How hot should a Pro Junior get?

MrT

Taking my Pro Jnr in for a service is something I need to do on a month when i haven't spent so much on pedals but how hot should it get when run at a fairly low volume (say 2 to 3). The face plate on mine was getting almost too hot to touch. Is this normal for the pro Jnr?

simonk

Mine ran hot. I'm not understanding "...fairly low volume..." though. Mine was LOUD and just got LOUDER! Great little amps though - miss mine!

Richardj

Not sure why you need to take it anywhere to be serviced, unless there is something wrong with it. It is pretty much a 'grab and go' amp and the valves don't need biasing so you can unplug the old ones and fit new ones yourself very easily. You just need decent quality 12AX7s and a matched pair of EL84s.  I guess you could get a tech to check the bias and cool it down a bit if needed (they tend to be set a bit hot at the factory), but apart from that........

ICBM

They do run hot. It doesn't matter what volume it's at, the heat is mostly from the bias setting at idle.

You could have it biased a bit cooler if it's worrying you.

MrT

Thanks all - agreed, if it's normal to run hot then no immediate need for a service. Just wanted to sanity check I wasn't ignoring a potential problem!

I probably will get the bias adjusted (with the associated mod) at some point. Just need a month when I spend less on the classifieds here :-)

ecc83

Yes, valve amps DO get hot! Some folks that have never had one don't quite get it.

I recall an Artisan 30 combo shipped back because "the front plate gets too hot to touch". Well it did, just, after about an hour but the valves were on specc for anode dissipation and the way the chassis is fitted causes the heat to rise to the top of the amp (the FP of the A30 head runs cooler) .

NASTY! HOT! INEFFICIENT things valves! Glad I am shot of them!

Dave.

Modulus_Amps

A small valve amp dissipates upwards of 100w of power depending on the configuration, most of that is heat. if the valves are biased too hot and red plating it will put out even more heat, so check they are not red plating at idle or when playing by watching them in the dark. you should see the heaters glow but not the plates.

like this picture




If you want the amp to run cooler you could install a small fan, it would probably make the electronics in the amp last longer.

benmurray85

Modulus_Amps said:

If you want the amp to run cooler you could install a small fan, it would probably make the electronics in the amp last longer.

Oooh i may have a look at doing this with mine (formerly @simonk 's) 

It does run hot and has started making some strange noises only at volume. I'm guessing somethings rattled loose/melted inside. Its off to see a man who can today so I may ask if he can get a fan in there, otherwise I might start using a standard desk fan and firing at the back of the amp. Cheers guys  

randella

ecc83 said:

NASTY! HOT! INEFFICIENT things valves! Glad I am shot of them!

Yeah! Boo! You forgot to mention the kilos of iron that go with them (my chief complaint).  Heavy.  Boo!

(They look so pretty though)

I had a Tubemeister 18 that you could fry eggs on.  I've a Marshall JCM900 1x12 that you'd never know was switched on.  The MESA Minirec is somewhere in between.  All of them funcitoned absolutely flawlessly.  So what that tells the uneducated (me) is that it really comes down to the case and chassis design I guess.

ICBM

randella said:

You forgot to mention the kilos of iron that go with them (my chief complaint).  Heavy.  Boo!

Solid-state amps with linear (ie transformer - even toroid) power supplies are just as heavy for equivalent output volume.

While it's true that they don't normally have output transformers - which saves some weight - a solid-state amp has to be typically two to four times the power of an equivalently loud valve amp, so it then needs a much bigger power transformer which removes most of the advantage.

If you don't believe me, try lifting my Peavey Special - 120W, and about the same volume as a decent 50W valve amp. It actually weights 1lb more than my Mesa DC-5 did - partly because it needs an even bigger speaker to handle that power.

I admit modern solid-state amps with switch-mode power supplies can be much lighter.

randella

@ICBM I don't doubt it, not for one minute!  I'm limited to my own anecdotal experience however - the last SS amp I had was that 160W Crate you gently (and helpfully!) advised me against repairing weighing in at 15kg (just about manageable) from memory, versus the 50W all-toob Marshall goliath weighing in somewhere north of 25kg (no way).

I know the Marshall could bury the Crate in terms of raw volume despite the SS amp having three times the output on paper, but either amp is too loud for my gigs down the Dog and Duck so it's kind of moot I guess.

Basically as soon as 'they' nail the dynamics with an Axe-FX and the price drops to £500 (don't laugh, it has to be that cheap one day!) I'll be using that with a switched-mode-supply power amp and some feather-light cab with neodymium speakers and valves can bite my shiny metal wotsit (I miss Futurama).  I have no affection for valves whatsoever, @ecc83 is right (whether or not he was joking!).

And as the OP's helpfully illustrated, you're forever worrying about the damn things.  Is it running too hot?  Can I move it yet?  Let me check for the 17th time I plugged the speaker in before I hit the 'standby' switch...

ICBM

randella said:

I have no affection for valves whatsoever, @ecc83 is right (whether or not he was joking!).

I'd be more than happy to use all-solid-state as well, if it sounded exactly like I wanted it to.

The clean sound on my Peavey Special is better than any valve amp I've owned, it's just the overdrive that lets it down slightly. It's not just the amp's own overdrive either, it doesn't even sound as good with pedals as a good valve amp does.