Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Travis8 on December 02, 2021, 05:28:31 am

Title: Help with my HT60
Post by: Travis8 on December 02, 2021, 05:28:31 am

Hi, I have a problem with my HT 60 stage.

Works fine but after a time playing It It start pops.

And one valve do this (look video)


Some recommendation??

Thanks everyone

https://drive.google.com/file/d/13GH_vrn6lRwZnU_CWc1eBc4sBsDwF7PQ/view?usp=sharing

Title: Re: Help with my HT60
Post by: Willabe on December 02, 2021, 08:27:17 am

The power tubes are biased way too hot! Their red plating.

Take them out and don't put them back in until you check that the -bias is working and getting to pin 5, control grid.

Can you post a schematic? I never heard of an HT60 amp.  :dontknow:

Title: Re: Help with my HT60
Post by: Willabe on December 02, 2021, 08:34:02 am

It's a Blackstar amp. No schematic in the on line manual.

Says 2 x EL34's @ 60w, must be fixed bias, not K bias. 

Title: Re: Help with my HT60
Post by: tmknight on December 03, 2021, 12:32:48 pm

Is it a MKII?  If so, then there should be four holes close to the output tubes.  These are the bias indicators and pots.  One set for balance, the other for bias - I cannot tell you which is which.  You'll likely note (at least) one of them to be red at idle on full power.  You want to get them both to turn off to achieve prescribed bias and balance.

If it's a MKI, then you have a bit a work ahead...though, still achievable.  You should search on the Blackstar forums (https://forum.blackstaramps.com/search.php?keywords=ht+stage+60+bias&fid%5B0%5D=2&sid=c7733d5d8cb6e33784b2ee61b093d792) or Google (https://www.google.com/search?q=blackstar+ht+stage+60+bias&newwindow=1&rlz=1C1CHBF_enUS974US974&sxsrf=AOaemvKyhNWSjVTGFBBzlk0stkDNGkGJow%3A1638556555054&ei=i2OqYc3QAomoqtsP5oi-8Ak&ved=0ahUKEwiNwqHrosj0AhUJlGoFHWaED54Q4dUDCA4&uact=5&oq=blackstar+ht+stage+60+bias&gs_lcp=Cgdnd3Mtd2l6EAMyBQgAEIAEMgQIABAeOgcIABBHELADSgQIQRgAUIgGWIgGYOUIaAJwAngAgAF6iAF6kgEDMC4xmAEAoAEByAEGwAEB&sclient=gws-wiz) for bias adjustment info/guidance.  Though, as always, this can be a dangerous undertaking.  If you aren't familiar with biasing, take it to a reputable tech.