Portadyne Model 230 Hum.

[gary_crutchley]

Hi all,

We've been working on a Partadyne Model 230 radiogram which has a Portadyne AG33 chassis and a Collaro 3RC 531 record deck.

We got the radio up and running, it seems to perform pretty well. The record deck also runs and does work. However, when playing a record with the radio set to gram there is a pronounced hum. The hum isn't audible when listening to the radio, it appears to be on the gram only.

I have uploaded a recording of the hum here:

https://onedrive.live.com/redir?resi...int=file%2cmp3

Can anyone suggest what the issue is please?

Regards,

Gary

[GeoffK]

That sounds like the pick-up cartridge is not connected fully, either a wire in the pick-up head or tone arm is broken, or the connection going to the gram input/switch is not connected or 'open circuit', also check the turntable chassis is connected to the radio chassis.

[gary_crutchley]

Many thanks for the reply, I appreciate it.

I should have pointed out that the hum appears to be associated with the radio chassis, when I recorded it we had the chassis out of the cabinet.

We only get the hum on the gram setting, the radio seems okay. However, with the chassis connected to the turntable we do get audio but the hum is there.

When the chassis is out, if I hold the end of shielded cable which would connect to the turntable the hum is louder.

Does this help?

Regards,

Gary

[boxdoctor]

The hum you have recorded is what, in the valve era, was commonly known as "Grid Hum"
as distinct from "Mains Hum" which is caused by power supply or heater - cathode leakage etc. and which is usually a much deeper, 'rounder' type of sound, with no raspy harmonic content such as you have in your sample. It is useful to learn to tell the difference as this can often speed up fault- finding.
I would agree with heterodyne's comment to check all the earthing of the screened pick-up wire, and ensure the record deck is properly grounded too. Tony.

[gary_crutchley]

Hi Tony,

That's brilliant advice, thank you very much indeed. I will check the screened wire, do you know if/where you can buy screened wire of this type these days?

Regards,

Gary

['LIVEWIRE?']

Good quality scrreened(shielded) audio cable should be available from any of the usual sources such as RS, CPC, Cricklewood Electronics & Maplin. I'm not familiar with the Portadyne 230, but I wouldn't have thought they used anything other than the standard type of screened leads available at the time the set was made.

[peter_sol]

Do you have to have the volume control up more when using the gram? if so the hum may be normal and the pickup suspect.

[smiler411]

if you have a safety earth and earth both ends of the screened cable this can cause hum

Only earth one side of the screened cable if you have a safety earth connected, preferably the chassis side.

Otherwise you may have ground currents inducing hum in the screened cable

[gary_crutchley]

Originally Posted by peter_sol

Do you have to have the volume control up more when using the gram? if so the hum may be normal and the pickup suspect.

Hi Peter,

Yes, that is it exactly. We re-soldered the earths and the hum now seems much less, but is still there. However, we have noticed that the record player volume doesn't go as high as the volume of the radio will do.

We plan to obtain a new stylus, but is there anything else that we should do?

Best regards,

Gary

[Edward Huggins]

A new stylus will make no difference to the output level on the record deck. It's possible that you may need a new cartridge, so don't waste you money on a stylus. What type of cartridge is fitted? Edward

[gary_crutchley]

Hi Edward,

Thanks, that's great advice. I will need to check on the type of cartridge, the gram is at my father's house, so I will get back to you if that's okay.

Regards,

Gary

[gary_crutchley]

Hi,

The cartridge is an Acos Hi-G, there doesn't appear to be a model number on it. Does anyone have any idea if a replacement mono cartridge might be available please?

I've attached an image, thanks in advance.

Regards,

Gary

[Edward Huggins]

This is an Acos HGP39-1. A suitable Stereo-Compatible equivalent would be a BSR X5M. If you are looking for a suitable Mono-only equivalent, you would need to seek a re-built BSR TC8M or an Italian "cloned" Ronette TO45V. Edward

[gary_crutchley]

Edward, thank you very much indeed.