Signal tube versus power tube, sound impact?

My mono block has eight KT 88 tubes(power tubes) and six smaller signal tubes. I'm using the stock tubes that came with each Mono. I think they are JJ tubes.

Rather than replace them all would it be best to change out the signal or the power tubes? Not sure how good the JJ tubes are but I hear they may not be the greatest.


Power tubes first, small tubes to fine tune. JJ power tubes are OK if you like them. I use their E34L's in a small amp in preference to some other excellent tubes. Power tube selection can make a big difference in the sound so the first thing you need to do is try to define what sound you want to hear. While tubes do interact with your amp to get this sound power tubes do have a intrinsic sonic signature (as do small tubes). FWIW new production tubes are generally good, NOS power tubes are exceptionally hard to find and very expensive. 


Likely only 1 preamp gain tube  in each channel will make a noticeable SQ difference. Could be subtle or quite noticeable.

If your amp accepts different model tubes-EL34 for example, it will be a noticeable move. YMMV, but typically enhanced mids/less bass with EL34.

Look up what other type will work and their sonic character.

Going on about 30 years ago I spoke with Andy of Vintage Tubes (in Michigan) with basically this same question. I was interested in retubing (with NOS) a pair of ARC VTM 120s (6922s and 6550s) and a Cary SLP90 (12au7s).  Andy's advice (which I followed) was to start "closest to you" which meant the preamp and then the signal tubes in the amp.  The improvement in SQ was significant.

A few months later down the road I talked to Andy again about output tubes, and he wound up selling me a pair of quads of NOS Tungsols (not the Russian reissues that are out there now) to replace the Svetlanta 6550s I had in them.  For as much money as I paid for those NOS Tungsol 6550s I was expecting a huge sonic dividend and I was disappointed.  I really didn't hear any improvement.  Maybe because I was expecting too much?

Anyway, going by that experience and Andy's advice, I would start replacing tubes from the front and work backwards.  And I have heard good things about JJs for the price.

We have one answer that says power tube> signal tubes and another that says signal tubes>output tubes.  Hmmm.

@hilde45  , I am only relating to OP what I was told by Andy of Vintage Tubes many moons ago, and what my own experience was with replacing Svetlanta 6550s with NOS Tunsol 6550s.  I do not claim that either Andy's advice or my own experience is gospel that will apply to everyone. 

We have one answer that says power tube> signal tubes and another that says signal tubes>output tubes.  Hmmm.

. . . and actually, it looks as if it was two answers for outputs>signals versus one answer for signals>outputs. . . .

Start with the small tubes/preamp tubes. If you go with power tubes first, you will correctly wonder if you are hearing them for what they are...and the answer is no. Marginal signal tubes fed to exceptional power tubes stands a better chance of remaining marginal. An exceptional signal tube sent to marginal power tubes stands a better chance of improving things. If you feed your amplifier the best signal possible, then you will be hearing them at their optimal. My 2 cents and most will change both, otherwise, it will feel like a Larry David skit.

I have noticed more difference changing the output tubes.

@ellajeanelle This has been my experience too. Especially recently, swapping from KT88 to KT120 (in amps that support this) effects a huge difference. Swapping between different brands of KT88 also makes a large difference, though not quite as much.

That said, yes small signal tubes can make a significant difference as well. Especially whatever tubes are tasked with driving multiple KT tubes.

Many folks claim small signal swaps are more cost effective since NOS / vintage types are still reasonably available, and these tubes can last several times longer than their power counterparts. And certainly, amps that use an octet (of more) or KT88 (or whatever) really rack up the tube bill! I just swapped an octet of Tung-Sol KT120 in place of Gold Lion KT88 for a VAC statement 450S. Made a HUGE difference. I also swapped its sextet of 6SN7’s (mix of NOS and new). That made a smaller (but still large) difference - and yes I tried many various combinations! In other amps I have preferred Gold Lion KT88 over KT120. And EH KT88 also sound different from GL KT88, despite being made in the same factory - just a matter or personal preference (GL are voiced more "audiophile").

