Sunday, July 12, 2009

Blackstar HT-5H amp head review and preamp tube comparisons

Blackstar HT-5H amp head review and preamp tube comparisons

I've benefited from reading amp reviews online, and wanted to do my part for the community and post a review and some observations on the Blackstar HT-5H amp head. The amp comes stock with a ECC83/12ax7 preamp tube and 12bh7 power tube. Farther below I've made observations on this amp after swapping out different preamp tubes.

The Blackstar is a 5 Watt amp, but has a master volume that lets you convincingly pull back volume for practicing at home. Full volume on the overdrive channels is probably more than you need for home use, but is probably loud enough for practicing with drums at moderate volume levels. For gigging you'll need to mic or use the amp simulator line out to get extra volume from the PA. Noise levels on this amp seem very low to me. Not much buzzing at all.

The amp has 2 channels (clean/overdrive and a footswitch), an effects loop, a headphone/line out amp simulator, power switch, standby switch, 3-band EQ, and some type of knob called ISF that lets you blend between “American” and “British” type tube tones. To my ears the American side of sound is “cleaner/tighter” while the British tone is “warmer - mid-rangier.” Leaving the ISF knob in the middle is a pleasant blend, and that tends to be where I leave it unless I'm wanting to create a sparkly clean sound.

Minimalist setup used for sound testing:
Guitar: Yamaha Pacifica (humbucker/single/single) – tested primarily with position 2 for clean and used the bridge humbucker for the rock sounds. These are standard stock pickups; nothing high gain.
Amp: guitar plugged directly into the Blackstar HT-5H amp's input
Speaker cabinet: 2x12 8ohm cab with Eminence Legend speakers

CLEAN: While the amp is marketed primarily as a rock-n-roll amp, I've got to say the clean channel will give you some nice chimey tones. I've been unable to get a silky Fender-y tone similar to what Stevie Ray Vaughan gets in tunes like “Lenny” or “Little Wing”, but I've yet to find that tone in any amp I've tried and think it might be more the mojo in SRV's fingers than anything else. For everything else this amp's clean will probably work – although it might become a bit harsh and spiky clean at the highest volume levels. (I found that adjusting to lower gain preamp tubes than the 12ax7 can help tame this amp a bit in that regard.)

OVERDRIVE: The overdrive channel has both a gain and volume setting. You will have a full range of overdrive and distortion sounds from this amp. With a 12ax7 tube it quickly goes far past tones that I typically use in my playing. I find that minimal gain 8-9 o'clock setting on the gain on single coils is good for classic overdrive (similar to “China Grove” by the Doobie Brothers). An ACDC “Back in Black” like tone starts kicking in when you switch to the humbucker pickup and put the gain at about 9-o'clock. Pushing the volume up at a given gain setting just makes everything sound more solid and strong. The character of the tone is consistent. For most classic rock and 80s hard rock riffs I found gain above about 12 o'clock wasn't really needed very often. If you like to hear the amp cookin' with massive sustain for solo playing push the gain on up to closer to 3-o'clock or beyond. This amp has so much gain above what I normally use that I experimented with other pre-amp tubes to calm it down a bit to expand the usable range of sound. (SEE BELOW)

1) It's very difficult to read the knobs that are on the amp. They're silver with a little indentation indicating the setting. Maybe I'm getting old and blind, but even at normal lighting levels I needed a flashlight to figure out my settings on more than one occasion. Chicken-head type knobs are much easier to read. See the manufacturer's photos - even there you can barely see amp settings in pics.
2) Some of the jacks don't hold the plugs very well. In particular, the plugs for the speaker cabinets are not very tight. It's not good that the speaker cable can pull out very easily. I don't know if they have protective circuitry should this occur to protect the power-amp, but as any of us with tube amps know – we don't want to find out the hard way on that one.

OVERALL: This is pretty awesome little amp head for the low $ cost ($299 street) – especially for those of us who do most of our playing at lower volumes at home but still crave good tone. The feature set is pretty incredible at this price point. The rock and hard rock tones are really the highlight of what this amp delivers, but the clean really is pretty usable also. If you like to tweak sound on the fly you'll probably want to seek out some replacement knobs that let you see your settings more easily.

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Blackstar HT-5H - preamp tube comparisons

Because of the high gain characteristics of the amp – more than I could generally use on the overdrive channel and maybe a slightly harsh clean channel when turned up loud – I experimented with different preamp tubes to try to tame some of the amp's more aggressive characteristics to give me a wider range of "in-between" sounds.

WARNING: The manual says no user serviceable parts are inside the amp and that only qualified technicians should open up the box. I probably shouldn't have opened my amp up, except the preamp tube was non-functional when I got it – so I had to change the tubes to make it functional.

Preamp tubes tested include:
Tung-Sol 12AX7
Electro-Harmonix 12AX7
Jan-Philips 5751
Jan-Philips 12AT7WC
Electro-Harmonix 12AY7

In guitar amps, the 5751, 12AT7 and 12AY7 are lower gain substitutes for the 12ax7, with the 5751 being about 70% of the 12AX7, the 12AT7 being about 60% of the gain of the 12AX7, and the 12AY7 being about 45 % of the gain of the 12AX7.

