Stereosound Carousel Buzz

[AndiiT]

Hi,
I am currently attempting to restore a Stereo Sound Carousel "Junior Radio tape" which has a very annoying buzz (not hum).
I have managed to narrow this down to the ECC83 stage but am now at a loss as to what may be causing this.

All appropriate capacitors, electrolytics, inter-stage couplers etc.have been changed and also the bridge rectifier which was faulty.

I have enclosed a snapshot of the part of the circuit where the problem is and also the rather strange, to me anyway, mains filtering arrangements. I did disconnect the mains filter capacitor and try earthing the recorder chassis via the mains earth (it has a two-core mains lead) as I was wary of leaving the capacitor in place connected between the earth and what appears to be the 200 volt tap of the mains transformer; This did reduce the buzz but still not to what I would consider a satisfactory level.

It may be that this buzz is how the unit was intended to be, as it is only noticeable when the recorder is "idle" however does anyone know if this is the case or should I still be looking for a fault?

Regards and Thanks in advance

Andrew

[yestertech]

'Buzz' is likely to be pickup on the grid circuits of the highest gain valve ( the first ECC83 here )
To prove this, ground the grid and see if the noise disappears. It may be something as subtle as the route mains wiring takes near to signal wires, or signal wires to something like a motor or transformer.
Sometimes these kind of problems are near impossible to fix completely - as you say, it may have been considered 'adequate' performance for the time.
Check also any metal covers or screening materials are in place and are adequately earthed.

Andy

[AndiiT]

Originally Posted by setsappeal

It may be something as subtle as the route mains wiring takes

Hi,
Have checked this and all seems to be OK in that area

Originally Posted by setsappeal

Check also any metal covers or screening materials are in place and are adequately earthed.

Once again checked

Originally Posted by setsappeal

'Buzz' is likely to be pickup on the grid circuits of the highest gain valve ( the first ECC83 here )
To prove this, ground the grid and see if the noise disappears.

I shorted pin 2 of the ECC83 (first stage grid) and the buzz remained, shorting pin 7 (second stage grid) completely mutes the buzz which does suggest that the noise is entering in the highest gain stage of the amplifier.

To be fair I have never heard any tape recorder using an ECC83 in the first stages buzz quite this badly, the valve has even been checked by substitution.

Once again thanks for your help.

Andrew

[david freeman]

Hi
I owned one of these tape recorders and cannot recall any buzzing whilst it was at 'idle'. It was very quiet, and its recordings were rather good, particularly at 7.5 inches per second. Mine had the BSR TD10 deck, although some were made with the TD2.

[AndiiT]

Hi,
According to the servicing information that I have, there were a few different models, which had different amplifier circuitry as well as different decks; Mine is a Junior Radiotape with a BSR TD2 deck and an AM tuner, which was probably the "budget" end of the range.

As an update to the buzzing issue, whilst poking around last night the unit decide to produce some other strange sounds, one of which was a nasty "howl" at certain settings of the volume control - this appeared after the amplifier had been switched on for a short while.
I seem to recall having a similar symptom with a Murphy TR1 some years ago which was traced to faulty coupling capacitors in the equalizing and tone control stages (if I recall correctly) so that's my next point of attack.

Thanks for the help so far

Andrew