The KT88 and KT120 are close enough to be reasonably compatible (bias, loading etc), but different enough to sound quite different. It’s a fun swap :)
Just clear it with your amp maker first. Anything running a KT120 near its limits would fry a KT88, and KT120 draw a bit more heater current from the power transformer.

As for JJ - I had a run of bad JJ encounters in the past (~15 years ago) and never gave them another chance since then. My rule for the longest time has been to bin JJs immediately, whenever a component arrives with them inside. 

all of the above but try the small tubes first, you may find you tune the sound to your liking without expensive power tube trial and error experimentation.

jj tubes are like $40 apiece and the cheapest versus others in the $80 to 150 range

I’m looking for a cleaner Open sound. There are for preamp tubes and it seems this tube is the beginning which sets the stage for the signal and then the power tubes. So I guess starting at the beginning of the food chain makes more sense.

Although I do hear that the JJ tubes are more durable and reliable which is why I guess they use them as stock tubes.


What kind of amps are you running? 16 power tubes? WAG, but sounds like some Primalunas I've seen, but not heard. What kind of 'signal' tubes are you running? What kind of pre-amp are you running, with what kind of 'signal tubes?

Specificity might get you a better quality of response. 

Although I do hear that the JJ tubes are more durable and reliable which is why I guess they use them as stock tubes.

Says who, JJ? 😂

I will preface what I am going to type about JJs and EHs by emphatically stating that I do not have the golden ear, I do not own a tube tester, and I make no claims whatsoever to be a tube or audio guru.

My current preamp (SLP 05) came with six EH 6SN7s (two for the left and right balanced inputs and the other four were the left and right gain stages). I had the good fortune of getting numerous pairs of moderately used vintage tubes to roll in the balanced input sockets and I heard significant improvements with some (not all) of them. In the past, what I had been MOSTLY hearing was that the EHs were crap and that JJs were not bad for the price, so I recently took the remaining four EHs out and replaced them with JJs from Tube Depot. I thought that I heard an improvement, but I will admit that, on this, I may have been hearing confirmtion bias.

The generous individual who gave me the deal of a lifetime on those numerous pairs of vintage 6SN7s (in those two balanced input sockets I am currently running a pair of ’52 Sylvania "Bad Boys" that I got from him) also told me that he was done chasing NOS signal tubes (he no longer runs 6SN7 based gear) and from now on he is sticking to JJs for signal tubes, and to quote him as best I can, he told me that for his money, JJs were as good as it gets now. He actually favorably compared JJ 12AX7 sound to Telefunkens.



On the subject of signal tubes...
I like the EH 6SN7, but they absolutely have a very "solid state" sound, totally lacking the tube warmth you’d expect - especially from a 6SN7. They’re a "situational" player for sure. As @immatthewj referenced, this tubes certainly has its detractors! For this very reason. A preamp that ships with a battle squadron’s worth of EH 6SN7 will either have to be voiced VERY specifically for this tube, or it will improve massively from some 6SN7 rolling - which further contributes to the tube's bad rep, no doubt.

EH 12AX7 is voiced to be quite bright, really just too damn bright - I have never found a use for them. I’m flummoxed the Herron VTPH-2A shipped with them. EH power tubes like KT88 and EL34 have a more "fun" and brash voicing; I like them but they’re not for your typical audiophile.

As for the other Russian sub-brands - Gold Lions generally have a refined smooth sound with a more traditional tube voicing, Mullards are always extra warm (with relaxed treble), and Tung-Sols generally have a great balance - good for all genres but especially for rock.

Vintage 6SN7 can be super but they’ll always measure a lot weaker (transconductance) than the modern Russian 6SN7’s (EH and Tung-Sol 6SN7GTB), so I really like the latter in driver slots. The Tung-Sol GTBs are just a little sweeter than the EH, still a far cry from the "sweetness" of a good vintage 6SN7. Vintage Tung-Sol round plate black glass 6SN7GT are super lush and sweet btw. But many vintage 6SN7GT’s also have issues with noise and microphonics, so I’m glad I only have to stick them in power amps - you’ll drive yourself crazy with these tubes in a preamp or (God forbid) phono stage.

