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Post subject: Re: Help Bandmaster blowing fuses
Posted: Sun Aug 05, 2012 7:21 pm
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BMW2002Ti wrote:
:D Ok... cautiously going where NO MAN has gone before... :lol:

You know, I read that thread about the 400VDC on the 12AT7 anodes about three times before it hit me that it's supposed to be around 400VDC. Both halves are tied together to get the most mojo (ok, current flow) out of that 12AT7. And the 12AX7 (7025) recovery half should be around 250VDC.

Awaiting re-boot...

http://www.webphix.com/schematic%20heav ... _schem.pdf


Right. So MusicMan's statement "Still a little worried about my voltage on the pin on the reverb tube. Should be 280 but I'm still getting 460." Applies to WHICH reverb tube? I assumed he meant the recovery 7025. :?

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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 10:27 am
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Hey all, sorry I haven't replied until now but I got a chance to work on my amp last night. Right now I'm not at my workbench and at work... I will post voltages at all pins tonight if that would help. Did a stupid thing and thought if it is still ok, I'll put that puppy back in the cab. (then the guy on my left shoulder said,"try the new tubes again because it couldn't be them.") So I did and instantly as soon as I turned the standby on it popped. Took them back out and put the old 6l6's in and turned it back on. It played for about ten minutes and popped again. Let it cool off for about 15 min. and tried again. This time it stayed on.
As for the iso t, the fuse that popped was a 3 amp. Then I replaced it with a 2. Not sure what the amperage is but voltage is 120. The high voltage is coming in on pin 1 on the 12ax7 in the vibrato stage. It shows I should have 460 at the point from my opto to the 220 resis. but 280 on the pin. Do I need a pedal in to bring that down? Took tube 1 out and had a scratchy sound. Un hook guitar cords and tried to locate. Tapped tube for ch.2 and it chimed so I replaced it. So far it is holding on. It seems that voltages are a little high all around but not extremely high.


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 10:57 am
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" Do I need a pedal in to bring that [voltage] down? "

Wow! No... :wink:


" So I did [put in new 6L6GC] and instantly as soon as I turned the standby on it [fuse] popped. Took them back out and put the old 6l6's in and turned it back on. It played for about ten minutes and popped again. Let it cool off for about 15 min. and tried again. This time it stayed on. "

You seem to have a some more basic issue(s) with the output section, power supply, and/or bias circuit. IMHO... a more systematic approach to find the problem(s) is needed.

Maybe time for a good amp tech.


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 11:38 am
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musicman3858 wrote:
Hey all, sorry I haven't replied until now but I got a chance to work on my amp last night. Right now I'm not at my workbench and at work... I will post voltages at all pins tonight if that would help. Did a stupid thing and thought if it is still ok, I'll put that puppy back in the cab. (then the guy on my left shoulder said,"try the new tubes again because it couldn't be them.") So I did and instantly as soon as I turned the standby on it popped. Took them back out and put the old 6l6's in and turned it back on. It played for about ten minutes and popped again. Let it cool off for about 15 min. and tried again. This time it stayed on.
As for the iso t, the fuse that popped was a 3 amp. Then I replaced it with a 2. Not sure what the amperage is but voltage is 120. The high voltage is coming in on pin 1 on the 12ax7 in the vibrato stage. It shows I should have 460 at the point from my opto to the 220 resis. but 280 on the pin. Do I need a pedal in to bring that down? Took tube 1 out and had a scratchy sound. Un hook guitar cords and tried to locate. Tapped tube for ch.2 and it chimed so I replaced it. So far it is holding on. It seems that voltages are a little high all around but not extremely high.


You blew a 3 amp fuse in the iso tranny and replaced it with a 2 amp fuse? :shock:

What schematic are you using? Please post it. Earlier you said the voltage on a reverb tube was 460 VDC and should be 280 VDC. Now you are talking about the vibrato tube? Which is it?

