Crossover for 1940-41 optional hi-fi system

[David C. Poland]

Need some input.

Anyone have the optional speaker system in working order for your Scott Philharmonic, Phantom Deluxe or Laureate?    

And did you service the crossover, replacing the pair of caps inside?

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The outboard crossover has the output transformer and sockets for woofer and tweeters.

Seem to be 5 crossover versions that plug into the Amp in place of the standard 38 ohm spkr.

The optional hi-fi speaker system uses an 8 ohm woofer and 16 ohm tweeters.

Overview - crossover type chronology from early 1940 to early 1942:

1st:  large crossover - with 2 K cycle  cut off. No small cable to receiver.

2nd  large crossover - with 6 K cycle cut off. No small cable to receiver.

3rd   large crossovers - with 6 K cycle cut off - and small cable to receiver.

4th  small crossover - with 6 K cycle cut off - no rectifier & small cable to receiver.

5th  small crossover  - with 6 K cycle cut off - rectifier tube for tweeter field coils & small cable to receiver. 

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I followed the Riders diagram (Vol 14 -pg 12) to change a type 3 to a type 2, removing the small cable because my early Phantom Deluxe receiver lacks the small socket that controls tweeter function of later receivers. I have double checked the wiring against the diagram and all components have proper continuity: field coil, output transformer, point to point wiring, woofer voice coil, tweeter voice coils. I replaced the 2.35 MFD caps inside. My early Phantom Deluxe plays fine with the standard 38 ohm speaker. But the optional speaker system fails to produce audio.

I just returned from Kent's. We compare my recapped crossover with another unrestored crossover he has. And tried both mine and his on another working Phantom Deluxe. Neither his crossover nor mine produced audio using the correct 8 ohm woofer.

Kent just finished restoration of an FM Phantom Deluxe. - a late production with Jones plugs. It plays fine on a standard speaker. His crossover is unaltered wiring but for replacement  of the 2.35 MFD caps inside. But his recapped type 5 crossover speaker system fails to produce any audio. 

So we are both perplexed with our respective multi unit hi-fi speaker systems at the moment.

Hence,  a request for comments from anyone with functioning optional multi unit speaker system.

[Karl Sherwin]

David, I don't have my notes and crossover infront of me, but a thought - Do you have the 4 pin external speaker plug installed, and, does it have the jumper that connects the OT to the crossover?

I had a dickens of a time comparing my crossover wiring to Riders schematic, especially denoting the correct pin numbering on the jacks (and plugs). I have a hand drawn schematic, LMK and I can scan it if needed.

[David C. Poland]

Hi Karl.   So your optional speaker system works fine.

I removed the crossover's small 4 wire cable with 4 pin plug that fits the receiver socket, because my 1939 AM/SW Phantom Deluxe does not have the small crossover socket like later receivers (nor the band switch wafer that controls speaker operation). Yes, the jumper is installed in the auxiliary speaker socket of the crossover.

(Being an earlier production Phantom Deluxe, the small 4 pin receiver socket is the phono input. And being a remote control set, the radio/phono switch is operated by a relay, which is fully tested using a CD player.)

In removing the small cable, I followed the earlier crossover diagram (Riders, Vol 14, pg 12) to assure circuit completion path matches the page 12 diagram. Field coil with tap is good. Continuity checks follow the diagrams. The all 3 speakers show proper continuity and the pass the battery click test. This earlier version crossover wiring should run both woofer and tweeters full time, which is what I want for for my non-FM radio.

It seems wrong that the audio for the woofer travels through one of the crossover coils, but that seems to be the design of both early and later crossover wiring diagrams. I actually can hear a very faint audio as though the output transformer is bad, but the transformer continuity seemed fine. 

I will again trace all  the wiring and recheck continuity. Next, will try moving the woofer connection to the far side of the one coil.  That Kent is also having optional speaker system problem prompted this Scott site inquiry.

[Karl Sherwin]

David, according to the schematic I drew up (and I checked it numerous times), the signal does not go through either inductor to the woofer when the crossover is "off". In the "off" position one lead of each of the caps is still tied to the OT secondary "ground" along with the "ground" of the woofer, but everything else in the circuit is open.

