Jet City amps

ICBM

clarkefan said:

I can't imagine why an amp currently biased at 40% at idle won't sound better at 65%

Because - as long as the 40% is not low enough to cause crossover distortion - it’s an illusion. Biasing hotter will increase the power stage gain slightly, but that’s all - and it’s that which produces the impression of better tone. You would get the same improvement by turning the volume up by the same amount. Biasing by percentage also makes the assumption that the amp designer always uses the valves up to their maximum capability, which is not necessarily true.

It is quite likely that with most amps 40% would be low enough to cause crossover distortion though. That’s the critical factor - *not* the percentage of maximum dissipation. The correct bias point is just above where the crossover distortion disappears, regardless of what percentage or idle current that is - that’s why Mike Soldano was biasing an amp using a scope.

With a particular type of amp the two are of course related, because they all behave in roughly the same way and so the crossover distortion tends to disappear at about the same idle current, so you can do it that way as a shortcut. For the standard Marshall 50/100W power stage it’s usually around 27-28mA - 13.5W or 55% of maximum dissipation. Hotter than that tends to just increase the risk of valve failure when the power stage is overdriven.

This is also one of the many reasons the DSL/TSL series is unreliable, they were biased up to 40mA - nearly 19W or 75% - from the factory. If you set them at 30mA they tend to be more reliable.

If you do it by ear, you need to be aware of the trap of the old hi-fi salesman's trick that slightly louder always sounds better, as well as listening for the crossover distortion. It’s easy to just turn up the bias a bit and hear what sounds like an improvement, but you don’t know if that’s due to tone or volume unless you measure the output voltage.

clarkefan

Thank you @ICBM , what an interesting post! I've only heard of crossover distortion, I'm off to read up, appreciate you sharing

Fez

Another 50H owner here great amp paired with a Harley Benton 2x12 v30.

JMP220478

lincolnblue said:

Anyone had any experience with Jet City Amps? They are cheap but no idea if they're any good

yes - currently have a custom 22 and prior to that the 22H  ; custom has a better loop n 2 channels - have giigged both with various cab mixes - 1x12 => 4x12  - cant go wrong - new theyre a steal , used prices are just stupid good ..  

Creed_Clicks

jonnyburgo said:

I’ve got the 20w combo with reverb, single channel version with an Eminence  Private Jack in it, it roars!

and I’m selling it

Is it the vintage one you have? You're selling? Pickup only?

lincolnblue

Are they generally more gain-y amps or do they do any more clean, fendery models?

PolarityMan

Fez said:

Another 50H owner here great amp paired with a Harley Benton 2x12 v30.

Im rocking one of those but i replaced the v30s with neo versions, did you get them when they were not much more than the resale price of 2 V30s new?

Creed_Clicks

Jet City 20hv just showed up locally for guide price €249. This or a Laney Cub head..... Decisions....

not_the_dj

Creed_Clicks said:

Jet City 20hv just showed up locally for guide price €249. This or a Laney Cub head..... Decisions....

Second hand price? That seems high compared to new UK prices. Whereabouts are you?

Creed_Clicks

not_the_dj said:

Creed_Clicks said:

Jet City 20hv just showed up locally for guide price €249. This or a Laney Cub head..... Decisions....

Second hand price? That seems high compared to new UK prices. Whereabouts are you?

In Ireland. I'd obviously offer a lot less than €249/£220....

matthewwensor21

A guy who I know used to use a JCA100H. He also owns a Soldano SLO100 but for small time gigs said the Jet City sounded ridiculously close, so close he hardly took his SLO out.

Creed_Clicks

Hmmmm, so tempted to pull the trigger on the 20watt head

lincolnblue

lincolnblue said:

Are they generally more gain-y amps or do they do any more clean, fendery models?

Bump

Creed_Clicks

I think the 20HV is more on to a Fender? One channel etc.

clarkefan

Creed_Clicks said:

I think the 20HV is more on to a Fender? One channel etc.

No, if anything more Marshall, they took the 20H and darkened it a bit, and dropped the gain a bit.  There's a lengthy video up on YT by the long - haired Brummie bloke who gives one a blast with various guitars, it'll give you a good idea.

Creed_Clicks

Yeah, I've seen that video. Quite good. I wonder how it compares to the Marshall Origin or an OR15. Based on videos, I'd say the OR15 isn't as "clean" sounding as the other two...

Dave_Mc

lincolnblue said:

lincolnblue said:

Are they generally more gain-y amps or do they do any more clean, fendery models?

Bump

I already answered you earlier in the thread... from what i hear (haven't tried it) the 50 watt 2x12 combo, if you can find one, was supposedly a lucky 13 clone which has a fendery clean channel.

p90fool

Dave_Mc said:

lincolnblue said:

lincolnblue said:

Are they generally more gain-y amps or do they do any more clean, fendery models?

Bump

I already answered you earlier in the thread... from what i hear (haven't tried it) the 50 watt 2x12 combo, if you can find one, was supposedly a lucky 13 clone which has a fendery clean channel.

So did I. 

timmysoft

I do have a chuckle when people say “my jca50 sounds exactly like an SLO”. It doesn’t, it sounds like a hot rod 50 +, which doesn’t sound anywhere near as good as an SLO.

Ive owned most of the current range from Jet City and they’re bloody good amps, they destroy every other brands budget offerings. Currently getting to grips with the Amelia, which is pretty cool! 

Crazed_Fandango

I'm interested in the Amelia.  Pairing that with a 2x12 cab looks like it would suit my needs.  I just need to consider what speakers to go for.

Then I can get rid of my Fender HRDiii