Why are you swapping tubes around?

I agree with BMW. You need to start looking at your troubleshooting in a more systematic manner instead of the shotgun approach you are taking. Just the fact that you replaced a blown 3 amp fuse with a 2 amp fuse scares the crap out of me. I really think you need to take this amp to a competent tech before you do some major damage to the amp or yourself.

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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 1:15 pm
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Sorry if there was any confusion but the voltage is on the vibrato tube. And the reason I replaced the fuse with a smaller one is that it was a Sun. And the only fuse I had on hand was a 2 amp so I figured it was a safer fuse than a 5 amp. And it may be best to drop it off to a tech but I waould like to systematically finds out what is wrong myself. I'm not an electronics expert, I'm a HVAC man so I've dealt with voltages,current and so forth but I'm just not that familiar with DC. I really want to work on these babies and understand them. If you can give me one specific thing to look for and where and why I would apprecdiate it. Thank you :mrgreen:


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 1:20 pm
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musicman3858 wrote:
...If you can give me one specific thing to look for and where and why I would apprecdiate it...


A good tech is the only thing that you should be looking for!

BMW2002Ti wrote:
...You seem to have a some more basic issue(s)...


Basics is an understatement. From reading the OP's last post, one issue seems to be the knowledge of how to use a meter, and where to measure. The DC voltages should be read with the negative meter lead connected to the chassis(ground) and the positive lead at the point where the reading is desired.

musicman3858 wrote:
...The high voltage is coming in on pin 1 on the 12ax7 in the vibrato stage. It shows I should have 460 at the point from my opto to the 220 resis. but 280 on the pin....


And admittedly having no knowledge of electronics, using an iso tranny for no reason, doesn't know how to check a diode, blowing a dozen fuses (so far) and still trying the same thing over and over, replacing lots of components that probably shouldn't be replaced, I'd say that this project is way over his head, not for a beginner at all. "A pedal to bring down the voltage?" Really!?!?

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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 2:06 pm
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+1000!

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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 4:46 pm
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Sounds like someone has sand in his v----a... but luckily you aren't the norm on here.. Thanks anyway


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 4:48 pm
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p.s. you sound like the kind that prefers to give up than learn.


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 5:03 pm
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I feel I should apologize to eveyone here for my last posts but couldn't help the spur of the moment reply. Anyway when I was talking pedal I was referring to the vibrato switch, the vibrato doesn't function without it so was curious how that would affect the circuit. And for the multi-meter, been using one probably longer than he was alive. Some shouldn't get involved with the helping process if they can be of no help. I will refrain from this forum and if I have offended anyone or pushed for too much I'm sorry. Thank you to all that have been of help. I'm not giving up!


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 5:32 pm
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musicman3858 wrote:
Some shouldn't get involved with the helping process if they can be of no help. I will refrain from this forum and if I have offended anyone or pushed for too much I'm sorry. Thank you to all that have been of help. I'm not giving up!


With the exception of one person who I won't bother to identify, all of us that have tried to help you are extremely knowledgable in the diagnosis and repair of Fender amps. We have tried to answer all of your questions and follow you through your convoluted postings. At this point it seems that we are no closer to resolving all of your amp's issues then we were several pages ago. Trying to diagnose serious amp problems on-line without physical access to the amp can be next to impossible. Based on your current level of progess in getting your amp to work, several of us have recommended that you consult in person with a good amp tech. Instead of accepting that recommendation, you chose to throw a hissy fit and insult ... me? Shimmilou? I don't know nor do I care at this point. Good luck getting your amp to work. I'm finished trying to help.

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Last edited by bluesky636 on Mon Aug 06, 2012 6:35 pm, edited 1 time in total.

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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 5:57 pm
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musicman3858 wrote:
Sounds like someone has sand in his v----a... but luckily you aren't the norm on here.. Thanks anyway


Sorry to sound so harsh, but someone has to say it. You really should learn to walk before trying to compete in the Boston marathon. No one here or anywhere can help you if you don't know the basics, like checking a diode.

