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Posted: Sun Oct 17, 2010 2:55 am
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mydeadblues wrote:
Hey man thanks! Ya I was definitely curious and I do want to learn more about the electrical circuitry so I dove right in ha. I'm hoping I'll find an amp tech soon and I'll ask him if I can overlook as he diagnosis the problem. Hopefully I can get a basic understanding and develop my knowledge of the circuitry. I am also going to e-mail fender and ask for an updated schematic or for the reissue schematic because it differs from my amp.


Here is the service manual. It says "Blues Deluxe Reissue", but the schematic inside is for both the Blues Deluxe and Blues Deville Reissues. It is current and correct for the Reissue series.

http://www.blueguitar.org/new/schem/fen ... eissue.pdf

I agree with Johnny Z that you need to know the plate voltage in order to properly set the bias, but I disagree that you should leave the bias setting alone when changing tubes. Different tubes have different bias requirements for best performance. To do it properly, you should use a bias probe. Many different types are available in different price ranges. This is the one I use and makes bias adjustment quick, simple, and safe:

http://www.amp-head.com/product_info.ph ... ucts_id=70

You might also want to look at these:

http://www.musicradar.com/forum/showthread.php?t=53041

http://www.eurotubes.com/euro-Fender-HRDV.htm

http://www.justinholton.com/hotrod/bias.html

http://www.youtube.com/user/TubeDepotTV ... 9IUadZJf-c

http://www.webervst.com/tubes1/calcbias.htm

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Post subject: BDvl problem
Posted: Sun Oct 17, 2010 6:48 am
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Thanks bluesky636,

It looks like there is only one test point on the BDvl. So much for my theory about two test points. :roll: Lot's of great info, good job. :)

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Posted: Sun Oct 17, 2010 2:33 pm
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Wow thanks a lot guys for everything! So now that I know it only has 1 test point I'm guessing the bias should be split up between the two output tubes so I would be looking to bias it between 30-45 instead of 60-90 right? So I ran it too hot at 52 which probably caused the resistor to start sparking.


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Post subject: BDvl problem
Posted: Sun Oct 17, 2010 3:33 pm
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If there is only one test point (TP26), that is where you want to see a reading of somewhere around 60 mV. It looks like I was wrong about the whole two test point thing, so it doesn't apply here.

And from your previous post, the C- voltage is a different TP than the bias TP. The C- voltage is a negative voltage applied to the output tubes grids, and will be in -V DC, this is the voltage coming from the bias adjust pot, I don't see a listed TP for that one. The TP that I think you wanted to begin with, is a voltage drop across a 1-ohm resistor, and will be in mV DC. Look at the schematic/manual link that bluesky636 provided to find each test point. Looks like TP 26 is the bias test point, and the TP for the C- isn't shown, but you can locate it easily. :)

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Posted: Sun Oct 17, 2010 6:59 pm
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"I agree with Johnny Z that you need to know the plate voltage in order to properly set the bias, but I disagree that you should leave the bias setting alone when changing tubes. Different tubes have different bias requirements for best performance. "

The reason I tell people not to mess with the bias is because of exactly the reason for the OP, people screw things up that were already correct. I'm not saying there isn't a better adjustment for different tubes, there may well be some special point of dissipation that is better than the factory average for a given set of tubes. At least the factory setting is usually a safe bet to use for any tubes since there is a industry standard for tubes and a range for correct bias. I'm not a Amp Tech but it's been a Hobby repairing tube equipment for over 35 years, including guitar amps and old radios. From my experience most people don't do a good job biasing their amp, I've seen a bunch of amps come in over the last 15 years or so because of this problem. Usually they fry the tubes or take out a power resistor and wonder why. "but Aspen Pittman, or some one else ______ said in their book I should do it." If all you are doing is replacing tubes and feel the need to rebias your amp, the first thing you should do is be sure your tubes are good, find a good Tube Tester and learn how to use it.

