[R-390] OT: Need advice regarding Blaupunkt tube radio

[bavarianradio at comcast.net]

Hi Barry, I have restored many Blaupunkt tube sets. The most common failure in these is the 460 kHz transformers. I have rebuilt many of them. Try tapping one while feeding your 460 kHz generator into the ECH81 grid and see if they act intermittently. Even though you seem to be getting a peak, there could still be a problem. Rebuilding the transformers requires removal from the chassis or circuit board, removing the aluminium can, removing the "sandwich" type mica capacitors and installing new silver micas on the bottom, 150pf for the input and 250pf for the output.  Otherwise, have you recapped the entire radio yet?? also check for proper B+ voltage as well.  Good Luck, Ross 
----- "Barry" <n4buq at knology.net> wrote:

Sorry for OT, but I know there are folks on this list that will know
this and I don't know who else to ask.
I have a 1962 Blaupunkt Verona (3-band - AM,FM,SW) with a classic 4-tube
lineup for AM (5 for FM, and the 6th tube is the magic eye).  It works
(sort of) on FM, but it is it deaf on AM and SW.  I've checked a lot of
things and, so far, have not found anything obvious.  It will hear a
very, very strong signal from the generator (on the order of 3mV) but
nothing on the order of the sensitivity it should have.
I'm suspecting the first tube (the osciillator/mixer) as a possible
problem.  It is oscillating nicely, but the grid bias for the oscillator
is very low (on the order of about -1V instead of the -5V to -8V or so
that it's supposed to have).
Referring to the following site for the tube (ECH81 / 6AJ8):
http://www.r-type.org/exhib/aaa0036.htm
It states the oscillator should be feeding the heptode mixer with "13
volts amplitude sine wave".  My question is: should that be 13V RMS?  I
realize it isn't absolute or critical (values somewhat lower than 13V
will still work), but I'm curious what it *should* be seeing.
I don't have it up and running with the scope at the present, but I
*think* I'm seeing around 1 or 2 volts PtP and I think that's entirely
too low.
I've inserted the 460kc IF signal and can peak the output transformer so
I'm pretty sure the problem is at the oscillator/mixer stage or upstream
from that.
Thanks guys,
Barry - N4BUQ
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