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Michael_B

NAD. New Tubes. Need to Rebias?

Question

I bought a Marshall '62 Bluesbreaker reissue, purportedly in mint condition.  While the amp hasn't yet arrived, yesterday I unexpectedly received new tubes from the seller.  He chose to ship it without tubes.  Am I correct in understanding that I now need to have the amp rebiased?

My local shop has a three week turnaround on rebiasing and a shop in Denver (90 min. drive with traffic) says they can turn it around in a week.  Is rebiasing something I can easily do myself with rebiasing probes?  Do most/many tube amp owners know how to rebias their own amps?

Finally, was shipping without the tubes and sending new tubes a nice gesture or a dick-move that should be treated with some suspicion?  'Cause if I have to drive 90 mins each-way, twice, and wait a week to use the amp, it feels more like a dick move than a nice gesture.

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What was the problem with the old tubes?  Were they doing anything weird or funky, or did he break one by accident?  Or were they a set of tubes that he wanted to keep for whatever reason (i.e., a brand or make not available for sale anymore)?  Granted, you're gonna need to replace tubes eventually, but this does make things inconvenient to say the least.

BTW, the Marshall Bluesbreaker is AKA a Model 1962, and the 1962 model number doesn't have anything to do with the year of manufacture or issue that I know of, it's just the number that Marshall assigned this particular amp model way back when, just like the Model 1960 4x12 cab doesn't have anything to do with the year 1960.  You're not the first person to think it did have something to do with the date, you can thank Jim Marshall for that!

Edited by crunchee
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Even if I had whatever proper biasing gear is needed, I'd don't know if I'd watch a YouTube video or two or read a quick meter manual, get my confidence boosted falsely and then be DIY playaround guy in a chassis filled with live and potentially deadly AC voltage.

Keep in mind too, a high percentage of shit that crosses my guitar repair bench is stuff where a guy watched a YT vid, became an overnight "expert" and the result is he's now paying me to not only correct the initial issue but his good-intentioned fuckery that worsened the issue exponentially.

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“good  intentioned fuckery”

That is a catch phrase!

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I had a RI BB and I don’t think mine had a bias pot, I took it in to get turned back to Beano specs with KT66s so I didn’t do it. 

Biasing is easy if there is a pot and bias measuring points. It’s all about a math equation. Without the bias points or a bias pot, it is a lot more difficult. A 3 week turn to bias an amp is ridiculous. The shop must be up to its ears in business.

Not a dick move to ship without tubes. Depending on how tight the tube sockets are...or how loose, he may have done you a favor. I would have simply wrapped them in bubble wrap and taped them in the back on the amp and packed paper in the cavity. Lots of people ship without tubes installed to ensure they don’t rattle loose and shatter inside the amp.

Are you sure those tubes haven’t already been biased for the amp? 

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Some think it's better to ship amps without tubes; definitely not a bad thing. It's not really necessary, though.

As for biasing, it's not difficult, but could be deadly if you're not careful. There are some good Youtube videos out there, but it's best to leave it to someone more experienced if you have any doubts about your ability.

Edited by Thundersteel
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Thanks, everyone, for the replies. I won't mess with biasing, based on the advice here.

1 hour ago, Jakeboy said:

Are you sure those tubes haven’t already been biased for the amp? 

I have no idea.  The tubes that he sent came directly from Tube Depot.

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2 hours ago, Jakeboy said:

Lots of people ship without tubes installed to ensure they don’t rattle loose and shatter inside the amp.

The smartest thing to do is to ship the amp in the box so the tubes are oriented "glass on top-plugs and sockets on bottom." This means almost all combo amps would be placed in the box upside down. Many manufacturers ship this way because the tubes won't rattle loose or fall out.

2 hours ago, Jakeboy said:

Are you sure those tubes haven’t already been biased for the amp?

These amps require bias resistors to be installed at the tube sockets for each tube. Even if these were tubes the seller had previously used and were properly biased at the time, unless he labeled which tube goes where, the amp will need to have a tech check to see which tube needs to go where, and still may need a rebias at that. 🙂

Edited by gtrdaddy
Bold face type is just to make sure Michael_B sees this, not yelling at you Jakeboy LOL
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Gtrdaddy brings up a good point.

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Especially if fedex or ups doesn't “reorient” your box😀

arniez

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44 minutes ago, ArnieZ said:

Especially if fedex or ups doesn't “reorient” your box😀

arniez

If the shipping label is on the box top, it’s doubtful they would transport it upside down where they can’t read the label. That only makes their job tougher. Just sayin’.

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IMO, sending you a full set of new tubes was definitely not a dick move.  Seems like a very nice gesture.  The original tubes may have been at the end of their lifespan or inferior quality. 

I'd install the new tubes and play the amp for a while.  If you think the amp sounds too harsh, cold, hot, or whatever, take it to shop and have the bias checked and adjusted to your taste.  In the meantime, you might want to watch some YouTube videos to see if you can get comfortable with doing it yourself.

 

 

 

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4 minutes ago, BadgerDave said:

you might want to watch some YouTube videos to see if you can get comfortable with doing it yourself.

Not advised unless one is very experienced and knowledgeable with working on electronics and amplifiers. As @Thundersteel pointed out earlier, it’s very dangerous and it can be deadly for someone with no proper training...even when the amp is unplugged voltage stored in the capacitors can kill you.

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Does the reissue still have the individual tube bias resistors, or did they change them to trim pots. Most of what I see regarding the reissues mentions a "vertical bias trim pot" as well as the hum balance control.