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Posted: Sun Oct 17, 2010 10:45 pm
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Johnny Z wrote:
"I agree with Johnny Z that you need to know the plate voltage in order to properly set the bias, but I disagree that you should leave the bias setting alone when changing tubes. Different tubes have different bias requirements for best performance. "

The reason I tell people not to mess with the bias is because of exactly the reason for the OP, people screw things up that were already correct. I'm not saying there isn't a better adjustment for different tubes, there may well be some special point of dissipation that is better than the factory average for a given set of tubes. At least the factory setting is usually a safe bet to use for any tubes since there is a industry standard for tubes and a range for correct bias. I'm not a Amp Tech but it's been a Hobby repairing tube equipment for over 35 years, including guitar amps and old radios. From my experience most people don't do a good job biasing their amp, I've seen a bunch of amps come in over the last 15 years or so because of this problem. Usually they fry the tubes or take out a power resistor and wonder why. "but Aspen Pittman, or some one else ______ said in their book I should do it." If all you are doing is replacing tubes and feel the need to rebias your amp, the first thing you should do is be sure your tubes are good, find a good Tube Tester and learn how to use it.


I hold a BSEE. Tubes were part of the curriculim when I went to college. With the proper equipment and knowledge, biasing an amp is not rocket science. Hence my recommendations in my earlier post in this thread.

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Posted: Mon Oct 18, 2010 2:39 am
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bluesky636 wrote:
Johnny Z wrote:
"I agree with Johnny Z that you need to know the plate voltage in order to properly set the bias, but I disagree that you should leave the bias setting alone when changing tubes. Different tubes have different bias requirements for best performance. "

The reason I tell people not to mess with the bias is because of exactly the reason for the OP, people screw things up that were already correct. I'm not saying there isn't a better adjustment for different tubes, there may well be some special point of dissipation that is better than the factory average for a given set of tubes. At least the factory setting is usually a safe bet to use for any tubes since there is a industry standard for tubes and a range for correct bias. I'm not a Amp Tech but it's been a Hobby repairing tube equipment for over 35 years, including guitar amps and old radios. From my experience most people don't do a good job biasing their amp, I've seen a bunch of amps come in over the last 15 years or so because of this problem. Usually they fry the tubes or take out a power resistor and wonder why. "but Aspen Pittman, or some one else ______ said in their book I should do it." If all you are doing is replacing tubes and feel the need to rebias your amp, the first thing you should do is be sure your tubes are good, find a good Tube Tester and learn how to use it.


I hold a BSEE. Tubes were part of the curriculim when I went to college. With the proper equipment and knowledge, biasing an amp is not rocket science. Hence my recommendations in my earlier post in this thread.


It seems to me that an small "amp guidebook" would be handy.

Topics covered
Tweaking Your Amp

Tubes (Most popular types and features - how to pick tubes for your amplifier with predictable results)
Adjusting Bias (What you need to know about the tube and the amp, the equipment and how to adj.)

Speakers & Cabs (Sizes, magnets, Watts and Ohms, Wiring, cabinets: Open and closed and construction materials)

Then an index of links to vendors that service this market.

As you can imagine, that's not a big list, but that is because I am
targeting a specific type of tube amp user who is likely to be brave
enough to make these two common modification and maintenance
tasks. Advanced modifications involve circuit modifications/maintenance
that are typically recommended to be performed by professionals.

Some statistics gathering
Somewhere I would like a see a popularity poll of opinions regarding choice of tubes, speakers and speaker configurations [and for what application (genre, clean, dirty) ]. Each respondant would identify the amp brand and model, stock or modified by responding to the poll in the text application.

Examples:
65% of those polled preferred tube amps for nearly all genre of music for Live, Studio, Home applications

50% of those polled preferred amplifiers 40 watts or less

90% of those polled preferred original NOS vintage vacuum tubes over late era tube if given a choice and could afford to aquire such tubes

50% of those polled preferred Brand X speakers over Brand Y speakers

25% of those polled preferred to do their own amplifier maintance and
modifications.

