Philco Model A3746

[u28909z]

Hi

I am new to this forum. I have recently become interested in old record players, and have bought a few tatty examples. I have limited knowledge of electronics, and need some advice on the Philco, which has a thin sound and low max volume.
The cartridge is a 'new' Astatic turn over crystal item so should be ok.
I intend to replace faulty caps.
There is a large (physically) resistor 500 ohms which connects to the diode valve UY85, which reads 800 ohms on the meter, but I don't know what power rating is needed to replace it with.
Please can someone advise me.

Thanks

[ukcol]

The manufacturer's manual is available as an instant download for £1.99 here.

The resistor (R9) can be replaced with a 500 or 470 ohm 5W wire-wound resistor.

Other components will need replacing for safety and reliability reasons.

[u28909z]

I have the service manual, but not sure how to interpret what I need to replace resistor R9.

[ukcol]

There are many suppliers of suitable resistors; there is an example here.

Don't just replace that resistor and expect the record player to work reliably and more importantly SAFELY.

[Edward Huggins]

Does the OP mean he cannot read the circuit diagram so as to be able to locate R9?
It sounds like a surge resistor to the UY85 anode or the smoothing resistor, but that's without sight of the circuit. Well worth repairing this record player as it has a good bass on it. Edward

[Techman]

This is another of those threads that looks like it's going off at a tangent before it's even started - so let's get back to basics!

The mention of a crystal cartridge and UY85 leads me to think that this is a simple single stage amplifier, so there's virtually nothing to go wrong (although I don't have the circuit in front of me).

I didn't think that there was anywhere in the world that made crystal cartridges these days, so it's doubtful that this cartridge will be 'new'.

Crystal cartridges absorb moisture from the atmosphere over time, so many 'new, old stock' examples 'are dead on arrival'!

So before jumping in, how about testing that cartridge for output, or injecting another signal into the input of the amplifier, or dare I say, even measuring some voltages around the amplifier valve.

WARNING - without seeing the circuit info. or the unit itself, the 'U' series valves may indicate that this is a LIVE CHASSIS design with one side of the mains connected directly to the chassis metalwork, so please exercise extreme caution!

[Techman]

Originally Posted by u28909z

I have the service manual, but not sure how to interpret what I need to replace resistor R9.

UKCOL has explained this in the second post of this thread. Although replacing this resistor will make some improvement, I'm not convinced that this will be the total cause of the low output you describe, but you never know. If the output is just a 'bit' down, then the increase in value of this resistor could be the cause.

[peter_sol]

What is the other valve type? UCL83?

[Techman]

Good point, Peter. What we need is a bit more info from the OP, even a clear photo of the innards, plus the exact part/model number of the cartridge.

[ukcol]

I answered the OPs specific question about the surge limiter resistor and was at pains to point out that other components will need replacing not the least for safety reasons. Although the resistor is unlikely to be causing a significant drop in volume it will have some effect. The main reason for replacing it however is that since it is already 60% high it will get worse and probably go open circuit.

Low volume symptoms often point to the cartridge but unless your new one is faulty the fault will lie elsewhere. The amplifier is a two stage one employing a UCL83 and so a high output type cartridge should not be needed.

Before you start some capacitors will need replacing, I left it there for others to follow however:

To be clear you need to replace C1 & C2 with class "Y" types for user safety. You need to replace C5 for the safety of the equipment and C6 for reliability. C7 may not need replacing if it is a ceramic type or similar. The electrolytic capacitor C4 could have dried up; if it has it will cause low volume and should be replaced.

Your will probably need more advise such as places to get the components but I shall leave that to others.

Finally take the warning from Techman in post #6 seriously.

[Edward Huggins]

As far as I know Philco never made a single-stage portable record player and they were all the better for it - they all sounded great! Edward

[RojDW48]

I had a 3754 for a while (an earlier model I suppose) - definitely not single stage and plenty of grunt. Yes, its crystal cart was dead - I think I replaced it with the ubiquitous BSR SC11. A good old RP and seriously expensive in its day. I would be inclined to do as Techman suggests and tap in another source - eg a CD player. A 'new' crystal cart could easily also be a dead crystal cart.

[u28909z]

Thanks for the responses, the other valve is UCL83.
The components are all mounted on a composite material board (not printed circuit) rather than a metal chassis.
I will replace the capacitors suggested as well as the resistor, and am aware of the shock hazards with these things.

This player has a Collaro Conquest changer with a detachable headshell. The Acos cartridge fitted to it was no good. Incidentally I have found that Collaros fitted with Ronette cartridges seem to be ok, those cartridges must have been well made.

[u28909z]

I have replaced the capacitors and the resistor, which made no noticeable difference. I then fed an input from a radio headphone socket directly into the amplifier, and it sounded really good.
I next tried the cartridge (it is an Adastra D5 by the way) directly into the amplifier, bypassing the capacitors and resistor on the motor board. Again the result was now a good solid sound with proper depth.
This has left me wondering what the purpose of those components are, they don't work with this cartridge?

[Station X]

The components on the motor board are to isolate the cartridge from the LIVE CHASSIS.

BE CAREFUL!

[ukcol]

Picking up on Graham's post.

There is a danger when the user handles the pick-up or touches the record deck metal work that he or she will receive an electric shock.

Referring to the diagram below.

When the chassis is live (arrowed) this voltage will be transferred to deck via the bottom pin of the connecting plug and socket (also arrowed). C2 connects this point to the record deck chassis (motor plate).

In the live chassis condition the user can still get an electric shock from the deck but the current is limit to less than 1mA by C2. C2 is 0.01uF and its reactance at 50Hz (the mains frequency) is over 300k ohms.

C1 provides a similar function should the user comes into contact with the cartridge connections. There is another path for the live chassis voltage to the cartridge via R1 and the volume control R3. But the current via this path is limited by R3 + R1 a total of 2.15M ohms.

If these capacitors are bypassed the user is exposed to the risk of a very dangerous electric shock because the possible shock current will be very much larger.

_________________________

Having got that out of the way your report that bypassing these components provides you with "good solid sound with proper depth" suggests a clue to the cause.

R1 will reduce the signal to the amplifier by a small amount but by an equal amount across the audio frequency range.

R4 and C3 provide bass boost at the lower end of the volume control by reducing high frequencies.

So for our purposes the input to the amplifier from the cartridge is resistance capacitance coupled, the resistor being the volume control (2M ohms) and the capacitance is C1 (0.01uF). Resistance/capacitance coupling falls off at the low frequency end of the signal in question.

For 0.01uF and 2M ohms this frequency is about 8Hz, well below what this player could reproduce and well below what you or anyone else can hear. So you should hear no difference when you bypass these components.

If C1 is in fact a healthy 0.01uF then perhaps something is shunting the input to the amplifier.

A short circuit or very leaky C3 would not help but I can't see it having a very great effect at high settings of the volume control.

I can't think of a cartridge fault that would be swamped by bypassing those safety components but someone else may know better.

['LIVEWIRE?']

Surely a high resistance or (almost) open circuit R1 would reduce the input to the amplifier - a highly unlikely fault perhaps, but one that is easily checked with an ohmmeter on a suitable range. Such a fault could be caused by a bad connection between the inner wires of the screened lead between the cartridge and R1/C1.

[ukcol]

I had understood from his post #14 that the OP had already replaced R1 although it is easy to misunderstand terms like "I have replaced the resistor".

You are right though that R1 could cause low volume if it has gone high resistance.

[Station X]

I assume that if the isolation components have been replaced, the new ones are of the correct value? I'm sure most of us have made the mistake of misreading a colour code, decimal point or W.H.Y.