Preamp valves for a JCA50H

tbm

I can't be arsed googling and trawling through various forums, so I'll ask here and hope @ICBM sees the thread...

I want to get 5 new preamp valves for my Jet City head. My inclination is to get 5 JJ ecc83s and just fire them in. I don't know what the positions v1, v2 etc mean with this amp. Will it make any difference? Like, it's a cheap high-gain amp. I just want it to run as good it can without spending a shitload on posh valves. 

ICBM

Why do you need to change them? If it's working fine now then leave it alone. Maybe get a spare.

I really don't like JJ preamp valves - they have a dark, middy/muddy tone. But if your amp is too bright-sounding now, they might be what you need. Even then I would be inclined not to change all of them at once until you hear what effect each one has.

tbm

Thanks fella.

I got this amp off a lad on here a few years back. Was always fine but started to sound a bit lifeless a few weeks back so I changed the power tubes which helped greatly. While I was in there I noticed that the 5 preamp tubes are a mix of the cheap Chinese ones I assume came in it, a JJ and an EHX one. Was thinking new preamp tubes would help too? happy to be wrong though. That’s why I asked about tube positions. Dunno what difference the positions make. 

p90fool

I spent an entertaining afternoon swapping in known good Brimar and Mullard preamp valves in my JCA100, and with careful listening concluded that I preferred the cheap Chinese valves it came with. I'm not alone in this experience with JC amps either. 

I know that doesn't help much, except maybe to say throwing lots of money at it might even make it worse. 

tbm

p90fool said:

I spent an entertaining afternoon swapping in known good Brimar and Mullard preamp valves in my JCA100, and with careful listening concluded that I preferred the cheap Chinese valves it came with. I'm not alone in this experience with JC amps either. 

I know that doesn't help much, except maybe to say throwing lots of money at it might even make it worse. 

This is exactly the type of advise I came here for. the amp sounds much better with the power tubes replaced. Maybe that’s all it needed.  

ICBM

Ah, sorry - I missed that you were actually asking what the preamp positions do, rather than just saying you didn't know .

V1 - first gain stage for both channels
V2 - second and third gain stages for lead channel
V3 - cathode follower driving FX loop
V4 - cathode follower driving tone stack
V5 - phase inverter

I have heard that newer JCA50s may have the tone stack and FX loop the other way round (like the 20W models), but I don't know if that's true.

It's probably also worth mentioning that any Russian-made and possibly JJ valves are a bad idea in V3 and V4, whichever way round they are - they have a high failure rate in cathode followers.

tbm

Thanks. So, looking in from back of the amp the preamp tubes are at the front. Is it v1-5 from right to left? The first two are covered. Are they 1 and 2? 

Maynehead

Usually the valve closest to the input jack is V1.

The Chinese valves don't actually sound too bad for a modern valve. A lot better than Sovteks and better than JJs I would say.

If you really wanted to swap a preamp valve I suggest swapping just the V1 to a TungSol 12ax7, but only if you don't think your amp is too bright already, as it will boost your top end chime, which can translate to more fizz. If you don't want to make your amp any more brighter, then I'd just stick to the Chinese 12ax7 in V1.

digitalscream

For what it's worth, I've always used Teonex CV4004s in the preamp section of my Jet City amps (JCA50H included):

https://www.ebay.co.uk/itm/Un-Branded-12AX7-CV4004-Military-Grade-Vintage-Valve-NOS-Teonex/254104965991?hash=item3b29d61367:g:aJQAAOSwBahVF~-W

I've had the same set in my JCA50H for about five years now, and they're still going nicely

EDIT: In terms of an effect on the sound...relative to JJs, I've found them less fizzy. It's a minor thing, though - the fact that they seem to last forever is far more important to me.

WiresDreamDisasters

ICBM said:

Why do you need to change them? If it's working fine now then leave it alone. Maybe get a spare.

I really don't like JJ preamp valves - they have a dark, middy/muddy tone. But if your amp is too bright-sounding now, they might be what you need. Even then I would be inclined not to change all of them at once until you hear what effect each one has.

What tubes do you like guv?

ICBM

WiresDreamDisasters said:

What tubes do you like guv?

Basically anything other than JJs and Sovteks, which I find too muddy - especially the Sovtek WBs, the As and the long-plates aren’t so bad. 

Surprisingly, EH valves are made in the same factory as Sovteks, but sound much better. Although they still have the failure problem in cathode followers, and a shorter lifespan in general.

Overall I prefer old-production valves - they’re far more consistent than new ones, and there’s much less variation between different brands, so you don’t need to pay through the nose for the most hyped ones. Although that said, the ones that are probably most different from the norm are RFTs, which are my favourites in Marshall-type amps.

I also like the cheap bog-standard Chinese Shuguang 12AX7s, for modern valves. They have a nicely balanced sound and are fine in cathode followers.

WiresDreamDisasters

I quite like the Shuguang's too. I don't mind JJ's too much. The EHX's I've used always seemed bright and brash. So sometimes you can mix and match JJ's with EHX's to kinda balance it out.

Back in the day when I did tone comparisons using my Satch JVM, and a whole range of tubes, I was actually very surprised at how much of a difference they made to the final tone.

