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Old 8th Aug 2008, 7:35 pm   #1
Variometer
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Default How about this for a challenge (Philco A535)

Today, I came across this in a damp lean-to shed where it has lain for at least 21 years to my certain knowledge. I vaguely remember buying it at a car boot sale in the 1980s. Can't really remember what make it is, Philco or Phillips seems to ring a bell, L, M & SW.

Maybe I will see if I can get it going again.
Bob
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Old 8th Aug 2008, 7:53 pm   #2
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Default Re: How about this for a challenge

Hi Bob, do I win a prize for identifying it?

It's a Philco A535...no excuses for not bringing it back to pristine condition now...Peter
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Old 8th Aug 2008, 8:39 pm   #3
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Default Re: How about this for a challenge

Many thanks Peter,
That jogged my memory & I recall that it was indeed a Philco A535.
Will let you know how I get on with it.
Bob
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Old 8th Aug 2008, 10:41 pm   #4
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Default Re: How about this for a challenge

Looks like the mains transformer and reccy valve are missing. I would guess, looking at those valves, the line-up to be something like 6K8, 6K7, 6Q7, 6V6 and (possibly) 5Z4. Good luck with getting all that rust off !



Rich.
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Old 8th Aug 2008, 11:21 pm   #5
Sean Williams
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Default Re: How about this for a challenge

Or it could be the series heater chain version......
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Old 9th Aug 2008, 7:57 am   #6
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Default Re: How about this for a challenge

The missing mains transformer & rectifier valve doesn't really bother me. Several months ago, I made a variable PSU that gives me 6.3 ac & HT of anything between 0 & 300V DC.

This set has 6.3 volt heaters. I don't suppose it will take much effort to get it working & the rust is just superficial.

I left it outside last night on the table is is photographed on. I can see it through the window (& lace curtain) when working at the computer, although anyone outside cannot see me. A few minutes ago, the back gate opened & in came the paper boy. I wondered if any interest would be shown it it. There was not the slightest flicker of curiosity, & he left without even a glance! It is rather sad thet modern youth has no interest in anything practical. If it had been me, I would definately have had a good look. I found my first radio in the river in the early 50s & still encounter the same thrill when I see a "junked" valve set.

Bob
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Old 14th Aug 2008, 5:40 pm   #7
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Default Re: How about this for a challenge

PHILCO A535

I got time to examine the radio in detail today. First, I removed all trace of the power supply section as the transformer & valve had already gone. The smoothing capacitor can next to the 6V6 was, in fact, an aluminium-painted plastic tube, open at the bottom end. Inside it were two more modern capacitors. I removed the whole lot. Before trying the set, I checked the output transformer & found it was open-circuit on the input. Connected the two leads to a jack socket so I could use my portable matching unit.

Fitted new LT & HT power leads. Connected 6.3 AC from my variable power supply & all four valves lit up. Then applied HT, starting with 90V. Much to my surprise, the set worked with reasonable volume and an HT current of 18mA. Very good tone as well! Turned the HT slowly up to 250V & the volume increased accordingly. Still good quality sound. The HT current on maximum HT had gone up to 61mA though. I feel this is rather a bit high & probably some of those waxy capacitors have started to leak, so further investigation necessary.

The clipped off wires sticking out of the top were to the dial lamps. I had to remove the mechanical tuning as it was seized solid. Put a new knob straight on the spindle.

A full restoration is really out of the question as the original case is long gone as well as the tuning dial & original mains transformer. But I am considering a complete re-build, maybe on a wooden baseboard with the whole thing converted to 100 Volts HT only. I am sure I can squeeze some more volume out of it after capacitor replacement etc.

This will probably follow after my homebrew 2 valve short wave receiver (Homebrew section). I have almost completed the baseboard-mounting components for that between doing other things.
Bob
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Old 14th Aug 2008, 6:11 pm   #8
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Default Re: How about this for a challenge

Just had the circuit up. The HT on the 6V6G is 238v. So 100V might be too low!

Cheers,

Steve P.
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Old 14th Aug 2008, 6:38 pm   #9
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Default Re: How about this for a challenge

Hi Steve,
I know 100V is too low, but started at that voltage for safety reasons as the set has been in a damp lean-to for 21 years. Even at 100V, the volume was moderate speaker strength. At 250V, it was very good, but not deafening! I feel that when the leaky capacitors have been changed, it will probably be OK at 100V. I have found this with lots of mains valves, they work OK on low HT. Since completing my variable HT PSU, I have confirmed my views that high (& potentially dangerous) HT is not essential.
Bob
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Old 14th Aug 2008, 6:41 pm   #10
Leon Crampin
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Default Re: How about this for a challenge

I once restored a (complete) A535. I don't collect American sets but my sister...

It's a strange set electrically with some illogical circuitry around the grid/cathode of the 6Q7 as I remember. I also found that the hum levels could be reduced simply by moving the HT feed for the 6Q7 anode load to the decoupled supply for the RF section of the set - this had a considerable effect.

After all that, it worked rather better than I thought it would. It's a pity you don't have the cabinet - it's a really good solid bakelite moulding. The scale is pretty too - switched dial lamps to show the 3 wave ranges in different colours.

I seem to remember "my" set had an energised 'speaker - did you have to incorporate a smoothing resistor/choke? I'm sure 100V will run this set if you're not too worried about the AF output. The valves seem to last for ever anyway - mine was well used but all the Brimar valves tested 100%.

Leon.
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Old 14th Aug 2008, 8:43 pm   #11
Variometer
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Default Re: How about this for a challenge (Philco A535)

The speaker had gone, but there was an output transformer on the top of the chassis, so assume it was normal speaker. Anyway, it works OK on 100 Volts but not very loud. Much better on 250V, but the power unit I am using is is external & variable, so I can choose whatever HT I want from 0 to 250V. It (power unit) has its own smoothing circuit (with choke).

I took all valves out & connected it up & leakage was only 1 mA, so maybe I am getting some positive volts on a grid by leakage of coupling capacitor. Will look into it.
Bob
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