Swapped KT88's to EL34's in my 20th Shiva. Findings/Results.

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RockStarNick

RockStarNick

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Hey guys. So last night, I finally bit the bullet and performed some minor amp-surgery, and swapped the KT88s with EL34s in my Bogner Shiva 20th Anniversary.

Here's my findings, in bullet point style:

TECHNICAL FINDINGS:

• A resistor change IS necessary to go from KT88's to EL34s. In my particular amp, R61 had two piggybacked resistors. There was a 33K resistor closest to the board (Blue 5 band resistor: Orange, Orange, Black, Red, Brown). Piggybacked on top was another 5 band resistor.

• With both resistors in place, it was *IMPOSSIBLE* to get the bias above 4 or 5 with EL34s.

• With the piggybacked resistor snipped, I was able to get the EL34s into the proper bias range, per Charley @ Bogner (28-29mA at idle).

• The bias pot is in correct range for EL34s at about noon or 1 o'clock (with the resistor snipped).

• Per Charley at Bogner, when you start cranking the amp, you can visibly see the bias drift upwards about 4-5 points. Even MORE so if you slam a big chord. I can confirm this.

• Plate voltage seemed to stay just about the same, with KT88s or EL34s, give or take 10 points.


THE MODIFICATION PROCESS:

• Performing this resistor snip was relatively easy, provided you do it slowly, and safely. I made sure to drain the filter caps, use very small and delicate rubber-handled wire-clippers, and kept one hand behind my back at all times. (I also covered the big can capacitor directly adjacent to the resistors, with a rubber jar-opener, to ensure that the metal from the pliers did not come in contact AT ALL with the cap.)

• This whole operation was very easy to do, BUT, is pretty much "USER IRREVERSIBLE" unless you know how to properly (and safely) solder on an amp PCB. (i.e. draining the filter caps so you don't get shocked to death).


MY PERSONAL OPINIONS:

• So many people said that the new 20th Anniversary shiva was a "total circuit overhaul" and "a totally different amp". I don't believe that. Especially now after I made the swap. I believe that the circuit had things ADDED, like the gain modes, the new clean channel EQ boost circuit, and the mid cut button. But I don't think the amp was totally redesigned from the ground up.

• I truly believe that all Shiva models, whether it be 20th Ann, or regular, were designed with standard tubes in mind. EL34s or 6L6s. The reason I say this: My Shiva had piggybacked resistors in the "R61" spot (the resistor which controls the range of the bias pot). If the amp was designed around KT88s, why not either a.) put ONE resistor in there, or b.) have two spots on the board?

• I think the KT88s DO completely change the overall EQ of the amp, and it's overall personality. Depending on your playing style, this can be good or bad.

• The KT88s sound harder, tighter, and much more present. They have a much more aggressive upper-mid cut than the EL34s. Much more cutting and modern sounding. The abundance of upper mids and presence definitely changes the percieved EQ curve of the amp.

• EL34's immediately changed the personality of the amp. It sounds more vintage, softer treble, less modern, less in your face. The softer trebles of the EL34s change the apparent EQ curve of the amp and make it more even across the board. The amp might seem like it has more low-mids now. It doesn't really - it just has MUCH less treble/upper-mids.

• Clean sounds are VERY different as well. The KT88s are bigger, bolder, and have a shimmering glassy top end. The EL34s are chimey, with that distinctive "hazy" top end - No sparkly fender cleans here. If you need presence and sparkle for cleans for modern chorus-delay arpeggios or tons of headroom, stick with the KT88s. If you like to have some breakup and warm grit in your clean, then EL34s will work.

• Neither tube sounds BAD in the amp, in any way! Both sound amazing. But it is nice to know that you can tweak the amp to your personal preference.

Nick
 
Nice review Nick. I wasn't under the impression that either the 20th Anni Shiva or XTC were rebuilt from the ground up, but tweaked; more aggressive gain stages and voiced for more upper mids. At least that's been my experience with both.

A few years ago, I made the opposite swap in my 101B- pulled the EL34's and dropped in KT88's. The bigger bottles definitely change the EQ characteristics of the amp and I'm much happier with the amp after the swap.

So are you sticking with the EL34's?
 
billm408":3h9r3a1l said:
Nice review Nick. I wasn't under the impression that either the 20th Anni Shiva or XTC were rebuilt from the ground up, but tweaked; more aggressive gain stages and voiced for more upper mids. At least that's been my experience with both.

A few years ago, I made the opposite swap in my 101B- pulled the EL34's and dropped in KT88's. The bigger bottles definitely change the EQ characteristics of the amp and I'm much happier with the amp after the swap.

So are you sticking with the EL34's?
Click to expand...

Bill, for me, I'm definitely sticking with the EL34s. I like the more vintage voicing.

