Blackstar. Got no QC? :o HT-20mkII...

Erlend_G

New member
Brought my Blackstar HT-20mkII to my mothers house to crank it up.

After some wierd fuzzed out notes on the low end, it started to squeal and make funny noises.

It would go away if I used the cleanest channel (1) only, and lowered the volume.

Wondering if I blew something serious, or if its just a mircophonic tube (which I suspect)-

going to do the "tap gently with a pencil" test to see if (which) tubes gone bad...

One thing that bothers me, is that they got NO customer service..! :/ not really promising..

what could be the issue?

-Erl
 
Things that also are bothering me about this amp is:

-Power supply cable keeps falling out/is rattly; cant be good at all
and

-the speaker cable!! is fitted with a jack socket connection, and loose as hell! If that falls out, I guess Ill burn the output tranny and tubes and whatnot...

What are these guys thinking...

So sad I didnt save up more money, and get a Fender Princeton instead :/.
 
Things that also are bothering me about this amp is:

-Power supply cable keeps falling out/is rattly; cant be good at all
and

-the speaker cable!! is fitted with a jack socket connection, and loose as hell! If that falls out, I guess Ill burn the output tranny and tubes and whatnot...

What are these guys thinking...

So sad I didnt save up more money, and get a Fender Princeton instead :/.


Both of these problems are easy to fix.

Get to the back of your speaker jack and bend the long arm slightly towards the cable, this will give you a tighter connection and prevent it from falling out:

As far as power cables go, sometimes cheap Chinese cables are a little out of spec. Sounds like yours might be slightly too small . . . so just take a little electrical tape and wrap it around the part of the jack that plugs into the amp. This will snug up the fit.
 
Thanks GuitarStv! ;)


Anyone know what might be causing the other issues ? :/

It's a squealing sound whenever I turn up the volume or gain.
 
You are playing a semi-hollow body correct? if so, Im not sure those and gain play really nicely together esp at higher volumes. How close are you to the amp when this happens?
 
You are playing a semi-hollow body correct? if so, Im not sure those and gain play really nicely together esp at higher volumes. How close are you to the amp when this happens?

this issue began just recently. after I cranked up the amp :( ..
 
Some of the easy stuff first, you are using a sheilded guitar cable and not a speaker cable from the guitar to the input, right?
 
The HT20 uses EL84 tubes if I am not mistaken. I love how they say tight, resonant low end... Resonant and tight are polar opposite sounds as it relates to bass. Anyway...

I suspect a couple of things. Screen grid resistors are one and the power tubes are the other. Unfortunately, EL84 tubes are worked pretty hard even when modestly biased. Mainly because designers keep ignoring datasheets. Not knowing exactly how much voltage is being sent to the plates of the power tubes, it is just a guess, but I suspect it is about 360 volts. Which is 60 volts more than the tubes are designed for. Biasing is another thing that kills the poor tubes. As much as some datasheets want to have you believe that an EL84 can produce as much as 17 watts, realistically they are rated for 12 watts, and in class AB ( fixed bias, push-pull amplifier topology ), they are only good for about 17 watts a pair. So 20 watts is pushing things and to get that amount of rated wattage, you have to have a higher HT voltage on the plates. This eats the tubes and screen grid resistors up pretty quickly while sounding amazing, admittedly.

You can try and do the " tap test ", but it will only show you if the tube is microphonic. If the screen grid is bad, tap testing won't tell you anything. You will have to open the amp in order to measure and see if screen grid resistors are ok. Generally, if the amp passes audio, it is nothing that is major with the exception that you are running on borrowed time.

