# Tube Amp...noise



## Rick31797 (Apr 20, 2007)

Today at the jam, i noticed a crackle sound coming from my Blackstar tube amp....it was quiet, until the bass player hit a note, when he stopped the noise stop...So what do you think i should look for, i know nothing about amp repair but i could handle putting in new tubes...if that is the problem.


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## LexxM3 (Oct 12, 2009)

Sounds like a microphonic tube, but there is slight chance it could a cabinet resonance. Probably tube, and probably an output tube. The usual way to diagnose is to sound the amp while tapping output tubes with a wooden pencil or a chopstick (possibly wrapped by an elastic to dampen the tube impact dinging), while trying to not electrocute yourself by sticking fingers at lethal voltages. If such tapping produces the sound you heard or really any change in amplified sound, that tube is microphonic (microphonic means that tube electrical properties change/are too susceptible to mechanical vibration).


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## Rick31797 (Apr 20, 2007)

Great information on how to diagnose a tube problem, The output tubes are they the big ones ECC83


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## LexxM3 (Oct 12, 2009)

That's a little conflicting. Yes, output tubes are the big ones. No, ECC83 are not the output tubes (ECC83 are aka 12ax7, pre-amp tubes).


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## Rick31797 (Apr 20, 2007)

ok it must be the EL34 , that are the big tubes,I will test it today...where is a good place to get replacement tubes..


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## 1SweetRide (Oct 25, 2016)

Some Sources
* Eurotubes: Eurotubes - Vacuum Tubes by JJ Electronic - ECC83, 12AX7, 6L6. 6L6GC, EL84, EL34, KT77, KT66, KT88 - Eurotubes Inc.
* Groove Tubes: Groove Tubes® - Hear The Difference™
* Tube Store: www.thetubestore.com - Your online source for audio vacuum tubes.


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## LexxM3 (Oct 12, 2009)

Yap, EL34 are output tubes.

The Canadian default is www.thetubestore.com - Your online source for audio vacuum tubes. in Hamilton, ON. They seem to have a promo on until end of June.

Before replacing output tubes, you need to consider biasing. That's an "idle" state voltage adjustment that sets the tube "operating point". Amps vary quite a bit on whether this is needed and how to do it. For example in some modern amps, there is a single internal pot to be adjusted while measuring a reference point voltage -- single point adjustment (pot or otherwise) requires "matched" tubes, the most common situation (with dual point bias adjustment, you can probably get away with unmatched tubes, but usually not worth the saving unless you're assembling random NOS tubes that are simply not available matched). 

What exact model of amp is yours? 

You can also call and discuss this with thetubestore.com and get their recommendation.

If you don't feel comfortable with this, you might have to get your tech to change the output tubes (preamp tubes don't require matching or biasing, so can almost always be done by yourself by most people). Regardless, if you ever have to disassemble amp to the point where you see exposed socket or wiring contacts, be aware of lethal voltages, even if unplugged and not discharged.

Some references to Blackstar EL34 amps (until we know your model):

EL34 Tubes // Bias check points on Series One 100 Head? - Official Blackstar Forum

HT-40 Bias Information - Official Blackstar Forum


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## Rick31797 (Apr 20, 2007)

The Amp is a Blackstar HT- 60 Soloist.


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## 1SweetRide (Oct 25, 2016)

LexxM3 said:


> Yap, EL34 are output tubes.
> 
> The Canadian default is www.thetubestore.com - Your online source for audio vacuum tubes. in Hamilton, ON. They seem to have a promo on until end of June.
> 
> ...


Good advice.


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## LexxM3 (Oct 12, 2009)

Needs a little more research, but it looks like this thread is pretty informative for your amp:

HT Stage 60 Bias questions - Official Blackstar Forum






In summary, your amp has dual bias adjustment pots which is more or less the best situation. If it was me, I'd bias that amp myself with new matched (for convenience only) tubes, but I am an electrical engineer and, more importantly, am fully aware of the care needed to deal with a live amp with lethal voltages (you need to perform bias on a live amp with speaker but not instrument plugged in, but you are more likely to get zapped/shocked while pre-disassembling it unplugged, while power supply capacitors are still charged).


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## 1SweetRide (Oct 25, 2016)

LexxM3 said:


> Needs a little more research, but it looks like this thread is pretty informative for your amp:
> 
> HT Stage 60 Bias questions - Official Blackstar Forum
> 
> In summary, your amp has dual bias adjustment pots which is more or less the best situation. If it was me, I'd bias that amp myself with new matched (for convenience only) tubes, but I am an electrical engineer and, more importantly, am fully aware of the care needed to deal with a live amp with lethal voltages (you need to perform bias on a live amp with speaker but not instrument plugged in, but you are more likely to get zapped/shocked while pre-disassembling it unplugged, while power supply capacitors are still charged).


