Yes, you need 135VDC, 67.5VDC B+ (Neg to chassis), +2VDC (Yes, 2 Volts, Neg to chassis), and "C-", 3V and 7.5V, (Pos to chassis)
For 2V, it would be best to obtain a 3V, 1A "Wall Wart" power supply. Here is a reprint of my previous post about running the filaments on 3V:
The A supply will be the most difficult because you need the most current (500 mA 0r 0.5A) at 2.0V. Since "D" size dry cells provide 1.5V and 2 in series provide 3V, you need to calculate the dropping resistor needed. The good news, is that I am going to do that for you right now:
Below is a chart with each tube in your radio and the current it draws:
Since these tubes are all connected in parallel, the total draw is 0.5A. Since a resistor has to be added in series to the A Battery connection to the radio to drop the voltage to 2.0V, and current is constant in a series circuit, we need to calculate the resistance needed to drop 1V at 0.5A. So if E=IR then R= E/I. So, if the voltage drop is 1V and the current is 0.5A, then R = 1/0.5 or 2 Ohm. Since the current is constant, in theory a 2 Ohm 1/2 watt resistor is sufficient, use a 2 Ohm resistor at 2 Watt or higher rating.
Since a D Cell delivers only about 1.5Amp Hours, 2 D Cells in series will last 3 hours or less running this radio. 3V 1000 MA "Wall Wart" power supplies can be found for $15.00 or less on the internet. This and the 2 Ohm 2 Watt resistor will power your filaments.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
I am following up on a battery question.
To whit: "A 3V/4.5V/6V/7.5V "C" battery to provide "grid bias" for various circuits."
Does this mean I need four separate batteries to meet this need?
If so, how do I insert the voltage into the circuit for the 4.5,6, & 7.5 positive leads?
The 2v + and - are clear to me.
Thank you.
"Radio C Batteries" (Not to be confused with "Size C" 1.5V Batteries) were used with early battery sets from the early to mid 1930s, especially with ones using the 2V tubes like yours, and are definitely not available in working condition. This was a package of several batteries in series with connections for the desired voltages that were, in fact, "taps" on these batteries. Since minute amounts of current were drawn from these batteries, they often lasted the life of the radio. Here is a picture of the battery that may have been used for this radio. It was used in my 1936 RCA 6BT and 1937 RCA 5BT:
To replace these batteries is relatively simple. Your radio needs 2 "C-" voltages; -3V and -7.5V. This is done by having five 1.5V AA Cells in series with a tap on this "battery" for -3V. I have done exactly the same thing on 2 RCA Farm sets; a 5BT and a 6BT. This is done by doing the following:
Obtain a battery holder for 2 AA batteries and a holder for 3 AA batteries from eBay, Amazon, local suppliers, etc.
Connect the positive (red) lead of the 2 battery holder (3V) to the A-B-C+ connection (likely chassis ground).
Connect the negative (black) lead of the 2 battery holder AND the positive (red) lead of the 3 battery holder to the -3V "C" lead on the radio.
Connect the negative (black) lead of the 3 battery holder to the -7.5V "C" lead on the radio.
There is practically no current flowing through these batteries when the radio is powered down, therefore, there is no need to have a switch between the batteries and the radio. These batteries should last to their expiration date.
Hope this helps.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
The transformer is likely a Hammond 125h. See the following link: https://www.hammfg.com/electronics/trans...audio/125h. Plate to plate impedance for a Type 19 in push-pull is 10KOhms. You can likely scavenge an output transformer from the many Philcos that used a pair of type 41, 6K6s or 7B5s in push pull. Plate to plate impedances for all of these tubes is 12KOhms. The mismatch is not critical.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
If it's the audio output transformer that should be very simple, if it's the audio interstage transformer it's not as straight forward as the push-pull outputs in most 1930s battery sets were class B, and actually require a step down transformer rather then a step up style like most AC sets would use.
Regards
Arran
PHILCO Model 338-123 ‘Farm’ Radio
Power Cable Wiring
B+ 135 Volts YELLOW
B+ 67.5 Volts Yellow with Black Stripes
A-, B-, C+: Black with White Stripes
C- 7.0 Volts: Green
C-3 Volts: Blue
A+ 2 Volts: White with Black Stripes
A+ 'AirCell' Tag: Brown/Tan
Or
A+ ‘Storage [cell]’: White with black Stripes
Just to be clear (and before I power this radio up):
If I attached 2 Volts to the White with Black Stripes labeled 'A+' (above) I DO NOT have to put any power into the wires labeled (with little cardboard tags) (wire color is brown/tan [it has faded after 90 years]) tagged as "A+ Aircell" or the White/Black wire labeled 'A+ Storage'.
Matt;
The Aircell was a type of dry cell battery that put out about 3 volts DC, so that brown/tan wire likely has a resistor or ballast connected in series between it and the tube filaments. The white/black wire is for a lead-acid wet cell which put out 2 volts DC, basically one cell out of a car battery back when the cells were connected with external buss bars, though they did have single 2 volt wet cells available as well I think many went for the car battery since they could charge them at a gas station, or in their vehicle.
