and resistor legs in the bottom photo? Also, additional photos from other perspectives might be useful. Is it possible to remark an image to show what switch connections you do have now in the

  Typically, KLH used a yellow wire to feed the tweeter, and sometimes put resistors across capacitors to shape the tweeter's response."

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  I'm thinking your schematic could be completely accurate Norm. And it follows typical KLH designs.   My guess is that the switch connects either the 9 o'clock, 10 o'clock  11 o'clock terminals to the 1 o'clock tab (8 uf capacitor).  This would always keep the 8 uf cap, 4 ohm resistor, and 3 ohm resistor/2 uf cap inline with the tweeter. Or, the maximum switch setting could connect the 10 o'clock and 3 o'clock terminals, but it seems less likely to me.

 Hopefully, Roy or Kent will chime in on this.

[jessiAV]

  Well, I just looked at information on these 33's at CSP that I was unaware of previously. Some rate them more highly than 17's apparently; very nice.  I'm excited for you!

   If you wish to bypass your 33's rear panel switch and set the level to "normal", I imagine you could simply jump the 7.5 ohm resistor, and cut off all tabs where they enter the switch, leaving all the caps and resistors connected as they were.

[jessiAV]

  Your Thirty Three's high frequency schematic:

 

Edited June 17, 2023 by jessiAV
needed to add "high frequency". Should have done a better job on modifying the 17's schematic, but I was in a rush.

[JKent]

Norman,

I think Jessi gives me too much credit. Roy's the crossover guru. But couldn't you use a new 3-position rotary switch? I use a Philmore #30-15303 for my KLH Model Eight aux input boxes. The switch is a 3 pole 3 position non-shorting type and I actually only use 2 poles but it works. 

If Jessi can suggest the correct 3-position switch type (2 pole? 1 pole?) I think my friend at Wayne Electronics should have it. That's not that far from you. Or if I have the right kind here I could send you one.

Kent

[jessiAV]

I believe Kent's Philmore switch should work nicely. Will the smooth shaft work with the Thirty Three's knob?

[RoyC]

I recommend replacing the rotary switch with a 3-way toggle switch. The rotary switch of the 33 is the same as that used in the 23 and 5 and was not nearly as reliable as the 3-way switch of the KLH 6, 17, etc...which is a standard on/off/on single-pole/double-throw type. In fact I think I still have some nice used KLH originals in the parts bin someplace.

On the other hand, Jessi's recommendation regarding the elimination of the switch is a simple solution and would work fine. I personally prefer the normal position for both the 17 and 6.

I once eliminated the rotary switch, opting for the "normal" circuit in the schematic Jessi posted above, but Instead of by-passing the 7.5 ohm resistor I replaced it with the series leg of an 8 ohm L-pad. This allowed me to vary the resistance from 0 to 8 ohms. It was fun, but certainly not necessary.

Roy

[Norman Nicolai]

 

33 minutes ago, RoyC said:

 

I once eliminated the rotary switch, opting for the "normal" circuit in the schematic Jessi posted above, but Instead of by-passing the 7.5 ohm resistor I replaced it with the series leg of an 8 ohm L-pad. This allowed me to vary the resistance from 0 to 8 ohms. It was fun, but certainly not necessary.

Roy

I really like the idea of eliminating the 3 position rotary switch for an L-Pad!

I guess I could keep everything else the same in the crossover wiring, just eliminate the rotary switch and place an L-Pad where the  7.5 Ohm resistor is.

Simplicity combined with more variability, I love it? Why didn't Henry Kloss ever implement something like that in any of his 2-way systems?

Do you know of a source for an appropriate L-pad?

Thanks, Roy!

 

 

 

 

 

 

 

[JKent]

I'd say here https://www.parts-express.com/L-Pad-15W-Mono-3-8-Shaft-8-Ohm-260-248?quantity=1 but I'm hoping Roy will give detailed instructions.

[RoyC]

6 hours ago, Norman Nicolai said:

I really like the idea of eliminating the 3 position rotary switch for an L-Pad!

We need to back up, Norm...I only mentioned the L-pad in reference to Jessi's illustration of by-passing the 7.5 ohm resistor, not replacement of the switch's 3 circuit options. The switch is providing a choice between 3 different circuits. As I said above, I only used the L-pad as a replacement for the 7.5 ohm resistor after "opting" for the "normal" position. I did completely remove the switch, but rebuilt the crossover up to the 7.5 ohm resistor. The L-pad was just an enhancement of the normal circuit. I essentially eliminated the "increase" option while providing the ability to variably attenuate the "normal" circuit to that of the original "decrease" position.

Unfortunately, If you want to retain the original increase/decrease/normal configuration a switch is necessary. I still like the reliable 3-way toggle used in the 17.

Roy

[Norman Nicolai]

Roy, just "spitballin" here, but would it be possible to rebuild the crossover to a single "increase" position (instead of "normal") and then place the L-pad between the crossover and the tweeter?

[RoyC]

1 hour ago, Norman Nicolai said:

Roy, just "spitballin" here, but would it be possible to rebuild the crossover to a single "increase" position (instead of "normal") and then place the L-pad between the crossover and the tweeter?

No...primarily because it wouldn't be able to compensate for the difference in capacitance. Besides, a toggle switch arrangement is more maintenance-free than any variable potentiomemeter (like an L-pad). Imo, there is no getting around removing the components connected to the old corroded rotary switches in order to proceed.

It should be noted that AR finally eventually went to toggle switches after the troublesome potentiometer era.

