Re: Marshall Mk 2 2204 Ann. Series...Blown Output fuse...Why?


"Xtrchessreal" <markgharrison@xxxxxxxxxxx> wrote in message
news:1136419225.634355.240330@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>I am only just now doing the troubleshooting - I had a date for the
> last two days - anyway, thanks for the info.
>
> B+ I assumed to be some sort of characteristic within the tubes, along
> the lines of alpha or beta when speaking about transistor based amps.
> I don't assume to know exactly what you are describing when you say B+.
> My initial thought was that you were talking about a B /magnetic
> field. It seems now that you are talking about a risidual current
> similar to an inductor after the real power is terminated. In anycase
> does AGA have a reference for this B+ so I can study it more
> thoroughly? Has anyone produced a document that describes this,
> perhaps in your archives somewhere?
>
> As far as Caps go, I am not a tech and I do not have the safety skills
> of one burned into my brain but I was planning on discharging the caps
> before I began working to replace them.
>
> I hope my tubes are not at fault here as they have less than 100
> working hours and I used LVs howto article on biasing the tubes when I
> replaced them. LV used to do all of my tech work for my amps and may
> end up with this problem if I cannot find the answer. After acquiring
> a BSEE it just seems silly in many ways to have some one fixing my amps
> anymore. I was successful in my first attempt to replace and bias the
> tubes for my two marshalls using LVs document.
>
> This fuse thing could be a fluke as I had stated somewhere in one of my
> posts that the amp was very close to a large fan motor while in
> standby. A static charge may have built up on the circuit and was
> discharged when I closed the switch out of standby mode. I just don't
> know...
>
> I will follow the suggestions you have stated here and work it out -
> hopefully.
>
> I have learned that a BSEE does not a know it all make and I will
> refrain from such commentary as I post here.
>

Mark:
References to B+ (DC voltage on the main amplifier circuit) and C- (negative
voltage on the bias circuit), and such are fairly antiquated terms that
aren't easily found in an on-line reference as far as I know. It's old
timey stuff. Someone here can probably explain it better than me, but these
are just shorthand terms. I'm just an amateur and don't know enough to
provide intelligent discussion.
Here's one reference I stumbled upon:
http://www.gbronline.com/radioguy/acpwrsup.htm

Anyway, B+ is the rectified (DC) high voltage from the power supply. You
might Google for "B+ voltage" and find some reading where you will be able
to get this from context.

Regards,
Phil


.

Relevant Pages

  • Re: Ping Prof Turner: Amplifier questions
    ... It's voltage tripled off an 18V tranny I'm using for the ... > Fixed bias did get the 4.6 watts out of hard clipping though. ... For any SE amps I like to have Vr < 10mV. ... output tubes, so hence the idea of a choke becomes attractive. ...
    (rec.audio.tubes)
  • Re: Matching power tubes, a little confused.
    ... I am primarily concerned with matching up sets of Output tubes so they ... This tube tester has a limit on Anode voltage of 300V, ... As an alternative to measuring gm, would it be better to simply measure ... up accurately to the operating voltages in the amps and again draw he ...
    (alt.guitar.amps)
  • Re: Matching power tubes, a little confused.
    ... I am primarily concerned with matching up sets of Output tubes so they can ... This tube tester has a limit on Anode voltage of 300V, ... As an alternative to measuring gm, would it be better to simply measure ... up accurately to the operating voltages in the amps and again draw he same ...
    (alt.guitar.amps)
  • Re: JCM 800
    ... IMHO also the less wattage, the better the sound of the single cahnnel amp, but this might be debatable... ... The channel switchers ain´t bad amps, ... The voltage on the remaining two tubes goes EVEN HIGHER! ... I haven't measured this on a Marshall, but on my vintage Univox voltage spikes from 685 to 720! ...
    (alt.guitar.amps)
  • Re: Blackface a Silverface Super Reverb
    ... You'd be better off putting the money into an amp that designed the ... By listening to the tone of various amps and making an informed ... The voltage differences between BF and SF are the bigger issue. ... High voltage on tubes run too cold causes what I believe you are talking about. ...
    (alt.guitar.amps)