The Fine Things are Always Hand Made
What I have learned about Scott speakers and optional tweeters. There are sets missing speakers and locating suitable speakers can be a challenge.
A) Tweeters were optional for the AW-23, Philharmonic, later Phantoms and the Laureate.
B) Prior to 1940, the optional tweeters were 1) in series with a 2 MFD blocking cap as a crossover and 2) were then connected in parallel with the main speaker voice coil.
C) There were 2 versions of the AW-23 field coil tweeters - early and late - corresponding to the early or late version 12 inch pedestal speaker. (Different voice coils: 38 and 19 ohm)
D) Until 1940, the Phantom and Phantom Deluxe (with 6V6 output tubes and no logging scale) used speakers incompatible with the Philharmonic on account of differing field coil designs and output transformers. These early Phantom models use the same speaker with octal plug as the 12 inch Sixteen and 14 tube Scots Masterpiece. The Philharmonic always had a 15 inch Pedestal speaker while the Phantom and Phantom Deluxe 12 or 15 inch speaker was flange mount.
E) While the Philharmonic always had available optional permanent magnet tweeters, no tweeters were marketed for the earlier Phantom models.
F) Effective early 1940, the Phantom amp was revised to use 1) 6L6 output tubes and 2) was designed to use a speaker with the same 925 ohm tapped feld coil arrangement as the Philharmonic had always used. And standard speaker voice coil was 38 ohm..
D) Early 1940, the 4 unit speaker system with outboard crossover was evidently developed as an option for the FM models (Philharmonic or Phantom) and evidently available for the non-FM models as well. This 4 unit speaker system used 8 ohm speakers and the main speaker seen may be 12 inch or 15 inch flange mount speaker with a High Fidelity tag. The main speaker field coil is the same as the standard speaker, although the voice coil is not. The crossover also has a cable with small 4 pin plug to fit a small socket on the back of the receiver to control tweeters.
E) In contrast, the standard speaker for Phantom or Philharmonic continued with a 38 ohms voice coil. An optional tweeter pair (each 16 ohm and in series with a 2 MFD low frequency blocking cap as a crossover) could be wired in parallel with the main speaker V.C. as before, but I have found no late owners manual instructions to do so.
F) My 1941 Laureate uses 6L6 tubes and the speaker requirements are the same as the Philharmonic and Phantom (using 6L6's). My Laureate also has the optional high fidelity speaker system with one 15 inch speaker and one center mount tweeter. Mine has a field coil tweeter and the crossover has a rectifier tube to power the tweeter field coil. The radio uses Jones plugs for the set and the speaker.
G) I also just acquired from an FM Phantom using Jones plug connectors a 4 unit speaker system 1) using the exact same outboard crossover as my Laureate including the rectifier tube and 2) curiously using two field coil tweeters identical to the Laureate tweeter. In addition, both crossovers have a cable with a small 4 pin plug that fits a small socket on the back of the receiver chassis both my FM Laureate and my late AM Philharmonic BOL. Diagrams indicate this cable is for control when the tweeter(s) function, which I will eventually verify during restoration. I speculate the field coil tweeters date the late 1941 perhaps due to war material demands for permanent magnets.
Curious for comments or observations on my findings or to expand on this topic.
Dave: My allwave 23, 5 knob early version, came without the tweeters, but apparently they were there originally, since the hole covers are gone and the screw holes have been used. I have a pair of 1960's Jensen tweeters that are almost the same size as the originals, that I can put in. I would wire them with the 2 mfd cap and a five pin plug wired to match the diagram, but without the field coils. The original pedestal 12 inch is in good condition and sounds great.
I also have a late 5 knob version Allwave 23 chassis that has been seriously messed with, and is in rough shape, but complete. No power supply, but I could make one for it. This one has the antenna connections for the double doublet antenna, so it may be in-between the early 5 knob and later 7 knob versions.
To use your later permanent magnet Jensen tweeters, you reverse the instructions for plugging in your tweeters. Leave the big speaker short cable plug where it is in socket #1. And plug your tweeters into the other base socket #2. Since your PM tweeters lack field coils for the bias circuit, you need to keep the big speaker's big resistor in the bias circuit by use of Socket #1. The correct 12 inch Magnavox for an early 5 knob AW-23 uses the speaker with a 38 ohm voice coil. The Scott (by Jensen) tweeters were Q4-7077A and Q4-7078A. Hope your Jensen tweeters are 16 ohm so when connected in series, they would approach 38 ohms.
- your 5 knob set - would be from 1935 to very early 1936. Would have a single antenna post and single ground post. Has the BFO button below the tuning knob. The radio does not have a radio/ phono switch. The phono input is in the first AF cathode which is after the volume control and, so, the phono or other device must have its own volume control and a bypass switch acting as radio/phono switch. The optional Scott double doublet antenna came with an outboard antenna switch hung off a tube shield.
