HT1R Tube Life

[Classicplayer]

I know some folks like to change tubes in their amps about on a yearly basis, especially if they are working musicians. Reliability is paramount with that type of player. I play mostly as a hobby and with my HT1R combo, now 2 1/2 years old, I notice after about 4 months that my sound starts to lose it's edge/brightness quicker into a playing session. Is this normal? Could it be that where this amp is designed to be pushed whether on the clean or gain channel, that tube life gets shorter? Right now I have Tung-Sols in both the pre-amp and power slots.

Classicplayer

[thephantum]

It could be a bias issue. To be clear, I don't own an HT-1...but if it's at least similar to the HT5, it's a fixed bias amp (meaning that the bias has to be adjusted or "fixed" in place). It just uses a 12AU7 as the power tube where the HT5 uses a 12BH7.

If 12AU7 is biased too hot, it will sound phenomenal for awhile, but wear out pretty quickly.

[Classicplayer]

When I replaced both tubes in my HT1R, I looked around for any sign of a bias adjustment method, but could
not see any. I thought that this was cathode bias type of amp with not adjustments necessary?

Classicplayer

[thephantum]

Like I said, I don't own one so I'm not sure. It's entirely possible that it's cathode bias....if there are no adjustment pots on the circuit board, that's most likely the case.

Here's the rub: you can adjust a cathode biased amp...it's just done with a soldering iron instead of an adjustment pot.

[Classicplayer]

Thanks for the input....all good info. I have read your other posts across theses forums. I'm guessing the average owner of the HT1 species does not get involved or too concerned with correct bias. I can say the past four months or so, my HT1R has been played frequently as a practice and not as a gigging amp. The pair that I installed four months ago have had a workout. Perhaps my best course is to order several 12AU7 tubes instead of a pair of the power and pre-amp tubes.

Classicplayer

[thephantum]

Yea. With the exception of a PI tube (which the HT-1 doesn't have), preamp tubes do not wear out nearly as quickly as power tubes. Besides, if the amp sounds good and it's saving wear and tear on your main rig, throwing a new tube at it every 4-6 months is better than replacing a pair (or quad) of EL34's every year.

I will say this though: on the HT5, they run the tube right on the edge of it's specs. It would not surprise me that they did the same thing with the HT1. The tube will most likely live a lot longer, but it would explain why it's starts to lose it's edge after a few months.

Only other thing I can think of is to try some other brands. There might be another brand that holds it's edge better. Of course the tradeoff there is that it might not sound as good. I personally think that TungSols are some of the best sounding new tubes being made today (a Winged C EL34 being the exception to that).

[Classicplayer]

All valid points you have made here! Next tube order, I will order 2 or 3 12AU7 tubes, just to test my theory.

The HT5 uses a different power tube, but it would be interesting to know what Blackstar's thought process is when it comes to designing both amps. If great tone is paramount with the designers, then they may figure that shortening tube "life" to get there is a fair trade off. The end user could tinker with bias to change that, but then the amp would (perhaps) not sound the way the user really wants it to.

Classicplayer

[JBS-1949]

Could this be the reason my HT-1R (1x8 combo) suddenly stopped producing any sound?

I mostly play with acoustic musicians & UN-amplified singers. I bought this amp so that I could occasionally play an electric with them without drowning them out. I bought the amp in January 2013. The next to last time I took it out to play several months ago it worked fine.

This week I took it out and nada! The power light is on, but there's no sound; no noise when I switch it on/off; no noise when I press the overdrive select; no change at any volume or gain level; no sound through emulated headphone output.

Known good instrument & cable (verified using another amp). I haven't tried testing with an extension speaker or the MP3/Line input.

[thephantum]

The emulated out (EO) comes from the preamp. So since the EO is not working, it's definitely not the power tube. So the problem has to be from the preamp back.

There's any number of things that could be the problem, but the first two I would look at is the preamp tube and input jack. I believe the HT-1 leverages the input jack as a standby switch, so if something is wrong with that jack, the amp could be stuck in standby.