[Antipodal]

Hi everyone,
 I'm hoping someone might recognise the valve lineup in this radio I got this morning. It is a single unit set with pushbuttons as well as a tuning knob.The plastic push buttons have seriously degraded. The valve lineup is as follows : 6A7  78  75  41  84.It has no R.F. stage and so only a two gang tuning condenser.I'm picking that the use of the 41 as output tube should help to narrow down the model as this tube  apparently did not "have a long time in the sun" as it were.Any ideas folk may have on what model this set may be would be much appreciated.Unusually for a Philco set this one had only a valve placement chart and no other notes or diagrams inside  .
 Thanks everyone.

[RodB]

I did a tube search on radiomuseum.com and got a large list of Philco radios from the mid to late 30s. Many are car radios. There's a start. Maybe you can post a photo.

[Joe Rossi]

You can try Philco models 805, 920, 921, 922, C-1606, and P-5.  As mentioned above, a photo would be helpful.  Cheers,

[Antipodal]

Thank you fellows, I have searched in the right volume of Riders (1939 PQR Page 43) and found  a  schematic  which is almost certainly the right one for this set.You were right ,Joe, it seems to be a Model 921 or 922 (Run No.2). The tube line up is correct but more importantly the  chassis parts location diagram shows the pushbutton station selector switch arms poking out the front. The other models you suggested do not seem to have this feature.As I dive into the  insides of this set I will use this schematic as my guide.What a wonderful resource we have in the Phorum.  Thank you all.
I have also noted that there are instructions on how to load photos onto the Phorum.As my grandaughter who used to help me do this has moved away I will have to swot this up and see if I can get a photo uploaded.(..Used to help me ! Pshaw ! She did it ! )

[Joe Rossi]

Glad to assist!

[Arran]

Most car radios from that era seem to use either #41s or 6K6s as power outputs, probably because they have lower current requirements then #42s or 6F6s. It must have been one of the lower cost models, most I have seen either have a tuned RF amplifier stage, or an extra If amplifier stage?
Regards
Arran

[Antipodal]

Thanks for your interest Arran. I think you are right that this set is a " cheapie "with no R.F. stage.You raise an interesting point about the use of the 41 rather than the 42 , attributing the use of the 41 to the gain made by reducing filament consumption by 300 mA. You are right in that this must probably have been a consideration to be taken into account by the engineers designing this set. The less current drawn from the battery the better.Yet they seemed quite content to continue to use an electro dynamic speaker drawing at least an amp to energise. My reading of Radiocraft of that era suggests that permanent magnet speakers were available in the U.S. (No Koil Speakers ) but perhaps they were too costly. Have I got this right? Is there an accepted view on why U.S. car radio manufacturers continued to use E.M. speakers for so long? Its a question which has intrigued us here in N.Z. for some time. Cheers everyone.

[Arran]

You have to remember that the tube heaters are all 300 ma each times 5 equaling 1500 ma. Is the fiield coil in the B+ or in series with the tube heaters? I kind of doubt that a field coil would draw an amp if it were used in the B+ supply as the #84 rectifier is only rated for an output current of 70 ma, which would also explain the choice of a #41 power output tube. I think the preference for F.C speakers had to do with filtering, P.M speakers of all kinds were in common use in farm battery sets of the era.

[MrFixr55]

Hi Antipodal,

Greetings to the "other side of the world! Though I may never get to Australia and New Zeland, I always had interest in your 2 nations.

Yes, the field coil is in series as a filter choke in the B+ Supply, so it did dual duty, without eating much current. Remember, the output of the inverter in this unit is practically a square wave, so the choke was a good way to filter the spikes. There were some 6V radios whose speaker field was directly across the 6V input. These likely drew current.

"PM" magnets for speakers were available prior to WWII but were expensive, heavy and not as strong as the field coil type. However, in battery operated radios, especially those using B Batteries instead of an inverter, there was not much choice other than the use of a permanent magnet in the speaker. In fact, some of the battery powered radios from the 1930s used the older magnetic style speakers, similar in function to the early cone type speakers of the 1920s before the "Kelogg - Rice electrodynamic" speaker, the archetype of all modern moving coil speakers. The invention of the AlNiCo alloy for magnets allowed for a stronger, cheaper permanent magnet. The dry electrolytic capacitor also allowed for larger capacity, thus eliminating the use of a choke (i.e. the field coil) in the power supply.

Good luck with the radio!

[David]

So you are on the South Island, in 2016 Wife an I were in Auckland planning on going to the South Island got up in the morning go down to have breakfast and on the news talking about the earthquake. We had been to New Zealand before never to the South Island. Read about Arthur's Pass.   https://www.newzealand.com/us/arthurs-pass/  Soon to be 75 guess I will never make it. Take Care David

[Antipodal]

Hi everyone,Yes N.Z. is on the "Circum - Pacific Belt of Fire " so earthquakes here are not uncommon.We have learned to live with them as best we can  and also to engineer our way towards mitigating them using N.Z. developed  lead and rubber base isolation bearings to allow us to build some taller buildings. 
Regarding electro dynamic speakers you are  on the money in radios powered from 117 or 240 volts (our N.Z. standard) where,as you say, the field coil serves to help smooth out B+ ripples and commonly appears wired with the first cap to the rectifier cathode.
However in most car radios that use e.m. speakers the field is wired ,as you suggest Arran and Mr Fixr55 ,in  parallel with  the filaments and so offers no smoothing function. In Philco sets of the Thirties and Forties from my reading of the circuit diagrams (Philco S4627 Studebaker,Packard P 4635) these field coils are only 4 ohms.Fed by 6 volts they draw 1.5 amps.
With the increasing demands placed on battery and generator as cars in the early fifties were fitted  with  power everything including air con it is small wonder that e.m. speakers faded away.
But they do sound nice when in good condition.

[Antipodal]

Hi everyone, At last ! The photo of the radio in question. If anyone recognises this set I'd be grateful to know what it is . Thanks all. Special thanks to my son in law who helped load it!