[morzh]

Atwater Kent 10A uses 90V for all the plates except the Detector which uses 20V or 45V, so, yes, two DC B+ voltages.

[SRv2]

Here is some info researched and an ARBE-III question

More research on the Model 38, it appears from Service Bulletin 166 and 166-A that this model needs:
A at +2V
B at +135V and +67.5V
C at -3V and -7V
(see attached pic)

Looking at connector closer on my unit, I have 2 individual wires, likely for the A 2V battery, then a 7 pin connector for the B/C battery.

I have tried researching the Philco batteries 172-R and P-962, and the only thing I can find is a 1942 Philco Parts catalog referencing replacement batteries, page 11 of the PDF.

Per service bulletin 166-A, the B current drain is 8-12 mA.  

ARBE-III
A - can be adjusted to 2V 
B - has connections for both 135 and 67V, with total B supply of 60 mA
C - has connections for -4.5V and -9V where model 38 calls for -3V and -7V

Questions for ARBE-III owners (or anyone smarter than me, which is pretty much everyone on this phorum)
- would using the -4.5V and -9V work instead of -3 and -7V?
- does it sounds like ARBE-III will work for Model 38?

I tried to do my homework, just gathering more feedback - thanks for any time spent on this.

               

[RodB]

To get the C voltage, you can use a 9 volt battery with a voltage divider. That way you can use high value resistors and adjust their values to get any voltage in between. For example you can use 330k to get -3v, 470k to get -7v and 200k to complete the divider. Remember, these are bias voltages and have a fuzzy tolerance. No need to be exact. Something like this, the battery would probably last a long time.

[MrFixr55]

Hi SRv2.
Instead of a Bonfire, you can ship them to:

11 Browning Drive
Greenlawn, 11740
and I will "fire" them

Both of these radios appear to be extremely restorable.

It appears that you have the Philco 38A which used a "combination" A/B/C battery much like the later 1.4 / 90V sets using an A/B battery. Your voltages are 3V A voltage if you have the ballast tube (that should have come with the radio because it uses the battery pack) 67V and 125V as Morzh said for B voltages, 3V C -for Output tube bias and 7.5V C- for 1st audio amp bias. The drawing is incorrect; it should be 7.5V, not 7V.

If you don't have the ballast tube, jumper the tube contacts and use a 2V power source. You can also add up the filament current, use Ohm's law and calculate the correct resistance to drop a 3V Wall Wart output to 2V.

This is an interesting set. Though released around 1934, it uses Tetrode or "Screen Grid" tubes. It may be possible that 2V RF type pentodes were not developed. The 15 has an indirectly heated cathode; it has to because it is an "autodyne" type oscillator - Mixer (1st Detector), similar to the 80 Jr and the dreaded (Sorry, Ron) 89 / 19 sets. I always thought this style cabinet was a little scary looking, but this set is an absolute "keeper"

An ARBEIII would power the set with no issue for A and B voltages. For the C voltages you could build a voltage divider but the easier thing would to obtain a 2AA Cell holder and 3 AA cell holder. (you could use AAA cells if you want. Wire these in series with the negative lead of the 2 cell holder to the positive lead of the 3 cell holder Wire the positive gf the 2 cell holder to chassis ground or the common pin. The junction of the 2 and 3 cell holders is you -3V and the black wire form the 3 cell holder is the -7.5V. These batteries will last a very long time, likely years, until internal leakage causes external leakage.

If you don't want to spend $180 on the ARBE, use the above mentioned Wall Wart and get a transformer that has a 120V input and 120V output at about 50 mA. a Bridge rectifier, 2 47uF caps and appropriate resistors will give you the 135V and 67 V on the cheap.

With either power supply, I would also put 4 1N4007 diodes in series, cathode to A-, anode to A+ to clamp any overvoltage.


I do not have this set, but I do have an RCA 5BT, using the same amplifier circuit with a 30 driver, a 19 Class B PP Output, interstage transformer and the same voltages. The amp is no slouch. I put out much more volume and better tone than the puny 0.1W to 0.24W of the later 1.4V / 90V sets.

The Zenith is really cool, as that one has the 6V / 117V power supply. That would be a bucket list set for me. Only issue is that Zenith "Black Dial" tombstones are quite collectible and expensive.

