Re: Help-diode of old Tandberg amp

From: Per-Åke Andersson (pake_at_extrafoi.se)
Date: 10/28/04 

Date: Thu, 28 Oct 2004 16:49:50 +0200

ed wrote:

> Hi,
> Can a kind expert soul help me (a novice) to indentify a diode(it is
> conducting both ways now) in an old(more than 20yrs.) audio amp.
> Tandberg TR2025 MB(220v,50Hz).There are 2 similar diodes IN SERIES
> in the Power Amp. section(total 4).Its cylindrical(3mm wide,5mm long)
> with 1 tapering(or sudden) step and colour bands-Black,white.light
> brown,dark brown,light brown,red.Red colour continues on step and on
> other side is golden colour.Its Location:One side of diode is
> connected to 2 resistors in series and then to collector of BC 557B.
> Other side of the other diode is connected to ground(of
> Motherboard).The ground through a resistor connects to collector of BC
> 447A.
> About a year back,i had replaced one of these with a glass
> encased one(1.5mm wide,4mm long-half purple,half orange-red) removed
> from the radio section(total 8 on power amp. section,many in radio
> section) and the amp. was working(now the output transistors and
> others are gone due to 1 speaker coil shorting and some other
> causes?).Here is some more info about power amp. section:
> 1.Transformer supplies about 26v-0-26v with no load.Two 4700 micro
> farad electrolytic caps.
> 2.Output transistors are Motorola BD609 and BD 610(1 pair for each
> channel) and BC 848B(?).
> 3.Other transistors are (per channel): BC 548B, BC 558B, BC447A, BC
> 557B, C828-C828(emittors joined), BC 547B, BD418(MOTOROLA),2(can't see
> any no.) with small heatsinks and 3 colour bands.
>
> Speakers used are 35 Watts,8 Ohms.
> Thanks.
> Ed(edsin333@yahoo.co.in)

Hope you will have answer here but
if you dont get any answer here. Try to contact members of
Norwegian Historical Radio Society.
Here is alot of info about Tandberg (but most in Norwegian)
http://www.nrhf.no/nrhf-eng.html
They have a forum here:
http://www.nrhf.no/phpBB2/index.php
Dont know if its only for members.
If not , use subject "Kringkastingsmottakere ol."
They have also a "radio doctor" with adress:
tor_fander.lende(at)chello.no

/Per-Ake
Tandberg 2025 made from 1976
http://www.nrhf.no/TR-2025.html 

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