Valvestate advice

Tavernor

Hello guys, it’s me again...

I decided to replace the the valve in the preamp of my valvestate head today, while it was open I used a good amount of contact cleaner too. Fairly liberally, left it all day to make absolutely sure it was dry (dry to the touch within a minute or so). Valve glowed correctly when I powered it up before I screwed it back together.

thing is, the clean channel is now significantly quieter than it was. The overdrive channels are a huge amount louder at the same relative setting.

Sounds good and it’s loud enough still but is this just a ‘new valve’ thing or is something wrong? 


https://ibb.co/hrBN3S

Theres the old valve snd the box of the new one if that helps.

As ever, any advice is very much appreciated

Dave

ICBM

Put the old valve back and see if it goes back to how it was. Filament glow is no guide to correct valve performance...

Spraying contact cleaner randomly over the whole circuit board is not a good idea either - some types can leave a conductive residue.

Tavernor

Yes, sort of regret that... it does all work though - only have it as a half stack from gigging days 10+ years ago and it’s still more than loud enough for the bedroom. Could a bad valve result in loss of volume? I’ll try the other one back in when I get time mind.

ICBM

Tavernor said:

Yes, sort of regret that... it does all work though - only have it as a half stack from gigging days 10+ years ago and it’s still more than loud enough for the bedroom. Could a bad valve result in loss of volume?

Yes. When you say 'Valvestate', I assume you mean a VS series?

In the VS series (and the older 80 series - although the valve is only on the dirty channel in those so I assume it's not one of them), the valve is used as a 'cathode follower', which some valves have a problem with... including some JJs.

If it's an AVT it's more complicated - I'll need to look at the schematic .

Tavernor

ICBM said:

Tavernor said:

Yes, sort of regret that... it does all work though - only have it as a half stack from gigging days 10+ years ago and it’s still more than loud enough for the bedroom. Could a bad valve result in loss of volume?

Yes. When you say 'Valvestate', I assume you mean a VS series?

In the VS series (and the older 80 series - although the valve is only on the dirty channel in those so I assume it's not one of them), the valve is used as a 'cathode follower', which some valves have a problem with... including some JJs.

If it's an AVT it's more complicated - I'll need to look at the schematic .

It’s one of these

https://ibb.co/gEXjYS

One of the the older ones I think. So does the valve only ‘do things’ on the dirty channels? For some reason I thought it was the other way round..! I can buy another valve if that’s the likely issue (hoping it’s not overly liberal contact cleaner spraying..)

ICBM

That’s a VS, so the valve is on both channels - technically ‘after’ the channels in the section where they’re switched and the FX loop and reverb are. In theory a loss of gain in the valve would affect both channels equally, but you would probably notice it more on the clean channel.

Try the old valve first, anyway - if it doesn’t fix it the problem is somewhere else. The old valve is Chinese-made, which don’t have the cathode-follower problem.

Tavernor

Solid (state) advice, if the old valve is louder/better is it unnecessary to get a new one or if there is even a small benefit to be had, could you link me to one which ‘should’ work properly? Ebay, Amazon etc. Doesn’t matter where from!

ICBM

If the old valve works fine then there's no real need to change it. If you do want to, or at least have a spare, actually the cheapest generic Chinese 12AX7 is likely to be the best. This one is good...

http://www.karltone.co.uk/shuguang-12ax7-ecc83-707-p.asp

For cathode-follower positions you need to avoid all Russian-made and usually JJ valves, which is most of the rest unfortunately. TAD and Ruby also do some good Chinese-made valves.

DJH83004

With the VS100, the valve is active on both channels, and as IC said, it is configured as a cathode follower, which can cause issues with certain makes of valve ( it is to do with the potential difference between the cathode and heater exceeding the valve spec.) I actually think you should be ok with a JJ, as It tends to br Russian valves that are more prone to problems. To be absolutely sure Chinese valves (e.g. TAD) cope much better. But as IC said at the outset, best to just swap the valves back and see if the amp reverts to its original tone & output. For what it’s worth IMHO, the preamp valves last an age in the Valvestates, they rarely need changing.

ICBM

DJH83004 said:

With the VS100, the valve is active on both channels, and as IC said, it is configured as a cathode follower, which can cause issues with certain makes of valve ( it is to do with the potential difference between the cathode and heater exceeding the valve spec.) I actually think you should be ok with a JJ, as It tends to br Russian valves that are more prone to problems.

Agreed, but I've come across a number of JJs that have failed in the typical 'Russian' way in cathode-followers too - not as common, but enough that I think they're prone to it as well.

Tavernor

ICBM said:

If the old valve works fine then there's no real need to change it. If you do want to, or at least have a spare, actually the cheapest generic Chinese 12AX7 is likely to be the best. This one is good...

http://www.karltone.co.uk/shuguang-12ax7-ecc83-707-p.asp

For cathode-follower positions you need to avoid all Russian-made and usually JJ valves, which is most of the rest unfortunately. TAD and Ruby also do some good Chinese-made valves.

Purchased..! Impulse overrode common sense in trying the old one again first. In a YouTube video it advised using a cloth and not touching the new valve with skin. The old one I just pulled out... is that valid advice?

ICBM

Tavernor said:

Purchased..! Impulse overrode common sense in trying the old one again first. In a YouTube video it advised using a cloth and not touching the new valve with skin. The old one I just pulled out... is that valid advice?

No, not really . Allegedly the oils on your fingers damage the glass. This is something that happens to halogen light bulbs, not valves... due to the extremely high temperature they operate at - valves don't run that hot.

Using a cloth can still be a good idea when you're changing a hot valve in a hurry though .

A spare valve is not a foolish thing to have, anyway.

Tavernor

New valve (recommended one) in - same issue... could it be the volume pot? I know swapping them (and the Marshall one back in) doesn’t take long but time is a premium these days.

ICBM

Tavernor said:

New valve (recommended one) in - same issue... could it be the volume pot? I know swapping them (and the Marshall one back in) doesn’t take long but time is a premium these days.

Unlikely if it seems to work evenly over its range. If it's not the valve it could be a large number of things unfortunately - or a fault with the overdrive channel making it much louder... in fact a failed *mid* pot can do that. If you're not familiar with fault tracing on fairly complex amps it's probably a job for a tech.

Tavernor

Old valve = same thing... it’s still balistically too loud on clean at 4 for home use, it just used to be that it was ballistically too loud on clean at 2 before. The definition of a non urgent problem.

Tavernor

Put the first replacement back in, although quitet I thought it sounded (maybe placebo) a bit sweeter. I could well be deservedly chastised for this but blasted round the clean volume pot with more contact cleaner...

volume back to how it should be

Tavernor

If anyone wants the old Marshall one and the one recommended above on the cheap then let me know. One recommended above works fine and played on for approximately 30 seconds.

ICBM

Tavernor said:

Put the first replacement back in, although quitet I thought it sounded (maybe placebo) a bit sweeter. I could well be deservedly chastised for this but blasted round the clean volume pot with more contact cleaner...

volume back to how it should be

It's unusual for them to cut volume like that without going intermittent or random in volume as you turn them, but if it worked, then it worked .

Tavernor

The end justifies the means, however illogical it may have been

Tavernor

I’m going to have to actually learn to play now I’ve done both guitars and the amp... cock wombles.