Regards
Arran
Matt;
If you want to supply 2 volts to the tube filaments then the white/black wire is what you want to use, it's not that used the brown wire would hurt anything but the resistor in series would drop the 2 volts down at least 1/2 a volt. The sets I have don't have alternative leads for the A+, what they have is a set of screw terminals, where you jump out the resistor for powering the filaments off of a wet cell, and remove the jumper wire when using an Aircell. Since you cannot buy Eveready Aircells anymore the dropping resistor, does not really have a purpose, I've always operated farm battery radios off of an AC powered battery eliminator.
Regards
Arran
+1 on Arran's and Morzh's comments. One should not get an AC Hum on a battery set. The ARBEIII is generally very well filtered. Is the hum there with the volume control all the way down?
The chassis and power transformer of an ARBEIII is grounded but I don't believe that the B- or any other terminal of the supply is grounded. You may need to check into that. Does the hum vary with tuning? If so, it is due to EMI interference. If 120 Hz hum, then there is an issue with the ARBE power supply.
Although I have an ARBE, I power the filaments of my 2V farm sets with a 3V PS and a resistor appropriate to drop 1V. The value of the resistor varies depending on tubes used. For example, for this set, the total current draw for all of these tubes in parallel is 0.5A. Per Ohm's law, to get a 1V drop across a resister where the total current draw is 0.5A, a 2 Ohm resistor is needed. Use a 2 W or higher. Belie e it or not, a 3V 1A Wall Wart switcher does not inject hum into the filament string, and in my experience, did not increase the (already high) EMI noise in my house.
Farm radios came in several different varieties depending on the region sold. Some areas had mechanization such as tractors and cars, some had generator-based power plants, either 6V or 32V, charging lead acid storage battery banks. Some had windmills charging batteries. Farm radios for these farms would run on 6VDC like a car radio or 32VDC. The 6V radios used vibrator power supplies for B voltage like car radios did. The 32V radios often used 32V as the plate voltage using specialized output tubes such as the '48. Sometimes on the 6V sets, schemes would be used to keep current draw to the minimum, such as using 2V battery tubes and a 4V to 135V vibrator supply (like my RCA 5BT and 6BT sets had an option for) or used 6V tubes that had lower current draw (like Zenith), or used 2V tubes in series parallel (like Silvertone), or merely used car radio tubes and circuits. Most of the sets using 2V tubes, A and B batteries used a C battery. Many of these sets used Class B audio output of about 2W using a '19 or 1J6 Dual Triode, compared to between 2 and 3W for a single end output transformer powered set. However, distortion was somewhat higher on these sets due to inherent "crossover" distortion on Class B output stages. However, Class B stages had lower "quiescent" current draw than Class A output stages.
Sets using 2V tubes were made from approximately 1930 to 1938 and fell by the wayside when sets based on the Sylvania 1.4V tubes (1A7 convertor, 1N5 RF or IF amp, 1H5 Diode-Triode detector, 1st AF Amp, 1A5 or 1C5 Output tube or 1Q5, 3Q5 Beam Power Output tube) were introduced in 1938-1939 along with the Loctal and Miniature variants of these tubes introduced in 1940. These sets ran on 1.5V A batteries, 90V B batteries. No C Batteries were used; bias was provided by a resistor in the B- line. Audio output was much less than the 2V sets; anywhere between 0.1W and 0.2WThe circuits for these 1.4V /90V battery "Farm" sets were virtually identical to the portable radios introduced at the same time.
Sets for farms that had no power available traditionally ran on a 2V lead acid battery and dry cell B Battery packs. Individual 2V lead acid batteries were available, or the user used a 6V car battery that may have had other uses in the house such as lighting and connected between the negative terminal and the first inter-cell strap. Back in the day, the connecting straps between cells of the battery were very accessible at the top of the battery. (Youngsters will not remember this, as internal straps came around only in the 1960s. Some industrial lead acid batteries still have these top of the cell straps.)
Of course, the lead acid battery needed to be charged. If there was no electricity from a windmill or generator, or mechanization available on the farm, the owner would have to carry the battery to a "service station" to have the battery charged. If this was too inconvenient, a 3V carbon-zinc dry cell A battery was used. A dropping resistor had to be used. In some sets, particularly Silvertone (Sears, Roebuck and Co, a BIG mail order supplier to farms), the resistor was a rheostat, because as the A battery aged, the voltage dropped.
Enter the Eveready A-600 Air Cell, a disposable battery that once "activated", provided a stable voltage, nominally 2.5V (but possibly really 2.35V) that remained the same until the battery was exhausted. A description of this as well as B and C Batteries is in this document by Eveready (National Carbon, part of Union Carbide), retrieved from the World Radio History website (a valuable resource for radio history information):
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