[Joe Rossi]

Joe,  how is the restoration coming along?  Joe

[Paul Philco322]

That dial came out super. People sometimes complain about daze, but they did nice job for you. Paul

[jrblasde]

Good morning, folks! I’ve got to admit that I haven’t made any further progress on this Air Castle since receiving the new dial. I’ve been working to button up the Philco 48-482 restoration, and then I was smitten by the opportunity to get the 47-1230. I need to post an update on those today, but also I need to get to work on this Air Castle! Not only am I juggling these restorations but, lower on the list, I also have a Sonora tabletop radio/turntable and a 1960’s portable GE AM radio which would be great to take to the office since it can be used with headphones.

[morzh]

Yes the dial is great.

[Joe Rossi]

Hey Joe, No pressure. Just interested in the progress. The dial is excellent! Joe

[MrFixr55]

Hi Joe,

Thanks for posting the schematic. Interesting set, looks like they were trying to build a console set on a budget. That an 8" or 6" speaker? The dial came out sweet.

The 6AC5 tube is an interesting beast. It's a high MU triode usually used in Class B Push Pull output stages, as it puts out quite a bit of power albeit with the higher distortion that class B is known for. In single end and in some push pull stages, it is paired with a triode connected as a "cathode follower, directly connected to the 6AC5 grid. The tube operates with positive bias in this mode, with high wattage and very high distortion (10-16% for single end per the RCA Receiving Tube manual). Class B was popular with RCA in the early 1930s and probably in car radios, but the only set I ever saw 6AC5s in was a 1941-42 Crosley 02-CA console. 10 tubes, Audio stage had 6 tubes:
1 6SQ7 Detector / 1st Audio
1 6J5 as a cathodyne phase converter
2 6j5s as cathode follower drivers for the output tubes
2 6AC5s as Class B output.

Distortion was higher at low output but the person I restored the chassis for likes to play Jazz guitar. I had put an external "Radio / Aux" switch and jack in the set. He plugs his guitar in and it actually makes a rather sweet guitar amp for jazz guitar through the 12" speaker. No overdrive, as one would expect, given not enough preamp stages, nice sound, in the way electric guitar was first played before the high distortion overdriven "metallic" sound.

[jrblasde]

I just ran out to the garage to measure -- it's an 8" driver. From what I can readily see, the cone is in tact!

[Arran]

Joe;
Your set is kind of like the console version of a Sparton tombstone, a guy on C.L has been trying to sell one for almost a year. Anyhow he has a photo from the back and it has the same 8'' Magnavox speaker my little tombstone has, it looks really strange with all of that empty space. The usual format in Canadian sets was to use a 6'' or 8'' in the table version, and a 10'' or 12'' in the console version with the same chassis, I can only speculate that Sparton got a good deal on these 8'' Magnavox speakers and decided to use them with both. The chassis isn't a bad one, it has a tuned RF amplifier stage, with a #42 power output, so it wasn't like it was a bottom rung set, it's pretty similar circuit wise to an RCA 128, with the latter having three bands, and a single ended #41.
Regards
Arran

[MrFixr55]

Hi Gang,

Same thing here in the US. Standard speaker in a console was 12", even with single ended output. Lots of RCA consoles had 12" speakers, especially post-war. Some of them rather cheap with small AlNiCo magnets but 12" nonetheless.

I think that cabinet size and pricepoint have more to do with speaker size than power output. I have a Truetone (Western Auto) built by Detrola. 2 41s (Older version of 6K6) output with a phase invertor. 8" speaker. Cabinet is definitely big enough for a 10 or 12" speaker and 2 41s in Push Pull are usually good enough for at least 5 W at 250VDC B+. I have 2 RCA battery farm tombstones, one with a 19 dual triode, the other with 2 49 triodes, both in Class B Push Pull with 2W output. Both have 8" PM speakers.

It seems that most mid 30s to 1940s table sets (not tombstone or "midget"), like my GE G-53 (single 6K6 output) Philco 41-255 (2 41s in push pull but only 180V on the plates), Westinghouse (Am Bosch) WR211 and Coronado 650 (2 950s in parallel) have 6" speakers. Add another inch or 2 to the cabinet and an 8" like most tombstones used would fit.

2 of my Zenith AM FM table radios (7H820 and 7H920) and my RCA 1R91 Livingston both have 8" speakers. Even though the Zeniths with their 35B5 or 35C5 output tubes have only about 1 - 1.5W output vs the RCA which has a 6V6 with 3.5W output, Those Zeniths sound almost as good as the RCA. The nice size speaker is the key.

[Arran]

Mr Fix;
I tend to exclude pre war battery sets with regard to speaker size due to the limitations they had, at least until the mid 1930s or so, with acquiring suitable material to produce strong permanent magnets. Even after that point the availability of larger PM speakers may have been more limited as electrodynamic speakers were in common use even in AC/DC sets, down to 4'' until the early 1940s, cost may have been a factor as well. In this case the Sparton uses an 8'' electrodynamic like most AC radios used in 1935 or 36, and they used 10''-12'' speakers in most of their other console models. I remember repairing one for a guy back in the 90s, the speaker was missing so I mounted a 10 or 12'' P.M dynamic in it, with a filter choke, it had a single ended #42 as well.
Regards
Arran