Hi, My name is Gary and I am new to Vintage Radio.
I have an AWA model 527 MA which has ceased operating, slight hiss from the speaker only, changing vol control, tuning or band makes no noticable difference. Can any one assist with cuircuit diagram or advice? I believe this radio is the same as a Hotpoint V5, can anyone confirm?

Welcome to the forum.

You can download the 527MA schematic from here:

http://www.kevinchant.com/uploads/7/1/0/8/7108231/527-ma_528-ma.pdf

Unless there is a glaring clue such as burned components, or oozing capacitors, or no sign of life from a valve, or a glowing anode in a valve, etc, the usual approach is "divide and conquer", with the division being between the RF stage and the audio stage, starting with the audio stage and if that's okay, looking for a problem in the RF stage.

Before continuing on the diagnosis path, a few questions ...

You say you are new to vintage radio, but do you have much experience in radio or electronics generally, and have you worked on high voltage circuits?

Hi GTC,
Thanks for he manual, much appreciated.
I held a Ham licence many years ago and worked on mobile plant electronics but all my experience was on solid state equipment. High voltage experience confined mainly to power supplies and plug in appliances and working around high voltage transmission and distribution systems.
Regards,
Gary

Okay, so you should be familiar with safe working practice around lethal voltages.

Please note that if the radio hasn't been used for a long time, and it's in original condition, then there's a high probability of dud capacitors all through it and you can really chase your tail without doing a "re-cap".

Nonetheless, here's a quick getting started routine:

Rotary switches have suckered me before. These days I start by hitting them with a blast of contact cleaner while rotating the switches through their limits to eliminate bad connections. If you're very lucky that may be all that's needed to cure the fault.

Regarding the following, be very careful to correctly identify valve socket pins as there is high voltage on some of them. (See the socket voltages table in the service manual.)

P is plate (anode, signal output)
SG is screen grid
SUP is suppressor grid
K is cathode
G is grid (signal input)
H is heater

From under-chassis view, valve pins number clockwise from the gap or notch.

AWA didn't give valve pin numbers in that schematic, so you can get them here:

http://tubedata.milbert.com/index.html

As your set has a phono/radio switch I'd start by switching to phono and putting a signal on the pickup input terminal. The signal can be as crude as a screwdriver with your finger on it to introduce some hum signal. See if this creates any output. If yes, then on the face of it the problem will be in the RF stage.

If no, then the problem is most probably in the audio section in which case tap the grid pin of the 6V6 with a driver which should produce clicks from the speaker.

If you get output here, then the problem is between the audio amplifier (6AU6) and the power output (6V6).

If no, then the problem is in the neighbourhood of the 6V6, including the 6V6 itself.

If the problem is determined to be in the audio stage, a very common issue with old sets is a faulty output transformer. A burned out speaker is also a possibility but a quick ohms test of the voice coil can usually determine that. (Disconnect one leg to do that, of course.)

Anyway, see how you go with the above.

And be very careful when working on a live set. Know when the power is on and when it is off. Think twice before touching anything and be wary of the charge retained by large capacitors.

Gary, Could you unlock your email address in your profile page for a day or two and I'll get in touch with you.

Cheers, Graham...

If there is hiss from the speaker I would wonder about the OP transformer being dodgy.

I would actually measure a few voltages C12, the plate bypass on 6V6 is the most likely to fail. If the set has wax paper caps, I consider it a waste of time fault finding until all of them and the electrolytics have been replaced.

I would use 500V types on the filters as it has a 5Y3. Some resistors can be checked "in circuit" others not so accurately. However, if you unsolder the end of a resistor when replacing a cap. check it and if it's more than 10% out replace it.

Plate resistors on Det Audio valves and the grids of 6V6 have a high attrition rate. Hiss can be a Silver Mica type cap letting go. These are not common failures In Australian sets, but you do get them and I did have to replace every one on in Astor RK and Philips 132L.

The most likely (not exclusively) to fail in them are the ones with HV DC on them.

The best way to get a rough idea with 6V6 if the OP transformer is not open, is to strike a 9V battery across pins 3 and 6 (plate & screen) & you should hear a definate snap & crackle in the speaker.

The logical sequence for fault finding is Voltages first (fix PSU) then the Audio. then the RF

AWA did make GE and Bandmaster & it is not unusual to see badge engineering. Where several different "makes" share the same chassis, and / or circuit. It happened in car radios as well. I have a Ford one on the bench with a dead oscillator (2nd to die this way) and it is an AWA. There were plenty of Astors, that appeared in different makes of vehicle with different facia's only

Marc

I agree that it's wise to check those voltage right off the bat.

(I mentioned OP transformer in passing due to its frequency of failure.)

If the audio was a loud and controllable hiss, then my next guess would be possible lack of local oscillation.

There is a black coated OP transformer in some of the HMV Nippers seen a lot of them die & Krieslers I dread, they are one of the worst for OP transformer failures that I have encountered.

I would expect hiss if the oscillator was generating IF freq as nothing would get through if it's dead.

Has the set got an external antenna on it? Won't get much if it hasn't, or is on the wrong terminal.

Marc

I had a set where the audio was okay but all I got was static, loud or soft depending on the volume setting. When I replaced the converter it came good. Granted that static isn't hiss, and I didn't look further as to which part of the converter wasn't operating, but what you say makes sense as it has to get through the IF filters.

Thanks for the replies, sorry for the long delay, a familly medical crisis got in the way of really important issues (like fixing stuff).
GTC I followed your advice and found touching the grid of the 6v6 produced faint scratching noises. When I place a multi meter probe on the plate of the 6au6 I get a loud click. when I place a probe with finger on the 6au6 grid I get nothing. Checking voltages around the 6au6 with a DMM I found plate to chassis voltage 186VDC, SGrid to chassis 180VDC,Grid to chassis 1.4VDC, Cathode to chassis 0VDC, Heater voltage 6.5VAC.
To my very inexperienced eye this points to the 6au6 not operating ( I would expect some output when touching the grid ). Any further advice gratefully received.
Gary

Grid to chassis 6AU6 1.4V I need to see the circuit of that, but the grid should be negative relative to cathode.

If there is a capacitor from a previous plate to it's grid and the grid is actually positive. The cap has failed.

If this has the original Wax paper capacitors & old electrolytics in it, they will have to go.

Marc