Blackstar HT-5 Tube Swap

Discussion - HT-5 amplifiers.
oldwannabe
Posts: 7
Joined: Sun Mar 25, 2012 1:00 am

Sat Jun 16, 2012 6:37 pm

Charlotte,

Thanks very much.

If you don't mind my asking, why did you get rid of the ht5? Just curious. I hadn't heard of the Haze series so I checked them out on line. Looks nice. More than I need, not just in terms of power but built in effects as well. I have an effects board so it'd be a waste to pay for built effects.

Peter

CharlotteM
Posts: 10
Joined: Fri Mar 16, 2012 1:00 am

Sat Jun 16, 2012 7:23 pm

Hi Peter,

No Thanks,

I already had a Marshall Jvm205H and a Jvm210H with cabinets,so the blackstar was for practice use etc. only,but I am a Marshall fanatic, ( it runs trough my blood :lol: ) and the Haze came on my path,to by it new would be to much expence, that's why I bought the Blackstar first,but I could make a good deal trading in the Blackstar on the 2nd hand Haze,and I bought it.

The original Haze40 sounds a little bit dull,like there is a blanket over the speaker,but after modifying it ,it sounds realy great.

Greets Charlotte. Image

oldwannabe
Posts: 7
Joined: Sun Mar 25, 2012 1:00 am

Tue Jun 19, 2012 7:29 pm

Hi.

I need help determining the biasing values for an EH 12BH7. I've read through CharlotteM's submission which shows the values for the stock set up (I assume for the TAD 12BH7) and a datasheet for a 12BH7-A. Here's the datasheet for the EH:
Image

I don't see a line reading "Negative DC Grid Voltage". So what should the readings be at R31, R35 and R6 (see diagrams in CharlotteM's first biasing submission) based on the data above?

Also, is it advisable to run the grid at max vdc? I read on the Eurotube site that a 4 volt increase in the line voltage can cause a 30 volt increase at the tube plate (Eurotube), which could be bad for the tube if the plate current was set close to the max. Is the same true for the grid voltage?

Hope someone can help.

Peter

jk441
Posts: 13
Joined: Fri Feb 18, 2011 1:00 am

Thu Jun 28, 2012 2:24 pm

Sorry to bring this up again guys but to double check.

So if I ONLY replace the PREAMP I do not need to be doin any rebias but if I change BOTH PREAMP AND POWERAMP the amp needs rebiasing correct?
And this should be same for a HT-5 Combo version right?

oldwannabe
Posts: 7
Joined: Sun Mar 25, 2012 1:00 am

Thu Jun 28, 2012 3:26 pm

You only need to rebias the amp if you change the "power" tube (12bh7), and even then only if you change tube types or possibly if you use the same tube type but change manufacturers.

jk441
Posts: 13
Joined: Fri Feb 18, 2011 1:00 am

Fri Jun 29, 2012 12:42 pm

oldwannabe wrote:You only need to rebias the amp if you change the "power" tube (12bh7), and even then only if you change tube types or possibly if you use the same tube type but change manufacturers.
So I may put in a 12BH7 but a different brand from the stock and I COULD be ok or am I guaranteed to be ok and no need of rebias?

oldwannabe
Posts: 7
Joined: Sun Mar 25, 2012 1:00 am

Sun Jul 01, 2012 1:55 pm

jk441 wrote:
oldwannabe wrote:You only need to rebias the amp if you change the "power" tube (12bh7), and even then only if you change tube types or possibly if you use the same tube type but change manufacturers.
So I may put in a 12BH7 but a different brand from the stock and I COULD be ok or am I guaranteed to be ok and no need of rebias?
I wouldn't say you are guaranteed to be "ok". The only way to be sure is to check the bias and bias balance voltages of your amp against the data sheet for the tube you are using. The problem I'm having is determining what these specs are for the tube I'm using. The data sheet for the EH 12bh7 that I posted doesn't show the same spec list as the sheet posted by CharlotteM and I don't know how to interpret the sheet to determine the max negative grid voltage. So, as it stands, I'm running the EH at the amps factory setting. It sounds ok. I believe the worse that will happen is I could be running the grid a little hot which could shorten the tube's life. I continue to search for the answer to my question. Sorry I couldn't be of more help.

Guitarist
Posts: 34
Joined: Sat Jun 30, 2012 12:00 am

Wed Aug 29, 2012 6:30 pm

I am thinking about swap the speakers and valves in my HT-5. I play early heavy metal stuff, as well as thrash metal, some progressive stuff and hard rock. my guitars are mahogany body with sh6 distortions in it.

Which tube would you reccomend me?

LonePhantom
Posts: 114
Joined: Tue Apr 20, 2010 12:00 am
Location: Canberra, Australia
Contact:

Thu Aug 30, 2012 5:56 am

Try a Tung Sol 12AX7, and a Celestion Vintage 30. That should do it for you. ;)

Guitarist
Posts: 34
Joined: Sat Jun 30, 2012 12:00 am

Thu Aug 30, 2012 1:07 pm

Well, i already have one celestion v 30 speaker waiting to be put in some box :) and i have blackstar ht-112 extension box, but its 30 % open back... so i will put in vintage 30. is it really neccasery to put v30 in all closed box?

About tubes, i already have 3 Electro Harmonix 12AX7 tubes, also waiting to be put somewhere :) would be the improvement in sound if i replace stock tubes with these? what difference in sound it will do?

thanks for suggestions 8)

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