[Norman Nicolai]

Just so I know that my interpretation is correct, if I remove the bad switch and set the Model 33 crossover permanently to one position, the "Normal" position, the wiring should follow this schematic:

[RoyC]

4 hours ago, Norman Nicolai said:

Just so I know that my interpretation is correct, if I remove the bad switch and set the Model 33 crossover permanently to one position, the "Normal" position, the wiring should follow this schematic:

Yes

[Norman Nicolai]

I much appreciate the help and advice I’ve gotten from RoyC and jessiAV. Jessi, for putting together the schematic that deciphered the crossover, and RoyC for his ultimate guidance on what would work, and what wouldn’t work. Thanks too, to JKent for suggesting a switch, even if I ultimately wasn’t able to use it. 

The CSP community really is special. I don’t know any other audio forum that provides such useful, knowledgeable advice, so readily.

I’m hoping to have at least one speaker done in the next couple of days. I promise to post with my initial impressions of the 33 set permanently to the Norm-al position, and a follow up with photos when the project is completed.

Thanks.

[Norman Nicolai]

 

Just finished the crossover and put one of the 33’s back together. Last night I put a coat of Roy’s goo on the woofer surrounds. They probably need a second coat since they were really dried out. I’ll do that tomorrow. The tweeters are from a set of 17’s I picked up at the Delaware Valley Antique Radio Society swap meet in Kutztown, PA a few weeks ago. The original tweeters from the 33’s were dead.

It’s interesting that the 33’s are stuffed with a ton of fiberglass insulation, at least twice as much as the Model 17’s in a cabinet that’s only a tad larger than the 17’s.

I only finished one crossover in one speaker so I listened to it on my Heathkit W5M mono blocks paired with a Conrad Johnson PV-10 preamp. The 33 was on the right side and an Advent OLA on the left. I listened to some Gershwin orchestral music (Porgy and Bess) and Copeland’s Appalachian Spring.  First impression was favorable compared to the Advent OLA. That’s not surprising since Advent OLA’s have been coming down in my estimation after listening to more AR and KLH speakers. Plus the Advents are a better “rock” speaker. Especially stacked Advents. The 33’s seemed to have just as good a bass as the Advents and cleaner, more defined highs.  The Advents also seem to be a bit more efficient than the 33’s. I seem to be getting slightly more volume from the OLA’s.

The next step is to compare them to my KLH 17’s, once I finish the other 33. So far, I’m pleased and a little impressed. Of course we’re talking about 15 minutes of listening to only one style of music. That’s not much to go on.

[jessiAV]

Looking forward to your review with both speakers.

[Norman Nicolai]

After I finished wiring the first 33 to a single position crossover I decided “what the hell” and took the three position crossover switch from the Model 17’s that I took the tweeters from, and used it in the second crossover. The only difference from the Model 17 wiring is that I wired a 4 ohm resistor between the 8 uF capacitor and the positive terminal of the tweeter, as in the original schematic. It worked well, so I retro fitted the other three position toggle switch into first 33 crossover.

Both speakers sound good. (But they still don’t hold a candle to my AR 91’s…)  I’ve yet to lug them up to the LR to A/B them to my set of restored KLH 17’s. That still will be the best comparison to a similar KLH speaker.

In the meantime, I have a set of KLH 17 cabinets and woofers lying around, so I may attempt to sell them on Craigslist separately. I also have to finish the cabinets on the 33’s. They’re both sanded, but do not have a finish applied to them. I’ll post photos when the cabinets are finished.

Anyone need a KLH Model 17 woofer? 

[jessiAV]

   I do!   😃

[Norman Nicolai]

Just gave the 33's and the 17's a side by side listen. The 33's definitely have more bass, although it can be just a little bit boomy at times. For some reason the mid-range is lacking on the 33's compared to the 17's. Odd when you consider that the speakers and crossovers are almost identical, except that the 33's are ported, the cabinets are slightly bigger on the 33's, and there is an additional resistor in the 33 crossover.

First impression: The 33 is a speaker more suited to rock than classical, jazz, or acoustic music. I'm guessing that Henry and the engineers at KLH thought that they were losing market share to other speaker makers, companies that manufactured "west coast" designs for younger listeners, so the 33's were born to fill in that niche. 

 

[RoyC]

23 hours ago, Norman Nicolai said:

Odd when you consider that the speakers and crossovers are almost identical, except that the 33's are ported, the cabinets are slightly bigger on the 33's, and there is an additional resistor in the 33 crossover.

Nice project, Norm.

On the surface it all makes sense. The larger ported cabinet would explain the difference in the character of the bass response, and an additional 4 ohms of series resistance with the tweeter would have a noticeable effect on the midrange response.

[Norman Nicolai]

The Model Thirty-Three restoration is done. Many thanks to the folks who helped me out along the way, RoyC, jessiAV, and JKent, specifically. I still think the 33’s shine as a rock speaker, but lack depth for classical and jazz. I think they may have been designed for that purpose, but that’s a discussion for another day.

I’ll let the photos speak for themselves. Some are “before” and most “after”.

[JKent]

Beautiful

[Norman Nicolai]

Thank, Kent.

Now, on to the Model Twenty-One radio! 

[jessiAV]

Wow! A remarkable improvement! And I really like how nice the wood surrounding the grills looks now. A lot of time and care in these cabinets, and the results show that.

  Thank you for this update 😀

[Norman Nicolai]

I don’t think the basement photos really captured how good the speakers look.

I also upgraded the original KLH binding posts and installed a 3 position crossover switch from a KLH Model 17.