Generally, it is the tube that takes out the screen grid resistors, not the other way around. However, that doesn't mean that the screen grid resistors can drift enough to allow the tube to run into self-destruct mode. Typical SGR ( screen gride resistor ) values range from 100ohm to 1.5kohm. The SGR acts as sort of a current flow limiter if you will. It is used in beam pentodes in order to control stray cathode emissions from getting to the plate. This helps allow the tube to have a little more power without over dissipation. When the SGR is not present, or too low in value, the electrons can flow too freely and can actually cause the grids to go into meltdown, which shorts the tube internally and tends to take out the output transformer with it. The hope of the SGR is that it will survive long enough without failing open that any internal shorts in the tube will blow the fuse first, before taking out the OT. One thing that generally helps increase the tube's life is to use higher value SGRs. A higher value SGR reduces overall dissipation through the tubes, bringing them that much further away from melting. The downside to larger value SGRs is that it often makes the amp sound too compressed, you do lose some volume and it can alter the sound and feel of the amp. lower SGR values have more output, less compression, and have a more open or natural feel when playing, but as mentioned, because it allows more dissipation through the screens, your amp is that much closer to meltdown.

You can try and simply replace the output tubes, and it may be prudent to take a good known preamp tube and try it in each position to see if the problem ceases as well first. The problem with just putting a new set of power tubes in is that if the SGRs are bad, your new power tubes will soon meet a similar fate as the last pair. I would first open the amp and locate the SGRs to see signs of burning and to test them ( using a multimeter ) and see if they are in spec. I would consider replacing them with a higher wattage resistor if they appear to be a small 1-3 watt model for something that is at least 3 watts and up to as high as 5 watts. If they are a lower value such as 100ohm or 470ohm, I would look into replacing them with a 1kohm instead. A 1kohm resistor won't kill too much volume and mojo while still adding a small bit of security.

Lastly is the bias. While not knowing for sure if the amp is fixed or cathode biased ( I assume fixed simply because of the wattage spec ) the bias of the tubes may have been a contributing factor. If actually biased to 20 watts, those two little EL84's are working! A hot bias will shorten tube life considerably. Couple that with a high HT and too low of an SGR value and you can burn through tubes quite regularly. Brian May's amp tech is constantly fixing his amps. They have 9 amps on stage and most of them are backups, and there are another 20 in the green room that the tech is fixing from the last show. He has those things cooking so close to the edge of death and working them so hard that they only last through a show or two. Same for Angus Young and his amp tech. They have multitudes of amps on the show and most are backups. While the band is playing the tech is in the back fixing all the ones that went up in smoke from the past shows. So the bias, along with a couple of other factors can greatly impact the life of your amp's tubes.

Unfortunately, you will have to do some digging on this one. Short of taking it to a tech, the only other way to really figure out why and what is to get dirty.
 
Ive never had an issue with my Blackstar Sonnet, which is an acoustic amp. I don't think they are a brand known for issues.
 
Ewizard;

Thanks alot! for your awesome reply.

Im at my mothers, dont got either a multimeter, spare tubes or nothing here. But is going to open it up, to see if anything is burnt, do the "Microphonic tube test", and maybe the tubes might be loose in their sockets. For all that I know.

I think I'll want to do things myself. The nearest tech is 2 hours drive away, and fixing my amp would easily cost like 30% if what it cost me new. I did electronics and electrics at high school.

Rock on \m/ :)

-Erlend
 
Where they are made is probably of little consequence. The Jet City Amplification stuff is made offshore and uses pretty decent stuff, is put together well enough, and sounds well enough. Being made in Asia vs the USA means little. There are several amps coming from Italy that are of less than stellar build and design quality. Heck, there are even a few " boutique " names you know that are cutting corners these days, using stickers that couldn't possibly have been earned ( CE, ROHS, etc. ), and downright take your money for what they provide and actually build. The only big thing that matters is will it not kill you ( as in not shock you to death ) and are you satisfied with the product you got at the price you paid?

