Hi

I have recently acquired a 2B receiver and its 2BQ multiplier. The
latter was missing all mounting screws and had a replacement speaker
fitted. I note the manual refers to fitting fibre washers behind the 2BQ
front grille when attaching it to the cabinet.

Can anyone advise me whether the earth speaker lead should be earthed to
the 2BQ cabinet? Likewise what purpose do the fibre washers serve? The
2BQ chassis seems to be earthed via the coax to the 2B and electrically
attached to the front grille, so that the sheet metal screws themselves
would electrically connect it to the cabinet albeit not very well,
whether or not fibre washers were used.

Thanks

Simon VK2UA

I have the matching 2AS speaker (currently undergoing cleaning and
restoration)
it also had fiber washers behind front grille.

w9gb

"Simon" wrote in message
...
Hi

I have recently acquired a 2B receiver and its 2BQ multiplier. The latter
was missing all mounting screws and had a replacement speaker fitted. I
note the manual refers to fitting fibre washers behind the 2BQ front
grille when attaching it to the cabinet.

Can anyone advise me whether the earth speaker lead should be earthed to
the 2BQ cabinet? Likewise what purpose do the fibre washers serve? The 2BQ
chassis seems to be earthed via the coax to the 2B and electrically
attached to the front grille, so that the sheet metal screws themselves
would electrically connect it to the cabinet albeit not very well, whether
or not fibre washers were used.

Thanks

Simon VK2UA

Thanks for the info; maybe the washers serve no electrical purpose but
are there to stop the grille vibrating if some screws are loose or missing?

Simon

gb wrote:
I have the matching 2AS speaker (currently undergoing cleaning and
restoration)
it also had fiber washers behind front grille.

w9gb

Fiber washers are also common in consumer grade vintage Philco radios.
Mostly they are missing but are present in un molested units.

They surve no eletrical or electronic fuction. They seem to be there for a
physical mechanical and or acousital reason.

This may help. I bet it may be mentioned in the RCA Radiotron book. I'll
look next time I am in the shop.


PP

Speakers in metal boxes are prone to resonate somewhere. I would be willing
to bet 5 cents that the reason they are there is to prevent unwanted
resonances.

Regarding the speaker common lead, it is common to avoid a common ground,
which could cause ground loop problems (hum). Usually, the manufacturer
knows best and all you need to do is put it back to the way the engineers
had it in the first place, and it will work as it was supposed to.

73, Colin K7FM

COLIN LAMB wrote:
Speakers in metal boxes are prone to resonate somewhere. I would be willing
to bet 5 cents that the reason they are there is to prevent unwanted
resonances.

Regarding the speaker common lead, it is common to avoid a common ground,
which could cause ground loop problems (hum). Usually, the manufacturer
knows best and all you need to do is put it back to the way the engineers
had it in the first place, and it will work as it was supposed to.

73, Colin K7FM


Thanks Colin, unfortunately ones gets boatanchor gear, as in this case,
where it is not as the manufacturer supplied it. The speaker had been
replaced and if the fibre washers had related to an electrical purpose,
an earth wire might have been relevant. I know than normally speaker
connections do not need to be earthed anywhere, but in the 2-B the
chassis is marked "spkr" and "earth".

This particular set also arrived with the 15 & 10 metre bands dead and
the problem was that the Xtal coil adjustment on 10m was way out -
people do fiddle when they don't know the consequences.

Simon