Minimalist setup used for sound testing:
1) Guitar: Yamaha Pacifica (humbucker/single/single) – tested primarily with position 2 for clean and used the bridge humbucker for the rock sounds. These are standard stock pickups; nothing high gain.
2) instrument plugged directly into the Blackstar HT5H amp
3) amp played through 2x12 8ohm cab with Eminence Legend speakers.

Comments on the tubes:
Tung-Sol 12AX7 - this was probably the “hairiest” of the tubes tested. On the overdrive channel it's going to deliver the rawest drive and power. Lots of harmonics. If your thing is ugly nasty rock-n-roll like this amp is designed for I'd say this is a good preamp tube to go with. For clean sounds I found this tube maybe a tad harsh in the Blackstar at high volume settings.

Electro-Harmonix 12AX7 - this to me sounded like a cleaner version of the Tung-Sol. Really nice rich chimy clean sounds. Still plenty of gain on the overdrive channels. For an amp that was a bit over the top for me – this tube seems to complement it nicely in overdrive and distortion tones. Plenty of power and sustain and harmonics for carrying single line soloing situations.

Electro-Harmonix 12AY7 – should be 45% gain of the 12ax7. I found myself grooving quite a bit to the clean tones with this tube. Even clean rock strums were very nice and easy without getting harsh – something that I fight with the higher gain tubes. As I listen back to my recordings and comments as I was working with demo tubes I also hear myself wondering if the tube sounded cleaner because of less gain on the tube – or whether actual volume was actually lower on the same amp settings. In any event – very nice cleans. Very nice mellow slightly overdriven cleans on the overdrive channel also. If you need that – this is a very nice tube to deliver. This tube still will deliver very nice overdrive and distortion sounds on the HT5H, you'll just need to use a higher level gain setting than you would on the higher gain tubes. Not quite as strong of sustain for solos, but still a lot of distortion to be had -sounds very good. I like this tube to help clean and tighten this amp if that's what you're going for – gives a lot of flavors if you don't need ultra-hairy ugly distortion.

Jan-Philips 12AT7WC - should be about 60% of the gain of the 12ax7. Very nice cleans. Similar to the 12AY7 in that regard. Clean electric guitar guitar strums still translate nicely without being harsh. Slightly overdriven rock guitar sounds translate very well also – tad harsher than the 12AY7 in that regard but still very good. (Think “Sweet Home Alabama” type tone here). When you move into the heavier rock-n-roll tones this tube provides a bit more bite than than the AY7. I really liked this tube for this amp also.

BOTTOM LINE ON THE 12AY7 and 12AT7: These tubes seem to open up the sonic range of possibilities on this amplifier in the realm of clean, slightly overdrive, overdrive, and distortion. With the 12AX7 the amp seems to me to want to be a full blown rock amp even at conservative settings – and will deliver to my ears intense amounts of gain at the highest settings on the amp. If you're into more classic tone the 12AY7 or 12AT7 just open up a bit more finesse in the flavorings while just giving up the extremely heaviest of the distortion sounds.

Jan-Philips 5751 – a mellower kindof clean from this tube than the others. Not as crisp and chimy or trebly in the cleans. I can tell that initially I wasn't liking this tube as much as the 12AT7 or 12AY7 in the clean finger-picking and clean strums. This tube really becomes strong in the mellow overdrive range of the spectrum – very beefy (Think the strum part in Doobie Brothers “Without Love” song here). It also brings a very solid presence and character to the rock tones and distortions - maybe doing it all with a bit more mellowness in all situations. Southern or Bluesy Rock tone is what this tube is saying to me as I listen back to some of the stuff I was playing while playing. But if you want to crank the amp there's still plenty of hard rock top end gain if needed – just a bit mellower – not quite as edgy as the 12AX7.

Anyhow, I hope these reviews are helpful to those of you considering changing some of the basic amp characteristics. I find these types of writeups helpful on the web and couldn't find a good preamp tube writeup for the HT-5H.

In the final analysis maybe a bit much is made of the power to shape tone with preamp tubes. Yeah it changes things some, but I think it's likely that some tubes are so close together in sound that changes in EQ or gain staging can produce similar results. It's not something I would obsess about, however if you want your HT-5H to be cleaner/tamer - some lower gain preamp tubes help produce that.


  1. The Blackstar HT5 head is excellent. The tube sound you get is unbelievable for such a low wattage!

  2. This comment has been removed by the author.

  3. Great post, and thanks for the preamp tube comparisons.

    I'm mainly trying to get the cleans to sound a bit richer on my HT-5 - what preamp tube would you recommend? I am ok with lesser gain, but wouldnt want a 12AU7 (that's too less gain)

    Also, Mind if I put your post up at my forum


  4. Do you have any sample?

    I am thinking to swap to a 12au7: can you achieve better blues sounds?


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