.

kt66

.

ICBM

That doesn't sound right at all.

My first guess would be that the power valves are overbiased - the Pro Jr is a fixed-bias amp, and doesn't have an adjuster - which would cause crossover distortion at very low volumes. However it doesn't usually sound good, so I suspect it's not that...

Try swapping the valves back in stages, power valves as a pair and preamp valves separately.

kt66

It's not right, but sounds so good.  

JDE

Just been mucking about on a PJ IV, I can confirm that something is not correct with your amp. Clean as a whistle until around 4/5 on the volume (with a Tele), which I can only assume is “correct.” Sorry I can’t offer any advice other than to say they don’t all sound like yours at low volume. 

kt66

This gets more interesting.  Pulled out the 2 replacement 12AX7s - looked again at the stock
Groove Tubes and I see one is actually a 12AX7-R and the other 12 AX7-C!! 

These of course are different to bog standard 12AX7s - so I go to put them in 
and see that the 12AX7-C is missing a pin, I put both in, "C" doesn't light up.

I put in a sweeeeeet old Telefunken normal ECC83 in there instead
So it now has 1 normal 12AX7 and 1 12AX7-R in there, and it sounds great, as 
it should, dimed Tweed sound gone. 
Gets a bit too loud too quickly, but that's for another day,

So Pro JR IV users - what type of 12aX7s does yours have?
And is the "R" on the side nearest the EL84s or the "C"? 
 if indeed those are the valves you have installed. 

olafgarten

kt66 said:

This gets more interesting.  Pulled out the 2 replacement 12AX7s - looked again at the stock
Groove Tubes and I see one is actually a 12AX7-R and the other 12 AX7-C!! 

These of course are different to bog standard 12AX7s - so I go to put them in 
and see that the 12AX7-C is missing a pin, I put both in, "C" doesn't light up.

I put in a sweeeeeet old Telefunken normal ECC83 in there instead
So it now has 1 normal 12AX7 and 1 12AX7-R in there, and it sounds great, as 
it should, dimed Tweed sound gone. 
Gets a bit too loud too quickly, but that's for another day,

So Pro JR IV users - what type of 12aX7s does yours have?
And is the "R" on the side nearest the EL84s or the "C"? 
 if indeed those are the valves you have installed. 

They shouldn't be that different. The -R and the -C are still both 12AX7's and should have the same amount of pins. The added letter is just Groove Tubes marketing based on the 'voicing' of the tube.

ICBM

Exactly that - there is no real difference. The 'C' valve is broken.

olafgarten

It's still interesting that a missing pin would cause pleasant distortion at low volumes.

I'm not familiar with the circuit in the Pro Junior but can't think of why that would happen. In most cases a broken pin would stop the amp producing any sound at all. 

ICBM

olafgarten said:

It's still interesting that a missing pin would cause pleasant distortion at low volumes.

I'm not familiar with the circuit in the Pro Junior but can't think of why that would happen. In most cases a broken pin would stop the amp producing any sound at all. 

It’s certainly puzzling!

Exorcist

I think you should quickly patent it and produce the 'bedroom tweedy' amp. 

kt66

Reading the replies, I think I may have been misunderstood or not totally clear - I'll lay it out better

1) Got amp - immediately took out the stock valves - which I assumed were normal EL84s and ECC83s
2) Put in new Golden Lion EL84s and two old but very good USA GE 12AX7s 
3) All valves were tested and all fine
4) The sound now was extremely distorted at 1-2 then cleaned up nicely
5) I went to put the stock valves back to see if it got cleaner, ie better
6) I noticed they were 12AX7-R and 12AX7-C - and that C was missing a pin, this could have happened at ANY time, but I'd guess it was me during testing. I put the "C" in for a laugh and sure enough the missing pin caused it not to work
7) I don't know what way they go back and take a chance, putting the "R" on the right (ie furthest away from the EL84s)
   and a normal ECC83, an old but wonderful Telefunken on the left.
8) Sounds comes back to how I think it should be

SO.........putting in the normal 12AX7/ECC83 in both sockets caused this weird but great distortion.
The "R" valve certainly does something different.

ICBM

kt66 said:

SO.........putting in the normal 12AX7/ECC83 in both sockets caused this weird but great distortion.
The "R" valve certainly does something different.

The valve which is causing the odd distortion is broken.

kt66

No,it's not  - both USA GE 12AX7s test fine, and work well in my Prima Luna and AC30 

ICBM

kt66 said:

No,it's not  - both USA GE 12AX7s test fine, and work well in my Prima Luna and AC30 

Which one is the one that causes the distortion in the Pro Jr?

That one *is* faulty, regardless of it not showing up on a tester or in an different amp. If it works fine in a different amp you can use it for that. Some valves will cause trouble in one position and not another in the same amp too, it doesn't mean they're not faulty.

kt66

Well I learned something new today, which is handy, as I appear to be as thick as shite
12AX7-R   Made in Russia
12AX7-C   Made in China, 
they are normal 100% 12AX7/ECC83 - so all my theories are out of the window. 

as per very helpful lady at Hot Rox. I did ring the retailer I bought the amp from, they were flippin' useless.
So still no nearer the mystery of what caused the 57 Tweed like distortion.

kt66

ICBM said:

kt66 said:

No,it's not  - both USA GE 12AX7s test fine, and work well in my Prima Luna and AC30 

Which one is the one that causes the distortion in the Pro Jr?

That one *is* faulty, regardless of it not showing up on a tester or in an different amp. If it works fine in a different amp you can use it for that. Some valves will cause trouble in one position and not another in the same amp too, it doesn't mean they're not faulty.

I don't know and not totally convinced it was a preamp valve now.  
Does anyone know is V1 the one furthest from the EL84s ?

ICBM

V1 is closest to the input jack. Have you tried putting the other valves back, one at a time, in both positions? That will quickly tell you.

Creed_Clicks

Picked up a used one yesterday for €250, made in Mexico. Sounds great, but I never knew how heavy these things are for a small amp. I noticed a small but of a rattle when I turned up the volume, but a lovely sounding amp overall.

bbill335

Creed_Clicks said:

Picked up a used one yesterday for €250, made in Mexico. Sounds great, but I never knew how heavy these things are for a small amp. I noticed a small but of a rattle when I turned up the volume, but a lovely sounding amp overall.

that's probably the valve retainer on the el84s. get it off! mine rattled like mad but the valves can hang on on their own well enough.

DannyP

Exorcist said:

I think you should quickly patent it and produce the 'bedroom tweedy' amp.