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Power tube matching advice: 16 tubes


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Morning All,

Looking for some advice.

I have a pair of autobiasing monoblocks.

Each one has 8 power tubes (EL34).

1. Do I need to get 16 tubes matched?

2. Can I use 2 sets of matched octets? 1 set for each amp, or in some sort of mixed configuration

3. Could I use matched quads in some sort of configuration

 

In a similar vain. Do I need to match driver tubes? I have 6x 12AU7 per side.

 

Many thanks for the help

 

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Driver tubes likely don't need matching, unless you have a tube that uses each half of It's double Triode for left and right channel respectively...one half for left and the other half for right. So in that situation you would need close matched halves for each tube that works in that way in the circuit.

 

I'd think that a matched quad of power tubes for each mono block would be fine.

Edited by muon*
clarified
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4 minutes ago, muon* said:

Driver tubes likely don't need matching, unless you have a tube that uses each half of It's double Triode for left and right channel respectively...one half for left and the other half for right. So in that situation you would need close matched halves for each tube that works in that way in the circuit.

 

I'd think that a matched quad of power tubes for each mono block would be fine.

Thanks.

Just to clarify. You mean 2 sets of matched quads per side. Instead of 1 matched octet, per side?

Edited by The Fresh Prince
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9 minutes ago, The Fresh Prince said:

Thanks.

Just to clarify. You mean 2 sets of matched quads per side. Instead of 1 matched octet, per side?

Oh! you have 8 in each mono block.

 

What does the manual/manufacturer say?

 

Personally if I couldn't get matched 8, I'd ask for quads that are close to matched between sets of quads if possible, or mix them evenly in each channel. So 2 from each quad in a channel rather than a quad in each channel separately.

Mirror how you mix them in each channel.

 

All this may not be too critical, but that's how I'd do it.

 

Edit: excuses my lack of focus as I have just woken up :D

Edited by muon*
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3 minutes ago, muon* said:

Oh! you have 8 in each mono block.

 

What does the manual/manufacturer say?

 

Personally if I couldn't get matched 8, I'd ask for quads that are close to matched between sets of quads if possible, or mix them evenly in each channel. So 2 from each quad in a channel rather than a quad in each channel separately.

Mirror how you mix them in each channel.

 

All this may not be too critical, but that's how I'd do it.

 

Edit: excuses my lack of focus as I have just woken up :D

Thanks.

I guess I should ask the manufacturer.

I’m hoping quads are fine- not so easy to find octects, or 16 matched tubes

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3 minutes ago, The Fresh Prince said:

Thanks.

I guess I should ask the manufacturer.

I’m hoping quads are fine- not so easy to find octects, or 16 matched tubes

It is worth asking what the manufacturer advises, but I think you could get fairly close matched quads to mix evenly from some suppliers that hold a lot of stock. And good stock would likely be close enough in matched quads to mix evenly.

Edited by muon*
typo
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I'd be thinking these amps are parallel push-pull, so if you buy two sets of quad-matched for each amp, then use them in a configuration where a pair from each matched quad are mixed with a pair from the other matched quad, on each side of the push-pull arrangement, then they would average out nicely.  In fact 4 sets of matched pairs for each amp might be the way to go.

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25 minutes ago, aussievintage said:

I'd be thinking these amps are parallel push-pull, so if you buy two sets of quad-matched for each amp, then use them in a configuration where a pair from each matched quad are mixed with a pair from the other matched quad, on each side of the push-pull arrangement, then they would average out nicely.  In fact 4 sets of matched pairs for each amp might be the way to go.

Sounds like excellent advice.

Is there a standardised arrangement to identify the sides of the push-pull?

pic attached

6642AC38-7E3A-4F25-8006-B7FD7243A704.jpeg

52A476E2-8F66-4136-823F-80459A8CCACC.jpeg

Edited by The Fresh Prince
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45 minutes ago, The Fresh Prince said:

Is there a standardised arrangement to identify the sides of the push-pull?

Not really, but I must say yours look like they are grouped, 4 on the left and 4 on the right.  Do you have a schematic?  What brand are they?

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From memory the PrimaLuna Auto Bias feature will "match" the tubes for you.  There is no requirement to fit "matched" sets.

Finding 16 "matched" power tubes is going to be difficult and expensive.

Info regarding tube matching is available on the PrimaLuna website.

 

 

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I feel your pain.

 

The primary reason for me selling my pair of VTL Deluxe Monoblocks 300. Eight KT90s per side. I was running the EI KT90s which are no longer available new as the factory had been destroyed by its then owner (?).

 

You are in the better position of using EL34s but even then the choices are huge. New or NOS.

 

Good luck with the tube rolling.

 

Edited by Paul R
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1 hour ago, Mpr_65 said:

From memory the PrimaLuna Auto Bias feature will "match" the tubes for you.  There is no requirement to fit "matched" sets.

That will ensure they run at the same bias point, but won't ensure the gain is the same.   Certainly helps though.

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What @Aussievintage said.

 

I too ran my VTL Monobloc 300s (16 x 6550) for years with no 'matching' but good biasing. I considered that the overall output of an octet of valves per side trumped the niceties of exact matching. For my (previous Kebschull and) now Leben valve preamplifier--and particularly the phono valves--this is another matter: matching is king.

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Banzai Music, Berlin can match 16 valves. Postage to Australia is €16. The unit price includes vat@16%, that comes off at checkout when you enter your destination.

