Philco 48-2810

[ms660]

According to the Trader sheet there's no provision for 110 volt operation.

Is just one section of the dropper open circuit or all sections?

Lawrence.

[Dick Glennon]

Hi again, The 48-2810 has provision for 110 volts but the110volt section has been snipped away. All the mains dropper is open circuit. Dick.

[ms660]

I don't have that schematic so I can't help.

Lawrence.

[Station X]

The schematic for the Philco 48-2810 is available from the Radio Museum site.

https://www.radiomuseum.org/r/philco_48_2810.html

[ms660]

Seems to be other threads about this same radio....maybe merge?

I don't do radiomuseum downloads anymore.

Lawrence.

[Station X]

Originally Posted by ms660

Seems to be other threads about this same radio....maybe merge?Lawrence.

I'll look into that tomorrow.

Circuit looks pretty straight forward. It's a case of replacing two dropper resistors, using a capacitive dropper or powering the set from a 110V or 120V supply.

[Boater Sam]

OK, so you have 2 open circuit dropper resistors and the lamp. Can you identify the 290 ?ohm section of the dropper, it will be the shortest part? If you can, wire a 75 Watt 240v light bulb across it, 60W may do but 100W may be a bit much, you need 150mA (0.15Amp) through the heater chain. This light bulb will drop the excess voltage so that the valves don't get over voltage.

Your valve with no ID is a 7B7. I gave you the valve line up in post #2.
The 5 valves add up to around 115volts, ( adding up the 1st numbers of the valves IDs) hence you need to drop another 115volts on the heater chain with the light bulb to run on our mains.

Please use capital letters in valve number else 1 and l is confusing.

Short out the other dropper resistor, 320 ?ohms, the diagram is terrible, and the pilot light bulb (else you will get no HT)

I would strongly suggest you run this up with a lamp limiter, search on here for 'Lamp Limiter construction', not involved, just a light bulb in a holder and a switch really. It will save you blowing fuses and having things go bang if there is a short anywhere.
If you look at the wiring diagram on the link you have been given, there is a capacitor shown close to the mains input. This capacitor may blow when you power up, not a problem but the lamp limiter will prevent a bang or you could disconnect one end of it first, its not essential that the radio has it at this stage.

Glad I didn't scare you off, have a go and tell us how you get on.
Remember when working on live equipment, keep one hand in your pocket, stay safe.

[ms660]

It's an unusual rectifier valve, from what I can make out the bulb is around 6.5 volts @ 150mA.

Lawrence.

[Boater Sam]

Lawrence, it would seem that the Trader sheet is an Anglicised version for 240v and the OP has an American version which did have switching fo 115v.
It is very difficult to read the resistor values of the dropper off either sheet, can you get it into high definition? The pilot bulb seems to be wired differently in the 2 models, on the USA model it is in the common heater and HT line. On the trader sheet its in the heater chain only.

[ms660]

48-2810 droppers:

Heaters & HT = 320 Ohms.

Heaters only = 290 Ohms.

Lawrence.

[Boater Sam]

Thanks Lawrence, hope that Dick can sort out which is which.

The unusual valve is on the USA version, 35Y4GT with tapped heater.
Fortunately Dick has a 35Z4 in this set.

[ms660]

Originally Posted by Dick Glennon

Hi again, The valve lineup is as follows 35y4, 35l6, 12q7 , no number, and14s7.The mains dropper is open circuit and the pilot light is blown. If I try it on 110voltswill I have to bridge the pilot light with something to create a circuit.? Dick.

Lawrence.

[Boater Sam]

Ah, missed that, thanks Lawrence.

Its a bit hot here, 31C ,sun on the screen, sweating like an old electrolytic.

Its going to be difficult to get Dick to sort the tapped heater wiring. Its all to do with shunting half the heater in the rectifier with the bulb.

So, Dick, Don't short the pilot lamp out! Put in a 6.3v 0.15mA bulb if you have one. I think however that it will work to a major extent without a bulb in.

[Station X]

The best I can do by way of a circuit.

The heavy dashed lines indicate ganged switches.

[Station X]

Three threads relating to the same radio merged. There may be inconsistencies.

[Boater Sam]

Dick, is any of this making sense to you? I don't want to overwhelm you with information but as the set is an unusual one and has obviously been got at before we are going to struggle to help you if you are not understanding fully what is being said.
Sam.

[Boater Sam]

In a previous post Dick says the valve line up has been changed and the bases rewired to suit.
BUT
The valve line up is as original for the USA set.
So has there been any rewiring or not? It's important as the wiring to the dual filament rectifier valve has to be correct with the pilot lamp across the correct half of the filament.

[Dick Glennon]

Hi Again, What I think I will try is the 110/120 volt supply. Is S100 the on/off switch or the voltage selector switch on the back of the set? The other question is, if the pilot lamp is short circuit how do I get a connection to pins 2 and 4 on the rectifier. More questions to follow. Dick.

[ms660]

Yes, S100 is the on/off switch, it says so on the schematic snippet.

If the pilot lamp is short circuit there will be a direct connection between pins 2 and 4 and part of the rectifiers heater won't function.

Lawrence.

[Station X]

Do lamps go short circuit? Won't the set work without a pilot lamp? It's wired in parallel with half the rectifier's heater.