Etc. with some additional polls within a given catagory of questions

Then there would be a percentage of owners who preferred x genre
This would help establish a breakdown list of the general consensus of what is popular and what works best for a given genre and playing style.
Amps noted should be recognized by brand, model output (watts and ohm)
The combined amp tube compliment tonal characteristics should help as well.
The ultimate being a referance chart for the convenience of amplifier users.

Well, anyway... I am falling asleep at the keyboard and I may have missed other considerations.


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Posted: Mon Oct 18, 2010 2:40 am
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Knee Grow


Last edited by Twinhit on Fri Oct 22, 2010 12:40 am, edited 1 time in total.

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Posted: Mon Oct 18, 2010 6:52 am
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[/quote]

I hold a BSEE. Tubes were part of the curriculim when I went to college. With the proper equipment and knowledge, biasing an amp is not rocket science. Hence my recommendations in my earlier post in this thread.[/quote]

The problem is, it's not rocket science so they tend to think they can mess with it.

Then would you agree most people don't know S..T about amps except what some body tells them and often it's miss information or a sales pitch. That's why I say leave it alone.

This poor Guy took some bad advice and screwed up his amp. I'm sure you or I could have biased it correctly if it even need adjusting, and I'm pretty sure you or I could fix his amp to work again for a very modest price.

I stand by my opinion, you should first know the condition of the tubes you plan to use. I've found many so called "New Tubes, and even some NOS" that were weak or had shorts or other internal problems, that WILL affect performance. Sure, most Tube Testers don't test for everything, but they do give you some idea of the over all condition of the tube. And I sure don't want to put a power tube in an amp with a GRID SHORT! And why would I want to try to bias an amp with weak tubes? So please tell me why I would want to put tubes in my amp before I test them and assume the bias is the problem? To me the bias is the last thing to check not the first when replacing tubes. But then, I'm just Retired Profesional Musician and a Electrical Hobbyist, not an electrical engineer or Amp Tech trying to make a buck.

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Posted: Mon Oct 18, 2010 7:33 am
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Johnny Z wrote:
I stand by my opinion, you should first know the condition of the tubes you plan to use. I've found many so called "New Tubes, and even some NOS" that were weak or had shorts or other internal problems, that WILL affect performance. Sure, most Tube Testers don't test for everything, but they do give you some idea of the over all condition of the tube. And I sure don't want to put a power tube in an amp with a GRID SHORT! And why would I want to try to bias an amp with weak tubes? So please tell me why I would want to put tubes in my amp before I test them and assume the bias is the problem? To me the bias is the last thing to check not the first when replacing tubes. But then, I'm just Retired Profesional Musician and a Electrical Hobbyist, not an electrical engineer or Amp Tech trying to make a buck.


+1

I've had to toss many a new tube because they failed one or more parameters when checked on my TV-7A/U -- even some vintage NOS bottles.

Arjay

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Post subject: BDvl problem
Posted: Mon Oct 18, 2010 8:58 am
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It would be great to have a really good tube tester, one that gives actual plate current, plate voltage, tests under working conditions, more than a pass or fail test. For the cost of a proper tube tester, you could buy several amps. If you are just learning about tube amps, and having trouble figuring out how to set the bias (fairly simple with the right schematics), a tube tester like that would be impossible to use. Buy tubes from a company that tests and guarantees them, and the worst that you'll get are mismatched plate currents, or the occasional microphonic or rattling tube. Groove Tubes, Mesa Boogie and many others test the tubes to such a degree that it is highly unlikely that you will ever get one that's shorted, or damaged such that it will hurt the amp. For beginners, reputable tube supplier + VOM + amp = tube tester. Like others have said, I wouldn't be discouraged over a few sparks, that is a lesson learned hopefully. :)

