Re: Replacement tubes for a Sonny Jr

    The best place to get advice would be from Sonny himself, who's good
at answering inquiries concerning his amps, his e-mail address is:
sonnytone@xxxxxxx   (unless he changed it recently.)  The Philips 6L6
WGB tubes can be found at Angela Instruments:
You can use the Sovteks for a replacement but the Philips are a much
higher quality tube.

Biasing: it's pretty technical, whole chapters in electronics books
dedicated to the subject.  You don't buy "biased tubes."  Tubes are
biased when installed, biasing is setting up the proper current that is
required for the tubes to operate correctly...this is a very simple
explanation, it's a bit more complex than that.  There are several
different types of biasing schemes, the two most commonly found in
instrument amplifiers is fixed biasing and cathode biasing.  Pre-amp
tubes are usually cathode biased, cathode biasing is also called self
biasing because the tubes will bias themselves when installed.  Power
tubes are usually either fixed or cathode biased.  Again with power
tubes, cathode biasing is usually self biasing, fixed bias has to have
the current monitored and then the proper biasing is set usually by
adjusting a pot or by changing the bias resistor (this should be done by
a knowledgeable amp tech.)  As far as cathode biased power tubes,
usually you can just plug in a new set and the tubes will bias
themselves to a working bias...there are instances (fairly rare) when
new tubes may draw current so drastically different from what was in the
amp previously that they will not bias correctly, even on a cathode
biased amp.  If I remember correctly, the Sonny Jr. amp is cathode
biased, (don't trust me on this, check with Sonny Jr. first), if so, you
should just be able to pop in a new set of tubes and be good to go.  If
you do put in new tubes, visually watch the tubes awhile after turning
the amp on and check to see if the plates on the tubes are glowing
bright red-orange...if so, shut amp off immediately, the tubes are not
biasing correctly, (as I said previously this is a fairly rare
occurance).  You'll have to bring the amp to a tech to have him change
the value of the cathode resistor to one that allows the amp to bias
correctly with the new tubes.

Hope this helps some, good luck,
Don D.

Robert Koch wrote:

>      Dear list,   I am the proud owner of a Sonny Jr amplifier (serial
> # 51) that I got this morning. Unfortunately, a tube broke during the
> transport. It is a Philips ECG JAN 6L6 WGB made in the US. A have a
> pair of matched Sovteks 5881 WXT. Can I use those for replacement? Was
> the 6L6 biased and do I need biased tubes to get my amp working? I
> don't know if the Sovteks are biased... And, BTW,  what does "biased"
> mean? I don't want to ruin this beautiful amp and all help/advice is
> welcome. ThanksRobert aka Sunnyside Bob.

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