. . . what a representative from the sales department at Cary Direct once told me (the Cary people will actually talk to you on the phone if you want to buy something) when I called to inquire about the Amperex Bugle Boy 6DJ8s that Cary Direct was listing:  "Tube rolling will make you neurotic."

That is a direct quote. 

And yes, I did buy a pair of those 6DJ8s for the front of my Cary V12.  I don't recall being overly impressed with any changes to SQ I might have heard, and presently those Bugle Boys are back in the "tube drawer" of a file cabinet I have and I have a pair of Gold Lion 6922s in those sockets.

. . . I also meant to say that although I personally never heard huge sonic differences when I was going back & forth with different HEALTHY output tubes in my first two 6550 based amps (I have never rolled tubes in my present EL34 based amp as long as it was running with HEALTHY tubes), if I had an output tube or tubeS that were getting sick or were getting tired, replacing output tubes was then  like listening to a new amp.

My experience is like @ghasley.  Small tubes in pre stages made way more noticeable change than output.  Using NOS recommendations from both maker (Raven) and Brent Jesse I chose military and or scientific grade pre tubes.  Stage expanded and bass tighter at every position tried. I ordered unit with one step up in 2 of the 3 positions too.  Most run cheaper than output tubes.  I then tried better/desirable/ recommended output tubes havibg been so happy but its much more subtle a change.  YMMV.  I set a budget and said I'd stop if if I didn't hear any improvement with each position.   But it did improve.  Done now.  2 years "sober".  Not neurotic. Besides, I now have perfectly decent spares.   

Not knowing what your tubes are definitively (did you actually confirm they’re JJ - you seemed uncertain…), nor the amp, speakers etc., this is not a realistic query for anyone to field.

More supporting input due from ya. 😉

In my experience with my Decware amp, it’s finding the right combination of tubes that is the key. The stock tubes that came with mine were really good. Then I started experimenting with different combinations and since I had several of each type, I ended up with 12 different possible solutions. 

In the end, I found that a ~1960 vintage Telefunken signal tube and generic Russian $28 power tubes were the best sounding.

Usually power tubes first then signal tubes in an amp. Also it’s the first signal tube in the series for a particular channel that has the most impact. For instance, if you have 3 -12 ax7s  for each channel, the first one in the series has the most sound impact, the others less and less as you go to the last tube in the series. 

Amperex Bugle Boy

f your amps are running 12au7’s the Amperex Bugle Boy tubes placed in the central "gain" positions can be very good. However, buyer beware as I have heard these are sometimes Asian fakes. The two linked above look almost too good to be true - usually the vintage tubes show wear to the Bugle Boy logo. If these are real, they look exceptional.

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Lot's of good suggestions here, although overall maybe a bit confusing/overwhelming (no surprise).

Personally I've had good outcomes with the front (small) then back (power) strategy, other than one KT150 based amp as there are no other options besides Tung-Sol. In this case replacing the stock JJ pre-amp tubes with some NOS Telefunken Diamond Mark Red Tips worked magic. 

I have not been impressed with GL KT88 tubes vs. JJ. I returned the GLs. This was in my first tube integrated - a LineMagnetic.

A trusted source is important and I have mostly used Brent Jesse at Everything he has is listed on his website, and he gives good advice without being pushy or overselling, and has a very reasonable return policy.  

Although expensive, if you want to warm things up, the NOS Mullards are pretty special and currently in my tube DAC - however, and this is where Brent Jesse comes in - I have some 1950's GE long plates (branded as Wurlitzer) that I rotate in and out of the DAC that sound remarkably good in the DAC at 1/4 the price.


I think mcIntosh is JJ tubes for stock. These tend to be generally cheaper and may be more reliable which may be why they use them.