I will say that even more recent Marshalls like my JCM2000 TSL have TWO bias trim pots, which are actually adjustable from the outside of the chassis. So, hopefully it has adjustable resistors, and not fixed.

As for why the seller sent new tubes instead of sending ones in the amp? Well, they were probably nice tubes, and rather than do the usual move of putting "Safe" tubes in the amplifier, he just sent you some.

As for safety, get some thick rubber gloves as well as a plastic handled screwdriver, or even a chop stick, depending on the type of bias trim pot that is used. ANd DO NO TOUCH anything inside the amp.

I got a weber bias rite years ago, and honestly, it has probably saved me hundreds of dollars in tech servide fees. I got the one that has both Octal and Nine pin, so I can adjust just about every time of power tube. The voltage and current readings mean simple math and no having to even go inside the amp except to adjust the trim pot.

Edited by tbonesullivan
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1 hour ago, tbonesullivan said:

As for safety, get some thick rubber gloves as well as a plastic handled screwdriver, or even a chop stick, depending on the type of bias trim pot that is used. ANd DO NO TOUCH anything inside the amp.

Excuse me while I re-bias my amp 😆Ld9EPXu.png

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That's the idea!  I mean, there is always the "rough and ready" way to do it: measure the current across the standby switch.

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2 hours ago, tbonesullivan said:

That's the idea!  I mean, there is always the "rough and ready" way to do it: measure the current across the standby switch.

No doubt... I've been working with electricity most all my career & I have tremendous respect for it & trust me, I've accidentally shorted quite a few high voltage/current circuits in my career... I send all my tube amps out to professionals for service... to me, it's not worth the risk of potential shock injury/death

Edited by Dave Scepter
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https://www.youtube.com/results?search_query=how+to+drain+electricity+from+amplifiers

Not rocket science, but yes, electricity can kill you.

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Unfortunately a video on how to drain filter caps is good for people to know, but won't help much.  When biasing, the amp has to be running while you adjust the bias.  You have to be VERY careful while probing around inside a running amp.  I recommend extreme caution when the bias pot is inside the amp.  Fender really did it right compared to other manufacturers.  On the old amps the bias pot is on the outside of the chassis and you can easily use one of those bias meters on the tube sockets and adjust the bias without even opening up the chassis.

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On 3/9/2019 at 10:19 AM, texwest said:

Unfortunately a video on how to drain filter caps is good for people to know, but won't help much.  When biasing, the amp has to be running while you adjust the bias.  You have to be VERY careful while probing around inside a running amp.  I recommend extreme caution when the bias pot is inside the amp.  Fender really did it right compared to other manufacturers.  On the old amps the bias pot is on the outside of the chassis and you can easily use one of those bias meters on the tube sockets and adjust the bias without even opening up the chassis.

I ended up giving it over to the local tech.  Despite telling me that he's three weeks out, he turned it around in less than a day.

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I have a long plastic screwdriver for adjusting bias pots.  I also use a chopstick as well, for those that have the little "handle" you can turn (carvin amps).

Marshall amps, at least my TSL100, have external bias trim pots, one for the PUSH tubes and one for the PULL tubes.  If a soldering iron is required, it goes right to my amp guy.

Things like cleaning pots, cleaning jacks, etc, that's stuff I'll do myself. I'm also one of those who does basic electrical work around the house. Replacing sockets, fixtures, etc.

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On 3/9/2019 at 11:19 AM, texwest said:

Unfortunately a video on how to drain filter caps is good for people to know, but won't help much.  When biasing, the amp has to be running while you adjust the bias.  You have to be VERY careful while probing around inside a running amp.  I recommend extreme caution when the bias pot is inside the amp.  Fender really did it right compared to other manufacturers.  On the old amps the bias pot is on the outside of the chassis and you can easily use one of those bias meters on the tube sockets and adjust the bias without even opening up the chassis.

Agreed on all counts.  The easiest amp to adjust I've come across is the Carr Mercury.  It has receptacles for a stadard multimeter on the exterior and the manual provides the recommended range.  No math needed!

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2 hours ago, BadgerDave said:

The easiest amp to adjust I've come across is the Carr Mercury.  It has receptacles for a stadard multimeter on the exterior and the manual provides the recommended range.  No math needed!

You should see the new FUCHS ODS II, comes with built-in illuminated meters!

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Or.. go for cathode-biased amplifiers?

My only issue with a lot of the amps that have "built in" bias adjustment lights or indicators, is that they are often based on NGV, which is the same thing that you get from external test points, which just isn't a very accurate way of getting a bias reading.

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28 minutes ago, tbonesullivan said:

My only issue with a lot of the amps that have "built in" bias adjustment lights or indicators, is that they are often based on NGV, which is the same thing that you get from external test points, which just isn't a very accurate way of getting a bias reading.

Some do have issues. If I were a betting man, I'd say FUCHS doesn't have the issue. Andy's quite the accomplished electronics engineer.

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This is probably too late but thought I’d comment anyway...

I have worked on a lot of Marshall’s, and what I can tell you is that MArshall ships their amps biased cold. Safer for them than going hot and having customer issues.

if the amp feels excessively stiff you may want to rebias it, but if it sounds and reacts to your satisfaction then don’t worry about it.

Interesting story... I once had a guy bring me a JCM800 reissue that “wouldn’t keep up”. I checked the bias and it was waaay cold. I couldn’t back off the negative voltage enough to get the bias where it needed to be so I started checking the divider on the bias supply. Marshall had put a resistor in there that was high by about a 200% factor.  I gave him the amp back and next time he saw me he said “I don’t know what you did to my amp, but it really opened it up”.  One of his playing buddies asked me if would do the same “mod” to his amp. 🤣

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