In the modern age of disposable everything, it has started trickling down into even pro-level " Boutique " gear, unfortunately. That's right, now even your Soldano SLO is no longer made to last 30+ years, it is made to get home and at least make noise before something fails. Diezel, Morgan, Dr. Z, and many others are on that list as well. Corners are cut in order to meet a price point and ensure a profit margin. They are no longer truly boutique, they are built as fast as they can put them out to fill the orders created through a distribution network. Chances are if it is a name you know, they are part of a distribution network, which means they have to meet certain levels of international trade laws, which means they are NOT selling amps out of their garage or the back door of the shop, which means they are NOT boutique, they are another mainstream business like any other whose sole objective is to separate you from your money.

Don't confuse that with meaning lack of integrity though. Many of them still have good integrity and provide excellent quality amplifiers, you just have to keep in mind how much of the money you spent on that amp is eaten by marketing cost, a legal team, distribution commissions, and highering bean counters to ensure they still make a buck? So no, being made Off-Shore is not a bad thing, the only difference is who you are giving your money to. Whether you want to go true boutique or just a name you know is also irrelevant, all I am pointing out is that if you are in search of true quality and the best you can actually buy, it is probably NOT with the common names you know and see in the Sweetwater hot items list, it is going to be one you have to search for on the internet through a website made by the same guy who made your amp.
 
What Is unique is how little it took for Boutique to become something that is mainstream. The '90s was the birth of " Boutique " when brands such as Matchless, Trainwreck, , Dumble, and eventually even Madamp and a few others were making amps and selling them at semi-standard prices out of their back door. I would say since the early 2000s, MANY companies have been trying to cash in on that market. What is sad is that it only took about 20 years to make the word " boutique " to become a worthless description of an amp made by conglomerated, distributed, and or costs-sensitive sellers. Now even the original Boutique brands are subject to the mainstream, consumerist, expendable ways. Matchless is a shell of what it used to be. Most of what they release now is PCB-based. Fuchs, Two Rock, Morgan, and many other expensive " boutique " monikered companies are all PCB-based now! The fever was so huge that brands such as Supro, Magnatone, and even Harmony were resurrected in order to cash in on the boutique craze. All are PCB amplifiers and bear very little from their past. Even Bad-Cat a Matchless sister company if you will, has gone to mostly PCB construction.

PCB in and of itself is not bad, and in some ways can be superior to turret, eyelet, and PTP constructions, but it is not even close to as robust, and time standing as the other methods. The biggest pitfall of PCB construction is that the core of its use is to reduce costs and labor. So any amp that has PCB construction is going to be cheaper to make, which to me lessens its value. Not only because of the construction method, but because of its projected life span. All amps will eventually require some amount of maintenance and work done to them, and PCB has proven without doubt to be problematic when even modest amounts of work are done on them.

And probably the least thought about issue with PCB amps is the solder used to make them... Since most amps made with PCB are done overseas and or done in factories, they MUST use a particular type of solder that is lead-free. Lead-free solder has shown to be problematic and is prone to cracking and oxidizing in ways which for an amplifier that moves and vibrates a lot, can be an issue. If you buy any amp made in a factory or under CE, and ROHS rules, it will have lead-free solder in it. It's not if it will become an issue, it is when it WILL become an issue for you.

I'm not saying buy only true boutique amps made by people who have weird, quirky mindsets, I'm only saying that when you buy a product, be sure that the price you pay is worth the use that product can ensure you. Obviously spending $4,000 on a new Soldano made with substandard modern production methods, is probably not as wise of a decision as spending $3000 on a Soldano amp made 10 years ago. Spending $4,000 on a brand spanking new Two Rock may be better spent on a Komet amp made by real people and not a machine. Of course, it is your money, so I have no say in that regard, but if you spend $300 on an amp made in a factory en-mass, you are also buying the problems that come with such build qualities. It isn't that they sound bad, they do sound great, but how long will it last?
 
It isn't that they sound bad, they do sound great, but how long will it last?

I've been using my PCB based Traynor YCV40 pretty often for twenty years . . . it may not last me 100 years (and it's definitely not as easy to work on as PTP wired stuff), but it's not like well made PCB stuff is just going to fall apart on you.
 
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