Here's a way of getting the voltages out of the caps...always measure before you start touching random parts just to make sure. Note that you don't need to do this if you are just pulling the tubes out. 

Billm Audio » Discharging Filter Capacitors


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## Rick31797 (Apr 20, 2007)

Mine is the HT-60 Soloist, i dont know if the Stage amp is the same.. So i take it, i need to still bias a set of matched tubes..


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## LexxM3 (Oct 12, 2009)

I was trying to find out if there are differences, that's the "a little more research required" part, but Blackstar seems to be very consistent within each product line and even across product lines, so it is extremely likely that the setup is the same as the Stage version mentioned in the linked post. So yes, need to bias.

Note that sometimes you get lucky and new tubes are same or close enough, but it's much better to know for sure by performing a bias as otherwise you'll at the very least be sacrificing either tone (if biased cold for the new tubes) or tube life (if biased overly hot).

Also, getting back to original problem, if you do have new tubes ready, you certainly can try them without re-biasing to see if the microphonics issue is resolved. Just don't do it for a year and don't expect best tone until re-bias. That doesn't even require opening the amp up, just unplug.


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## jb welder (Sep 14, 2010)

LexxM3 said:


> Some references to Blackstar EL34 amps (until we know your model):
> HT-40 Bias Information - Official Blackstar Forum


Just to emphasize one of the quirks mentioned in the link, some of the Blackstar's can not be biased unless you plug a cord into the input jack.
There is an auto stand-by circuit that shuts down the power tubes when you unplug your guitar cord from the amp. You must have a cord in the input jack to bias the amp.
Of course, as with all tube amps, you always need a speaker or load connected when operating the amp.


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## Rick31797 (Apr 20, 2007)

If you need to bias a matched set of tubes , what advantage is there buying a matched set..


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## gtrguy (Jul 6, 2006)

Matched pair just means the two tubes will bias at the same current. With an unmatched pair one might be biased properly while the other isn't.


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## LexxM3 (Oct 12, 2009)

As mentioned, for your amp, matched pair is not required, but is only a convenience.

Not required because your amp has a two point bias adjustment, one for setting bias current and one for balancing the bias current between the two output tubes. The balance pot when properly adjusted effectively matches the tubes in your circuit.

Convenient to still match because:

we don't know the range of the balance pot and unmatched tubes could be far apart to potentially be out of range (unlikely for your amp and modern tubes bought at same time of same make/model)
if you have other amps that can take these tubes, they may not have two point adjustment and matching may be required; this goes for carrying spares for yourself and others as well
if you instead decide not to keep them, easier to sell matched pair
because of matching, you know the shop had a bit more testing attention to the tubes, reducing probability of receiving a bad tube a little
Like I said, just a convenience for your amp, unlikely a necessity.


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## Dorian2 (Jun 9, 2015)

I have a BS HT-20 and what they say in the video should apply to yours as well. Not sure which resistor you have to measure across, but the BS HT20 is R221. It's also recommended to measure the plate voltage of the each tube at pin 3 and 8 to ensure they are balanced . You'll have to look up the specifics for the HT-60, but I understand that the HT20 is BIASed cold at the factory at 11.5V. I've just recently rebiased mine to read 12.5 as the company apparently plays it pretty safe. But please note I'm not a pro amp guy and I'm just relaying what I have found to be good info to you from others who claim to know WTF they are doing.

One of the many awesome Amplifier repair guys here can probably correct and/or clarify the little tidbits I've posted. And again like always, make sure the caps are drained properly. I just shut the BS off without putting it into standby and make sure not to get near the chasis when doing the plate measurements myself, but I have a bit of experience because of my EET certification from ASET.


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## fretzel (Aug 8, 2014)

If it sounded like this it could be wifi. Cellphones can also cause noise if close.


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## Rick31797 (Apr 20, 2007)

Something i just found out about Blackstar amps, is the business i bought it off of Cosmos music, is not authorized to repair these amps.It would have to go to the nearest Korg repair centre which for me is Quebec.


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## Rick31797 (Apr 20, 2007)

fretzel said:


> If it sounded like this it could be wifi. Cellphones can also cause noise if close.



It sounded something like that, but only made a sound when the bass guitar hit a note, once he stopped it was quiet...I have tried to get it to do it at home, but i wont do it, even when i play my bass through my bass amp....it stays quiet...the next jam i will take it back and see if it does it again, and try a few things suggested here..to see if i can trouble shoot the problem.


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## fretzel (Aug 8, 2014)

I would wait to see if it happens there again. If so it is environment specific.


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