I sent a messgae to Eurotube, requesting what they thought about clean headroom with a Valve Junior.. well this is the reply..

 We've been retubing a lot of these lately and a JJ EL84 in a grade anywhere between #26 to #28 are quite nice for tight clean headroom, and would also work well with pedals. A grade #30 up to #34 would still give a nice clean but would grind real good when pushed.
For the front end you can either use the JJ ECC83S or the ECC803S. We do not recommend the ECC803S for the VJ combo amps but they are just fine for the head version. The ECC803S is a slightly lower gain tube with a real thick mid and a little brighter high end so if you choose to use one of these I would recommend a matched triode ECC803S that is at 90+ in gain. For a more substantial gain reduction (about 40% less) you could go with a matched triode ECC81.
If you want to maintain the amount of gain the amp has now then you can use a matched triode ECC83S that is between 105 to 110 in gain.
If you choose to order online please let us know if you’re after more or less headroom and which way you want to go for the front end. You can leave this info in the comments section on the check out page.
A single EL84 and a matched triode ECC83S or ECC81 would run 19.00. A single EL84 and a matched triode ECC803S would run 23.00 or a single EL84 and a high gain ECC83S would run 22.00 and we can ship them for 6.50 by Priority mail with a 3 day delivery anywhere in the US.
The bad news is you caught us with no EL84's in stock!! Things have been so busy with the online store, combined with a big shipment from the JJ factory that was two weeks late in leaving that we ran out of stock. The good news is that we have a skid of tubes landing Tuesday and they should clear customs by Wednesday.