I'd be willing to bet your OT is good, but to verify, what I did on mine is to drive a 1v 1kHz rms sinewave into the secondary (use the 8 ohm tap and remove the external speaker jumper plug) and measure the plate to plate primary voltage. It should be about 21.7 v rms. I did that to calculate the primary load impedance which came out to be 3725 ohms, about right for a quad of 6L6s.

Karl

[David C. Poland]

Karl  -  Remember, I removed the small cable to the receiver so the switching is defeated. My expectation/plan is that my speaker system would operate like the initial version. 

The Phantom Deluxe uses only a pair of 6L6's. and thank for your suggestion which I will pursue.

[Karl Sherwin]

David, my bad, I read that but then wasn't thinking. So yes, the inductor is in series with the woofer and the cap is across the woofer. Its a 2nd order (12db/octave) Butterworth filter. Likewise, the cap is in series with the tweeters and the inductor is across the tweeters.

I was going to make a post a while ago about the impedance of the OT on the crossover box, but never did. I never understood why Scott would use the same transformer for both the Philharmanic and the Phantom, since one has a quad of 6L6s and the other a pair. Way different primary Z requirements for the two configurations. I suspect it was a matter of simplicity and economy. It would be interesting to see the difference in power output for the Phantom with the 38ohm setup (OT on the speaker) vs. the crossover OT. But this is getting off topic...

[Scott Seickel]

I agree with Karl about the primary impedance mismatch.  I honestly think the OT for the Philharmonics with this setup is way undersized too. 

Here is a crossover that I rebuilt (it was missing original OT) using a Hammond for quad 6L6's.  There is a whole lot more iron in it than the wimpy original one.  Honestly, I can't hear the difference with the replacement, but then again I have only played AM radio and can't get anywhere near full volume in the room it resides. 

The original capacitors really did not measure much leakage, maybe because they were potted in tar, but seeing as though this was a full rebuild, I replaced them.  I made up a new cord for too because the original was missing. 

[Scott Seickel]

Attached is my redraw of the network speaker unit.  It seemed to match well with my rebuilt unit the best I can recall. 

[David C. Poland]

Scott   thanks. Nicely redrawn. Especially the external switches diagram, so much better than as shown on the Laureate diagram - easier to follow.  

Karl - my speculation is that Scott Labs had one optional hi-fi system with crossover, which evolved. The only difference as it evolved being a 12 inch or 15 inch woofer depending on the radio model and/or cabinet size. I too wondered about differing output transformer requirements for a pair of 6L6's vs a quad. The optional speaker system was first announced by Scott News ( Vol 12 No 2 page 8 -about March 1940) for the FM Phantom Deluxe announced in same issue. The FM Philharmonic came out about 6 months later, so maybe Scott Labs tried the optional speaker system on the Philharmonic and decided it was good enough "as is" and, so, soon dropped the 15 inch pedestal (with optional tweeters) as standard making a flange mount 15 inch 38 ohm as standard and the existing optional speaker system for high fidelity.

We are doing house Christmas decorating, so won't get back to my speaker system until tomorrow.

Trying to digest the later crossover type switching - is a brain teaser, as the woofer is also switched.  

Hummm. But do need to understand, as my next project is my Scott Laureate with the tube type crossover and Scott 15 inch co-axial speaker using one field coil tweeter, for which I do have a diagram.

[Scott Seickel]

David,  is there a published diagram of the crossover that has the woofer switching? 

[David C. Poland]

Scott - re: your diagram above - pins 1 & 4 of the tweeter plug to receiver appear to me to involve the woofer.

Am I wrong?

[Karl Sherwin]

David, I can answer that.

Yes, in the AM & SW positions, the OT is connected directly to the Woofer, and the only parts of the crossover & tweeters still connected are the grounds. In FM the woofer is placed in series with its inductor, and part of the connection also connects the tweeters with their returns through their capacitor.

[Scott Seickel]

Sorry, I thought you meant switching the woofer in and out of circuit....yeah, the diagram shows switching components to change the response from the 15"  when the tweeters are active, which is reasonable.