I guess if they put in better tubes they see a lot of problems with people complaining about malfunctioning tubes when they buy the new amplifie…

So here is a case where durability and reliability may impact quality. So you maybe better off replacing these JJ tubes for something that may be better?

Sort of like the power cords which are kind of crappy that they supply with their amplifiers and they know the consumer will probably replace the cords.


He’s got a very interesting website with lots of commentary. Further his prices are incredibly expensive. Return policy is alluring but from a practical standpoint I doubt many even returning tubes because of the difficulties involved.

But it’s a pretty damn good website

Expensive? Maybe, but I’m some cases how would you compare as he likely has inventory that no one else has?

I have returned (exchanged) 1 set with no issues.

The way I look at it is value for money: good advice, no concerns about fakes or items not as described etc.

having said all that there are several other very reputable dealers out there. Good luck and have fun!

I guess "expensive" is relative. Brent's prices aren't out of line if you are willing to buy genuine vacuum tubes built to exacting standards from a time when the manufacturing of valves was at its apex....I believe a NOS Mullard or Bugle Boy 12ax7 is worth a significant premium over a JJ or Electroharmonix...

my manual for my amp and pre-amp - both from Decware - says to roll tube V1 - 12AX7 -  in the preamp and the 2 input tubes - 6922 - in the amp, before doing anything else. Amp is EL34. I currently have Winged C's and much prefer their bass and mid-range to current production from China that I have tried. Have not experimented with other EL34s or other types of tubes. My amp supports several other types, which I forget now. They are darn expensive.

I went back and forth experimenting with tubes in a little Japanese 300b integrated amp in this case the small 12v tubes definitely made a bigger sonic impact on the sound. There was a very big gain in the bass region

Seems to me the preamplifier tubes Carry the most weight when dealing with the sonic signature. It's at the beginning and why would you not want to amplify a quality signal right away. If you have a crappy preamplifier tube it's going to get amplified and sound crappy no matter how good the rest of the tubes are .

Anyone ever see a good diagram showing the circuitry flow within an amplifier or a good walk-through of the incoming power and incoming signal and how they ultimately do stuff before they go through the Cable leading to the speaker? And of course showing all the various tubes in series etc.  

Pleased to hear the opinion that power tubes matter more than signal tubes (only because that's what I have found to be true and I'm a confirmation whore.) Shirley you must know that this flies against common wisdom that pairs tube preamps with solid state power amps. 

Seems to me the preamplifier tubes Carry the most weight when dealing with the sonic signature.

This has been my experience, except in the case where the tubes in my amp were getting worn out & tired.

Shirley you must know that this flies against common wisdom that pairs tube preamps with solid state power amps. 

@mambacfa  , I cannot find the post in which Shirley weighed in on this one. 

I’m giving the new Apos Ray 12AU7 tubes a spin in my BHK pre and I am quite impressed so far. 36

Apos / Ray are cagey about their provenance (China, most likely) and they claim to only accept the top 4% of production, whatever that means.

At $180 per matched pair, they are priced near the top of new production tubes (e.g., Gold Lion), but much cheaper than almost any worthy NOS 12AU7s, and believe me, I have a ton of them in my stash.

WIth 100+ hours on them, they are quite impressive compared to the NOS Ciftes that preceded them, which were smooth and inviting, a bit on the warm side and not particularly incisive.

The Ray tubes are a different animal altogether–big, dynamic and quite detailed without any hardness or edge. They throw a huge soundstage, with powerful, yet tight and textured bass.

Worth a try…

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@djohn - I have a Herron as well. Much depends on the system synergy. Picking good quality NOS tubes from knowledgable folks like Andy’s Vintage tube service, Brent Jesse and the like - who can match really quiet samples will pay dividends. Myself I’ve got a quad of 60’s Telefunken 12AX7 because of the low output MC cartridges I use. The 5th tube is always a 12AT7 type, and using a premium E81cc, or a ECC801S also produces sonic dividends. (I have a 801) Brent Jesse’s web site has a good generic description of the sonic signatures between the vintage tube makers. (Mullard, Amerex, RCA, Telefunken ect.) For me, if I was to change anything, I’d swap Telefunken 12AX7 with Amperex for a little more mid range warmth. Again it’s about system synergy and your budget. All the best on your quest!