A bit over €300 for EH 6CA7, which is my recommendation, but they carry most EL34/KT77 reissue. Look for the platinum matched option when you're scrolling through.

https://www.banzaimusic.com/6CA7-EH-Platinum-Matched.html

Check them out, I've had nothing but good results dealing with Banzai. They don't charge gst at the checkout and I've never been clipped by Australian Customs.

 

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39 minutes ago, deanB said:

Banzai Music, Berlin can match 16 valves. Postage to Australia is €16. The unit price includes vat@16%, that comes off at checkout when you enter your destination.

A bit over €300 for EH 6CA7, which is my recommendation, but they carry most EL34/KT77 reissue. Look for the platinum matched option when you're scrolling through.

https://www.banzaimusic.com/6CA7-EH-Platinum-Matched.html

Check them out, I've had nothing but good results dealing with Banzai. They don't charge gst at the checkout and I've never been clipped by Australian Customs.

 

Hi Dean,

Thanks for the recommendation.

I contacted them earlier today, to see when they would have stock coming in.

 

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My personal recommendation would be matched tubes from tubedepot.

https://www.tubedepot.com/t/tubes/power-tubes/el34-6ca7

Huge range, they ship reliably to Australia, and they can match as many as you like at an affordable price. I also recommend the "24 hour burn in"; not because of the sound quality but because it rules out early failure tubes which are a pain to deal with.

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To be honest having bought 'matched' pairs, quads, over the years, unless tubes are fully burnt in, it's completely irrelevant.  Matched tubes new, do give a reasonable match to 'gain and current draw' however, I have found time and again that you need to re-bias a few times before they settle down and running the valves through my tester (which is an Avo VCM163 and among the best testers available outside a laboratory);  I have ended up swapping tubes around as the gain/current draw does alter while burning in. They have not ended up in the same configuration as they were when first installed. Frequently in the opposite channel amp to where they started.  Modern tubes just are not constructed with the attention, quality control, and constructional detail of tubes produced in the golden age.

  I will add that I have not purchased any of the high cost 'boutique'  (Shuggy/Psvane etc) type current power tubes to my mind they are ridiculously expensive, and you might as well buy NoS for similar prices. (Which I refuse to pay that exorbitant price, considering that I replace my power tubes about 2-3 yearly due to use). possibly those 'boutique' tubes may not drift and alter as much as the 'standard production' ones. However,  going by Matt Lachesky's thoughts on the re-issue Mullard 12AX7, compared by dismantling an original and a re-issue?? I highly doubt ANY modern factory produced tube currently equals the quality of old.

 

https://www.effectrode.com/knowledge-base/mullard-ecc83-12ax7-reissue-vs-original-a-physical-comparison/

 

and as an after test, the owner of effectrode did an electrical comparison between an original and a new production Mullard. Make of these two pieces of information what you will.

 

https://www.effectrode.com/knowledge-base/mullard-ecc83-12ax7-reissue-vs-original-an-electrical-comparison/

 

Edited by Graywulf
added more information.
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If the monoblocks are autobiased matched tubes are not required. However, new or near new tubes with plenty of life in them are required; same brand and same type preferred.

 

Whether you go for new or old stock is a personal preference. I am not into new Ruski toobs with glare and clinical sound nor Chinese hifi sounding equivalents. If you're after a nice sounding EL34 try sourcing Mullard Blackburn Xf2 vintage types from the 1960's. It will cost you a bomb to source 16 toobs but the sound will be well worth it. 🙂

 

For the 12 12AU7s get yourself some standard E80CC's including the Tungsram halo getter steel pin types. 👍👍👍

Edited by xlr8or
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32 minutes ago, xlr8or said:

If the monoblocks are autobiased matched tubes are not required. However, new or near new tubes are required; same brand and same type preferred.

 

Whether you go for new or old stock is a personal preference. I am not into new Ruski toobs with glare and clinical sound nor Chinese hifi sounding equivalents. If you're after a nice sounding EL34 try sourcing Mullard Blackburn Xf2 vintage types from the 1960's. It will cost you a bomb to source 16 toobs but the sound will be well worth it. 🙂

Thanks to everyone, who has taken the time to respond. Much appreciated.
Coincidently, I have been chatting to someone about sourcing 16 of the XF2.

What is so good about them? I have no experience to guide me.

Edited by The Fresh Prince
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As some have said PL amps are auto biased so power tubes don’t need to be perfectly matched, take it from someone who sells PL amps and KT150’s.

 

 

cheers,

Terry

Edited by TerryO
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24 minutes ago, TerryO said:

As some have said PL amps are auto biased so power tubes don’t need to be perfectly matched, take it from someone who sells PL amps and KT150’s.

However he also mentions they are testing for transconductance (gm).  Biasing won't fix that - the gain, as a result, will be different as they are not matched for gm.

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16 hours ago, aussievintage said:

However he also mentions they are testing for transconductance (gm).  Biasing won't fix that - the gain, as a result, will be different as they are not matched for gm.

Agreed.

Thanks to all who have contributed.

I have ordered 16 matched KT150 (with 24 hour burn in), and 12 Golden Lion 12AU7 selected for low noise and, microphonics. The decent vintage tubes were a bit pricey, and difficult to get hold of.

I think the Magicos will love upwards of 200W of tube power!

Edited by The Fresh Prince
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On 21/09/2020 at 11:02 AM, The Fresh Prince said:

I’ll have to contact the manufacturer for a schematic.

The amps are PrimaLuna EVO400 

Out of curiosity, how does the PLEVO400 sound with its stock standard tubes?

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