- The early 1936 change to 7 knobs configuration dealt with the phono input circuit and speaker change. One new control was a radio/phono switch ahead of the volume control. So now the volume control also controls phono volume. The other new control amounted to relocation of the BFO button for appearance sake. Still only one antenna post and one ground post. This is also when the speaker changes with revised terminal strip and revised voice coil to 19 ohms. Hence a different set of tweeters Q4-8685A and Q4-8686A. Continued with the same optional antenna system and receiver still has a single antenna post.
-Late 1936, the new antenna input circuit was introduced for a doublet antenna system with twin lead and the set now has 2 antenna posts, plus ground post. The outboard antenna switch no longer used. The new micrometer dial was introduced.
NOTE - And of course, there were some other running changes during the production run. Also some early AW-23s when returned to the factory were updated with later features, including the additional 2 controls.
Thanks for the reply. My radio has the switched adaptor for the antenna bolted to one of the IF cans. I am not using it,, since I have a 50 foot long wire antenna connected. I would love to use the doublet antenna, but don't have the space to put one up. The long wire is on the roof, and set up in a V shape on the west end of the house.
Interesting that the second chassis has the twin antenna posts, but not the extra micrometer dial. This set will be challenge to restore, if I even decide to do that.
Thanks for the detailed write-up, something I tried to do in the past, as I still am looking for a Philharmonic and want to understand as many of the nuances of the Philharmonics, the tweeters being one of them.
My dad had an AM Phantom, I think it was the Deluxe, but I do know it was the 7 knob version with 6L6s, and a 15" flange mount speaker. As he told me years later, in the early 50's he went to a local radio shop and bought the black bullet tweeters & crossover for $25!
My question, related to my dad's radio, and your point D, was the output transformer different, or did it have a 8 ohm tap to handle the 8 ohm speakers?
Karl, - The Scott output transformers of the 1930's do not have different "ohm taps". Such taps seem to have been a 1950's development of component hi-fi.
Cannot say what tweeters your dad added. Perhaps the optional 4 unit system announced in early 1940. But perhaps he added the simple Philharmonic tweeters with blocking cap to run in parallel with the standard 38 ohm speaker voice coil. I understand later Philharmonics are found with bullet shaped tweeter pair, as well as with the 4 unit speaker system. Later FM Phantoms designed for the optional speaker system were wired so the tweeters were off in AM and SW. Do not know if late AM Phantoms could control the tweeters - but I seem to have an unrestored late BOL logging scale AM/SW Philharmonic with the little 4 pin socket for the tweeter control cable.
The Scott diagrams for the Phantom show only the standard speaker. The previous 19 and 20 tube AM/SW Phantom amps 1) used 6V6 output tubes, 2) a 12 or 15 inch speaker with 2 field coils and 3) no mention of tweeters. In contrast, the Philharmonic always mentioned optional tweeters, which were run in parallel with the main speaker voice coil with a 2 MFD blocking cap as the tweeter crossover - until the 4 unit speaker system came along.
The new Phantom amp using 6L6's dates from late 1939 - per Scott News Vol 11 #6 of Fall 1939. This re-design may have been in anticipation of high fidelity FM radio warranting more volume output. The visual clue is the 6J5 driver pair relocated from the end of the amp chassis to the middle next to the output tubes ... and use of 5U4's instead of 5V4 rectifiers. Again, the Phantom 6L6 amp diagrams shows a single standard 38 ohm speaker and one tapped field coil and makes no mention of tweeters. The above Scott news has a lengthy description of the new Phantom stating the speaker is a 15 inch curved cone with a high frequency diffuser which is a stiff paper cone fixed to the the pole piece - but no mention of optional tweeters.
The first mention of tweeters for the Phantom appears to be in Scott News Vol 12 #2 of 1940 (about March) announcing the FM Phantom (no FM Philharmonic until later in 1940). This same issue also announces with picture the new optional 4 unit high fidelity speaker system. Claim is the standard speaker is good for 30 to 8500 cycles. The new optional 4 unit system claims 30 to 15,000 cycle to maximize the frequency range of FM broadcasting and the increasing quality of new phonograph records. It does not state if a 12 inch or 15 inch speaker - but both 12 and 15 inch flange mount speakers have been found with FM Phantoms (I bid on a 12 inch from a 4 unit system last year and lost ... and last month a 15 inch complete system which I now have.)
Scott documentation of the 4 unit speaker system shows all 3 speaker are 8 ohm. The outboard crossover holds not only the output transformer but also coils and caps much more like 1950s crossovers - to direct low frequencies up to 2000 cycles to the big speaker and above 2000 to the tweeters and has provision for a remote speaker, too. The output transformer is selected to match the speaker voice coil to the plate resistance design requirements of the output tubes for sake of maximizing the power transfer to the speaker and avoid stressing the output tubes. Although the 4 unit system main 8 ohm speaker and the 38 ohm standard single speaker both have 923 ohm field coils tapped at 525 ohms, they have very different voice coils and output transformer requirements and, so, are not interchangeable in my opinion.