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Valve advice

Postby Hewesy » Sun Jul 29, 2018 10:36 am

Hi all, long time no post!

I'm after some valve advice please, I've got an old Laney VC30 1X12 which I've had for years and love the clean tone. The drive channel though is a bit too fuzzy and edgy, so I've had a bit of a love/hate relationship with it.

I recently read the article below which suggests swapping the ECC83/12AX7 with a 5751 lowers the gain level and can remove or at least reduce the fuzz.

https://reverb.com/news/how-to-improve- ... tube-swaps

In my VC30 are 3x ECC83/12AX7's, looking at the schematic v2 is the drive channel (v1 is the preamp/clean and v3 sits after the FX loop). Do I need to swap all 3 to 5751's, or just v2? I've got a matched quad of power valves but do the preamps need to match??

https://www.manualslib.com/manual/75468 ... 0-212.html though mine is slightly older the schematic is about the same.

Thanks in advance!

Hewesy
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Re: Valve advice

Postby ef37a » Sun Jul 29, 2018 1:03 pm

http://tdsl.duncanamps.com/pdf/vm345.pdf

That data sheet gives the mu and other characteristics of the 5751 as identical* to the 12AX7/ECC83 and so I doubt you will hear much change. Yet the article in the link suggests a mu of 70?

In practice, the gain, that is V out for V in, is often set by the associated components, anode loads and following grid leaks or attenuators. If the stage has even a whiff of Negative Feed Back, changing the valve will have even less effect. Such feedback could come from an unbypassed cathode or a "presence" control around the whole output stage back to the PI.

Then there is always the slim chance of circuit damage if you fit the 'wrong' valve. Anode loads can be burned out. Not such a problem with the AT7 (81 ) but never fit a 12AU7 without checking the load ratings.

*So why might you ask, all the other numbers? Identical valves were made under license and there were also variants such as faster heater times. Some are beefed up for milspec but still have the same internal geometry and thus the same characteristics. I know many people claim "night and day" changes in sound but I am yet to see a decent proof!

Have a play by all means but don't spend silly money. Invest instead in Merlin Blencowe's " Tube Pre amps for Guitar and Bass".

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Re: Valve advice

Postby Wonks » Sun Jul 29, 2018 2:14 pm

The JJ 5751 is supposed to have a bit less gain according to Watford Valves. https://www.watfordvalves.com/product_d ... sp?id=3401
But 15%-30% less doesn't sound particularly rigorous or repeatable.

This GE 5751 is also quoted of having a mu of 70. https://www.watfordvalves.com/product_detail.asp?id=681

The data sheet bears this up. https://frank.pocnet.net/sheets/093/5/5751.pdf

So maybe there are 5751s out there with a mu of 100 and some with a mu of 70. But worth checking on the data sheet of the valve you actually plan to buy to confirm the mu (gain) of that particular valve.

A long while ago now, I fitted a set of 5751s to replace the 12AX7s in my old Mesa Boogie Nomad (mainly because they were supposed to be lower noise than a 12AX7) and couldn't hear any noticeable difference.

I'd suggest changing V1 first, as that will reduce the level of the signal running into V2. It's the recommended valve position to change for more headroom.

Note that a gain change of 100 to 70 is only a 0.5dB drop in gain, so don't expect miracles!
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Re: Valve advice

Postby ef37a » Sun Jul 29, 2018 2:40 pm

What ho Wonks!

I tend to just go to Duncan Amps for data as a default but yes, you can find different rating for nominally the same valve all over the shop (and sometimes it is right! There are two versions of the 6L6 with different anode dissipations. Caveat emptor!)

Just to pick up on your search for lower noise? In general virtually all the noise in a 12AX7 stage comes from the anode load resistors. Especially if the daft, arcane Carbon Comps are used! Of course this assumes a good ECC83! Many that came through my hands had "fizzy, crackly noise" and only some 10% (of 50) were good enough for a top line valve 15 or 30W amp. That however is a reflection of the poor quality of much modern valve production.

Output valves are not what they were either. The KT88 is very expensive but not capable of the performance of the GEC originals.

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Re: Valve advice

Postby Hewesy » Sun Jul 29, 2018 6:01 pm

Cheers Dave, Wonks, that's much appreciated.

It was a rating of 70 I was looking at, the Watford Valves site does recommend a 5751 for the Fender Hot Rod series to tame the fuzzy nature of the drive channel, which is what I was hoping it might do for my VC30 (more so than cure any noise, it's actually a pretty quiet amp all told).

Hmm, perhaps I'm trying to add something the amp just isn't going to offer - what I really want is a nice, low gain but warm crunch which maybe it just won't do (I think Laney copied the AC30 a touch too far with the drive side). The clean channel is beautifully warm and mid rich but the drive side just gets edgy more than overloading nicely.

