I have purchased a 1950 5 valve radio gram. I have managed to get it all working again. Replaced the cartridge as old one was dead. The replacement was a new BSR SC12M ceramic cartridge. Bridged the stereo output to a mono input into the amp.

The problem I appear to have is the sound has not base. It is very much like listerning to a telephone. The tone control works but needs to be right down to stop it sounding too higher pitch.

The radio is not quite as bad but still does not have that good old radio valve sound.

Any suggestions what I should start looking at.

Kind regards Roger

Roger,
What's the condition of the speaker ? If you have access to another one try disconnecting the original one and reconnect with the new one.
What's the brand and model number of the radio ? Perhaps you may also have leaky coupling paper caps. to the output valve as well as a high value resistor to the preamp valve.
The original cartridge would have been a crystal one which you replaced with a ceramic which has a lower output.
Hope this helps.

Rudy

A good indicator as to what is at fault is to compare the volume, tone and clarity of the radio to that of the stylus. If the radio sounds fine then the speaker won't be at fault and the fault will lie with the stylus or the wiring to it.

Sometimes the output of a stylus is strong enough to send the amplifier a signal even if the earth lead (usually the braid surrounding the wires from the left and right channels of the stylus coils) is disconnected and a shallow, toneless sound with weak volume will be heard, especially if a pre-amplifier is part of the amplifier circuit.

So you would need to check the output of your stylus as Rudy has suggested but I would also add a check on the earth connection and the polarity of the three wires coming from the stylus.

Roger,
When you said "The radio is not quite as bad" from that I assumed that it wasn't that good either, ie, weak and or distorted. You should come to some conclusion between what has been suggested by Brad and myself. Also check the polarity of your connections.
Rudy

Thanks Rudy and Brad,

The radiogram is a Radio Corporation of New Zealand, Colombus, Model 66N Serial No 20087, 230volt 60 watts.

On further inspection I would have to say that the radio and record player quality is equally poor.

With reference to the gram I need the volume higher to achieve the same audio level from the speaker, but I would suggest that this is due to the ceramic cartridge replacement. Is there a means to adjust the pre amp to suit the ceramic cartridge?

I went on to inspect the Caps and found that one was leaking a residue, it was a Hunts Capacitor, K 539 WDY, MFDS 16, DC volts 450.

I have not yet identified what its location in the circuit is. Do you know what would be a suitable replacement would be that is ready available.

I have checked all the earth and cartridge connections and re-soldered them all.

Do you think that it would be wise to replace the other Capacitors, and as a rule do valves semi fail or do they either work or not work?

Kind regards

Cheers Roger

Roger
It sounds a bit like this set needs a birthday

The 16μF 450V should have a mate or another of 8 or 24μF perhaps.
Both of these need to go, 22μF is the most common available.

I would identify & replace all of the electrolytic and paper type capacitors. Then look for faults. Leaking capacitors will drag down voltages & upset bias.

If you have, or free up the ends of resistors, check them while you are at it and replace them if they are out of tolerance...normally they go high. Pay attention to the plate resistor of the first audio valve.
Circuit will be handy.

Take a photo of the inside of the pan before you start ,so that you can check it if you make a mistake.

At this stage I would not worry about the valves. The squeaky voice is more likely to be the Plate bypass caps on the tone or the plate, the speaker poling, or the cathode bypass cap (if fitted) on the output valve. You will eliminate one of these by changing the caps.

If you have test gear? Running a tone into the PU of the set and looking at the result on a CRO would be helpful with the amp.

A systematic approach is desirable, get the amp working before proceeding, should the fault still be there after the capacitor job.

Marc

Marc,

Thanks for great advice, I will get into the capacitor replacements, its got a mate of another 16 μF. Do you think a .22μF is close enough for a replacement for these.

Cheers Roger

Roger,
In one word NO. Replace with the same value and voltage or higher volts. Could you tell us the number on the output valve then we can advise you which pin to check. There is no adjustment to compensate for lack of input. Follow the line from the pick-up wires through the phono/radio switch and see if they go directly to the valve.

