Blackstar HT-20 Biasing question?

Discussion - HT Venue amplifiers. Inspiration from Studio to Stage.
poweredbysoul
Posts: 3
Joined: Wed Jul 14, 2010 12:00 am

Wed Jul 14, 2010 8:16 pm

Hey everyone

I ownd a HT-5 combo and also head version and now a HT 20 watt combo. When it comes time to retube the HT-20 is it self biasing or does it need to be biased by a tech. I had my tech take the back off and look around the tubes for a bias adjustment, but none was there. Does the whole chasis need to come out to properly bias it?

Thanks

gt_jumper
Posts: 320
Joined: Sun Apr 11, 2010 12:00 am
Location: Queensland Australia

Thu Jul 15, 2010 1:54 am

Most biasing amps need the boards exposed to get to the bias pot.

The HT-20 does need biasing, just had my techy do it for me.

toneseeker
Posts: 64
Joined: Wed Jun 02, 2010 12:00 am
Location: Australia
Contact:

Thu Jul 15, 2010 2:15 am

HT20 amps need to be biased if changing power amp tubes....eg EL34,here is a reply i received from blackstar customer support on the bias of the HT20:

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

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

Thu Jul 15, 2010 2:34 am

Checking the bias voids the warranty!?!?! that is about the dumbest thing I have heard :roll:

toneseeker
Posts: 64
Joined: Wed Jun 02, 2010 12:00 am
Location: Australia
Contact:

Thu Jul 15, 2010 5:23 am

YEH SO DO WE HAVE TO TAKE IT TO THEIR PREFERRED REPAIRER???!!! 8) Image

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

Thu Jul 15, 2010 10:56 am

toneseeker wrote:YEH SO DO WE HAVE TO TAKE IT TO THEIR PREFERRED REPAIRER???!!! 8) Image
I guess i'll be voiding the warranty then. I do all of my own work on my stuff just for the plain fact that I dont have time to drive it somewhere and wait for it to be done. I dont have any Blackstar dealers closer than an hours drive. Biasing an amp takes five minutes so why not do it myself? :|

prsfreak01
Posts: 31
Joined: Mon Jun 21, 2010 12:00 am

Fri Jul 16, 2010 6:55 am

Hi Guys,

Just replace the pre-amp and power tubes on my HT20 to Tung Sol Brand Tubes.

Power : 2 x Tung Sol EL34B
Pre-Amp: 2x Tung Sol 12AX7

As for installation is just plug and play. Remove stock tubes and place new ones.

No need for biasing cause it's cathode bias (self biased) already. Bought a vacuum Tube book to know all this terms.:)

Anyway as for tone now. Tung Sol made a difference. My HT20 Studio now has more gain and the clean tone has more depth in bass and mids.

Try it out. Hope this helps to your inquiry. I'll be posting some you tube clips later with regards to the newly attached Tung Sol Tubes to my HT20 Head.

\m/

toneseeker
Posts: 64
Joined: Wed Jun 02, 2010 12:00 am
Location: Australia
Contact:

Fri Jul 16, 2010 10:59 am

prsfreak01 wrote:Hi Guys,

Just replace the pre-amp and power tubes on my HT20 to Tung Sol Brand Tubes.

Power : 2 x Tung Sol EL34B
Pre-Amp: 2x Tung Sol 12AX7

As for installation is just plug and play. Remove stock tubes and place new ones.

No need for biasing cause it's cathode bias (self biased) already. Bought a vacuum Tube book to know all this terms
.:)
Who told you that it is self biasing Image ,because whoever it was is WRONG
THE HT20 HAS TO BE BIASED IF CHANGING THE POWER TUBES... eg EL34'S

ONLY PREAMP TUBES DON'T NEED TO BE BIASED

prsfreak01
Posts: 31
Joined: Mon Jun 21, 2010 12:00 am

Fri Jul 16, 2010 1:09 pm

Hi Toneseeker,

I bought this book "All About Vacuum Tube Guitar Amplifiers" by Gerald Weber.

As quote on page.66 "On cathode-biased amp, the bias adjustment is not necessary beacuse there is a large resistor on the cathode of the tube (hence the name cathode-biased). When current comes through this resistor, a voltage develops on the cathode. As more current flows, the voltage become greater until enough voltage develops to level the flow of current and the tube reaches a state of equilibrium. You could say the tube is biasing itself, hence the nickname: self-biased"

I don't know if this guy is right or wrong. As a first time owner of a tube amp and this particular HT20 Studio Head can you advised then what i should do to biased the power tube. Have you tried doing it?. Are you working with blackstar Amplifier Company?.

Anyway i installed new tubes to my HT20 already, jam a few songs to it and still working till now.

Any blackstar employee reading this can you help us out on this inquiry.

Thanks.

darrenw5094
Posts: 8
Joined: Tue Jun 08, 2010 12:00 am

Fri Jul 16, 2010 1:35 pm

Firstly, it's good to see Blackstar actually replying to their customers. We really need them to give us more details on the schematic for bias settings etc.
But to assume that this amp is self biasing, could be a mistake. We should really wait for some more info from Blackstar before replacing power valves.

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