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Post subject: Unmatched 6L6GC's in push pull
Posted: Fri May 27, 2016 7:49 am
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My amp has a bias adjustment for each of two 6L6GC's.
If I install a pr of unmatched tubes....but match the bias, will one tube wear faster than the other?
Is there any other issue?


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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Fri May 27, 2016 1:42 pm
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Unmatched tubes with 5 ma to 10 ma between each tube sound better than perfect match wich may sound steril .

I never bought matched tubes and they are alway under 8 ma


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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Fri May 27, 2016 2:37 pm
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ckmckool wrote:
If I install a pr of unmatched tubes....but match the bias, will one tube wear faster than the other?


No. The dynamic parameters and specific load of each tube will be nearly the same.

Arjay

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Sat May 28, 2016 10:31 am
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ok ok ....so an unmatched set will sound better than the "matched set" we are told to use all these years? are you guys yanking chains? so just order 2 6l6 tubes of the same manufacture? what kind of who ha have we been fed? are the tubes actually that closely matched to start with? i'm not new to tube tech but this goes against all i have been taught about amps and tubes that go in them. clarify please.


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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Sat May 28, 2016 10:46 am
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Everyone has their own philosophy but the theoretical paradigm is this:

In a push-pull output stage, optimum *electronic* efficiency is achieved when the circuit is operating symmetrically. Of course this ignores the specious-but-significant factors of compression, overdrive, and even/odd harmonics that are difficult-to-quantify parameters but greatly impact an audio amplifier's sonic performance as perceived by the human ear.

Arjay

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Sat May 28, 2016 11:09 am
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i get it brother, but just speak the truth. is it necessary to have a matched set? my ear sometimes says my matched set is sterile. i often thought of not using a matched set. hopefully you won't have a musical manufacturer hit squad sent after you.


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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Sat May 28, 2016 12:18 pm
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My primary concern has always been maximun tube performance/lifespan.....and then rely upon technique and maybe pedals to color my sound. It's been so long since I tried employing unmatched tubes that i forgot what sonic qualities may result.


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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Sat May 28, 2016 12:52 pm
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ckmckool wrote:
My primary concern has always been maximun tube performance/lifespan.....and then rely upon technique and maybe pedals to color my sound.


+1

That's the same protocol I've always used.

Haven't seen hide nor hair of any hysterical "hit squad" yet.

:lol:

Arjay

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Sat May 28, 2016 2:08 pm
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so basicly "keep on keeping on" with the matched sets. 10-4 retro.


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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Sat May 28, 2016 2:42 pm
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I said that's how I do it.

You're free to do as you will.

Arjay

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Mon May 30, 2016 5:39 am
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Just bought a Peavey Delta Blues II 115. it sounded pretty good except the "drive" was a bit harsh, and some static sounds when pushed hard. I was considering some options for different preamp tubes to smooth out the "drive", so I decided to look at what was involved in accessing the tubes by removing the cage.

Much to my surprise, the V5 power tube had a white powdery substance where the others had the black/silver mirror-like look. When I touched the V5 tube, an EL84 (power off and cooled) the bottle fell off. Apparently a circumferential crack existed in the glass. I'm amazed the sound wasn't that bad!

Image

I damaged the innards of the tube removing it from the socket which didn't matter since it wasn't any good anyway. I can only suspect that the glass bottle was faulty????

So as I contemplated what to do, I did a lot of searches about mismatched power tubes and found quite a few (seemingly knowledgable...but how can one be sure?) people saying that there is no damage to be done if the amp does not produce unwanted distortion and the tubes do not redplate. In fact a couple of sources even claimed there could be an improvement of desirable harmonics. The claims were that it takes significant mismatch to cause one of the tubes to wear faster than another???

I had a matched pair, not quad (which is in the PVDB), so I put the two in V5 and V6 (the two innermost power tubes). Also, I do not have the wherewithal to bias a fixed biased amp. Also read on the websites of a couple of major tube suppliers, that it should be OK to do so with the same brand (JJ) and especially with EL 84's.

Gave it a quick test and all seems well so far....more testing today.

Am I flirting with disaster or is it a case of "no red plating and good sound" means it's fine? Appreciate any feedback, and sorry for the long post.

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Mon May 30, 2016 8:49 am
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Did the drive mode smooth out and did the static disappear once you'd replaced those tubes?

Arjay

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Mon May 30, 2016 9:01 am
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Retroverbial wrote:
Did the drive mode smooth out and did the static disappear once you'd replaced those tubes?

Arjay

The drive did seem to smooth out and is more useable through a larger range.
I'm not 100% sure of the total disappearance of the static as yet. It did not occur all the time before and after 1-1/2 hours this morning, I won't conclude it's gone. I thought I heard it once briefly, but it'll take more time for me to be positive.

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Mon May 30, 2016 9:29 am
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As long as the tone is pleasing, the output tubes are not red-plating, there are no weird smells, and no magic blue smoke is visible, I suspect you'll be fine.

I've only worked on this particular Peavey platform twice but in each instance the output stage was freshened up with new bottles (matched quartet) after I checked that the plate voltage was within operating parameters for the EL84. That was several years ago and neither client reported any issues since that servicing. These are nice amps though I do not care for the tone of the Sheffield speaker.

Arjay

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Post subject: Re: Unmatched 6L6GC's in push pull
Posted: Mon May 30, 2016 9:50 am
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Retroverbial wrote:
As long as the tone is pleasing, the output tubes are not red-plating, there are no weird smells, and no magic blue smoke is visible, I suspect you'll be fine.

I've only worked on this particular Peavey platform twice but in each instance the output stage was freshened up with new bottles (matched quartet) after I checked that the plate voltage was within operating parameters for the EL84. That was several years ago and neither client reported any issues since that servicing. These are nice amps though I do not care for the tone of the Sheffield speaker.

Arjay

The new Delta Blues II has a Stephens True Sonic Speaker which I never heard of. I've read it's history is from the audio/stereo sector. I've not played the amp through anything else and I'm also adjusting to my first Gretsch guitar, so I have too many variables going on to assess it properly. One day soon, I'll get out one of my more familiar guitars and see what I think. By then, the speaker should be broken-in. Wish it had a plug like the Fenders have so I could unplug the internal and try another speaker by itself. I do have a Z-matcher so I could use the cabs I normally play with Fender amps.

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