Blackstar HT-20 Biasing question?

Discussion - HT Venue amplifiers. Inspiration from Studio to Stage.
toneseeker
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Fri Jul 16, 2010 2:14 pm

hi,i have worked on many amps,mainly marshall jcm's dsl etc with el34 and all have had to be rebiased,also all fender with 6L6 or 6V6 have to be biased,the only ones i have had that didnt need rebiasing were el84 amps,and blackstar would have told me if the ht20 was self biasing,they told me what to set the bias at if i was to change power tubes,so as far as i reckon and this is from all amps i have owned that have had el34 tubes,THEY ALL HAD TO BE BIASED!

NOTE:THIS IS FROM BLACKSTAR,IF IT WAS SELFBIASING THEY WOULD HAVE TOLD ME:
here is a reply i received from blackstar customer support on the bias of the HT20:
question: does HT20 amps need to be biased if changing power amp tubes....eg EL34


Thanks for your enquiry regarding your HT Studio 20. The bias settings for the el34’s should be 11.5v across a R221 resistor but please be aware that performing any sort of technical maintenance on your amp will void the warranty. We also recommend that any operation such as this is carried out by a qualified engineer. I hope everything with your HT Studio 20 is going well!
Thanks for getting in touch.
Customer Service

NOW I DONT AGREE WITH THE WARRANTY PART AS IF YOU ARE A PROFESSIONAL GUITARIST ON TOUR AND YOUR POWER TUBES STUFF UP,WHO IS GOING TO REPLACE THEM IN A HURRY.MOST GUY'S WOULD CARRY A BACKUP AND NORMALLY WOULD KNOW HOW TO REPLACE AND BIAS THEMSELVES.
I DONT THINK BLACKSTAR WILL HAVE A SERVICE VAN DRIVING AROUND WITH A QUALIFIED ENGINEER!!!
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prsfreak01
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Joined: Mon Jun 21, 2010 12:00 am

Fri Jul 16, 2010 3:14 pm

Hi Toneseeker,

Thanks for the advise. Probably i'll just remove the tungsol power tube el34b then and put back the stock ones. I dont want to damage my ht20.

As for the pre amp tubes 12AX7 do you think i should retain as it is or it still have to be biased again.

Any advise will be greatly appreciated.

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VENTGtr
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Fri Jul 16, 2010 3:25 pm



Pre tubes (Eg: 12AX7s), don't require biasing. Nice to see that Blackstar replied. I never got a reply, which is kind of disheartening. Would still be interested in hearing from them why they chose not to go with EL84s, since it seems a better choice for an amp of this wattage. I'm assuming it's for continuity in production with the higher wattage versions, but am still curious.

Anyone tried/considered throwing in Yellow Jackets to run 84s?

darrenw5094
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Joined: Tue Jun 08, 2010 12:00 am

Fri Jul 16, 2010 6:04 pm

VENTGtr wrote:
Pre tubes (Eg: 12AX7s), don't require biasing. Nice to see that Blackstar replied. I never got a reply, which is kind of disheartening. Would still be interested in hearing from them why they chose not to go with EL84s, since it seems a better choice for an amp of this wattage. I'm assuming it's for continuity in production with the higher wattage versions, but am still curious.

Anyone tried/considered throwing in Yellow Jackets to run 84s?
There goes the warranty right there.... :lol:

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VENTGtr
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Sat Jul 17, 2010 12:48 am


Ooh. Yep. Bet yer right.

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darrenw5094
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Sat Jul 17, 2010 12:51 am

VENTGtr wrote: Ooh. Yep. Bet yer right.

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Although worrying about a warranty isn't very rock and roll.....is it. Image

Bet Jimi wasn't to bothered about warranty when he smashed his axe. Image

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VENTGtr
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Sat Jul 17, 2010 1:02 am

True. And never been one of my strong points anyway.

toneseeker
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Sat Jul 17, 2010 1:03 am

prsfreak01 wrote:Hi Toneseeker,

Thanks for the advise. Probably i'll just remove the tungsol power tube el34b then and put back the stock ones. I dont want to damage my ht20.

As for the pre amp tubes 12AX7 do you think i should retain as it is or it still have to be biased again.

Any advise will be greatly appreciated.
putting tubes back to original wont hurt anything,changing out preamp tubes is ok and will only change the tone,i recommend JJ EL34'S,and jj 12ax7 ecc83's tubes,they are the one's i found the most reliable and can take pushing to the limits,as the jj el34's have a higher plate voltage than most tubes,they have performed very well in marshall amp's for a long time,that is where you get the growl :D ,you can push the gain stage hard but also has a real nice clean tone when you roll off the gain.

jshaffer23
Posts: 186
Joined: Sun Jun 13, 2010 12:00 am

Sat Jul 17, 2010 3:07 am

I just got a set of Ruby EL34's for my Stage60 after hearing a TON of great things about them. I am gonna put them in next week. I will report back and let you guys know how they do :D

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VENTGtr
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Sat Jul 17, 2010 3:15 am

jshaffer23 wrote:I just got a set of Ruby EL34's for my Stage60 after hearing a TON of great things about them. I am gonna put them in next week. I will report back and let you guys know how they do :D



Kewl. Look forward to seeing what you think.

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