It's amazing how different the sound of KT88s are. I don't think the amp was voiced for more upper-mids, as much as I think that the KT88s *HAVE* more upper mids. Just dropping those tubes in would be enough to give someone the impression that the amp was "revoiced".

As far as gain stages, I had a chance to try the Standard EL34 shiva, and the 20th KT88 a while back. The 20th, with the "gain mode" button out, has the same exact gain level and EQ curve as the old shiva. With the button it, it's MUCH more modern and aggressive. So yes, definitely a circuit tweak, but a user-selectable one, which is great.

Again... this is just my opinion. Not based on fact. Just my two ears. :D
 
Nick, I also agree....the 20th Shiva is so much better for me with EL34s. I have tried KT88s in numerous amps and could not get on with it! I fell in love again with any amp once switching to EL34s.

The new 20th amps are rebuilt from the ground up. I talked to a Bog tech who said it is a different amp.

Nick....do you think I need to open mine up and snip any resistors or change anything? Mine cam built from the factory with EL34s!

By the way, I emailed Charlie to let him know there is nothing wrong with biasing the 20th SHiva in the 30-35ma range. Mine is at 34! Has been for a while! All amps jump while playing. Hell...the VHT ST I have will jump to 70 at times while playing! The best tubes for handling this are the JJ Electronic EL34s, but my SEDs did fine and the Tung Sols as well. I set the SEDs at 34 and sounded great. Not sure I could tell a big difference in a blind test but I just feel more comfortable knoing it is biased warmer. :D

With a tube amp there is always trade off. Some of our songs use modern chorus-delay arpeggios, etc but I use the EL34s because I can't live without them for dirty tones. I compromise. Heck we play stuff similar to The Police and U2 clean but when I turn to dirty or high gain it has to be EL34. I make due! LOL. If not this.....I'd have to go digital into a PA to get best of both worlds.
 
I wouldn't say that it's better or worse with KT88s. Just better for *me* personally. Same for you. For someone wanting that more tight, modern sound, then KT88s all the way.

Rich, I'm sure that yours came stock from the factory with the proper resistors. Bogner knows what they're doin! :thumbsup:
 
Nick, you should bump your bias up to the 33-35 range and see what you think. That is typically where I like things but remember the test I said Bruce ran. :D
 
Awesome, detailed post Good Sir, thanks for taking the time to write it out... Super helpful. Worthy of a sticky :D

V.
 
Rockstarnick- Is the powertube layout on the 20th the same as regular Shiva, or did they space the power tubes farther apart for the KT88. Would 88's fit in a reg. Shiva?
 
fishyfishfish":2npcx561 said:
Rockstarnick- Is the powertube layout on the 20th the same as regular Shiva, or did they space the power tubes farther apart for the KT88. Would 88's fit in a reg. Shiva?
Click to expand...

I have no idea.... I don't have a standard Shiva here to compare it to. :(
 
Grow some balls and try some 6550s in that thing and let it come alive!! :)
 
ON a serious note for those that have a Bogner Shiva 20th. SED =C= 6550s in that amp is amazing. I have one for sale, and tried it w/ a set of SED =C= 6550s and was blown away. If you think that the KT88s have are really stiff, harsh, and grindy, but like the big open clean tones, and big bottom end and want a mid range more like a warm saggy EL34 mid-range, the =C= 6550s are your tube.

Clean tones are amazing w/ =C= 6550s. With a strat and some reverb, I could easily coax some SRV likeness with that amp. Add the boost to the clean tone, and it had a really big sounding Fender Deluxe spank and grind to it. Country players and chicken pickin rockabilly players would LOVE this tone.

Distortion tones are warmer, less bitey, smoother but with a good growl and snarl to it. Bottom end stays tight and punchy and the top end is just right.

W/ KT88s it was good, but not great for me. W/ 6550s it was awesome!!!! If I didn't a 2555 Silver Jubilee w/ Mercury Mag PT / OT / choke with Trace @ Voodoo Amps magic dust on it...I'd definitely be keeping this amp. But that 2555 is MY amp. It's the best amp for me for sure!! :)

Anyways. I highly recommend the SED =C= 6550s in the Shiva 20th. Ahem...this means you mr. "RockStar". Move yer ass, get some t00bs from the Valve Queen before I kick your arse! :) Don't make me bitchslap your Joisey ass! ahahhahahah ;)

Eric
 
El34s rule the stage. Nothing is
more toneful nor sits in the mix better. 20th. Shiva and 34s is da bomb!
 
Nick, I got in an argument with Charlie over this and I think I proved him wrong. All amps drift in bias. Hell, my VHT drifts even further! I tried both to see.

I keep my Shiva biased at 35 and it works like a champ. As long as you know the plate voltage, what the tubes can handle, etc. No different than other amps.
 
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