Thanks to the OP for getting this started. I know it’s been argued about over and over and round and round. But I’ve enjoyed reading the posts, including the links.  This all will be settled by approximately never. Yet it remains interesting to read about. To me. 

I would replace to signal tubes first, research and get the best you can afford.  Why they will last.  You will have to replace the power tubes because they burn out much faster.  Just my experience.  

I use JJ KT77s. They sound fantastic on my Primaluna. I have not tried their preamp tubes.

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My comments relative to tube types would be the same with either gain (12AX7 or 12AT7) 

if you need more info pertaining to the Herron, let’s start a new thread or move to PM and keep this thread on topic.

Back to the original topic…..

OP - I’m definitely in the camp the that the driver (signal tubes) have a larger sonic imprint. Where there is budget and availability, NOS from the big makers from the 40’s to 60s were vastly superior to the modern stuff. The only time that’s not entirely true is with 300b. Today’s EML and the like are outstanding.

I don’t know why manufacturers of expensive tube amplifiers don’t provide better tubes in their equipment. Lots of people form opinions about amplifiers and if these amplifiers came with better tubes peoples impressions would be a lot better.


I think they are shooting themselves in the feet when they put JJ tubes, which consensus seems to say are lower quality, into their tube amplifiers. Hardly a way to provide a product to a customer especially when they’re so expensive.

Amp manufacturers know that people are going to roll tubes anyway - it's part of the charm -  so why not let them do that for themselves.

I think they are shooting themselves in the feet when they put JJ tubes, which consensus seems to say are lower quality, into their tube amplifiers.

Hmmm . . . I just looked at your "JJs suck" thread and counted the positives and negatives, and then I did the same on this thread, and I came up with 5 "JJs are okay or I like them" and 8 "JJs suck," is this your "consensus"? Not that it matters to me . . . just asking for my friend’s grandmother.

As far as why (most?) manufacturers don’t ship their gear with NOS or moderately used vintage tubes, my own personal theory on that is because I would think that most manufacturers buy tubes for the products that they build in bulk, and for that reason they buy affordable bulk priced tubes. If they went out and, for example, loaded up on NOS Tung Sol output tubes and NOS RCA black glass signal tubes, that would dramatically increase production costs and the cost  of the effect produced by that expensive combination would have to be passed on to the consumer, but that particular effect may not be what all consumers are looking for, so perhaps the manufacturer feels better to give the consumer a bit of a price break and let him or her do his or her own fine tuning by rolling high dollar tubes.

Or maybe not. I make no claims to being an audio or tube or electrical guru, so that is just a theory. Maybe pose the question to some manufacturers.

Amp manufacturers know that people are going to roll tubes anyway - it's part of the charm -  so why not let them do that for themselves.

That is also what I think, @bolong  .  +1. 

Manufacturers must spec a tube that is currently manufactured and readily available in bulk. In addition, with the uncertainty surrounding Russia and China trade channels, a European built tube like the JJ is both politically expedient and more reliable. Be thankful manufacturers dont go out and buy up what little remaining NOS tube stocks are in existence. If they did, then there would be multiple threads about greedy manufacturers “stockpiling” all the great tubes and driving the prices through the roof or better yet, company A has 1,000 NOS Mullards on the shelf and won’t sell me two backup quads.

And maybe if the manufacturers did a better job putting better quality tubes in the amplifiers when manufactured the demand on the industry would be to produce better tubes.

Manufacturers spend a lot of money designing their amplifiers and then screw things up by sticking a poor tube seems odd. I'll be curious to know what VAC puts in their amplifiers. I know Conrad Johnson uses NOS tubes for their pre-amplifiers.