For example, why were you using an isolation transformer? Are you aware that it can actually cause more problems, and it is absolutely useless in this case.

As has been pointed out previously, there is no black-face version of this amp, so to say that you are black-facing it is just wrong, and pointless to attempt.

BTW, the tremolo (vibrato) works without the foot switch, and the switch is used to turn it off.

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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 8:09 pm
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Sorry Shimmilou and you're right but the post had a bit of degradation in it. I am sorry. Honestly, working on this amp has been a blessing to me. I am in-between treatments right now and this project has been frustrating but the most rewarding and relaxing thing I've done. I finally have it working but my voltages are a little weird. So close... I'm trying to learn as I go and I know that's not the brightest thing to do but it is a great feeling to move forward on it, and I am learning a lot. It might not seem like it but it is. The iso transformer was given to me by a friend because of the high voltages. If I shouldn't be using it then I won't. I took the voltages and jotted them down tonight and will try to follow the schematic tom. to see what areas I could be having problems with. Thanks for all you and everyones help. :)


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 8:17 pm
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MM, really ppl who post here are ultimately the happiest when the amps are reliabiy working. A popping fuse is a big "red flag" in any circuit. Must be addressed.

Parts of the amp which usually causes fuses to pop are the power tranny (PT), rectification for the main B+, output section, bias power supply circuit, and output tranny (OPT). As a HVAC tech you know when you see bigger gauge wiring = more current flow. And excess current causes fuses to blow.

The one BIG caveat we all have is DC current kills at a much lower amperage than AC. It's the nature of the beast. 1 amp can kill you. So, you really need to be very careful when dealing with a live amp.

Your posts on voltage on anode plate of 12AX7 and 12AT7 indicate your don't really understand these circuits. Yes, that can be an issue. But, I'd bet $25 this is NOT the cause of fuses popping. And the use of an iso-tranny is kinda worrysome.

A good site to brush up on tube guitar amplifiers, is Aiken's site.

http://www.aikenamps.com/TechInfo.htm

Click onto Introductory (Aiken) and later, Advanced (Aiken) to get a better feel for how these amps work. And a good strategy to go about finding fuse blowing issues.

There are also a lot of good books on fixing tube amps. Gerald Weber, Morgan Jones, Kevin O'Connor, and Merlin Blencowe are just a few authors, whose books I've worn out ---as indispensble technical resources.

Merlin Blencowe's Valve Wizard site:

http://www.freewebs.com/valvewizard/

See if the answers to some basic issues make more sense. Try to follow a logical path of current flow & the idea of how AC signal riding above DC B+ works to get amplification. I think this will help reduce some of the frustration you are experiencing. In my mind, I try to break the amp down into sections. Like a block diagram, To follow B+, bias voltage, and signal path. What is the function of each section and how it interacts with others, up-&-downstream.

We cannot recommend one easy answer to your amp's problem --- without a little solid dectective work on your part. And there maybe several issues at hand.

Good luck with the amp. We all hope for a tone-meister, reliable instrument in the end.

:mrgreen:


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Post subject: Re: Help Bandmaster blowing fuses
Posted: Mon Aug 06, 2012 9:49 pm
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By all means, Musicman, keep at it if this makes you happy! Rule # 1- BE SAFE!!! Beemer has given a lot of great resources! I started with the Naval Manual on Basic Electronics, from the library, a '60's edition. Have dog-eared many of the books that Beemer suggested. Viewing the amp in sections is also my method. But I also draw diagrams and make a punch list of the work to be done. That way, I can review the process, make notes, and remember where I left off, after a break or ordering parts. You'll find your own way of gettin' the job done! Just go slow, be methodic and SAFE. Here's a site about current flow, it pertains to Marshall's, but the principal is the same:http://www.el34world.com/charts/currentflow.htm Art

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