Preamp Vacuum Tube Sound Comparison - Blackstar HT 20 Studio Amp

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hellomayday
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Tue May 29, 2012 3:05 pm

Hey guys,

Thought some of you might be interested in hearing a sound comparison when switching out preamp tubes. This is far from a scientific test, just switched out the preamps and compared the different tones.

The details: replacing the stock preamp tubes (TAD 12AX7 ECC83WA) on a 2012 Blackstar Venue Series HT Studio 20 20W Tube Guitar Combo Amp with a new pair of JJ Electronics 12AX7 / ECC83 S preamp vacuum tubes. The guitar used is a Fender Thinline Telecaster. The stock speaker in the Blackstar amp is a 12" Celestion Rocket 50.

As a new member to this forum, I cannot post an external link for 7 days. You can find the video by running a google or youtube search for "Preamp Vacuum Tube Sound Comparison - Blackstar HT 20 Studio Amp"

http://www.youtube.com/watch?v=liHI4Zir32c

Thanks.
Last edited by hellomayday on Thu Jun 07, 2012 8:50 pm, edited 1 time in total.

cayle
Posts: 33
Joined: Mon Oct 17, 2011 12:00 am

Wed May 30, 2012 12:21 am

Nice. Thanks for this. I wasn't able to do a comparison video of the stock Sovtek 12AX7 and TAD EL34s on my HT20 when I swapped it with Tung Sol 12AX7/EL34 sets. As with your video, I noticed a big difference on the clean channel but not as much on the dirty channel. Speaker swap made a big difference on the dirt channel.

hellomayday
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Wed May 30, 2012 7:12 pm

Thanks!

I'm going to do a similar sound comparison soon when I replace the stock speaker. While the gain sounds similar when playing rhythm, I can hear a bit more bite during the dirty solo bits.

If someone is able to post the link it would be much appreciated. I won't be able to post it until next Tuesday.

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Markystang
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Location: Wellesley, Ontario, Canada

Thu May 31, 2012 4:21 am

Here ya go man!
Great comparison btw.

hellomayday
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Fri Jun 01, 2012 3:05 pm

Thanks, Marky.

TheMcCown
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Joined: Thu Feb 20, 2014 8:22 am

Thu Feb 20, 2014 8:28 am

Hi! New to the forum and to tube amps in general. I've had my HT-20 for a good 3 years now and I think its time to change the tubes. My tone has not been as bright as it used to be and is just lacking overall. I know the EL34s are not the cleanest sounding tubes and have a grit about them and I'm a fan of those chiming, Fender-y sounding clean tones. I was wondering if there is a way to put another TYPE of tubes (6L6s, 12AX7s, something) into the slots where the El34s are in now. Also, what type of tubes could I put in my preamp section to give me less gain? I love the headroom that the HT-20 has but I never use it! I only ever have the gain set to maybe 11 o'clock at the highest. I just want a nice, crisp distortion that has more of a precise way to dial in nice, tones. Any feedback would be great. Thanks!

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Sonofarich
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Thu Feb 20, 2014 5:49 pm

No...only will take EL34s safely in the power section. Look at different manufacturers for characteristics you desire. For preamp tubes, try a 12AY7 or 5751 in place of the 12AX7 in the Gain channel. In the clean channel try different manufacturers for desired chime.

FWIW...I have an Electro Harmonix 12AY7 in the gain channel and Mullard 12AX7 in the clean channel and a matched pair of Winged Cs (EL34s) in the power section of my HT-20. Sounds brilliant. Also swapped out the Rocket 50 for a WGS Vet 30.

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thephantum
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Location: Virginia, United States

Fri Feb 21, 2014 3:25 am

Sonofarich wrote:No...only will take EL34s safely in the power section.
Not quite true. You can use a 6CA7's or a KT77's in place of EL34's in the power amp. Both are direct replacements.
  • There is no real difference between the EL34 and the 6CA7. The U.S. uses 6CA7 as the type code, and Europe uses EL34 (similar to ECC83/12AX7). Functionally, they are identical and swappable. Of course, like all tubes, different brands have different tonal characteristics. I know EH makes a few 6CA7's and there's a bunch of Chinese ones as well.
  • While the KT77 is direct replacement for the EL34, the internal design is different: The EL34/6CA7 is a true pentode, while the KT77 is a kinkless tetrode. They have a harder vacuum which results in a little more dynamic (more low end) but with less compression. The impedance is also a little higher (closer to a 6L6), so you will absolutely have to re-bias the amp when switching from EL34 to KT77 or vice versa.
In my experience, KT77's don't last nearly as long as an EL34/6CA7 tube. To my ears, they sound great when the amp is close to dimed out, but as soon as you roll the volume/gain back to get warm crunchy tones, they have more fizz than bite. Most likely due to the lower compression.

To reduce gain on the preamp side, you have a lot of options. Using the 12AX7 as a benchmark:
  • - A 5751 will have roughly 30% less gain
    - A 12AT7 will have roughly 40% less gain
    - A 12AY7 will have roughly 60% less gain
Hope that helps,
Steve

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Sonofarich
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Fri Feb 21, 2014 11:18 pm

thephantum wrote:
Sonofarich wrote:No...only will take EL34s safely in the power section.
Not quite true. You can use a 6CA7's or a KT77's in place of EL34's in the power amp. Both are direct replacements.
  • There is no real difference between the EL34 and the 6CA7. The U.S. uses 6CA7 as the type code, and Europe uses EL34 (similar to ECC83/12AX7). Functionally, they are identical and swappable. Of course, like all tubes, different brands have different tonal characteristics. I know EH makes a few 6CA7's and there's a bunch of Chinese ones as well.
  • While the KT77 is direct replacement for the EL34, the internal design is different: The EL34/6CA7 is a true pentode, while the KT77 is a kinkless tetrode. They have a harder vacuum which results in a little more dynamic (more low end) but with less compression. The impedance is also a little higher (closer to a 6L6), so you will absolutely have to re-bias the amp when switching from EL34 to KT77 or vice versa.
In my experience, KT77's don't last nearly as long as an EL34/6CA7 tube. To my ears, they sound great when the amp is close to dimed out, but as soon as you roll the volume/gain back to get warm crunchy tones, they have more fizz than bite. Most likely due to the lower compression.

To reduce gain on the preamp side, you have a lot of options. Using the 12AX7 as a benchmark:
  • - A 5751 will have roughly 30% less gain
    - A 12AT7 will have roughly 40% less gain
    - A 12AY7 will have roughly 60% less gain
Hope that helps,
Steve
Right...I probably should have qualified my response better. I was referring to anything but an EL34 variant, in contrast to the ones the OP mentioned (6L6s, 12AX7s) that are not direct power tube replacements. Would definitely require a re-bias, not sure if it would effect BS's incredibly restrictive warranty policies, if concerned.

Good info Steve.

TheMcCown
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Joined: Thu Feb 20, 2014 8:22 am

Sat Feb 22, 2014 5:32 am

Thanks guys! Y'all have been very informative! I really appreciate it! I think I might go with the 12AY7s in the drive section. Will that give me more tone as result? I don't know if my thought process is correct or not, but to me, it seems as though if you took away more gain, the tonal characteristics of the amp would be more pronounced, right? I never do any sort of wailing solos or any screaming, extreme chunk rhythm stuff, most just slightly broken up chords. (I'm more of a backup lead/rhythm guitarist and looking to get into more ambient stuff and play for my worship band as a reference) so I don't have much use for anything high-gain but would still want a nice tone.

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