The Zenith is a very interesting setup. With the multi-contact wafer switch in battery position, the tube filaments are hooked across the 6V battery, the vibrator is on and the thing runs off 6V. In AC mode, the multi-contact rotary switch switches the filaments to the 6V center tapped secondary of the transformer, turns off the vibrator, disconnects the battery and you plug it in. Interestingly enough, the power supply appears to put out about 135VDC to the Class B Push Pull output stage. The 1J6 is essentially an octal based version of the 19.

No C battery is used on this set. The bias for the output is zero volts because a60 Amp Hour battery would run this set for an easy 100 hours, and they likely swapped the battery out with the one in their car, truck or tractor, or had a windmill charger or gas generator. The bias needed for the driver stage was generated by a cathode resistor. The secondary of the power transformer is center tapped to reduce 60 Hz hum on the filamentary cathode of the 19. Otherwise, radios of this vintage did not center tap the heater winding if all the tubes had indirectly heated cathodes.

Keep us posted, Both of these radios are absolutely restorable and will perform rather well, especially the Zenith.

BTW, yes, the power cord looks like it would fit a 7 Pin tube socket similar to the one used by a 2A7 or 6A7.

[SRv2]

Incredible feedback and help, thanks MrFixr and also Rod, Mike, Arran, David and everyone. These two are on my list after I wrap up the Butterfly and Arvin units, finish the 49-500 and a Zenith T.O., then repair a Royal 500 transistor for a gift. Oh and then look at the Fada 1000. Who knew this radio gig would be so much fun? I should have retired years earlier. Anyway, thank you all for the great support and encouragement. I’ll keep you posted. George

[MrFixr55]

SRv2,

You are well on your way with this hobby with an interesting inventory!  Does the FADA 1000 have a Catalin cabinet?  I think the FADA 1000 is merely an AA5, but the Catalin cabinet makes them worth a MINT!  As in US Mint.

Yes, retirement is good, my only 3 problems:

• House is real small, only 1,000 sq ft but I do have a basement and garage.
  
• Ms. Fixr is not a fan of my hobbies.
  
• Every time they ask for volunteers at Church, my right hand goes up and gets recognized before my left hand can pull it down and smack it into submission.
  

[SRv2]

MrFixr,

Yeah, the Fada is a Catalin, I got lucky in getting it.  Cosmetically it needs a dial cover and rear panel, both on order.  Chassis repair seems straightforward.  Not sure if I will resell it or keep it afterwards.  It is the one and only Catalin unit I have, so I'll probably hold on to it.

My workshop and bench is in my garage which makes it nice.  My wife collects southwest native pottery, so she can't say a lot about my radios!  And I understand the volunteering, I go the local food bank couple times a week to help out and can't seem to stop myself, but good problem to have and I guess we are fortunate all things considered.

Thank you, again, for the support with this farm model.  Oh and I also have a dreaded 89.  It sits up high on top of a cabinet over my workbench and stares at me all day, biding its time.

George
   

[Arran]

George;
The FADA 1000 used the same circuit as the FADA 1001 I have, it has an extra tube as an untuned RF amplifier, a 12BA6. I'm guessing that it was a last minute addition as all of the others tubes are your typical metal, and GT style octals. In any event the 1001 is one of the better performing AC/DC sets I have for DX, so if I were going to choose a catalin set to keep it would be something like that since it's not just a pretty face. Be careful with it though, these sets have an actual HOT CHASSIS where one side of the power line is soldered directly to the steel for common negative, though I suppose it could be modified.
Regards
Arran

[MrFixr55]

+1 on Arran's comments.  Best thing to do is the following:

• Move the power switch from the neutral (chassis ground, B-, 1st AF Heater and cathode) to the hot side (Rectifier plate and /or heater).  there will usually be a connaction between the power switch and one end of the volume pot.  Be sure to remove this and connect the Volume pot to the common B- (See next step)
  
• If possible, create a B- and heater return ground "Mecca" separate from the chassis.  Move the "neutral" conductor of the power cord and all chassis ground connections except the tuning condenser to this isolated Mecca.  Connect a 0.1uF cap between this Mecca and the chassis.  This duplicates the "warm chassis" as opposed to the Hot Chassis.
  
• Install a polarized power cord or if the power cord and plug are original and you want to keep it, widen the prong connected to the "Neutral " conductor (the one connected to the above mentioned "Mecca")
  

These steps will eliminate a common problem with sets of this vintage where there is always a danger of the chassis being "hot" or "warm" connect to hot through a capacitor depending on whether the switch is on or off and the direction that the power cord is connected.

Ther is somewhere an article on making this mod, possibly in Phil's Old Radios.  If I find it, I will link it.