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Posted: Mon Oct 18, 2010 3:26 pm
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Actually Tube Testers arn't that expensive. You can find a good one for $200 or less at HAM swap meets, and sometimes some really good NOS tubes for cheap. Maybe I shouldn't let the Cat out of the bag but even in some TV Repair Shops they still let you use them, if they have them and sometimes they will even sell you one. My friend bought a Jackson for $150 in great shape from a local TV Shop. I have 3 Tube Testers from my Dad's TV Repair Shop, my favorite is a Sencore 109 but the best one is a B&K 707 and the other is a Enco like you would find in Grocery Store in the '60's it's just good for quick testing, shorts and emission. I'll pull out my RCA Radiotronics book and post some testing info.

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Posted: Tue Oct 19, 2010 12:19 am
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Johnny Z wrote:
The problem is, it's not rocket science so they tend to think they can mess with it.

Then would you agree most people don't know S..T about amps except what some body tells them and often it's miss information or a sales pitch. That's why I say leave it alone.

This poor Guy took some bad advice and screwed up his amp. I'm sure you or I could have biased it correctly if it even need adjusting, and I'm pretty sure you or I could fix his amp to work again for a very modest price.

I stand by my opinion, you should first know the condition of the tubes you plan to use. I've found many so called "New Tubes, and even some NOS" that were weak or had shorts or other internal problems, that WILL affect performance. Sure, most Tube Testers don't test for everything, but they do give you some idea of the over all condition of the tube. And I sure don't want to put a power tube in an amp with a GRID SHORT! And why would I want to try to bias an amp with weak tubes? So please tell me why I would want to put tubes in my amp before I test them and assume the bias is the problem? To me the bias is the last thing to check not the first when replacing tubes. But then, I'm just Retired Profesional Musician and a Electrical Hobbyist, not an electrical engineer or Amp Tech trying to make a buck.


I'm sorry, but I fail to understand why you are opposed to someone setting the bias on their amp when changing tubes. The OP trying to measure the bias on his amp did not cause the problem he had. In my opinion, the amp was problematic to begin with if it could not even reach a measurement of 60 mV at the Fender bias test point (Yes, you measure millivolts across a 1 ohm resistor with the Fender test pont. Not the most accurate method, but accurate enough and safe.). How many average musicians own a tube tester? Not many I would be willing to bet. I wish I did, but I don't and I don't really feel I need one. I will continue to check (and adjust if I feel it is necessary) the bias of an amp anytime I change tubes. Contrary to what you seem to believe, bias is not a one size fits all thing. I will also continue to advise people to do the same when they change tubes as well as provide them with information on the proper tools and methods to use.

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Post subject: Re: BDvl problem
Posted: Tue Oct 19, 2010 12:20 am
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shimmilou wrote:
It would be great to have a really good tube tester, one that gives actual plate current, plate voltage, tests under working conditions, more than a pass or fail test. For the cost of a proper tube tester, you could buy several amps. If you are just learning about tube amps, and having trouble figuring out how to set the bias (fairly simple with the right schematics), a tube tester like that would be impossible to use. Buy tubes from a company that tests and guarantees them, and the worst that you'll get are mismatched plate currents, or the occasional microphonic or rattling tube. Groove Tubes, Mesa Boogie and many others test the tubes to such a degree that it is highly unlikely that you will ever get one that's shorted, or damaged such that it will hurt the amp. For beginners, reputable tube supplier + VOM + amp = tube tester. Like others have said, I wouldn't be discouraged over a few sparks, that is a lesson learned hopefully. :)


Concur 100%.

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Posted: Thu Oct 21, 2010 5:13 pm
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So I just brought my amp to a tech and oddly enough the resistor isn't sparking anymore. He powered it up and everything seems to be fine. He's going to replace a couple cap filters to eliminate some of the idle hum so I'm hoping it was a freak accident and everything will work out. thank you everyone for all your posts!


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