Regards

Rudy

On second thoughts Roger, why don't you check with your local society, I've dealings with them before and they are most helpful.

Rudy

http://www.nzvrs.pl.net/

We are being a bit pedantic here.

At the time of this sets manufacture the electrolytics had a tolerance of plus or minus 40% I have not had any hum problems with 22uF's in some of the hundred plus radio's that I have serviced in the last 12 months.

We need a little more info:-- If the rectifier is an indirectly heated type like 6X5, 6V4 or 6X4 the voltage will be lucky to get past 350 for a 250V HT on startup.

Marc

Marcc,
I agree that 22 ufd is fine, but I thought I saw point 22.
"Do you think a .22μF is close"
Rudy

Me thinks someone accidently read the comma.

The only thing you would use 0.22 μF for on the HT(and thats big) is for RF decoupling and lots of sets, perhaps this one do that.

Normally its more like 0.1 or 0.047 μF ( Electrolytics do not filter RF)

I find they're essential here as the long runs of HV aerials bringing in power and locally large transmitters ensure around 5 to 6 Volts of RF riding on the mains. I have actually resorted to putting a 0.22 μF mains MKT across the bench mains supply rail to try & filter some of it out.

That RF manifests as hash and can be seen on the HT with a CRO.

Marc

Sorry about that I did read the , as a . and then ran with it. So we are talking about 16 MFDs being replace with 22μF if that's is all I can get. It appears the rectifier is a 6X4.

There are three fairly large round light brown wax coated capacitors about 2" long by 1/2" round.

They are all rated at 500vdc but one says 0.25 MFD, another says .25 MFD and the third is marked 25 MFD. They would appear to be round paper type sealed with wax. (not electrolytic). Do you think that these would be more likely to be all 25 MFD / 500vdc?

Is a mfd now labeled uF?

I am planning to replace all these capacitors.

There are two electrolytic capacitors rated as 25mfd / 25 w.v / 40p.v. Would I be correct in assuming these are 25μF at 25vdc?

I will plan on replacing the two 16 mfds / 450 vdc electrolytic can type capacitors with a modern type under the chassis and leave the cans there for a cosmetic original look, (disconnected of course).

I have taken photos and will relace one at a time and check that all still works before moving to the next one.

The valve line up is; 6X4, 6AQ5, 6AV6, 6BA6, 6BE6, 6BA6.

Have not yet made contact with the local club forum but will keep trying.

Thanks again for all your fantastic advice.

Cheers Roger

Mfd and μF are both normally used and interchanged and stand for microfarads.

You can get 22μF (mfd) 450V axial type Electrolytics, that will be a lot easier to get along with. Make sure that one of those pair is not sitting on a bakelite plate.... Thinks will be different if it is, but the next two caps suggest its not as they are likely to be the cathode bypass caps for the 6AQ5 and probably the 6AV6?

This is where a circuit is handy. 25 volts is their working voltage an 40V the maximum surge that they will take before destruction.

The Cathode of 6AQ5 will be around 12.5 Volts (250V HT) above ground. Jaycar RE-6092 would do here, thats 35V and 22μF (some vintage suppliers have 25 uF) Do not be tempted to go higher in voltage as they may prematurely fail, by loosing polarity (another story).

These will be around a quarter of the physical size...... check the cathode resistor while you are at it, as that going seriously high will shut off the valve.

6AQ5 may have a grid stopper resistor of 50K (47K) and another grid leak of 500K (470K) The attrition rate of these is is quite high. In most of the radio's that I have serviced recently (100+) In those with 6AQ5 and 6V6, most have been well out of tolerance.

G'day Roger,

Capacitance is expressed in microfarads though for some reason we've gone from the abbreviation of MFD to the Greek letter μ, pronounced mew, which stands for micro and the capital letter F, meaning farad, which is named in honour of Michael Faraday, an English chemist.

For the purpose of this website, and indeed others, where knowledge of special characters is seldom acquired by users it is okay to use a lower case u in place of a μ but to make life easy for those wanting to use the correct character I have tonight included a rendering code, that being [mu]. If you type this then when your post is displayed the site will automatically render it as a letter μ.