Thanks guys, for a few quid I might pick up a JJ 5751 and try it in V1/V2 but I suspect it's not worth going crazy on costs.

Cheers!

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Re: Valve advice

Postby Hewesy » Sun Jul 29, 2018 8:58 pm

As an addendum, would the same go for the Blackstar HT valve pedals?

I bought a HT Drive years back as I'd worked out I wanted valve drive but it's way to hot for me. Would swapping to a lower mu 5751 or 12AT7 be worth a try?

Or another hiding to nothing?!

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Re: Valve advice

Postby ef37a » Sun Jul 29, 2018 9:04 pm

Hewesy wrote:As an addendum, would the same go for the Blackstar HT valve pedals?

I bought a HT Drive years back as I'd worked out I wanted valve drive but it's way to hot for me. Would swapping to a lower mu 5751 or 12AT7 be worth a try?

Or another hiding to nothing?!

Hewesy

No! By the very compact nature of the pedal the resistors are wee, adequate but no more. A 12AU7 would I am sure burn a load out.

If you feel up to diving inside with a solder iron I can give you some ideas via PM.
Is it an early one with the 16V AC supply?

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Re: Valve advice

Postby Hewesy » Sun Jul 29, 2018 9:57 pm

Thanks Dave, that would be amazing. Yes it is an early one with the much hated 16v PSU.

Rather than change the vale can any other tweaks be made, along the lines of What Keeley etc do to existing pedals to sort drive levels, EQ etc on Tubescreamers and other drive pedals?

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Re: Valve advice

Postby ef37a » Sun Jul 29, 2018 10:37 pm

Hewesy wrote:Thanks Dave, that would be amazing. Yes it is an early one with the much hated 16v PSU.

Rather than change the vale can any other tweaks be made, along the lines of What Keeley etc do to existing pedals to sort drive levels, EQ etc on Tubescreamers and other drive pedals?

Hewesy

Why hated? Anyhoos, I'll look up a schematic (prob' all on'tweb now anyway!) but I am sure there is an attenuator network pre the first triode in the OD FET path. There is certainly an some attenuation in between triode stages. Both networks could be finagled.

Note, stripping down an HT pedal is quite tricky as is subsequent assembly. As I say, the components are small (but NOT SMT!) so you will need some good electronics skills.
There is a check and mod you can do that saves that AC PSU which only requires the base off and the power PCB dropped down. N.B The diode pump produces 300V. Not likely to kill but it don't arf 'urt!

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Re: Valve advice

Postby Wonks » Sun Jul 29, 2018 11:19 pm

'Hated' probably because it's not a standard pedalboard multi-output PSU voltage output, so needs to be used with the supplied one, making it very non-pedalboard friendly.
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Re: Valve advice

Postby ef37a » Mon Jul 30, 2018 7:39 am

Wonks wrote:'Hated' probably because it's not a standard pedalboard multi-output PSU voltage output, so needs to be used with the supplied one, making it very non-pedalboard friendly.

Ah! I see. Well of course you cannot generate over 3 watts of "proper" valve power from a PP3 easily or for long!

The HT range also got stick for being "too tall" but again, nature of the valve beastie.

The AC-AC line lump is now of course 'illegal' in the EU (they are dreadfully inefficient but are a simple solution) and the later pedals use a 22V 1A SMPSU. Still not that wimpy, headroom limiting 9 volts of course!

Shameless spam: The LT range are supposed to be very close to the sound of the HTs and they are of standard size and power requirement. Much cheaper to boot.

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Re: Valve advice

Postby Hewesy » Mon Jul 30, 2018 9:26 am

What the Wabbit said! A pedal board PSU that kicks out 9v and 16v is pretty rare, generally it's (v, 12v and 18v (for feeding twice 9v to some pedals for a higher headroom).

Hmm, maybe the LT range is worth a nose, I can solder but I don't trust myself not to melt something. I do use the HT Drive as a preamp for bass recording (no drive, level up and tone to suit). helps add some valve goodness into the recording chain for recording direct.

I think I'm heading back to the drawing board for either an amp that drives, or back to the pedal hunt...

Cheers both, good to talk :-)

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Re: Valve advice

Postby Hewesy » Mon Jul 30, 2018 12:12 pm

And after reading a few reviews I've bought an LT Dual. Will update when it arrives...

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Re: Valve advice

Postby Hewesy » Sun Aug 12, 2018 5:40 pm

Finally got chance to fire up the LT Drive and first impressions are good!

Channel 1 is a very natural feeling overdrive, great for warm crunch.

Channel 2 is essentially a typical distortion pedal tone as far as I can see, I think the idea is that it's a dist pedal into channel 1 as a solo boost.

Its a bit fizzier as you'd expect but actually as a 2nd drive option it's very cool to have both a natural OD and a distortion for heavier tones in one.

I like, and for the price... winner.

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