I've noticed more tonal variance when switching out preamp tubes than poweramp tubes if I'm honest.

ICBM

WiresDreamDisasters said:

I've noticed more tonal variance when switching out preamp tubes than poweramp tubes if I'm honest.

Very much.

What power valves affect is the dynamic response and presence at higher volume, especially if the power stage is overdriven - which I know is something both of us rarely do since we generally use powerful master volume amps.

tbm

ICBM said:

What power valves affect is the dynamic response and presence at higher volume, especially if the power stage is overdriven - which I know is something both of us rarely do since we generally use powerful master volume amps.

This is exactly what was lacking, and was rectified by, the two new 6L6s. I run it pretty hard - normal channel gain 6ish, master 6/7. The new tubes made quite the difference. 

One thing I'd read about Jet City amps was that in comparison to the Soldano's they were fizzy sounding, with less body. I run the presence low, 2/3, but it's defo not fizzy to my ears. The shop where I got the tubes has a early Hot Rod 50 in stock, so I got to A/B them through a nice Mesa 2x12. Now, it had just had two new power tubs installed, but the Jet City sounded better to me. I set them both up identically, and the Soldano was a bit lifeless on comparison.

Checked the preamp tubes in mine. it goes:

V1 JJ ECC83
V2 no name 12ax7
V3 EHX 12ax7
V4 JJ ECC83
V5 no name 12ax7

Given whats been said here, the only thing I'd be tempted to do is swap the JJ out of V4 as @ICBM mentioned them not doing well as a cathode followers, so just swap 4 and 5 maybe?

ICBM

tbm said:

One thing I'd read about Jet City amps was that in comparison to the Soldano's they were fizzy sounding, with less body. I run the presence low, 2/3, but it's defo not fizzy to my ears. The shop where I got the tubes has a early Hot Rod 50 in stock, so I got to A/B them through a nice Mesa 2x12. Now, it had just had two new power tubs installed, but the Jet City sounded better to me. I set them both up identically, and the Soldano was a bit lifeless on comparison.

The problem there is the extra bright caps - the SLO/Hot Rod doesn't have them. (The SLO does have a switchable one on the clean/crunch channel.) A lot of people cut the bright caps out of both channels, although I would prefer to do it just on the overdrive channel.

tbm said:

Checked the preamp tubes in mine. it goes:

V1 JJ ECC83
V2 no name 12ax7
V3 EHX 12ax7
V4 JJ ECC83
V5 no name 12ax7

Given whats been said here, the only thing I'd be tempted to do is swap the JJ out of V4 as @ICBM mentioned them not doing well as a cathode followers, so just swap 4 and 5 maybe?

It's more important to get the EH (Russian made) out of V3, that's a definite failure risk.

I would put that in V1 as it's probably the nicest-sounding. JJ in V2 for the most midrange/chunky overdrive tone, and V5 (phase inverter), and the no-name ones (which are probably Chinese, so fine as cathode followers) in V3 and V4. Chinese 12AX7s are easily identifiable by the double chrome strips on each side of the internal structure.

digitalscream

ICBM said:

tbm said:

One thing I'd read about Jet City amps was that in comparison to the Soldano's they were fizzy sounding, with less body. I run the presence low, 2/3, but it's defo not fizzy to my ears. The shop where I got the tubes has a early Hot Rod 50 in stock, so I got to A/B them through a nice Mesa 2x12. Now, it had just had two new power tubs installed, but the Jet City sounded better to me. I set them both up identically, and the Soldano was a bit lifeless on comparison.

The problem there is the extra bright caps - the SLO/Hot Rod doesn't have them. (The SLO does have a switchable one on the clean/crunch channel.) A lot of people cut the bright caps out of both channels, although I would prefer to do it just on the overdrive channel.

For what it's worth, I cut the bright caps on both channels of my JCA50H and I don't regret it. That gets rid of some of the apparent gain (if you see what I mean), but a small boost in front gets you back there without the fizz.

p90fool

I put both bright caps on switches, and ended up leaving the overdrive channel one switched off, and the crunch channel one switched on. 

tekbow

digitalscream said:

For what it's worth, I've always used Teonex CV4004s in the preamp section of my Jet City amps (JCA50H included):

https://www.ebay.co.uk/itm/Un-Branded-12AX7-CV4004-Military-Grade-Vintage-Valve-NOS-Teonex/254104965991?hash=item3b29d61367:g:aJQAAOSwBahVF~-W

I've had the same set in my JCA50H for about five years now, and they're still going nicely

EDIT: In terms of an effect on the sound...relative to JJs, I've found them less fizzy. It's a minor thing, though - the fact that they seem to last forever is far more important to me.

I second these. They look to be 6N4-J's with the double supported square dimple getter which I literally always go on about every time these threads happen.

I use these in V3-V5 of my Soldano. Nice even toned tubes, I'd happily use them in V1 and V2 btw, but RFT's are my preference for V1.

I'm also a supporter of Chinese tubes in general these days. If you buy from a good reseller who tests them properly, you get very good tube.

I've recently upgraded my recording gear. I think a new tube comparison vid is due.